Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: JMW on May 21, 2013, 01:25:22 pm
Title: Plug in modular EL34 power amp
Post by: JMW on May 21, 2013, 01:25:22 pm
I’d like to start out with a big thank you to all. I have been lurking and learning around here for years, and applying it to amp builds / mods. I have a (don’t flame me) multi watt mesa triple rectifier that I have tweaked to the point of only being a mesa in name, and now is the almost perfect amp for any type of tone I could want (of course I’m sure the TC-15 I’m building will also be perfect, and the next amp after that).
The amp sounds just as good in my room quiet as it does cranked and which is why I chose the triple over any other 3 channel amp regardless of output. I don’t need the volume anymore and the thought of 6 6L6’s and 3 5U4’s cooking for low volume late night playing keeps my wallet nervous. I know common sense is to sell it, but at this point I've built in too many relay controlled circuits and tweaks to dream of parting with it. I have in the past pulled the power tubes and 2 rectifier tubes (voltage increase is negligible) and used my black pearl or SE amp as a power amp & while it sounded good, I know there is a better option.
Unfortunately, I'm much better at modding than designing and definately lacking when dealing with power tube ops. I have a Hammond 125ese OT, and a male octal tube base from Hoffman, my latest idea is to build a plug in el34 se power amp module that is powered by plugging the tube base into an empty 6L6 tube socket. I have a copy of an se el34 amp I built (schematic from surf on JVM forum) but no longer have the amp and can’t remember the operating voltages for the el34. Based on the attached schematic and supplied voltages from my mesa can somebody help sort through this? Any guidance would be greatly appreciated. Usually, I would jump right in, or dig in to reasearch, but young kids and a looming cross country move are limiting my free time. The voltages on the schem can be dropped to about 415 in spongy mode. I also have the schem for the mesa if needed.
Sorry for the long winded post. Thank you
Title: Re: Plug in modular EL34 power amp
Post by: PRR on May 21, 2013, 09:03:55 pm
What voltage do you HAVE? We'll figure the best-fit tap for the ESE.
200V-300V : 2.5K 300V-400V : 5K 400V-600V : 10K
Looks like 10K loading, and I would start at least 500 ohm cathode resistor for 470V supply.
Title: Re: Plug in modular EL34 power amp
Post by: JMW on May 22, 2013, 12:20:40 am
Thanks for PRR, I'll pull the mesa's tubes tomorrow night and make a list of the exact voltages at the sockets in all the different power modes. If there is a more suitable tube for the job, I'm not opposed to sticking with 6l6 or other octal. Is the cathode resistor the only component i need to change from the original schematic? I forgot to mention, i have both 8 and 16Ohm cabs. Thank you
Title: Re: Plug in modular EL34 power amp
Post by: sluckey on May 22, 2013, 02:18:49 am
Is the mesa a fixed bias amp? If so, I'd move C15 to between the input jack and the volume pot. That's probably a good idea in any case.
Title: Re: Plug in modular EL34 power amp
Post by: JMW on May 22, 2013, 01:26:40 pm
Thanks Sluckey, I'm really a NOOB when it comes to what's going on around power tubes and the OT. I was looking at the .047 after the PI to block DC, but the neg bias comes after that. Thank you
Title: Re: Plug in modular EL34 power amp
Post by: JMW on May 22, 2013, 10:59:50 pm
PRR, I had a chance to pull the tubes and take a few readings at the mesa's empty 6l6 socket tonight. I can run the amp at whichever operating voltage is better for the 125ESE, I would like to keep the option of a bias switch for 6l6 or el34 if possible.javascript:void(0);
Tube rectifier Silicone rectifier PIN# spongy bold spongy bold 3 382 v 475 v 391 v 485 v 4 381 v 474 v 389 v 483 v 5 6l6 bias -43 v -53 v -43 v -53 v 5 EL34 bias -29 v -39 v -29 v -39 v