How do I change this design from EL34 to 6L6?

[MellowTone]

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.

[richwalters]

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.

[MellowTone]

Originally Posted by richwalters

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.

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.

[Poindexter]

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

[Cassiel]

I'm with Richie here, besides EL34 is a better tube.

[MellowTone]

Originally Posted by Poindexter

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

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...

Originally Posted by stalker

I'm with Richie here, besides EL34 is a better tube.

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)

[TubeHead Johnny]

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.

[MellowTone]

Originally Posted by TubeHead Johnny

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.

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?

[TubeHead Johnny]

It all depends on the voltage range you can achieve with the bias pots. Frankly, I don't see why you're so crazy about those Russian 6P3S-e's. I had a set of them a few years back and the sound was muddy and harsh. You can get them dirt cheap however.

[rmyauck]

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