Fender Twin Mods
Graham
Having never liked the sound of my Twin that much, I did some serious
research and tried out a couple of simple mods that I found on this
site: http://fenderguru.com/amps/twin-reverb
The ones I did were:
(1) pull out valve 1 (reading from the right, rear panel) - this is
the 'normal' channel preamp, so you don't need it if you go through
the 'vibrato/reverb' channel all the time.
(2) Pull out valve 6 (phase inverter) and stick valve 1 in there
instead. This changes the type of valve from 12ax7 to 12at7.
I don't fully understand all the technical explanations (see the
website), but boy does this improve the sound dramatically! Now the
amp sounds really mellow and rich at low volumes, ideal for jazz. I
think you lose some volume and clean headroom but that doesn't matter
for the levels I play at.
Wish I'd known these tricks years ago! I still can't lift the damn
thing though, so I'll keep my Cube 80x as well. Funnily enough, to my
ears the Twin now sounds very similar to the Cube's clean channel,
though I haven't tried them side-by-side yet.
Graham
Lord Valve
> A while ago there was some discussion about modding Fender amps.
> Having never liked the sound of my Twin that much, I did some serious
> research and tried out a couple of simple mods that I found on this
> site: http://fenderguru.com/amps/twin-reverb
Some rather laughable misinformation there.
And no, I don't want to argue with the dude who
wrote it, so leave me out of it, please.
> The ones I did were:
>
> (1) pull out valve 1 (reading from the right, rear panel) - this is
> the 'normal' channel preamp, so you don't need it if you go through
> the 'vibrato/reverb' channel all the time.
This slightly increases the gain on the Vibrato channel, for reasons I
won't go into.
Derek Trucks runs all his BF/SF Fenders this way.
> (2) Pull out valve 6 (phase inverter) and stick valve 1 in there
> instead. This changes the type of valve from 12ax7 to 12at7.
...
If that's what happened in your case, then you
had incorrectly-installed tubes to begin with.
If you swapped V1 and V6 and wound up with
a 12AT7 in V6, what you did was put the tubes
*back* to the way they were supposed to be
in the first place.
I find incorrectly placed tubes in Fenders *all
the time* - I just did a Vibrolux Reverb yesterday
which came in with the tremelo not working; it
had a 12AT7 in the #5 position. Naturally, the
owner had misdiagnosed the problem and
hacked his footswitch up, figuring the switch
was fucked or something. By the time it was
all over, his bill was $117 (he had some other
things that needed looking after) - but had
he taken the time to pull each preamp tube
and compare the number on the glass to the
number on the tube chart, I'd never have seen
him in the first place.
> I don't fully understand all the technical explanations (see the
> website), but boy does this improve the sound dramatically!
...
If you indeed now have a 12AT7 in the #6 hole,
that's not surprising. Most folks (including me)
think Fenders sound like ass with a 12AX7 in
that position. Some folks like it, though - mostly
shredders and other vermin. The tube chart
calls for a 12AT7 in the #6 hole, as God and
Leo Fender intended. There *is* a reason.
> Now the
> amp sounds really mellow and rich at low volumes, ideal for jazz. I
> think you lose some volume and clean headroom but that doesn't matter
> for the levels I play at.
>
> Wish I'd known these tricks years ago! I still can't lift the damn
> thing though, so I'll keep my Cube 80x as well. Funnily enough, to my
> ears the Twin now sounds very similar to the Cube's clean channel,
> though I haven't tried them side-by-side yet.
So -
You've managed to make your Twin sound like
a solid state amp, and now you like it. Perhaps
there's a lesson in that for you, eh? ;-)
Lord Valve
Expert
Tom Walls
>
> You've managed to make your Twin sound like
> a solid state amp, and now you like it.
Sounds like a SS amp that is designed to emulate a tube amp.
Graham
EXACTLY what the website says, i.e. I removed a 12at7 from valve 6 and
replaced it with a 12ax7. So my amp was correctly set up in valve 6
to start with, but I have now changed it to 12ax7.
Now it sounds a lot warmer, and I prefer it that way.
This amp had quite a thin 'glassy' tone before, now it sounds great
for jazz. So does my Cube 80x.
Graham
sheetsofsound
Lord Valve
I never tell people what they should like.
I can report, however, that the vast majority of
Fender owners (including some of my rather
famous and highly talented guitar-playing clients)
prefer the 12AT7 in the PI hole.
There are a *shitload* of different Fender "Twins."
Which one do you have? The year, if known?
Lord Valve
Expert
Graham
> There are a *shitload* of different Fender "Twins."
> Which one do you have? The year, if known?
Not sure, but when I looked into serial nos. and so on some time back,
I thought it could be mid-1970s. I bought it used in 1980. It has
the silver control panel, a single 15" speaker, and the 'push-pull'
volume knob.
Lord Valve
> Those sound like gerald weber "mods" and are laughable IMO.
Some of them have been around quite a bit longer than Gerald.
The NFB (he calls it NBF, for some reason...) thing is
valid, although he doesn't seem to understand how it
works. It's better to leave the 820-ohm feedback
resistor in place, putting it in series with a 5- or 10-K
pot. When such a pot is turned all the way down,
the amp will have a "stock" PI stage, so the "mod"
is completely defeated. Turning the pot up lessens
the amount of negative feedback, which increases
the amp's gain a bit, along with an increase in noise
(not huge, but hearable) and distortion...which many
guitarists enjoy. I recommend it - but not the way
"the guru" implements it. If you use a switch to completely
remove the NFB from the PI stage, there's a good
chance that the amp will oscillate if it's one of those
sloppily-wired silverface models. (Those amps
have a whole lot of extra wire in them, and this
causes problems.) Using a pot makes much more
sense.
When it comes to replacing the output transformer
and operating the amp into an upward mismatch -
which "the guru" describes as a "built-in attenuator" -
"the guru" strays into total electronic whacktardism.
Operating a tube amp - *especially* one which has
had the NFB loop disabled - into an upward impedance
mismatch (i.e., running a 4- or 8-ohm load on a 2-ohm
transformer tap) flirts with a condition known as
high-tension flyback. If this occurs, an arc will
jump from the plate circuit into the filament string.
This will fry - at the very least - one of the power
tube sockets. It also usually fries the tube in that
socket, and in amps which have a "hum balance"
control, it fries the control, too. It can also kill the
output transformer, the power transformer, filter
caps, and preamp tubes. It's bad mojo, and it's
just a stupid fuckin' idea. I fix lots of amps which
have arced sockets (or worse) from people
running them into higher impedances than the
transformer is expecting to see; many Fenders
have 4-ohm outputs, and lots of them get plugged
into Marshall 4-12 boxes, most of which are 16
ohms. Whoops, time to make a large contribution
to my favorite charity, The Lord Valve Home for
Lord Valve. ;-)
Don't get me started...
Lord Valve
Expert
Lord Valve
A single 15"?
And it says "Twin Reverb" on it? If this is the
case, your Twin has been modified by the
installation of a new baffle to accept the 15"
speaker. There were never any Twin Reverbs
made with any speaker complement other
than two twelves. There were some amps
made which used the 100- and 135-watt
chasses ("Twin" electronics) with a single
15", but all of them were known as "Vibrosonics"
and they had a different output transformer
(8-ohm output instead of 4). (In this vein, the
"Twin" chassis was also used in the Super
Six, which had six 10" speakers in it, and
in the Quad Reverb, which used four 12".)
Please look on the back and see what it says
underneath the speaker output jacks. You
should see either "100 watts" or "135 watts."
Also, take a look at the speaker and see if
you can tell what impedance it is. If it's
8 ohms (most common value) then that
may well explain why you didn't like the
way your amp was sounding; a stock Twin
has a 4-ohm output transformer, and you've
been running it into a mismatch unless the
speaker is a 4-ohm type, or unless the
output transformer was replaced with one
that matches the speaker.
Lord Valve
Expert
Graham
> Please look on the back and see what it says
> underneath the speaker output jacks. You
> should see either "100 watts" or "135 watts."
> Also, take a look at the speaker and see if
> you can tell what impedance it is. If it's
> 8 ohms (most common value) then that
> may well explain why you didn't like the
> way your amp was sounding; a stock Twin
> has a 4-ohm output transformer, and you've
> been running it into a mismatch unless the
> speaker is a 4-ohm type, or unless the
> output transformer was replaced with one
> that matches the speaker.
>
The amp says 'Twin Reverb' on the front panel and no other name. On
the rear are 2 speaker jacks next to each other, one called 'Speaker'
and one called 'Ext Speaker'. Under these it says 'Total load 4 ohms
100 Watts RMS'.
The speaker is an Altec Lansing 8 ohms, so this looks like a
mismatch. It does have the original flat-headed Fender speaker plug,
but I guess this could have been retained and re-used.
Either way I'm happy with the sound it now makes, compared to before,
so those mods made it sound better, which is ok by me!
Lord Valve
And that, folks, is why The Lord gets the big money. ;-)
Lord Valve
Expert
Gerry
> Not sure, but when I looked into serial nos. and so on some time back,
> I thought it could be mid-1970s. I bought it used in 1980. It has
> the silver control panel, a single 15" speaker, and the 'push-pull'
> volume knob.
I thought the Twin Reverb had two 12" speakers, and that was the "twin"
part. There's a twin reverb out there with a single 15 inch speaker?
Interesting.
--
-- At this point Sharazad saw the approach of morning and discreetly
fell silent.
Graham
> I thought the Twin Reverb had two 12" speakers, and that was the "twin"
> part. There's a twin reverb out there with a single 15 inch speaker?
> Interesting.
I always thought that, but maybe it's the twin channels it refers to.
I have never been able to find out if mine was some weird custom job
or not. If it is, it's been done so well that everything looks
original.
Tim Sprout
The faceplate may not be original. My 70's SF Twin, bought used in the
80's, came with a faceplate that says "Quad Reverb".
-Tim Sprout
Graham
> The faceplate may not be original. My 70's SF Twin, bought used in the
> 80's, came with a faceplate that says "Quad Reverb".
I have done some more digging on this, and one possibility is that my
amp was converted to a single 15" by a pedal steel player. There are
some pedal steel forum threads I found where they rave about how great
an Altec Lansing 15" 418B (same speaker as mine) sounds in a Fender
Twin!
I also found a reference to B.B. King favouring Altec Lansings in
Fender Twins.
Ray
> On 2011-08-18 09:02:26 -0700, Graham said:
>
>> Not sure, but when I looked into serial nos. and so on some time
>> back, I thought it could be mid-1970s. I bought it used in 1980. It has
>> the silver control panel, a single 15" speaker, and the
>> 'push-pull' volume knob.
>
> I thought the Twin Reverb had two 12" speakers, and that was the
> "twin" part. There's a twin reverb out there with a single 15 inch
> speaker? Interesting.
I thought it referred to the speakers. After all, the Quad Reverb had 4
spkrs. Eh, what to they know? They've been calling tremolo "vibrato" for 50
yrs or more.
Jonathan
LV,
I don't understand all this electrical mumbo-jumbo, but
I have a Twin Reverb that I bought new about 10 or 12 years ago, and
It sounds a little brighter than I would like for Jazz.
Is that typical for amps of this era?
Thanks,
Jonathan
Lord Valve
That would make it around a 2000 vintage?
It would be a '65 Twin Reverb Reissue, yes?
Those come with the horrible Sovtek 5881
power tubes installed. (They may say Groove
Tubes on the glass, but Sovtek 5881s are what
they are.) These amps can benefit from a tube
change, and they will certainly sound a *whole*
lot better with different speakers; I'd suggest the
Weber Chicago ceramic, paper dome. With
proper tubes, speakers, and tweaking, the '65
reissue can sound about 85% as good as the
real thing, and that's a fine neighborhood in
which to reside. Making one of those "perfect"
takes a lot of money - so much that you can
almost get a real '65 for the same bread.
Unless you're a tone fanatic (like me) I
wouldn't go beyond re-tubing and better
speakers; if you have an extra $200 or so
to put into the mix, then a Mercury Magnetics
output transformer certainly wouldn't hurt.
Beyond that is "downdating" (some techs
call it "born again"), which involves ripping
everything out of the chassis and replacing
it with high-quality vintage-type components,
old-school eyelet boards, solid-core cloth-
covered wiring (I prefer Teflon, myself, but
the Vintage Wankers are relentless on this
kinda shit...) and using Mercury Magnetics
stuff for all the iron. Really, the only thing
that gets used from the original parts is
stuff like knobs. Can't even use the old
pots - they're cheap-ass Chinese circuit
board mounted types. Last one I did a
full-tilt boogie like that on cost the dude
$1200, and he bought the amp off CL
for $450. (It was blown up.) So, for
$1650, he got the equivalent of a brand
new '65 blackface Twin Reverb, which
will still be workjing just fine 50 years
from now like most of the original ones.
Was it worth it? He wants another one. ;-)
Lord Valve
Expert
Tim McNamara
Jonathan <gosto.d...@gmail.com> wrote:
> I don't understand all this electrical mumbo-jumbo, but I have a Twin
> Reverb that I bought new about 10 or 12 years ago, and It sounds a
> little brighter than I would like for Jazz. Is that typical for amps
> of this era?
I find it to be true of blackface and silverface Fenders in general.
Great for other types of music, but too bright and too lacking in mids
for what I want to hear in my sound for jazz. The earlier tweeds are
usually better to my ears (both old Gibson and Fender "tweed era" amps)
with a nice warmth. However, some might argue that the blackface and
silverface era Fenders had better clean headroom than the tweeds;
they're probably right.
--
We are buried beneath the weight of information,
which is being confused with knowledge;
quantity is being confused with abundance and
wealth with happiness. -Tom Waits