Peavey Classic 50 Bias?

[Joe]

Wha daa hell is this!
Buddy just brought me his Peavey Classic 50 amp biased way to hot.
"Not the Classic I remember"
All folded in PC boards and I have no schematic, looks like a High-Z
Williamson output.
Looks like no HV bleeders also, what a lousy layout for servicing !
Eats Phillips 6BQ5's every month (Plates just about glowing red)
Forget about using the *E* EL84's !
Anyone have bias info ?

[ACLARKE3]

Joe, I saw one of those recently. Four EL84's. Can you determine how on earth
that fan cools anything? The air has no open passageway to the power tubes.
Maybe it faces forwards to keep the band cool!

NC

>Wha daa hell is this Buddy just brought >me his Peavey Classic 50 amp biased
>way to hot "Not the Classic I remember"

>All folded in PC boards and I have no >schematic, looks like a High-Z

>Williamson output Looks like no HV >bleeders also, what a lousy layout for

[Joe]

ACLARKE3 wrote Snips:

>Can you determine how on earth that fan cools anything?
>The air has no open passageway to the power tubes.
>Maybe it faces forwards to keep the band cool!

LOL ..........That Fan, I cant believe it :) :)
This amp is a Joke !
What did I get myself into, I am so busy with other sh*t
I thought a friend was bringing me one of them Real Classics that he could
have back tonight
This retube favor (a every day adjustment) is turning into a can of worms.
Guess I am getting old with classic meaning "Watch out for reissued garbage"
What a piece of crap !

ACLARKE3 wrote in message <20000905224450...@ng-cv1.aol.com>...

[JER]

On Tue, 5 Sep 2000 22:23:59 -0400, "Joe" <joe...@mindspring.com>
wrote:

Joe,
You can follow the circuit from the grids back to the bias supply.
IIRC, there is a 33K resistor on the power tube board; this is the
pull-down resistor. It's been a while since I worked on one of these
but I think the resistor is between the two power tubes that is
closest to the PI tube. You can replace this temporarily with a pot
(or replace it all together with a pot/resistor combo) and bias using
the transformer shunt method.

--Jack

[3rd...@my-deja.com]

The fan is meant to cool the transformer. The tubes are left alone to
burn and wail.
In article <20000905224450...@ng-cv1.aol.com>,

Sent via Deja.com http://www.deja.com/
Before you buy.

[To...@amprepair.com]

There is a -27 volt supply which performs a few functions:
Reverb opamp supply, relay control, output stage grid bias and (I think)
first couple tube filaments in series.

An easy place to start looking is:
Look at pin 4 of the 4558 (reverb circuit) opamp. You should see -27 volts
there. You may have a bad 4558 which pulls the raw -27v supply down which
affects the -bias supply, etc, and burns up power tubes. If you dont
have -27v there: check the two resistors R61 & 62 (both 22 ohms in parallel)
which are between this supply's filter caps. You should see the -27 on both
sides of these two paralelled resistors. Also, if that IC is hot, replace
it.

If the -27 volts is there and that IC isn't hot; then you may just need to
adjust a resistor value somewhat. The bias (-15v) supply is fed from
this -27 supply via the series resistor R16 (18k). Decrease the value of
this resistor to increase the amount of bias. There is also a shunt resistor
R18 (33k). If you can't get enough bias by decreasing the value of R16, then
you may want to increase R16 a little though this normally isn't necessary
(and also regulation will suffer some).

Factory set bias is -15 volts to the power tube grids via R49 & R50 (both
220k), which feed a 47k to each EL84 grid.

My experience with this amp and current production EL84's is the Sovtek's
will typically exhibit a much lower quiescent current value than anything
else out there. Unless you want to mess around with those PC mounted
resistors (R16 & 18) in there which are tuff to work on without pulling all
the PC boards!.....stick with the Sovtek's.
Good luck.

Todd@ Nashville Amp Service

Please see our website: www.amprepair.com

[Rich Koerner]

Damn, I had posted a comment on this post and it did not show up here.

TAKE TWO!!!!!!!!!!!!!!!!!!!!!!!!!!! :)

THANKS Todd!!!!!!!!!!!!!!!!!!!!!!!!!

Just recently I had a Classic 50 walk into the shop and it had toasted
EL-84's in it.

After some measurements, I knew the EI and other EL-84's were not going
to like the 400 volts B+ that would be sitting on them.

I just want to let EVERYONE Know that Todd's information is right on the
money!!!!!!

Yes, those Sovteks are the answer here for this unit. Also his
information on the circuit is also dead on the money. I did make a
resistor change to cool things down a bit and get a little life without
power loss.

Again, *Thanks* Todd for taking the time to post this info and saving me
some bench time not having a print for this unit.

Regards,

Rich Koerner,
Time Electronics.
http://www.timeelect.com

Service * Repair * Modifications * Design Engineering

Live Sound & Studio Production

[Joe]

I had disastrous results with Ei EL84's in the Classic 50 *properly biased
changing R-18 to*
2 hours then 1 Ei EL84's started arcing internally.
Amp 2 the spare same deal ...............lucky it was the band last song.
"Both did not blow the fuse but made a racket, no damage"

The problem is the Sovtec EL84 tubes sound weak muted compared to the Ei and
NOS Phillips
The 1st amp is currently bouncing about the US with the Zen Trixters with
loaner NOS Phillips pulls.....no problems

Rich Koerner wrote in message <39C66270...@timeelect.com>...

>Damn, I had posted a comment on this post and it did not show up here.
>
>TAKE TWO!!!!!!!!!!!!!!!!!!!!!!!!!!! :)
>
>THANKS Todd!!!!!!!!!!!!!!!!!!!!!!!!!
>
>To...@amprepair.com wrote:
>>

[Miles O'Neal]

I'll agree with Joe and Rich. If you want to run
high voltages (like 400), especially with any kind
of current, in an EL84 amp, you better get a really
top notch NOS tube, or see if you can live with the
Sovtek EL84Ms.

I have watched Sovtek non-Ms, Ei and Tesla all go
belly up pretty fast at 440V set to dissipate near
12 watts. Don't go there, you won't be happy.

-Miles

[Miles O'Neal]

Miles O'Neal wrote:

> I have watched Sovtek non-Ms, Ei and Tesla all go
> belly up pretty fast at 440V set to dissipate near
> 12 watts. Don't go there, you won't be happy.

I meant 400V, of course.

I'm not a typist, nor do I play one on the net.

[JER]

I've had no problems using Tesla EL84s in these and Classic 30s. I
replace the pull down resistor in the bias supply with a trimmer and a
series resistor. Depending on the player's preference, I bias them
between 6 to 9 watts static dissipation per tube. Somewhere within
that range seems to satisfy most folks. So far, they are all still
working fine.

--Jack

>Damn, I had posted a comment on this post and it did not show up here.
>
>TAKE TWO!!!!!!!!!!!!!!!!!!!!!!!!!!! :)
>
>THANKS Todd!!!!!!!!!!!!!!!!!!!!!!!!!
>
>To...@amprepair.com wrote:
>>

[To...@amprepair.com]

Right on Rich. Glad to be of help. Thank you for your often helpful posts.
Todd

"Rich Koerner" <ri...@timeelect.com> wrote in message
news:39C66270...@timeelect.com...

> Damn, I had posted a comment on this post and it did not show up here.
>
> TAKE TWO!!!!!!!!!!!!!!!!!!!!!!!!!!! :)
>
> THANKS Todd!!!!!!!!!!!!!!!!!!!!!!!!!
>
> To...@amprepair.com wrote:
> >