couple of questions on my silverface Bandmaster Reverb

[adbrunner]

First off, wanted to say hello and thanks. have used the amp guide so
many times, such a great resource. Never had occasion to post a
message, until now.

I'm having difficulty reconciling a few things and trying to date my
amp and cabinet. It's a silverface bandmaster reverb. I bought it at a
highly reputable shop, Willie's American Guitars in St Paul, and the
salesmen told me it's a '74. The stamp reads "A741914" and the dating
charts I've found online seem to confirm that stamp to date to
'74....here's where I run into the question -- the amp guide and
everyone else seems to say the logo should have a tail, but it most
definitely does not.

Also, I recently bought a cab to put under the head. I know cabs can
be tough to date, but I wanted to at least get one from the right era.
My buddy has one of the shorter ones from 1976-1980, and I knew that's
not what I wanted. I did end up finding the 39" tall cab, which amp
guide dates as 78-75 - and it doesn't have the chrome trim so I guess
that means 70-75. But again, the logo has no tail. The taller cab was
only made 'til '75, right?

What are the chances that I bought a separate head and cab from two
different places, 3 years apart, and they both accidentally had the
wrong logo on them? what gives?

pics of my amp and cab are available:
http://www.flickr.com/photos/37711849@N00/5262729418/in/set-72157625604109166/


Thanks a bunch!

[adbrunner]

correction, in my 3rd paragraph I obviosuly meant 68-75, not 78-75.

Also, in looking around online, on craigslist and on ebay, etc, I'm
finding a LOT of amps labelled '74 without the tails on the logos.

[B L]

Couple thoughts.

1. "No-tail" logos actually started showing up earlier than many folks might think. They were originally introduced as early as 1968 but only on the  Bronco...Well, we all know what that means. two parts bins, two production lines...It's Friday at Fender, I need to finish this amp and we're out of Fender logos AGAIN. :-) I'm sure someone could have snuck a no-tail on a tailed amp, especially by early '74.

Yes, I've personally seen a few 73 amps with no-tails over the years. I happen to own a "no-tail" 74 Vibrosonic...which I've owned since the mid 80's...way before ANYONE cared about tail vs. no tail. Yours very easily could be real.

2. Someone might have swapped the less desirable "tail" for the "no tail" and sold it on Fleabay. They're coming from somewhere, right? :-) Check for misaligned screw holes, "extra" holes, and discoloration on the grille cloth, etc. Should be obvious under a magnifying glass.

3. re: the actual manufacturing date. Why use the tail method at all? Check the transformer codes, the pot codes and the chassis rubber stamp and the date code stamp on the tube chart. A combination of these should easily reveal the true age of the amp, tail or no tail.

CoolBlueGlow

The Arkansas Fender King

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[adbrunner]

Thanks friend. I'll definitely take a look at the additional codes and
stamps and go from there.

Have a few other questions. Is there anyplace to source the knurled
studs and "cab hooks" listed in the hardware sections for these amps
and cabs? found the handles, glider feet, and chassis straps.

cheers and happy holidays :)

[B L]

Ampwares / Mojotone has (had?) the studs fairly recently. I've seen them around, and the straps as well. They're fairly pricey. You might try fleabay as well...for some used ones pop up there from time to time. I have a couple nice used sets, but I'm not selling at this time.

Congrats on a really nice amp. Enjoy her by playing! 

Merry Christmas,

CoolBlueGlow

The Arkansas Tube King

--

[adbrunner]

cool, thanks again. nothing available right now, but i'll keep an eye
out.

I've definitely been enjoying the amp. I've had the head for a couple
of years and love it more every time i plug in. Was playing it thru a
vibroking 2X12 until I picked up the matching bandmaster cab recently.
(lifted my vintage 30's out of the vibro king, they sound great in the
larger cab).

now that I'm no longer taking this particular amp to gigs or out on
the road, I'm trying to restore it as best as I can, so I can enjoy it
aesthetically as well.

cheers, and merry christmas to you as well.

Adam

[B L]

Adam,

Believe it or not, it looks like Fender piggyback hardware is still an item you can get from Fender. (!)

http://www.fender.com/products/search.php?partno=0990721000

You'll have to get with an authorized Fender dealer and order it...but check the link above for the SKU number or the proper product name before you call them. Shouldn't be too hard from there.

Cheers!

CBG

[Joel Bienvenu]

Hi All,

 

Thankas for the great advice in answering all of my questions regarding my Fender Twin SF restoration. That, and the outstanding service from Mojotone, Antique Electronics and some vintage tuibes found on Ebay made the entire restoration an easy project.

 

I bought this amp in 1982, it was a 1972 model (first thing Mojotone helped me confirm). The only thing I've ever done to it was change the tuces once, and repaired the reverb tank. It spend about 10 years playing out several times a month, and actually fell down and entire flight of stairs once when the handle broke, zero damage, just a few scuff marke and a cracked knob. The amp sat un a closet and in the garage, covered with junk for the last ten years. When I pulled it out, it was covered with mold and caked on crap, the reverb cable was broken, the speaker grill frame was broken and the whole thing smelled of modl. So bad my wife didn't want it in the house. Well before I decided to do the tolex, which was done once in the late 1970's, I decided to give it a thorough cleaning, so I pulled out the amp assembly, stripped off all or the hardware and speakers, and scrubbed it down with soap and water. Then painted all of the exposed wood with flat balck paint.

 

I fabricated a new speaker cover frame, and replaced the covering, after (cleaning the logo and added new velcro). The handle, corner protectors and hanger straps were replaced. The amp worked OK but hummed quite a bit, and all of the pots were dirty, one of the knobs was broked, and most of the preamp tubes and the filter caps were original. The filter caps were replaced with Sprague Atom 80 MFD/500V and 20 MFD/250V and all of the tubes were replaced. The pots and jacks were thoroughly cleaned and everyhting re-assembled. I did replace the speakers sometime in the 1980's with a pair of Eminence speakers that I pulled out of a 1974 Ampeg 100w, 4-12 amp that I had, so the speakers are not original, but is great shape and sound good.

 

When I powered it up, I though I may have screwed something up because it made ZERO noise. This thing is now so quiet it is unbelievable, but absolutely screams, and the sound is phenomenal ! !

 

I did screw up the speaker cover cloth, but will take care of that when I install the new tolex in a few months, the main goal of this investment was functional more than cosmetic, and of course I spend more money and time that originally budgeted, but I am very pleased with the results. Total cost of all components, $225 and about four hours of time. Original cost of the amp in 1982 was $50, so I think I got a pretty good deal.

 

JB ;-).

 

The main guitar is a 1983 Fender Tele that I bought new, modified with a Kahler tremelo, Seyour Duncan mini humbicker in the bridge and Duncans in the middle and neck poitions (both with coil taps). I rewired it with a five way switch, toggle switches for the coli taps, and a push pull knob (on the tone) to change the phase of the bridge and middle pickups. Definitely a 'hot rod' Tele, I did all of the work myself from 1983 through 1985, the last thing was the addition of the SD mini humbucker a few years ago.

--
Joel B. Bienvenu

Research Manager, Production and Wide Format Print

IDC Research
5 Speen Street
Framingham, MA 01701
Phone (954) 326-8966
email: jbie...@idc.com
personal email: joel.b...@gmail.com

[frank]

check ebay. that's where i got mine when i restored a dual showman bf cab and a 15" "tone ring" cab.

[adbrunner]

BL -- just noticed the link for the piggyback hardware, thanks a bunch
for that! Now seems like I shouldn't worry about the piggyback
hardware, I looked inside my head and there is no evidence that the
hardware was ever part of this piece. no holes, marks, etc, for the
hardware to attach to.

I still haven't gotten around to looking more closely at the

transformer codes, the pot codes and the chassis rubber stamp and the

date code stamp on the tube chart to verify the date. But I did just
read that the master volume switch only appeared starting in '76, and
I definitely have one of those, which can be pulled out for a fatter
tone. So I'm guessing it's more of a late 70's model at this point,
which would make sense with the no-tail logo. Frustrating because I
wouldn't have purchased the taller cabinet if I had known. It's a
silly little thing, but I like things to match up and it looks as
though I should've gone with 29" cab instead.

[frank]

bm rev's did not have hold down hardware. a bolt went through the wood into the countersunk nuts.

BL -- just noticed the link for the piggyback hardware, thanks a bunch
for that! Now seems like I shouldn't worry about the piggyback
hardware, I looked inside my head and there is no evidence that the
hardware was ever part of this piece. no holes, marks, etc, for the
hardware to attach to.

I still haven't gotten around to looking more closely at the
transformer codes, the pot codes and the chassis rubber stamp and the
date code stamp on the tube chart to verify the date. But I did just
read that the master volume switch only appeared starting in '76, and
I definitely have one of those, which can be pulled out for a fatter
tone. So I'm guessing it's more of a late 70's model at this point,
which would make sense with the no-tail logo.  Frustrating because I
wouldn't have purchased the taller cabinet if I had known. It's a
silly little thing, but I like things to match up and it looks as
though I should've gone with 29" cab instead.

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[adbrunner]

definitely wouldn't work with this cab then, as the countersunk
threaded pieces are a bit wide of where the head sits on the cab.
probably meant to suit the bandmaster head with the hold-down pieces.

[frank]

you have the wrong cab, then. bmr's had the tall cab only. the head has two holes on the bottom. these will line up with the proper cab. i guess they do not line up with a reg bm or bassman cab holes.

-----Original Message-----
From: adbrunner <ambr...@gmail.com>
To: The Amp Guide <the-am...@googlegroups.com>
Sent: Thu, Dec 30, 2010 10:14 am
Subject: [The Amp Guide] Re: couple of questions on my silverface Bandmaster Reverb

definitely wouldn't work with this cab then, as the countersunk
threaded pieces are a bit wide of where the head sits on the cab.
probably meant to suit the bandmaster head with the hold-down pieces.

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www.mojotone.com
www.guitarandampshow.com

[adbrunner]

Well, my BMR has no holes in the bottom. and the cab IS the tall cab,
39" -- but according to amp guide, the BMR had the tall version only
68-75, then switched down to the smaller 30" cab with the diagonal
baffle config, from 76-80.

my friend has one of the shorter 30" cabs and the silver plate on back
indicates BMR.

On Dec 30, 9:18 am, frank <fanza...@aol.com> wrote:
> you have the wrong cab, then. bmr's had the tall cab only. the head has two holes on the bottom. these will line up with the proper cab. i guess they do not line up with a reg bm or bassman cab holes.
>
>
>
>
>
>
>
> -----Original Message-----
> From: adbrunner <ambrun...@gmail.com>
> To: The Amp Guide <the-am...@googlegroups.com>
> Sent: Thu, Dec 30, 2010 10:14 am
> Subject: [The Amp Guide] Re: couple of questions on my silverface Bandmaster Reverb
>
> definitely wouldn't work with this cab then, as the countersunk

> hreaded pieces are a bit wide of where the head sits on the cab.

> robably meant to suit the bandmaster head with the hold-down pieces.
> --

> ou received this message because you are subscribed to "The Amp Guide" group.
> Thank you for your support.

> ww.ampwares.com
> ww.mojotone.com
> ww.guitarandampshow.com

[B L]

Yeah, pull switch = 76 or later. Bummer about the cabinet, but still a cool amp with great tone and potential. Don't fret too much over the cab thing. You have a great amp!

cheers,

CBG

--

[adbrunner]

yes, i absolutely love the amp's tone. Now that I know it's a mis-
match with the cab I think I'll have a little fun with it anyway. I
was going to restore the tolex and grill cloth, now I have a bigger
project in mind, turning it into a silverface version of the blackface
configuration -- cabinet turned horizantally with the logo moved into
the "new" upper-left corner (may need to fabricate a new frame for the
grill cloth to do that), maybe adding the tilt-legs? relocate the
countersunk threaded nuts.

a little crazy, but now that I'm not worried about the the value of
the cabinet much, why not?

[frank]

i've only seen the tall cab model with the holes in the head cab, and i spend a lot of time on ebay.

 i'll bet the 30" cab is the variation on the "sunn" cab after fender bought the sunn brand. i've seen bassman cabs in this config. it is the cab with the wide port exposed on the bottom front. does your head have large feet, which would go into recesses on a speaker cab, ala ampeg, et al?  is this how your buddy's works? could you or he post pix?

the 30" model must have produced in very low #'s.

 there is lots info on gibson amp production #'s, but i have yet to find fender production info.

-----Original Message-----
From: adbrunner <ambr...@gmail.com>

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www.mojotone.com
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[adbrunner]

i'll try to snap a few photos the next time i'm at his place. i don't
recall the shorter cab having a port, but not sure.

[B L]

Heck yes... why not. Good idea. Strap some tilt backs and tie downs on her and turn the reverb up to 11.

hehe

--

[adbrunner]

speaking of, i think i need to replace/repair the reverb tank. i'm
getting some really awful farty/distorty noises when i crank the
reverb right now. the trem sounds great, the reverb, not so much.

[frank]

jeese, this amp's a mess...

-----Original Message-----
From: adbrunner <ambr...@gmail.com>
To: The Amp Guide <the-am...@googlegroups.com>

[adbrunner]

best sounding mess i've ever owned. there's nothing at all wrong with
the amp other than the reverb. happens to have a mismatched cab that i
want to play around with, but i wouldn't exactly call that a mess...

[frank]

you were talking about the tolex and grille, no reverb. what else?

-----Original Message-----
From: adbrunner <ambr...@gmail.com>
To: The Amp Guide <the-am...@googlegroups.com>
Sent: Thu, Dec 30, 2010 1:06 pm
Subject: [The Amp Guide] Re: couple of questions on my silverface Bandmaster Reverb

best sounding mess i've ever owned. there's nothing at all wrong with
the amp other than the reverb. happens to have a mismatched cab that i
want to play around with, but i wouldn't exactly call that a mess...

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www.mojotone.com
www.guitarandampshow.com

[adbrunner]

the tolex and grills are fine. some minor discoloration to the grill
cloths, a few minor dings to the tolex but nothing major. I want to
recover them eventually so they look nice and crisp. didn't mean to
imply the amp was falling apart :)

http://www.flickr.com/photos/37711849@N00/5262729418/in/set-72157625604109166/

On Dec 30, 12:30 pm, frank <fanza...@aol.com> wrote:
> you were talking about the tolex and grille, no reverb. what else?
>
>
>
>
>
>
>
> -----Original Message-----
> From: adbrunner <ambrun...@gmail.com>
> To: The Amp Guide <the-am...@googlegroups.com>
> Sent: Thu, Dec 30, 2010 1:06 pm
> Subject: [The Amp Guide] Re: couple of questions on my silverface Bandmaster Reverb
>
> best sounding mess i've ever owned. there's nothing at all wrong with

> he amp other than the reverb. happens to have a mismatched cab that i

> ant to play around with, but i wouldn't exactly call that a mess...
> --

> ou received this message because you are subscribed to "The Amp Guide" group.
> Thank you for your support.

> ww.ampwares.com
> ww.mojotone.com
> ww.guitarandampshow.com

[adbrunner]

for what it's worth, based on serial numbers, no-tail logo, and master
volume pot, I'm now dating this to '77.

can anyone recommend the proper reverb tank from mojo tone? I'll test
the cables, solder joints, and jacks before actually buying a new
tank. the tube must be fine because the clean on that channel sounds
great.

thanks again to all for the help.

[B L]

Yeah, bummer on the reverb. 

Here are a couple things to check that are easy, and that any decent tech will check out for you for a fee. :-)

Verify the correct tubes in the correct positions...INCLUDING the rectifier tube. (I can't tell you the number of times I see 5U4G in place of a GZ34 or vice-versa. When you use a 5U4 in place of a GZ34, you drop 25 additional volts from the DC buss. When you do this, the reverb on a number of Fender amps gets weak and wierd.)  Moral is: Put in what your tube chart shows. Don't use a 5u4 because it fits, or a GZ34 because you've heard they are cool. Use what your amp specifies, unless you want to do the correct mods through the entire circuit.

12AT7 is the correct driver tube for your reverb. Not a 12AU7, not a 12AX7, not a 12AV7 or a 5751 because a guy told you it would work. It won't... they are not "almost" the same, and don't let anyone tell you they are.

This also might sound really obvious, but make sure that the reverb driver output jack (from the 12AT7 driven reverb transformer) is connected to the input of the reverb tank. The return from the tank drives the grid of a 7025/12AX7  :-) Those wires CAN and DO get swapped around on accident. They're not well labeled, carrying only a red dot of corona dope to help you figure out which wire is which at the tank. 

Here's the correct way they go: First, note that the RCA jack which actually carries the "OUTPUT" signal is actually labeled "INPUT" on the backplate of your amp. Go figure. Anyway, that means the jack labeled "input" on the tank goes to jack labeled "reverb input", and "ouput" of the tank goes to the jack labeled "reverb output". Sometimes confusing and often gotten wrong by people in a hurry and careless techs. While you're at it, temporarily swap in another set of RCA cables to verify that your cables aren't shorted. I see that sometimes.

Again, might seem very obvious, but not all reverb tanks are created equal. Check online to get the codes from your tank.  Here's a great explanation of how they work along with some code info. Examine your tank. If it looks like the wrong tank, (like a replacement, labeled "made in korea", etc.) it is probably the wrong tank. You should have an Accutronics tank in your 76 Bandmaster Reverb.

http://www.tubesandmore.com/scripts/foxweb.dll/extpage@d:/dfs/elevclients/cemirror/ELEVATOR.FXP?page=TECH_REVERB

As you can see from that link, there are vast differences between identical appearing tanks, having to do with the input impedance, number of springs, and decay time. The right tank can sound heavenly, the wrong one can sound plain bad. I see wrong tanks in Fenders all the time.

1 broken spring in your three spring tank can make things go south quick in the reverb tone department. 

Check the bias point on the 12AT7 driver. It should be about 8 volts. The 12AX7 return should be about 1.7, if memory serves me correct.

Of course, there are several other places things can go wrong, but the things I've given above are easy to check. Be careful if you open her up. A pissed off Fender can kill you in about half a second and not break a sweat. Don't guess...even a little. :-)

Cheers!

CoolBlueGlow

the Arkansas Tube King

[adbrunner]

thanks again. i'm 99% certain all the proper tubes are in the proper
places, i've been playing this amp for almost 3 years and the reverb
used to sound perfect and brilliant. just recently has it taken a turn
for the worse, and no tubes have been moved, no connections changed,
etc. from what you describe it seems likely that one of the springs
broke.

On Dec 30, 2:14 pm, B L <coolblueg...@gmail.com> wrote:
> Yeah, bummer on the reverb.
>
> Here are a couple things to check that are easy, and that any decent tech
> will check out for you for a fee. :-)
>
> Verify the correct tubes in the correct positions...INCLUDING the rectifier

> tube. (*I can't tell you the number of times I see 5U4G in place of a GZ34

> or vice-versa. When you use a 5U4 in place of a GZ34, you drop 25 additional
> volts from the DC buss. When you do this, the reverb on a number of Fender

> amps gets weak and wierd*.)  Moral is: Put in what your tube chart

> shows. Don't use a 5u4 because it fits, or a GZ34 because you've heard they
> are cool. Use what your amp specifies, unless you want to do the correct
> mods through the entire circuit.
>
> 12AT7 is the correct driver tube for your reverb. Not a 12AU7, not a 12AX7,
> not a 12AV7 or a 5751 because a guy told you it would work. It won't... they
> are not "almost" the same, and don't let anyone tell you they are.
>
> This also might sound really obvious, but make sure that the reverb driver

> output jack (from the 12AT7 driven reverb transformer) is connected to the *
> input* of the reverb tank. The return from the tank drives the grid of a

> 7025/12AX7  :-) Those wires CAN and DO get swapped around on accident.
> They're not well labeled, carrying only a red dot of corona dope to help you
> figure out which wire is which at the tank.
>
> Here's the correct way they go: First, note that the RCA jack which actually

> *carries* the "OUTPUT" signal is actually labeled "INPUT" on the backplate

> of your amp. Go figure. Anyway, that means the jack labeled "input" on the
> tank goes to jack labeled "reverb input", and "ouput" of the tank goes to
> the jack labeled "reverb output". Sometimes confusing and often gotten wrong
> by people in a hurry and careless techs. While you're at it, temporarily
> swap in another set of RCA cables to verify that your cables aren't shorted.
> I see that sometimes.
>
> Again, might seem very obvious, but not all reverb tanks are created equal.
> Check online to get the codes from your tank.  Here's a great explanation of
> how they work along with some code info. Examine your tank. If it looks like
> the wrong tank, (like a replacement, labeled "made in korea", etc.) it is
> probably the wrong tank. You should have an Accutronics tank in your 76
> Bandmaster Reverb.
>

> http://www.tubesandmore.com/scripts/foxweb.dll/extpage@d:/dfs/elevcli...

[KT]

Regarding tube subs in reverb driver situations...emphatically yes others will work...ax7 or at7 or 5751...done it for years with zero adverse effects, no fires, no melt downs. Let your ear tell you what you like. There is wiggle room here.

[vshe...@aol.com]

Good info on reverb issue - speaking of which, I have a 75 Silverface Twin and have been trying to get Reverb to work - have new tank, driver,tubes but there have been mods done to this amp and the AA270 schematic can't be trusted completely.....would anyone have any pictures of working unit inside chassis ?

 

Thanks and Happy New Year!

Vince Shemansky
vshe...@aol.com

-----Original Message-----
From: KT <thoms...@gmail.com>
To: the-am...@googlegroups.com <the-am...@googlegroups.com>
Cc: the-am...@googlegroups.com <the-am...@googlegroups.com>
Sent: Thu, Dec 30, 2010 11:14 pm
Subject: Re: [The Amp Guide] Re: couple of questions on my silverface Bandmaster Reverb

[vshe...@aol.com]

Forgot to add most important point - its a 135 W w/ Master Volume

[adbrunner]

Hope you find the help you need, vince.

As for my BMR, happy to report that today I took the tank out and
inspected. Everything looked pretty good inside, springs still nice
and tight, and clean. All wires and connections looked good, etc.
However, I have a feeling it was previously installed with the output
end near the end of the head w/ the power transformer. I cleaned all
the connections, inspected the cables, etc. It had the rubber/foamy
piece installed on the top of the pan to prevent vibration, but I also
read that it can help to place a piece of cardboard on the bottom of
the unit, so I went ahead and did that, put it back in the bag, hung
the bag, etc. Let the tubes warm up for a half hour or so, and it
sounds better than I've ever heard it sound. the verb was brilliant,
sounded great with the trem as well.

thanks again everyone.

On Dec 31, 12:43 pm, vsherm...@aol.com wrote:
> Forgot to add most important point - its a 135 W w/ Master Volume
>
> Vince Shemansky

> vsherm...@aol.com

>
>
>
> -----Original Message-----
> From: vsherm...@aol.com
> To: the-am...@googlegroups.com
> Sent: Fri, Dec 31, 2010 1:26 pm
> Subject: Re: [The Amp Guide] Re: couple of questions on my silverface Bandmaster Reverb
>
> Good info on reverb issue - speaking of which, I have a 75 Silverface Twin and have been trying to get Reverb to work - have new tank, driver,tubes but there have been mods done to this amp and the AA270 schematic can't be trusted completely.....would anyone have any pictures of working unit inside chassis ?
>
> Thanks and Happy New Year!
>
> Vince Shemansky

> vsherm...@aol.com

>
> -----Original Message-----
> From: KT <thomson...@gmail.com>
> To: the-am...@googlegroups.com <the-am...@googlegroups.com>
> Cc: the-am...@googlegroups.com <the-am...@googlegroups.com>
> Sent: Thu, Dec 30, 2010 11:14 pm
> Subject: Re: [The Amp Guide] Re: couple of questions on my silverface Bandmaster Reverb
>
> Regarding tube subs in reverb driver situations...emphatically yes others will work...ax7 or at7 or 5751...done it for years with zero adverse effects, no fires, no melt downs. Let your ear tell you what you like. There is wiggle room here.
>

> On Dec 30, 2010, at 3:14 PM, B L <coolblueg...@gmail.com> wrote:
>
> Yeah, bummer on the reverb.  
>
> Here are a couple things to check that are easy, and that any decent tech will check out for you for a fee. :-)
>
> Verify the correct tubes in the correct positions...INCLUDING the rectifier tube. (I can't tell you the number of times I see 5U4G in place of a GZ34 or vice-versa. When you use a 5U4 in place of a GZ34, you drop 25 additional volts from the DC buss. When you do this, the reverb on a number of Fender amps gets weak and wierd.)  Moral is: Put in what your tube chart shows. Don't use a 5u4 because it fits, or a GZ34 because you've heard they are cool. Use what your amp specifies, unless you want to do the correct mods through the entire circuit.
>
> 12AT7 is the correct driver tube for your reverb. Not a 12AU7, not a 12AX7, not a 12AV7 or a 5751 because a guy told you it would work. It won't... they are not "almost" the same, and don't let anyone tell you they are.
>
> This also might sound really obvious, but make sure that the reverb driver output jack (from the 12AT7 driven reverb transformer) is connected to the input of the reverb tank. The return from the tank drives the grid of a 7025/12AX7  :-) Those wires CAN and DO get swapped around on accident. They're not well labeled, carrying only a red dot of corona dope to help you figure out which wire is which at the tank.
>
> Here's the correct way they go: First, note that the RCA jack which actually carries the "OUTPUT" signal is actually labeled "INPUT" on the backplate of your amp. Go figure. Anyway, that means the jack labeled "input" on the tank goes to jack labeled "reverb input", and "ouput" of the tank goes to the jack labeled "reverb output". Sometimes confusing and often gotten wrong by people in a hurry and careless techs. While you're at it, temporarily swap in another set of RCA cables to verify that your cables aren't shorted. I see that sometimes.
>
> Again, might seem very obvious, but not all reverb tanks are created equal. Check online to get the codes from your tank.  Here's a great explanation of how they work along with some code info. Examine your tank. If it looks like the wrong tank, (like a replacement, labeled "made in korea", etc.) it is probably the wrong tank. You should have an Accutronics tank in your 76 Bandmaster Reverb.
>

> http://www.tubesandmore.com/scripts/foxweb.dll/extpage@d:/dfs/elevcli...

>
> As you can see from that link, there are vast differences between identical appearing tanks, having to do with the input impedance, number of springs, and decay time. The right tank can sound heavenly, the wrong one can sound plain bad. I see wrong tanks in Fenders all the time.
>
> 1 broken spring in your three spring tank can make things go south quick in the reverb tone department.
>
> Check the bias point on the 12AT7 driver. It should be about 8 volts. The 12AX7 return should be about 1.7, if memory serves me correct.
>
> Of course, there are several other places things can go wrong, but the things I've given above are easy to check. Be careful if you open her up. A pissed off Fender can kill you in about half a second and not break a sweat. Don't guess...even a little. :-)
>
> Cheers!
>
> CoolBlueGlow
>
> the Arkansas Tube King
>

[vshe...@aol.com]

Wow! Congrats - you got lucky A.D.

Vince Shemansky
vshe...@aol.com

-----Original Message-----
From: adbrunner <ambr...@gmail.com>

[B L]

Yeah, 

You know...don't overlook the obvious: Tubes do go bad. That 12AT7 driving your reverb circuit is under considerable strain, and it does wear out. If you don't have a spare handy, you can simply swap the two 12AT7's in your amp. When you  make the swap from reverb driver into phase splitter position, and if you notice an obvious problem with your overall tone, you can presume the 12AT7 you swapped into the phase splitter from the reverb driver is toast. Again, it'll be fairly obvious. :-) Same thing could be true for the 1/2 of the 12AX7 that acts as the return mixer for the reverb tank output. You can do the same swap with that AX and any other AX / 7025 in your amp.

Cheers!

CBG

[B L]

re: preamp tube substitutes in Fender designs "others will work with no adverse effects".

Not trying to start a tone war here and definitely not trying to disrespect KT.  - and KT is correct - various 9 pin dual triode tubes will work in various holes, sort of. If, however, by "no adverse effects" one ignores the premature destruction of at perfectly good 12AX7 due to prolonged operation far into cutoff due to an way-wrong bias point and a way-overloaded plate, then yes one can technically fit the 12AX7 in the same socket as the 12AT7 for the reverb driver (and the phase splitter) and yes - some kind of sound will come out and there won't be smoke. Heck, you might even like the tone. 

If, however, we mean to make the amp sound as it was designed, (and have the tone for which Fenders are legendary) then we cannot expect to swap most Fender 9 pin DT's around with impunity. The sought after holy grail of brand-establishing tone for which 50's and early 60's Fender amps are known is not based on the logo's tail, the color  of the face plate, or even the year in which it was manufactured or (mostly) whether you have NOS Mullards in the amp. It is based on close adherence to operational and design values built into the particular circuit in question. It really is just about that simple.

Some Fender circuits sound great, some not-so-great, but in any particular circuit, those values are really not very negotiable...at least if one wants the Fender tone for that particular circuit. Now, if we want to invent a new tone, swap away. Before swapping, I think an honest question is in order, namely; Do we really think we can make a known excellent performing Fender design better in five minutes by swapping in a few wrong value tubes? Certainly one can try...in fact, that's what CBS engineers did when they took over the R&D in the late 60's. I'll leave it to the reader to decide if they made it better. Remember, CBS guys spent way more than five minutes swapping tubes around, and they still managed to screw up that which Leo had carefully built over two decades of design, tinkering, experimentation and continuous feedback from performing musicians.

Sure, I've heard and modded plenty of Fenders over they years...we all have. A few of the mods I've heard/done sounded pretty good. IMO, most were/are tone-rubbish, when compared in an A/B shootout of a properly functioning stock circuit of the same design. Again, this is all just my particular philosophy of mods. For what it is worth, (which some inform me is about 1 cup of coffee :-) it is based on 30+ years of professionally working on and professionally using Fenders as a live and studio musician, engineer and producer on hundreds of sessions and thousands of gigs.

So, before I swap ANYTHING in a particular design - I always ask myself a simple question. "Is this amp operating EXACTLY as designed in stock form?" If the answer is yes, and if the tone is less than wonderful when compared to a known-good reference tone (Say my bone stock original 63 Vibroverb, 65 Princeton Reverb, or 66 Pro Reverb, etc.) now I have a basis for tinkering. If the answer is no, then I am first in need of returning the circuit to its original specification before deciding that a tube swap is the right solution for a bad sounding amp. In my experience, there is a simple way to determine with reasonable accuracy if the amp IS working as designed. Put it on the bench and check each and every Fender-specified operating point, verifying that it is spot-on voltage correct That means each and every Fender specified value at each and every test point. That's why they're on the schematic. Once one has done that, and learned why they're what they are, and corrected any issues making them err, then IMO that person has begun to pay the dues to make meaningful sensible and tone-worthy mods. Anything less is really just uniformed guessing with no baseline reference of good vs. bad tone.

re Tube substitutions that can hurt you:

Besides the non-Fenderish tone issues in mis-tubed preamp circuits, there are most certainly very serious adverse effects possible by swapping in a near-fit substitute rectifier tube. One obvious one is the meltdown of the 5V filament winding in the mains transformer of smaller Fender amps (Princetons, Deluxes, etc.) If you don't believe me, examine the RCA tube data sheet for filament current on a 5R4 or even a 5U4 compared to a 5AR4. Sure, you can put that 5U4 or 5R4 right in that rectifier socket, it'll work for a while. A 5U4 in a GZ34 designed circuit will definitely not sound the same (or as good IMO) and it will almost certainly add an unacceptable level of additional load to your primary transformer. That additional filament load will, sooner or later, do bad and unwanted things to your Fender amp. Solid state plug in rectifier have their own no-no issues as well. In many earlier Fender designs, the additional B+ and PIV spikes of a "made for TV replacement" solid state rectifier substitute will exceed the rating of the electrolytic caps in the filter pack, sometimes causing them to fail with rather spectacular results.

So, yes - Fenders are very forgiving, and will tolerate a lot of abuse. Do they sound "better" because of it? I'm not so sure. IF they did, every guy who could swap a few tubes around with no understanding of load lines, tube ratings, bias points, etc. would be a 'tube amp guru'. :-)

I've been working on Fenders for over 35 years. When I have an amp on my bench, and the owner is complaining that it doesn't sound good, I don't start with mods, tube swaps, and esoteric vintage parts hunts. I simply return it to the design values as described by Leo Fender and his cohorts.  Usually that involves the following;

1. Measure the values. Observe variations +/- 10%, then remove the broken or aged component(s) to restore the values to stock.

2. Undue the "special mods" done by someone else who didn't bother to do #1 when trying to make the amp sound right.

After this simple procedure, 95 percent of the time the owner leaves amazed, shocked, and happy...simply because he's never heard his amp as it was originally designed. Just my opinion, but when trying to find that magic Fender tone in a Fender design that is ailing, I always ask a simple question "what would Leo do?" Then I look at the schematic and make it so. Peace to KT though. He's correct technically correct to say you can swap them around in there and not get smoke.

Cheers,

cbg

[kevin thomson]

fully worthwhile perusing, cbg!! No hatin' here...and I should have mentioned that it is necessary to be sure you are not overloading plates or providing too much or too little bias when performing swaps. Check those RCA tube manuals for each tube in question or find the specs here online.

There is much to say in favor of going bone stock...but hey, sometimes you have to try a Holley carb in place of a Carter and vice versa...no? 

It's always all in the fun...especially when we are dealing with fender amps from the mid to late seventies.

Thanks for all the good info and happy new year!......kt

[B L]

:-)

true, true... and thanks for the grace. Comes right back to you my friend...and you're right on both counts. Nothing wrong with swapping out a Q-jet OR a 12AT7. hehe :-)

A great new year to you as well!

k

[adbrunner]

very good reading, much appreciated on all accounts. Thanks again and
happy new year :)

On Jan 3, 7:41 am, B L <coolblueg...@gmail.com> wrote:
> :-)
>
> true, true... and thanks for the grace. Comes right back to you my
> friend...and you're right on both counts. Nothing wrong with swapping out a
> Q-jet OR a 12AT7. hehe :-)
>
> A great new year to you as well!
>
> k
>
>
>
>
>
>
>
> On Sun, Jan 2, 2011 at 3:05 PM, kevin thomson <thomson...@gmail.com> wrote:
> > fully worthwhile perusing, cbg!! No hatin' here...and I should have
> > mentioned that it is necessary to be sure you are not overloading plates or
> > providing too much or too little bias when performing swaps. Check those RCA
> > tube manuals for each tube in question or find the specs here online.
>
> > There is much to say in favor of going bone stock...but hey, sometimes you
> > have to try a Holley carb in place of a Carter and vice versa...no?
>
> > It's always all in the fun...especially when we are dealing with fender
> > amps from the mid to late seventies.
>
> > Thanks for all the good info and happy new year!......kt
>

> > On Sun, Jan 2, 2011 at 1:50 PM, B L <coolblueg...@gmail.com> wrote:
>
> >> re: preamp tube substitutes in Fender designs "others will work with no
> >> adverse effects".
>
> >> Not trying to start a tone war here and definitely not trying to
> >> disrespect KT.  - and KT is correct - various 9 pin dual triode tubes will
> >> work in various holes, sort of. If, however, by "no adverse effects" one
> >> ignores the premature destruction of at perfectly good 12AX7 due to
> >> prolonged operation far into cutoff due to an way-wrong bias point and a

> >> way-overloaded plate, then *yes* one can technically fit the 12AX7 in the

> >> same socket as the 12AT7 for the reverb driver (and the phase splitter) and
> >> yes - some kind of sound will come out and there won't be smoke. Heck, you
> >> might even like the tone.
>

> >> If, however, we mean to make the amp sound *as it was designed*, (and

> >> have the tone for which Fenders are legendary) then we cannot expect to swap
> >> most Fender 9 pin DT's around with impunity. The sought after holy grail of
> >> brand-establishing tone for which 50's and early 60's Fender amps are known
> >> is not based on the logo's tail, the color  of the face plate, or even the
> >> year in which it was manufactured or (mostly) whether you have NOS Mullards
> >> in the amp. It is based on close adherence to operational and design values
> >> built into the particular circuit in question. It really is just about that
> >> simple.
>
> >> Some Fender circuits sound great, some not-so-great, but in any particular
> >> circuit, those values are really not very negotiable...at least if one wants
> >> the Fender tone for that particular circuit. Now, if we want to invent a new
> >> tone, swap away. Before swapping, I think an honest question is in order,

> >> namely; Do we *really* think we can make a known excellent performing

> >> Fender design better in five minutes by swapping in a few wrong value tubes?
> >> Certainly one can try...in fact, that's what CBS engineers did when they
> >> took over the R&D in the late 60's. I'll leave it to the reader to decide if

> >> *they* made it better. Remember, CBS guys spent way more than five

> >> minutes swapping tubes around, and they still managed to screw up that which
> >> Leo had carefully built over two decades of design, tinkering,
> >> experimentation and continuous feedback from performing musicians.
>
> >> Sure, I've heard and modded plenty of Fenders over they years...we all
> >> have. A few of the mods I've heard/done sounded pretty good. IMO, most
> >> were/are tone-rubbish, when compared in an A/B shootout of a properly
> >> functioning stock circuit of the same design. Again, this is all just my
> >> particular philosophy of mods. For what it is worth, (which some inform me
> >> is about 1 cup of coffee :-) it is based on 30+ years of professionally
> >> working on and professionally using Fenders as a live and studio musician,
> >> engineer and producer on hundreds of sessions and thousands of gigs.
>
> >> So, before I swap ANYTHING in a particular design - I always ask myself a
> >> simple question. "Is this amp operating EXACTLY as designed in stock form?"
> >> If the answer is yes, and if the tone is less than wonderful when compared

> >> to a known-good reference tone (*Say my bone stock original 63 Vibroverb,
> >> 65 Princeton Reverb, or 66 Pro Reverb, *etc.) now I have a basis for

> >> tinkering. If the answer is no, then I am first in need of returning the

> >> circuit to its original specification *before* deciding that a tube swap

> >> is the right solution for a bad sounding amp. In my experience, there is a
> >> simple way to determine with reasonable accuracy if the amp IS working as
> >> designed. Put it on the bench and check each and every Fender-specified
> >> operating point, verifying that it is spot-on voltage correct That means

> >> *each and every Fender specified value at each and every test point*.

> >> amazed, shocked, and happy...simply because he's *never *heard his amp as

> >> it was originally designed. Just my opinion, but when trying to find that
> >> magic Fender tone in a Fender design that is ailing, I always ask a simple

> >> question "*what would Leo do*?" Then I look at the schematic and make it

> >> so. Peace to KT though. He's correct technically correct to say you can swap
> >> them around in there and not get smoke.
>
> >> Cheers,
>
> >> cbg
>

> >> On Thu, Dec 30, 2010 at 10:14 PM, KT <thomson...@gmail.com> wrote:
>
> >>> Regarding tube subs in reverb driver situations...emphatically yes others
> >>> will work...ax7 or at7 or 5751...done it for years with zero adverse
> >>> effects, no fires, no melt downs. Let your ear tell you what you like. There
> >>> is wiggle room here.
>

> >>> On Dec 30, 2010, at 3:14 PM, B L <coolblueg...@gmail.com> wrote:
>
> >>> Yeah, bummer on the reverb.
>
> >>> Here are a couple things to check that are easy, and that any decent tech
> >>> will check out for you for a fee. :-)
>
> >>> Verify the correct tubes in the correct positions...INCLUDING the

> >>> rectifier tube. (*I can't tell you the number of times I see 5U4G in

> >>> place of a GZ34 or vice-versa. When you use a 5U4 in place of a GZ34, you
> >>> drop 25 additional volts from the DC buss. When you do this, the reverb on a

> >>> number of Fender amps gets weak and wierd*.)  Moral is: Put in what your

> >>> tube chart shows. Don't use a 5u4 because it fits, or a GZ34 because you've
> >>> heard they are cool. Use what your amp specifies, unless you want to do the
> >>> correct mods through the entire circuit.
>
> >>> 12AT7 is the correct driver tube for your reverb. Not a 12AU7, not a
> >>> 12AX7, not a 12AV7 or a 5751 because a guy told you it would work. It
> >>> won't... they are not "almost" the same, and don't let anyone tell you they
> >>> are.
>
> >>> This also might sound really obvious, but make sure that the reverb
> >>> driver output jack (from the 12AT7 driven reverb transformer) is connected

> >>> to the *input* of the reverb tank. The return from the tank drives the

> >>> grid of a 7025/12AX7  :-) Those wires CAN and DO get swapped around on
> >>> accident. They're not well labeled, carrying only a red dot of corona dope
> >>> to help you figure out which wire is which at the tank.
>
> >>> Here's the correct way they go: First, note that the RCA jack which

> >>> actually *carries* the "OUTPUT" signal is actually labeled "INPUT" on

> >>> the backplate of your amp. Go figure. Anyway, that means the jack labeled
> >>> "input" on the tank goes to jack labeled "reverb input", and "ouput" of the
> >>> tank goes to the
>

> ...
>
> read more »