Peavey Deuce II (220 series) Restoration

[misterc57]

I picked up a c.1974 Deuce II. It has one dead 6L6. It appears to have the original filter caps with the following arrangement

1st node 100uF in series with (can cap 40uF and 20uF in parallel)
2nd node 100uF in series with 40uF can cap.

The two 100uF reside in the chassis. The can cap has 4 elements, 40, 40, 20, 20.

My amp does not have a standby switch. Attached is the best example schematic found so far.

Bad tube has been replaced with an old working tube. The amp has two issues since I started working on it.

1. Sound is distorted. Almost a desirable crunch distortion but I think this amp should be sounding pretty clean.
2. After playing the amp for about 5 minutes the sound faded fast and disappeared,

I want to replace the filter caps which appear original and are now 50 years old.. In circuit the two 100uF test good but I get strange readings from the individual cap cap elements.

I am wondering if old caps could cause the two issues I am having?

I am also wondering if there is a simpler solution to the arrangement of filter caps. Highest V I am seeing with 4 tubes installed is around 475V.

If I use a series cap calculator I get the following 1st and 2nd node results.

1st node 100uF/350 in series with 60uF/500 (40 and 20 in parallel) = 37.5 uF at 850V
2nd node 100uF/350 in series with 40uF/500 = 28.6 uF at 850V

Could I get away with using a 47uF/500 in the first node and 33uF/600 in the second node? These are caps I have. Or is there a concern of limiting the first node to 500V?

Thank you, MarkO

PV Deuce2-Festival.pdf

[Jon Snell]

You shouldn't need to touch the pre amp section but I would replace the two orange high voltage electrolytics and examine the multicap for bulging. If not bulging, it is more than likely OK to continue with.
It looks like someone got exited with the mains lead and killed the 6L6 on the end when throwing the lead into the cabinet.
A set of 6L6s and you will be away for another 10 years.

[misterc57]

No bulging in the cap can but due to its age I would rather not use it. I am leaning towards switching to the 4 x 100 uF filter scheme used in later models.

Anyone see a problem with that? This would provide 50uF at 700V in the first two filter nodes.

Thank you

[TomCarlos]

For background reading, here is an old MEF thread on this subject - Parallel vs. series vs. one filter cap

[g1]

I am leaning towards switching to the 4 x 100 uF filter scheme used in later models.

Anyone see a problem with that? This would provide 50uF at 700V in the first two filter nodes.

My concern would be that the original configuration you have in there is not what it seems. 100uF in series with 40uF would be a bizarre combination.

[The Dude]

No bulging in the cap can but due to its age I would rather not use it. I am leaning towards switching to the 4 x 100 uF filter scheme used in later models.

Anyone see a problem with that? This would provide 50uF at 700V in the first two filter nodes.

Thank you

That should not be a problem at all.

[misterc57]

My concern would be that the original configuration you have in there is not what it seems. 100uF in series with 40uF would be a bizarre combination.

I have never seen this config before and thought it strange. I verified the wiring and it does confirm that the 100uF are in series with the different cap can elements.

[glebert]

Maybe Hartley got a good deal on a bunch of cap cans...

[misterc57]

Finished replacing all the filter caps. (2) sets of 100uF/400V in series and (1) 22uF/550V. Can cap is still there but out of circuit. .

That "desirable crunch distortion" is still there but if I dial down the channel volume pot and raise the master volume pot it sounds clean. I guess this is the way this amp is suppose to sound/work. The "desirable crunch distortion" nails the Skynyrd "Gimme 3 Steps" tone.

[misterc57]

Getting to fizzy/buzzy a sound with preamp above 5. Any thoughts on this? Thank you

[glebert]

That "desirable crunch distortion" is still there but if I dial down the channel volume pot and raise the master volume pot it sounds clean. I guess this is the way this amp is suppose to sound/work. The "desirable crunch distortion" nails the Skynyrd "Gimme 3 Steps" tone.

My opinion on Master Volume (at least with older amps) is that the starting point should be wide open. This essentially gets you to a "non-master volume" ballpark. Set gain to get desired tone, and if too loud use the MV to bring it down. Adjust EQ as necessary at new MV setting.

[misterc57]

I'm no longer finding that desirable crunch I had heard at one time. Perhaps I am focusing too much on the buzz/fizz that I hear out of the speakers.

I have tried different settings as suggested. Different tubes. Different speaker cabinet. Different speaker cable.

Could the changes from that odd filtering scheme have caused a change to the sound? I wish there was a pre-amp out to see if I can isolate if the fuzz comes from there or the output.

[misterc57]

The main preamp filter 200uF/75 is still original. Perhaps that should be swapped. I do not have a 200uF but have several 100uF/100, I could place two in parallel there.

[misterc57]

Replaced 200uF/75. Still got FIZZ, don't want it, does not sound right. Lower settings of channel volume pot sound clean but as it gets turned up sound turns to FIZZ and sounds like bad speakers especially in the lower notes.

[misterc57]

Seeing a mismatch in V at the preamp final 4278 transistor collectors. One side reads 151 VDC the other 171 VDC. Could this in-balance cause noise?

Both 100K resistors read about 83K in circuit. Each of the 100K resistors read direct continuity to both 4278 collectors, seems odd.

If I understand correctly, 150V is the max V for these transistors.

Base and emitter of both 4278 read around 24-25 VDC, which seems right.