1970s Fender Super Reverb - Suggestions for 5U4GB rectifier replacement
Bluesbreaker
has way too much sag at full volume with an overdrive pedal in front.
I'm interested in a solid state rectifier replacement. The amp
currently uses a 5U4GB.
The 5U4 drops 50V at max, which accounts for a very noticeable sag
(SWOOP) when the amp is being pushed hard with a strong input signal.
I'd like to try a solid-state rectifier with 1N007 diodes. I'm just
afraid of the 50V bump in B+. What do most folks do to convert to SS
rectifier? Would the increase in B+ need to be reduced with a Zener
or something?
OR
Perhaps a 5AR4 (which drops only 17V at max)? Would this be a safe
substitution to try? What readings should I take before/after to
determine?
RS
I doubt that it's the 5U4's sag that you're hearing. The usual effect
at top volume is a sort of over-the-top compression that's caused by
grid conduction. There's not a lot that you can do about that, and in
fact, it's one of the things that in lesser amount, makes the amp
sound alive.
If you're positive that you want to swap the rectifier, you could look
at WeberVST for the Copper Cap rectifiers:
http://www.webervst.com/ccap.html
However, if you're routinely cranking the amp to 10, I don't think
that raising B+ is a great idea. If you need the volume, why not get
a bigger amp?
Phil_S
"RS" <R...@saynotospam.com> wrote in message
news:6934m5hg2pgak8v19...@4ax.com...
As I understand it, a copper cap is designed to give some sag and emulate a
tube rectifier.
What are you really chasing here? Changing to SS diodes will push voltage
up into the 400's (don't know where your amp actually idles now). This is
going to change some operating parameters. I'm not sure more = better and
you've expressed your own concerns on this point. Be careful what you do to
this antique. FWIW, I think RS may be on the right track. If it's not
enough watts, get another amp. Don't try to make this one do what it wasn't
designed for.
If it's in good condition, it will fetch a very good price, which is why I
said to be careful. Don't do anything you can't reverse. If you stress it
with high voltage, you might do something to the amp that was unintended.
You might actually be better off changing the PT for one that fits the
existing holes and puts out less voltage. Then you can go for the SS
rectifier, which you can hang right on the tube socket. Save the old PT.
Peter Alerich
<bluesb...@gmail.com> wrote:
I ran a Weber Copper Cap WZ68 in my 1972 Super Reverb without any
problems. The CC is a solid state device built to emulate the behavior
of a tube rectifier (including sag) and is a drop in replacement. The
WZ68 has a voltage drop of 17vdc like GZ34 tube but will supply twice
the current. I seem to recall my B+ was about 465VDC. I recapped it
with fresh Sprague Atoms and was running Chinese Shuguang 6L6 tubes
and it was happy as a clam. It seemed to improve the sag
characteristics over the stock 5U4 rectifier and I liked the extra B+.
It seemed to add a touch more clean headroom.
I have a solid state rectifier but never tried it in my SR. I'm not
sure what the upper end B+ is for those Shuguangs. Depending on your
current B+ is you may not have to go the zener route with a solid
state rectifier.
Lord Valve
OK, Slick -
Just shove a 5AR4 in there and get on with things.
It won't change your B+ by more than a few volts, but
when you drive the amp hard the B+ won't drop as
far as it does with the 5U4. In addition, the 1.9A
filament draw of the 5AR4 is 1.1A less than the
3.0A drawn by the 5U4; this will result in a modest
reduction in power transformer core temperature,
which is beneficial. One of the reasons the old
blackface super reverbs sound better (and "better"
is a judgement call, but my judgement's fairly good)
is the fact that they used 5AR4s instead of 5U4s.
You'd be surprised at the improvement you might
obtain just by using a 5AR4 - and it's plug-n-play,
just shove it in, check bias, and rock.
The Weber Copper Cap (in this case, the WZ-34)
is another thing you can try; it doesn't sound like a
real rectifier tube, but some folks actually prefer it
to the real thing. The WZ-68 is a candidate here,
too; it's rated at twice as much current and will
sag the least of any of the rectifiers we've been
discussing. It'll be about as close as you can go
to straight diodes and still have a bit of sag. And
since the Copper Caps have no filaments, the
transformer core temperature will go down quite
a bit, as the 5.0 VAC rectifier filament winding
will be unloaded.
You can also go to straight diodes - three in
series on each leg of the PT's HV winding -
but you'll do well to measure the voltages
across all the HV filters and make sure
you're not exceeding any of their ratings.
If you do this, note that you can increase
the capacitance of the main filter stack
(which is now two 70uF/350V caps in
series, for an input capacitance of 35uF)
to quite a bit more than normal - I've seen
as much as 220uF here on SRs with SS
rectifiers in them. The low end will get very
tight and punchy (like a Twin) with a setup
like this, and you'll have better transient
response. I don't care for SRs set up like
this myself, but I've turned out a few for
people who requested it. And note that
if you put large capacitors in the input
position, you *cannot* go back to a rectifier
tube without removing them, as a 5AR4
loaded with (for instance) 220uF will
probably last less than 100 hours.
That's my story and I'm a-stickin' to it.
Lord Valve
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Peter Alerich
<detr...@ix.netcom.com> wrote:
>You can also go to straight diodes - three in
>series on each leg of the PT's HV winding -
>but you'll do well to measure the voltages
>across all the HV filters and make sure
>you're not exceeding any of their ratings.
Sometimes you see people recommend installing small capacitors in
parallel with each diode to quiet transient switching noise. What is
your take on this, LV? Real deal or cork sniffing?
Lord Valve
Sometimes you can hear a small difference, but it takes so long to do that
you usually forget what it sounded like in the first place.
I invoke the Chicken Soup Principle - it couldn't hoit.
LV
Dave Curtis
<bluesb...@gmail.com> wrote:
>I'd like to try a solid-state rectifier with 1N007 diodes. I'm just
>afraid of the 50V bump in B+. What do most folks do to convert to SS
>rectifier?
I made up a SS replacement out of an old tube base, and I've been
running it in my '76 Pro Reverb for a couple years, now. Like LV
said, you want to make sure your PS caps are up to snuff, and rebias
at the new voltage. You might have other issues, though, as mine
wasn't terribly saggy with the 5U4, but I do have quite a bit more
headroom with the SS rect.
DC
Bluesbreaker
filter caps should be performing well. The PS filter caps were
replaced with stock values (as close as possible), with the following
exceptions:
- 2 x 70uF/350v caps (totem pole) were replaced with 2 x 100uF
- 1st 16uF/450v cap replaced with 40uF, for a little extra bass
response
I think I'll try swapping in a 5AR4. I think I have an extra laying
around. Why in the hell did Fender start using 5U4's in the
Silverface amps, while the Blackfaces used 5AR4 (GZ34) rectifiers? If
they were trying to achieve more clean headroom, seems like the 5U4
(direct heated) would achieve just the opposite effect.
Thanks for all the help here!
Lord Valve
> I gave the amp a complete electrolytic cap-job last week, so the
> filter caps should be performing well. The PS filter caps were
> replaced with stock values (as close as possible), with the following
> exceptions:
>
> - 2 x 70uF/350v caps (totem pole) were replaced with 2 x 100uF
That's about as far as you can go if you're going to use a rectifier tube.
> - 1st 16uF/450v cap replaced with 40uF, for a little extra bass
> response
If there was a 16/450 in there, chances are someone re-capped it earlier.
I don't think I've ever seen a super reverb
with anything besides 20/500s in it. Increasing
the value of that particular cap will stiffen up
the screen supply, which some folks like and
some don't. (I like it.) Just for grins, try bypassing
the last 20uF cap in the supply with a .22uF/600V poly.
While you're at it, pull the Normal channel tube
and play through the Vibrato channel. Kickass!
> I think I'll try swapping in a 5AR4. I think I have an extra laying
> around. Why in the hell did Fender start using 5U4's in the
> Silverface amps, while the Blackfaces used 5AR4 (GZ34) rectifiers? If
> they were trying to achieve more clean headroom, seems like the 5U4
> (direct heated) would achieve just the opposite effect.
Probably got 'em cheap.
Bluesbreaker
> with anything besides 20/500s in it.
You are correct about the filter caps -- they were originally 20uF
(not 16uF). I'm also working on a Deluxe Reverb, so I mixed up the
values in memory.
> Just for grins, try bypassing
> the last 20uF cap in the supply with a .22uF/600V poly.
Will this boost the high response?
> While you're at it, pull the Normal channel tube
> and play through the Vibrato channel. Kickass!
Awesome, I'll try that out.
I've still gotta get the reverb sounding better and the vibrato isn't
working at all. I think the reverb tank is bad because -- the reverb
rings (high freq) for quite a while -- way too long for a medium decay
tank. As for the vibrato -- the opto-isolator is working (I can see
it flash) but I think a bad cap is somewhere in the mix.
Thanks again for the great advice!
Stephen Cowell
"Bluesbreaker" <bluesb...@gmail.com> wrote
>I think the reverb tank is bad because -- the reverb
>rings (high freq) for quite a while -- way too long for a medium decay
>tank.
The little tiny foam dampers are gone, crumbled.
>As for the vibrato -- the opto-isolator is working (I can see
>it flash) but I think a bad cap is somewhere in the mix.
The CdS cell has gone south... they wear out.
New roach will fix it.
__
Steve
.
Jim
Rich Koerner, who refurbished my Super Reverb, prefers solid state
diodes. Somewhere, I have the bench specs for my amp. It was a
significant increase in power.
I made a plug in solid state unit with 1N1007's in a tube converter
base. But I like the tube rectifier. I don't NEED more power. It's
way loud as-is. (If you do this, you will need to check bias.)
Did you replace the filter caps? Are you hitting the front end too hard?
Try WITHOUT the overdrive pedal, at volume. Or reduce the output on the
pedal.
You shouldn't have to hammer the front end to get a good overdrive tone.
Of course I'm running RCA preamp tubes and Sylvania 6L6GC (I have a
bunch of RCA black plates, but it's got Sylvania in it at the moment).
And Rich went through it with a fine tooth comb when he did his thing.
Mine gets a GREAT overdrive tone at loud volume, without giving up and
dropping volume.
Dave Curtis
wrote:
>I made a plug in solid state unit with 1N1007's in a tube converter
>base. But I like the tube rectifier. I don't NEED more power. It's
>way loud as-is.
You don't play out. I wanted more clean headroom at gig volume, and
my Pro Reverb's lighter than the VT22.
RS
<detr...@ix.netcom.com> wrote:
>Bluesbreaker wrote:
>
>> I'm repairing a 1970s Fender Super Reverb (40W) for a friend. The amp
>> has way too much sag at full volume with an overdrive pedal in front.
>> I'm interested in a solid state rectifier replacement. The amp
>> currently uses a 5U4GB.
>>
>> The 5U4 drops 50V at max, which accounts for a very noticeable sag
>> (SWOOP) when the amp is being pushed hard with a strong input signal.
>>
>> I'd like to try a solid-state rectifier with 1N007 diodes. I'm just
>> afraid of the 50V bump in B+. What do most folks do to convert to SS
>> rectifier? Would the increase in B+ need to be reduced with a Zener
>> or something?
>>
>> OR
>>
>> Perhaps a 5AR4 (which drops only 17V at max)? Would this be a safe
>> substitution to try? What readings should I take before/after to
>> determine?
>
>OK, Slick -
>
>Just shove a 5AR4 in there and get on with things.
>It won't change your B+ by more than a few volts, but
>when you drive the amp...
[snipped 300 lines of advertising]
He said the amp was turned up full. You think 5u4 'sag' is the main
cause of the 'sag' effect?
Bluesbreaker
cranked the amp. It sounded great.
Then I hit the input with a high-gain pedalboard to see if it still
had that same "SWOOP" effect. The 5AR4 handled the high-gain signal
with the amp full up. There was a little sponginess past 7 (on the
dial) as I would expect.
Thanks for some great suggestions. I'm hopeful that I can help my
friend keep this amp a great classic while also allowing him to play
some modern high-gain music with it.
I was surprised to see that switching from 5U4 to 5AR4 only increased
plate voltage slightly -- from 430v to 440v. Still a bit below the
AB763 schematic, at 460v. Keep in mind this was a SF that was modded
to BF, if that makes any difference (different PT turns ratio?).
Also, both rectifiers used have some age on them and I think are 70s
era. Not sure that amounts to a hill of beans though?
Peter Alerich
Was it a 5U4 or a 5U4GB? If the info I have on hand is correct:
Typical Rectifier voltage drops
5Y3 -60 volts @ 125 ma
5U4GB -50 volts @ 275 ma
5U4 -44 volts @ 225 ma
5V4 -25 volts @ 175 ma
5AR4/GZ34 -17 volts @ 225 ma
there is a slight difference in voltage drops in the two types of 5U4
rectifiers but that still doesn't address your voltage readings. Did
you maybe bias it up a little hotter after the recifier switch? That
might explain the final 10 VDC difference.
The 5U4GB has a large voltage drop but actually could supply more
current than a 5AR4 (again if this info is accurate). I understand
votlage drops and current capacity individually but I'm not real clear
on how they interact with one another. I always assumed that higher
voltage drops and lower current capacity went together but evidently
that is not the case.
I hope your buddy is as pleased with the amp as you are.
Jim
I'd like to jam more often, but I haven't been playing much at all for
the last few months.
I have jammed with my Super. One time I used an A/B with my Marshall
2204. There were a bunch of guys at the jam, I had no problem with
volume -- without mic'ing.
If I had a problem with volume, I *could* put a good pair of GE 6L6GC in
it (got some), plug in the SS tube socket, and rebias. But it'd be
pushing the vintage AlNiCo's!
I'd sooner mic mine with the rectifier tube. Or grab one of my Twin
Reverbs (even though they sound different).
If I wanted LOUD, I'd bring my Mace. But I can't take high volumes like
I used to. The last time I played, I used my THD Univalve with the
built in Hot Plate attenuator. My sub-watt Killer Ant is also fun.
gigh...@yahoo.com
FirstName LastName
> I dealt with this guy once and he turned out to be a major asshole. He had a bully attitude. I was nothing but nice and respectful to him. It seemed because I was this way he took me for granted. All while bringing up his opinions of politics ... I don’t talk about politics unless it’s with someone I can agree with . This guy was very disappointing and what really took me back was how disrespectful he was. Lord Valve.. What an arrogant SOB. Someday he’s gonna talk like that to the wrong person.
Lord Valve
mysteriously resurrected by some schmuck with
n axe to grind. My, my...one never know, do one?
Fuck you with a rake, cuntface.
Lord Valve
Cannonfodder hops on the #MeToo bandwagon. Astute
readers, should they wish to take the time, will note
that everything I told the OP was spot-on, he copped
killer tone and was quite satisfied with his results.
What we have here is an archive-diver (probably the
same one who was playing games a week or two ago...
these poor schmucks are usually someone who got owned
in a debate way back when and have been smoldering
about it for a decade...) who has decided to rake up
some old shit so he (and you) can enjoy the smell.
So...am I supposed to get upset that some putz lied
about something that never happened? You'll note that
no names, dates, locations or other particulars have
been forthcoming. I'm kind thinkin' this is another
AGA fairy tale - from another AGA fairy. Anyway, happy
Easter, and fuck you with a post-hole digger, schmucks.
Lord Valve, ThD
Proud Owner, AGA (and resident AGAtards)