Hi all,
I am thinking I might buy one of the PP EL34 kits from MableAudio (minus chassis, I have some ideas in mind for that). The amp is PCB based (I feel more comfortable with that) and it looks like a good quality board. I plan to use Russian PIO coupling caps and Nichicon or Rubycon caps in the power section.
Anyways, the reason for my post; I seem to have fallen quite well for the Russian Military 6P3S-e tube (a 6L6/G equivalent) and so I want to see what I have to do (if anything) to make this amp accept 6L6 tubes. I've attached the schematic below.
Any help would be greatly appreciated, if you feel like throwing your ideas out there, go nuts.
Regards, Nic.
PS: here's a few shots of the PCB, kit and whatnot.
I am thinking I might buy one of the PP EL34 kits from MableAudio (minus chassis, I have some ideas in mind for that). The amp is PCB based (I feel more comfortable with that) and it looks like a good quality board. I plan to use Russian PIO coupling caps and Nichicon or Rubycon caps in the power section.
Anyways, the reason for my post; I seem to have fallen quite well for the Russian Military 6P3S-e tube (a 6L6/G equivalent) and so I want to see what I have to do (if anything) to make this amp accept 6L6 tubes. I've attached the schematic below.
Any help would be greatly appreciated, if you feel like throwing your ideas out there, go nuts.
Regards, Nic.
PS: here's a few shots of the PCB, kit and whatnot.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
I'm suprised you want to do this change: I'm tempted to keep to original. EL34's with roughly 460V+ should give you 50W output; This design was the basis of many 1960's tried and tested guitar amps.
6L6's would be forced to get this with shorter life with lower primary Z. Thus the power match isn't optimised.
6L6's would be forced to get this with shorter life with lower primary Z. Thus the power match isn't optimised.
Regarding the B+ the transformer's windings output 335v (although with my grid power being closer to 250 volts that would mean 380v)
I am curious as to what I would need to do to be able to put 6L6 tubes in there, as I said I love the look and sound of the 6P3S-e tubes. In regards to the power, I'm not too fussed; I've got a SimpleSE running around 12 watts for so and it sound good. I'm doing this more because I'm interested to do a push pull amp more than anything.
Since they're following the normal practice with EL34s of tying the supressor grid to the cathode, all you have to do to try a 6L6 type is turn the bias (operating point) of the EL34s down to a low value, say 15 - 20mA, and put your 6L6 types in, rebias, and go. I used to use the wafer-base commie 6L6 tubes in my trioded ST70, yonks ago, and they worked pretty well.
Aloha,
Poinz
AudioTropic
Aloha,
Poinz
AudioTropic
Excellent, that's what I was hoping to hear. I personally think the 6P3S-e (wafer base) tubes are fantastic. They sound great and can take pretty much anything that you feel like hurling their way. Cheap too. The regular issue 6P3S on the other hand doesn't fare so well...
I'm disinclined to get into a 'which tube is better argument' but from what Poindexter said, it sounds like I should be able to have both (with a rebias)
A lot would depend on the primary Z of the OPT's. If it's optimized for the EL34 (around 4.3K), it's not good for a 6L6. I have a couple amps with 5K primaries, which will work with both. Also, make sure you have enough neg voltage from the bias supply, or they'll run way too hot. You may have to mess around with the value of R22 to something like a 2.2K-4.7K.
Last edited:
I've shot off an email to check on the primary impedance of the Output Transformer.
From your response, I take it you think just biasing lower (~20mA) may not be enough to keep the tubes cooler?
Hi,
I found an interesting mod for EL34 on the Decaware site called the Hazen Mod. On any amp with pins 1 & 8 (suppressor grid & cathode) of EL34 tied together try replacing the wire with a 0.1 uf 400-600V polyester film cap or mylar (non-polarized) This can be done to Russian 6P15P-EV also.
Quote : "In all the years of mods and tweaks, we have never come across a more dramatic improvement in sound quality." There may also be other small changes to be made depending on amp that are mentioned on this site.
Maybe a good reason to keep EL34.
Take care!
Randy
I found an interesting mod for EL34 on the Decaware site called the Hazen Mod. On any amp with pins 1 & 8 (suppressor grid & cathode) of EL34 tied together try replacing the wire with a 0.1 uf 400-600V polyester film cap or mylar (non-polarized) This can be done to Russian 6P15P-EV also.
Quote : "In all the years of mods and tweaks, we have never come across a more dramatic improvement in sound quality." There may also be other small changes to be made depending on amp that are mentioned on this site.
Maybe a good reason to keep EL34.
Take care!
Randy
Last edited:
There's some dispute about that mod, since it allows the suppressor to float. I'd like to see an EL34 modded like that on a tracer. I find that for small signal valves, tying the suppressor to a small positive bias improves linearity and gain, and was often done toward the end of the tube era for big sweep tube circuits. You can make a 6SK7 act like a 6SJ7 this way! Of course, since 6p3s-e automagically connects the suppressor to cathode, the issue is somewhat irrelevant.
I have succesfully used el34 output transformers in a 807 PP amp, and as you probably know, the 807 is a close relative to a 6l6.
They normally want between 5k - 7k primary. Assuming the EL34 OPT is a typical one, its about 3,5k primary. So the best thing you can do, is connect your 8 ohm speakers to the 4 ohm tap. Its about 7k then... In my case it worked perfect, but I also connected it triode. ( a triode is less critical to primary impedance than a pentode/tetrode)
They normally want between 5k - 7k primary. Assuming the EL34 OPT is a typical one, its about 3,5k primary. So the best thing you can do, is connect your 8 ohm speakers to the 4 ohm tap. Its about 7k then... In my case it worked perfect, but I also connected it triode. ( a triode is less critical to primary impedance than a pentode/tetrode)
Oh damn, I forgot about the AC peaks. Are caps rated at peak voltage, not RMS? To avoid getting a whole new transformer (or removing a cap, as I would think removing capacitance from the circuit would be a bad idea) what sort of wattage and value of resistor would be required to bring it down, say, twenty volts? (I used to understand this, but I always forget my rules.)
Mable just got back to me and the output transformer's primary impedance is 5.5K, so that sounds like a pretty decent trade off between EL34 and 6L6. I'm now tossing up between EL34 and 6L6, but I think I'd like it to be usable for both. I figure at the moment that I'll start off with the EL34 tubes (just ordered some JJ's which happened to be going cheap.) to make sure it works correctly, then have a crack at the 6P3S-e tubes, biasing lower (perhaps pushing them up after 20 hours or so)
Should 70v at 100mA between the four 6L6's be enough to bias them down to 20 or 25mA?
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.