Converting Fender from 6L6GC to EL34 trouble

[vibrovox7reverb]

I have a silverface Vibrolux Reverb that I've decided to run with EL34's because I like their overdriven tone, but the problem i since I converted the tube sockets to accept EL34's my EL34's don't run right. When I play there is very little volume even at around 7 and up, but the sound is pretty distorted (not in a normal, good-sounding fashion either). Switching to 6L6GC's fixes the problem. Plate voltage is around 430, the bias resistor was lowered from 27k to 12k and the pot was turned all the way down and the problem persisted. I know that's not even close to a precise measurement for the bias, but that seems like it should be low enough for most any EL34.

[vibrovox7reverb]

I forgot to mention that I did increase the value of the screen resistors as well. I didn't have any 1k 2w or higher resistors available so I used the closest I had which was 910 ohm 2w, an awkward value I know, but for some reason the local electronics store doesn't carry 1k, perhaps tomorrow I'll grab some 1.2k or 1.5 resistors.

[big_teee]

what about the strap between 1 & 8 required on EL34s?
Terry

[diagrammatiks]

need to ground pin 1.

it still won't sound right though. you might like it but the transformers aren't specced for el34s.

[Enzo]

And you can't leave the resistor wired from pin 1 to pin 5 either.

[vibrovox7reverb]

Yeah I've tied pin 1 to pin 8, and I've lifted the resistor from pin 5 to pin 1 and wired it back up with it free standing to pin 5. Btw, thanks for all the quick replies. i had already ordered a heyboer OT specced for a jtm45 for a trainwreck build I planned to do, so I could always throw it in there before I finish my build just to see how it sounds, and if ordering another would be worth it. Personally, I hate sound of the Vibrolux's current transformer as it does a terrible job of holding lows and just doesn't sound that good.

Thanks again for the quick replies

[MWJB]

I sounds like you have wired the sockets OK, the Vibrolux OT whilst not the beefiest may have exactly the right Primary Z for EL34s (can be as low as 3.6K:4ohms).

So your problems may be down to excessive heater current draw on the PT (unlikely - If in doubt pull any unused 12AX7s like V1 Normal channel - whilst rebiasing V2 pin 8 with a 1500ohm resistor - & Vibrato tubes?) or related to biasing, you mention plate voltage (sounds low) and bias resistor value, but no negative grid voltage and plate current in mA figures? Just because a tube is "an EL34" does not specifically mean that rebiasing is necessary compared to 6L6, it varys from tube to tube - of either type.

[Jazz P Bass]

Yeah, at the very least measure the bias voltage on pin 5.
Post the answer.

[vibrovox7reverb]

I did not even think about heater current, I did have all six tubes in when I tried the EL34's. I'm not home right now but I should be in a couple hours. I'll get some measurements and post them up here asap. In the meantime I need to look up heater current draw for EL34's vs. KT66's because my KT66's work fine in there with all six tubes and even though I love their tone I can't use them because the bottle of v8 touches the PT and rattles at loud volumes Thanks again for your responses everyone has been really helpful so far

[vibrovox7reverb]

After taking a look at the heater current figures I see why the KT66's could work while the EL34's couldn't. Unfortunately I don't have any PT specs, so it's hard to whether or not it can handle the extra current draw, but taking away v1 should do it, and if not I rarely use v5.

[big_teee]

I like the Classic Tone Transformers for the Price.
They have many current Load Options.
ClassicTone Transformers By Magnetic Components, Inc.
They show the prices you pay at the Triode Store.
Good Luck,
Terry

[vibrovox7reverb]

I just popped out v1 and the EL34's work! Thanks everyone for your advice, and thank you big tee for the transformer supplier!