Before you go much further,,Un solder *C26* (1uF /100V) It hangs off pin 14 of IC1d. That will totally cut the reverb return from the audio path. if the amp then works ok,, replace IC1. ( I still have a strong feeling it's the reverb circuit.)

Next find ZD1 and ZD2 (top left corner page 2) Establish the voltage between ground and the +/- supply rails for the preamp. (they should read close to 15+ 15-)

Now follow all the rails around the board not all are the same pinouts, most of the power pins are noted on the schematic. The idea is to make sure power is getting to all the opamps.
(Note the chorus has a seperate positive supply)

If no luck then pull *Con 1*
which should isolate the power amps from *ALL* the preamp circuits.

Inserting some kind of line audio (CD line out or similar source) onto pins 3 and 5 should give the poweramps full power. (pin 4 is common /ground for both amps)
That will establish that the power stages are ok.
(Don't short out pins 1 and 2)

Bear in mind that the schematic is a different model so it may not be exactly the same,, use your head.
Phil.

Good to hear. :tu:
Phil.

Forgot,,
Re Bridge for clipping?? I breadboarded a few a lot of those clippers and the extra diode did little for me but heck try it out and make your own judgement.

Marshall used this idea in JCM 900's I think. The only way they could get more crunch from the amps as triodes alone can't do that trick.

Edit: please note I drew this the wrong way Phil

Hi Brymus,
              If it helps just look at how some reverbs are driven.
Phil.

Quote from: Brymus on November 14, 2009, 06:34:16 PM
What kind of sound do the 4X4148s to ground give after the first triode?
I just tried something similiar with red LEDs and found 2 sounded great but 4 only added a little dirt not very noticable.
How does the low plate voltage affect the clipping the make?
My triodes are closer to 250V- 300V plate voltage 80v seems low.

Also why are they biased with 2k2 instead of 1k5 or 820r?
Is it because of the low plate voltage?

And finally have you tried added a bypass cap to either triode?
Seems like the first one could have a 4.7uf on a switch for a nice warm boost or even a .2 - .68 for some top boost .
Thanxs for sharing the schematic and pics,Its nice learning about new stuff.

The 1k5 k resistor will just turn the gain of the stage up a bit (even with low HT)
Depending how big the incoming signal is,,you might even get some half wave clip at 80 VDC by turning tubes up.
but as should be obvious,,, very hard to get triodes to work as full on distortion units on there own,,the diodes are doing that here.
Phil.

Quote from: J M Fahey on November 15, 2009, 08:09:15 AM
Thanks for the schematic and comments.
I'm always learning, everyday, everywhere.
I liked the simple voltage doubler idea very much, and if used carefully, they can power some 12AX* to get something useful.
Here, the real distortion comes from the diodes.
It's a pity, they could have done more, but I guess the Marketing dept. pressures were greater than the Sound dept ones. Oh well.
Most of my "bread and butter" 100W SS amps use around +/- 40 volts, so I'll get those "free" 80V and experiment some tube preamps.
Personal opinion: those +9V "tube pres" are toys, but 80V *start* to look reasonable.
Up to now, the only tubes I could get "serious" results from with +42 to +35V are 12AU7.
This trick opens aup the field.

Hi JMF, If you are looking for ideas on Voltage Double circuits using cheap parts then have a look here.
http://ozvalveamps.elands.com/ava100/ava100psu.htm#andrew_k

I've built a valve HT kit which delivers 260VDC using an auto Tr Smode circuit to run some preamp experiments. The Vtwin being one such circuit I built.
Phil.

Yes but you should be wondering why it was arching in the first place!
I'm not familiar with your amp but I've worked on enough tube gear to say that most are now cutting to many corners.
Read your HT voltage I'll take a stab and say it will be well over 300VDC.
These modern amps really do push the limit and some EL84 amps have voltages closer
to 400VDC,,, Yes it can be done but don't expect long tube life.

now back to the other issue;
The interconnecting harnesses that go between the boards are a common failure point.
Amps like this have so many points of potential failure due to multi switching relays and use of cheap connectors. All the big names are cutting costs, giving many options but with reduced quality. The old stuff had issues but so much easier to fix.

This map might help unravel the needless complexity of your amp.
http://www.blueguitar.org/new/schem/peavey/modnotes/c50twdbm_sch.pdf
I would loose C16 (as shown) for a start, a cap here is kinda strange,, the right
value *in front* of the input will pull some magic tricks but not after the input
where it does little.
Phil.

You say it gets louder if you turn the volume up,,, then my guess,, The problem is *Before* the volume control.
Possible fixes,
dirty/ loose/ worn valve sockets. gently nudge the preamp valves see if it goes away.
Dirty terminals on switching mechanisiums on input sockets and EFX in out sockets.
Dirty or worn tracks on one or more pots.
Bad solder joins.
an interstage cap going futt.

What really Does concern me is you've made mention that the power tubes destroyed themselves . just replacing the burnt track won't fix that.
Sounds like the whole amp needs to be looked at.
Phil.

Oh dear!

Well check for broken tracks and solder joins especally on the PCB mounted RCAs.
The *RED RCA* short it right on the board.
(Rev circuit is all at the top left corner.)

My other thoughts are;
IC, 1 is blown, as these current drive reverbs using stacked opamps can leed to an early death.

Possibility that chorus or delay circuit has gone belly up,, never had that happen but something is definitly osscilating.
I don't know how good you are with electronics but if you have the schematic that *Guitar picker * kindly posted then check all the opamps voltage pins and see if something is wrong in the supply.
Phil.

Hi billy ,,no harm done

Here are just some differences for you to ponder, don't hold me to it cause I can't see the valve pin connections. I'm using the DR210 schematic JMF posted as refference. Then looking at your board.

C1 on your board is 4u7, DR= 220n (so different Value)
R5 is scary as it looks like 2x1k giving 500 ohms (not a common value)
The print on board says 1k5,, again diff from DR
**I would get that changed back to 1k at least as it could take out the triode **
C5 or 3 is 2u2,, DR says 220n
Past that point I can't tell but at the other end of the circuit is a *Presense knob usually only found on amps with *Feedback*  Again the DR has *No Feedback*

So the only thing the same is the name

Now something I just noticed that may help;
You may have a Ground loop,, Follow the *Green* wire that comes from the board and bolted via an eyelet to the chassis. Then Note the wide track that it's soldered to on the PCB. "That is the Ground plane/track on the board".
Now Follow that ground track all the way across until you come to the *Blue* wire.

(It's the only blue wire there in the middle)

That Blue wire is *Also grounded* at the *main Earth bolt*. *If* that is true and they also join on the board then it's almost certain that you have an ground loop issue.
This would not help by any means.
The blue wire looks as though it has been tampered with at some stage.
PS,
The 2 yellow twisted wires mounted on the back side of *V4* should be the heaters.
Phil.

Quote from: billyjoe24 on November 11, 2009, 11:18:38 AM
Take a look at some other hiwatt amps. The 4 tube preamp design is classic hiwatt.This is not regular hum! Hiwatt amps do not distort like crazy.
It's not some kind of super high gain sounding amp.

That is a big asumption on your part,, When the truth is you have no idea (and niether do I) that this is a direct copy of a Hiwatt.
It looks as though it is a cheap copy,
And the way the heater wiring is laid out it will have some hum.
JM Fahey has already asked you to check the heater circuit ground issue
and you have not replied.
If you want help you will have to do some homework.
I doubt there will be a quick cheap fix for your amp.

Replace all valves,, replace all Electros and see what happens?
Hope it helps somewhat.
Phil.

Quote from: jon.zilla on November 11, 2009, 11:45:10 PM
So you are talking about the rca jacks that go to the reverb?  If so the return one I need to connect a shorted plug to ie: inner conductor to outer shield?  Just wanted to clarify before attempting it.

YES, one RCA *Sends* the signal the other *Picks up* the reverb sound.
It can get confusing I know but as with most audio stuff you get a mental picture of something going *Out* has to connect with something going *In*.
So looking at the back panel of the Amp chassis there should be one RCA sending the signal to the reverb tank and the other one is picking up the returning signal. Try shorting out *The Return RCA* socket.

I doubt shorting the *Send* will do harm but I have no circuit to work with.

Phil.

Quote from: billyjoe24 on November 11, 2009, 09:32:32 AM
Hi,
It's not a high gain amp though.
At low levels everything is fine.
There seems to be a buzz coming from the gain control.
The thing is it was diagnosed as 60 hz hum and static. That's not normal.
The amp sounds quite good in actual fact. Very much a Hiwatt vibe.
Great clean sound and nice distortion, not high gain.
I think the mod was to get rid of the buzz.
The real Custom 20 has the exact same valve configuration.

Note bold text, Sorry billy but with that many stages there will be hum.
I agree static noise might mean some other problem, like dirty valve pin or cold solder somewhere.

Second;
           The schematic of the DR210 custom 20 shows 3 AX7's and your board has 4 AX7's so something is wrong there for a start.

Yes at low level it might be clean but once you want to open up the master all hell will break loose. This is a serious hi gain amp and I doubt it has DC heaters so even worse with 2 more triode stages.
If it does not distort like crazy when you wind it right up something is very wrong.
Phil.

JMF, just gave me another thought, You may need to short circuit the *Input/Return* Socket to stop the howling. I had that issue when designing my maxiverb unit.
And since then I've noticed that some Amps squeal if the return pickup rca falls out or goes open circuit. These are usually just RCA type plugs.
don't short the *Output socket/Driver side* on the Amp as that may cause more problems.
Phil.

Quote from: J M Fahey on October 18, 2009, 08:51:56 PM
*If* you have an Alembic preamp, or any tubed type "pulled" from a Classic Fender, you´ll have to do the following, to keep the good original sound; not screeching trebly, chip killing level, noisy , etc.
Let´s do some math:
To begin with, a tube fed with 300 Vdc can swing some 40 volts less, say around 260 Vpp , or around 80 Vrms.
To safely lower it to chipamp levels, you´ll need a *resistive* attenuator (flat response) , and not a capacitive one (bass killer).
I suggest the following: take your signal from the triode plate through a .047x400 cap, as originally specified, and connect it to the hot pin of a 10K pot, *through a 470K resistor*.
That way, the triode will be happy seeing a load higher than it´s original 100K plate resistor, overloading gracefully as intended, and you´ll get somewhat more than 1V rms at the chipamp input.
You will need no cathode/voltage follower, and the output impedance will be acceptably low: 10K (the pot´s value)
I think it´s clear enough, but if not, I´ll post a drawing, now I´m on a borrowed computer away from home.

Sorry JMF,, I missed this one,,,,
Once again you nailed it ,,,Yes of course that idea would be the better way to go.
Good on you,,, :tu:  your a wealth of info.  Phil.