EL34 36watt with the Universal PCB

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jamesrr
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EL34 36watt with the Universal PCB

Postby jamesrr » Mon 01/27/14 5:33 am

After successfully building a 6V6 'Superlite' with the Universal PCB I've decided to try an EL34 based '36 watt'.

I've finalised the schematic and a layout for the 'Super 36'. I should have the EF86 version layout done RSN [update] yes done now. (BTW - The '36 watt' amps are the 10th, 11th & 12th pages of the pdf)

I'm still pondering which one to do. I was originally thinking of doing the 'Superlite' version, but seeing as I just did a 'Superlite 6V6' I'm now thinking I should do the EF86 version. Hmmm...

[update] OK - I've decided. I'm going to do the EF86 Pentode pre-amp but with a silicon diode rectifier and the Antek Toroid TX.

[update 2]Actually I've done it with a Triode/Pentode (6U8-A) pre-amp tube up front, 5AR4 rectifier, AC-30 PT and an Edcor CXPP30 OT. It's the circuit called "Club Secret" on page 12 of the schematic PDF.

Pictures of progress to come.
Last edited by jamesrr on Wed 06/01/16 3:30 pm, edited 3 times in total.
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Re: EL34 36watt with the Universal PCB

Postby JMPGuitars » Mon 01/27/14 2:27 pm

I haven't really looked at the board, but can you do a 2 channel - channel 1 EF86, channel 2, Superlite TMB?
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Re: EL34 36watt with the Universal PCB

Postby jamesrr » Mon 01/27/14 9:18 pm

JMPGuitars wrote:...can you do a 2 channel - channel 1 EF86, channel 2, Superlite TMB?
Unfortunately not with the PCB tube compliment alone. It takes at most 2 noval 'pre-amp' tubes & two power tubes. There is provision to add additional external tube sockets via the PCB pads providing heater power, HT & signal path, but the straight PCB is intended to make 'single channel' amps only.
When we were designing the latest PCB we thought about adding another noval pre-amp socket, but we decided that it was too much of an outlier case to justify raising the base cost. We figured making it easy to add an external tube socket was the more flexible cost effective route.
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Re: EL34 36watt with the Universal PCB

Postby JMPGuitars » Sat 08/16/14 3:45 pm

Did you ever wind up building any of the 36Watt versions? I'm still deciding on a 36W with EL34s to build.
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Re: EL34 36watt with the Universal PCB

Postby jamesrr » Wed 08/27/14 5:59 am

Yes absolutely !

It's wonderful. I thoroughly recommend it. It's convinced me completely on EL34s vs 6L6-GCs for this sort of power range.

Obviously you could do a quad of 84s but I honestly think a pair of 34s is the better choice.

Here are some photos of the build: -

Image

Image

The internal wiring is a little 'dodgy' because I converted it from silicon diode rectified to tube rectified and minimised my rewiring.

With this one I used a Triode/Pentode pre-amp tube up front which I really like. The topology is Triode -> Gain pot -> Pentode -> MOSFET Cathode Follower driven TMB -> Vol pot -> "18 watt" LTP PI -> EL34s @ around 390v 3.8K OT.

And here's an audio clip.

https://www.youtube.com/watch?v=DA--HUr ... e=youtu.be" onclick="window.open(this.href);return false;

Apologies for being so slack in getting around to posting this.
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Re: EL34 36watt with the Universal PCB

Postby JMPGuitars » Wed 08/27/14 7:42 am

That's awesome. I'm probably going to build one soon, I love EL34 tubes. What transformers did you go with?
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Re: EL34 36watt with the Universal PCB

Postby jamesrr » Thu 08/28/14 5:39 am

JMPGuitars wrote:... What transformers did you go with?
I used a W@b@r "AC30" style Power Transformer. It has 300vCT@250mA main secondary and a 6.3v & 5v set of filament secondaries. I used a 5AR4 for the rectifier to get a B+ of around 390v.
I used an Edcor CXPP30-MS-3.8K for the OT. The Edcor CXPP OTs are really, really good. Huge too. Way bigger than your average wimpy piece of iron ;-) These are full 20-20KHz @ continuous 30watt RMS load transformers. Highly recommended.
You just have to be prepared to wait for the 4-6 week lead time. They are made to order.
I'm sure Heyboer et al have suitable TXs, but they'll be more expensive.

I'll try and put together an 'as built' schematic in the next couple of days.
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Re: EL34 36watt with the Universal PCB

Postby JMPGuitars » Thu 08/28/14 8:11 am

That would be great.

I'm familiar with the Edcor wait. I built a SE project with one of their OTs. Great quality stuff if you're patient enough for it. :)
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Re: EL34 36watt with the Universal PCB

Postby crgfrench » Sat 05/04/19 11:50 am

jamesrr wrote:
Thu 08/28/14 5:39 am
JMPGuitars wrote:... What transformers did you go with?
I used a W@b@r "AC30" style Power Transformer. It has 300vCT@250mA main secondary and a 6.3v & 5v set of filament secondaries. I used a 5AR4 for the rectifier to get a B+ of around 390v.
I used an Edcor CXPP30-MS-3.8K for the OT. The Edcor CXPP OTs are really, really good. Huge too. Way bigger than your average wimpy piece of iron ;-) These are full 20-20KHz @ continuous 30watt RMS load transformers. Highly recommended.
You just have to be prepared to wait for the 4-6 week lead time. They are made to order.
I'm sure Heyboer et al have suitable TXs, but they'll be more expensive.

I'll try and put together an 'as built' schematic in the next couple of days.
No Antek, just curious why you changed your mind? Toroids are unusual to see in guitar amps.
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