Building AC30 from Peavey C30

[munkeyboy]

Hello,

First time posting here.   I have a few successful guitar builds and now getting into pedals and amps.   I've been working on fixing a peavey classic 30, but I've come to the conclusion the pcb board is too far gone from so many mods and I'm kind stuck.  It is a tough one to learn on.  So I thought I'd like to reuse the chassis, PT and OT to build a simple(r) AC30 or AC15.  I'm open to any simple 15/30w amp really, but I want to keep cost down by reusing the PT and OT.  Problem with that is the peavey PT.  I think the PT is around 235vac (332vdc at plate) and 25vac (not the typical 5 and 6.3).   The peavey tubes are in series, not parallel. 

I think if I wire the tubes up the same way (3x 12ax7,4x el84) I can reuse the PT.  I get a little lost in the power sections tho.  I think the AC30 needs 280v, not 235v.  The older AC15 might be a better fit for the PT, which I would prefer, but not sure what would happen with the OT if i remove 2 power tubes.  Can someone familiar with peavey review the attachment of the layout I have so far.  I'm building off the Hoffman AC30 layout, by using the C30 layout and schematics.

http://el34world.com/charts/Schematics/files/peavey/c30%20layout.jpg
http://el34world.com/charts/Schematics/files/peavey/c30%20schem.gif

Thanks in advance!

[munkeyboy]

The only changes I made to the ac30 layout are around the preamp tubes (wired in series), power tubes (ground, output, and heater wiring) and the 2nd page related to the PT and filter caps... i think.

[tubenit]

The schematic shows 332v on the plates of the EL84's.  I think that's fine for your conversion.  The PT uses solid state rectification instead of a tube so 5v is not needed.

I will confess that I am not sure what's going on with the filament voltages in this amp.  Never seen a schematic drawn that way before.  Having said that, there obviously is filament voltage needed to make the amp work, so I'd presume that it's there.  Note there is a AC fil 1 and an AC fil 2.

Hopefully, someone smarter then I am can answer your question about filament voltage per this schematic?   You could always simply buy a 6.3v transformer for the filaments IF needed because of some complication of the Peavey design. Those 6.3v trannies are inexpensive.

The AC30 amps are pretty loud.  I'd be inclined to have each pair of output tubes have their own respective cathode resistor and cathode cap.
That way, you could simply pull a pair of tubes to go from 30 watts to 15 watts.   I've attached a schematic to illustrate what I am referring to , but note this isn't a AC30 schematic.

The Peavey appears to have been fixed biased.  The AC30 or AC15 would be cathode biased, so removing a pair of tubes could easily be done IF they each have their own cathode resistor and cap.

With respect, Tubenit

[tubenit]

I'm open to any simple 15/30w amp really, but I want to keep cost down by reusing the PT and OT.

The other amp that I think would be worth considering is DaGeezer's  HoSo56 using a 5879 pentode in V1.  GREAT amp!  Super touch sensitive.

And you could also do this with the idea of two pairs of EL84's each having their own cathode resistor and cathode cap.

There is a layout for this amp also.  You'd need to download the free ExpressSCH program to open the files:

     http://el34world.com/Forum/index.php?topic=6176.0

With respect, Tubenit

[PRR]

> The peavey tubes are in series, not parallel. 

What a frikkin' maze.

[tubeswell]

PV C30/DB heaters are wired in series, but they are series-AC for the output tubes and series DC for the pre-amp tubes - and the PT heater winding is configured accordingly. So if you want to re-use the PV PT, be my guest, but you'll probably want to copy the C30 heater configuration and you will be restricted to 4 x EL84s and 3 x 12AX7s. Also, the PV PT is wound on a small core and runs characteristically hot, and is prone to failure. It also has an built in fuse, so once that's FUBR'd you might as well start your build from scratch with a replacement. So all in all, you'd be better off obtaining a better spec PT for a Vox AC30 to begin with IHMO. YMMV.

[shooter]

Vox AC30

If you do an AC30C2, the heater circuit is also quite unique, well done for such a simple thing

[munkeyboy]

What a frikkin' maze.

Yes, I tried doing a layout for the c30, but my eyes started glazing over.   I also started running out of room on the 13" board.  I may still do it, simplifying it by removing boost switch, reverb, efx loop, maybe something else.   I now I understand why peavey built the silly "U" shaped pcb (for more room in the chassis). 

PV C30/DB heaters are wired in series, but they are series-AC for the output tubes and series DC for the pre-amp tubes - and the PT heater winding is configured accordingly. So if you want to re-use the PV PT, be my guest, but you'll probably want to copy the C30 heater configuration and you will be restricted to 4 x EL84s and 3 x 12AX7s.

Hmm,  I guess I read the schema wrong.  Looked like V6 and V7 are in series and V4 and V5 are in series, but not all four.  Not sure if my PDF attachment showed up in the first post, but if so could someone review the tube section wiring(top of page 1) and the bottom of 2nd page as well?.  Maybe I didn't get the layout right.

Regarding the peavey 4x power tubes, I saw something about cutting all but two pins of [V5/V6?] tubes to drop the power down to 15watts.  Any way to simulate that with a switch?

[tubeswell]

PV C30/DB heaters are wired in series, but they are series-AC for the output tubes and series DC for the pre-amp tubes - and the PT heater winding is configured accordingly. So if you want to re-use the PV PT, be my guest, but you'll probably want to copy the C30 heater configuration and you will be restricted to 4 x EL84s and 3 x 12AX7s.

Hmm,  I guess I read the schema wrong.  Looked like V6 and V7 are in series and V4 and V5 are in series, but not all four.  Not sure if my PDF attachment showed up in the first post, but if so could someone review the tube section wiring(top of page 1) and the bottom of 2nd page as well?.  Maybe I didn't get the layout right.

Have another look. The AC fil goes through V6, then V7, then V4, then V5 to the other end of the winding


http://www.blueguitar.org/new/schem/peavey/c30schem.gif

[munkeyboy]

PV C30/DB heaters are wired in series, but they are series-AC for the output tubes and series DC for the pre-amp tubes - and the PT heater winding is configured accordingly. So if you want to re-use the PV PT, be my guest, but you'll probably want to copy the C30 heater configuration and you will be restricted to 4 x EL84s and 3 x 12AX7s.

Hmm,  I guess I read the schema wrong.  Looked like V6 and V7 are in series and V4 and V5 are in series, but not all four.  Not sure if my PDF attachment showed up in the first post, but if so could someone review the tube section wiring(top of page 1) and the bottom of 2nd page as well?.  Maybe I didn't get the layout right.

Have another look. The AC fil goes through V6, then V7, then V4, then V5 to the other end of the winding


http://www.blueguitar.org/new/schem/peavey/c30schem.gif

Yep I got it wrong.  Thanks for clearing that up, Tubeswell.   Not sure what I was doing there.

[munkeyboy]

So more like the image attached?

[PRR]

>> maze...
> boost switch, reverb, efx loop, maybe something else.   I now I understand why peavey built the silly "U" shaped pcb

I meant just the heater maze.

The amplifier, Normal and Boost, is straightforward. Skip the reverb, it is all-tube except for one innocent PNP for the loop output.

> Looked like V6 and V7 are in series and V4 and V5 are in series, but not all four.

Did you not see my image above? I cut/moved all the heater stuff together. The four EL84 heaters are series. There is a small capacitor to ground at the center; I do not know why (or why not).

To cut two power bottles, bring their cathodes together on a switch. You have to leave the heaters in-string. Power will be less than half but that is not a problem.

[munkeyboy]

>> maze...
> boost switch, reverb, efx loop, maybe something else.   I now I understand why peavey built the silly "U" shaped pcb

I meant just the heater maze.

The amplifier, Normal and Boost, is straightforward. Skip the reverb, it is all-tube except for one innocent PNP for the loop output.

> Looked like V6 and V7 are in series and V4 and V5 are in series, but not all four.

Did you not see my image above? I cut/moved all the heater stuff together. The four EL84 heaters are series. There is a small capacitor to ground at the center; I do not know why (or why not).

To cut two power bottles, bring their cathodes together on a switch. You have to leave the heaters in-string. Power will be less than half but that is not a problem.

Ah, I didn't get it at first.  I knew about the preamp tubes, just not the power tubes.    If you couldn't tell, I'm new to reading schematics, so please forgive the dumb mistakes.  I'm learning each time and I figure reading the c30 schematics and producing a layout would help me understand.  I have a little ways to go     

So what you drew on the bottom was a proposed change or just a simplification?    I see the diodes changed direction, just making sure.   Either way, this helps me understand it a little better.

[sluckey]

heaters...

Edit... Corrected label on drawing.

[munkeyboy]

heaters...

well that's a lot cleaner than mine  :)   Where are these glorious source files (ai?).  I got mine from importing the pdfs to illustrator.  Is there another vector file where the component are nicely grouped and layered?


So for the cathode switch it would look something like this?

[sluckey]

The drawing was created with Visio.

[PRR]

> So for the cathode switch it would look something like this?

Cathode is pin 3. Your sketch doesn't touch any pin 3s.

Yes, reading schematics is a learning path. This particular Peavey may be like reading Torah or Quran before you finish Dick And Jane and Tom Swift's Atomic Outhouse. I may have 10,000 schematics on my retina and _I_ had to stare a long while just to find all those heater points. So no apologies from you for working it out slowly.

[sluckey]

I wanted to mention an error on your power supply layout drawing (page 2 of your pdf). You show the PT high voltage center tap connected to ground. ***REMOVE THAT CONNECTION*** on your drawing. I suspect the Peavey PT doesn't even have a high voltage center tap. If so, there is no real danger.

[munkeyboy]

I wanted to mention an error on your power supply layout drawing (page 2 of your pdf). You show the PT high voltage center tap connected to ground. ***REMOVE THAT CONNECTION*** on your drawing. I suspect the Peavey PT doesn't even have a high voltage center tap. If so, there is no real danger.

Got it.

Thanks for the help guys.  I have a lot to review and change.    If i can sell my silvertone, i might just splurge on a PT and not worry about reusing the peavey one.   

[munkeyboy]

So I've redone my layout.   Decided to go with a Trainwreck Liverpool instead of AC30.  I'm basing the layout on a few sources, but the main one being the Ceriatone TW Liverpull. http://www.ceriatone.com/ceriatone/wp-content/uploads/2016/08/LiverPullCeriatone.jpg

I'm still planning on using the peavey classic 30 PT and it's weird in-series heaters.  Note, I've added a half-power switch too.  Not sure I got that right.  There is a lot going on in that power tube section.  Not sure how that will workout when I physically wire all that up.

I learned a lot, but I think I still need some assistance reviewing what I have here. Any feedback is welcome.  (see attached pdf)

Thanks!

[sluckey]

Pretty drawing.

[shooter]

Pretty drawing.

Very nice, you both win for some of the finest digital art I've seen in awhile.