Mark IV - odd tube combinations

[yfeefy]

Has anybody (else) tried this:

JJ 6v6s in class A (plate voltage is 404 in tweed mode, which should be perfectly safe) - I've been doing this for a couple months and it sounds great, esp. the clean and r2 channels. Going to simulclass with these tubes really hurts the sound because the middle pair are very underbiased) I have the 8 ohm speaker in the 4 ohm jack.

Here's what i want to try:

6v6 in outer sockets, substitube/yellowjacket el84 in inner sockets on tweed/simulclass setting - seems this would work and provide a nice sound, or at least be a fun experiment.

 

[dkiss4ck]

yfeefy
I haven't tried this but I am thinking of doing.
Thanks for your post because it seems to rule out the 4x6v6 option.
But it seesms the 2x6V6 is worth hearing
I wanted to try YJ/EL84s in the outer sockets as a low-power option using class A mode.

BUt in simulclass I can see I'd have to move them to inners and put 6V6s outside (or stick with 6L6s in the middle)

Which of the Groove Tubes substitute options would you be using ?
I'm thinking it would be:

928 for the outer pair in class A
928-PR for the inner pair
Not sure for the outer pair in simulclass

(And it has to be tweed setting when there are any 6V6s ?)

Thanks
Dave

 

[yfeefy]

thanks for the comments, I think my problem with the 4 6v6 ihas been with the particular tubes I have. They are JJ's and they idle in the middle slots at 3 mA. I also subbed an old GE that I have in one of these slots, and it idled at 5. I think one must needs really high idle current tubes in the inner two for the four 6v6 to sound good. Mesa says to only use all four in simulclass, but the JJs are supposed to be tough, and I haven't had any problems running in class A (knock on wood). I do always run in tweed this way. I think the recommendation probably stems from voltage concerns, the HV does drop a little when all four tubes are in use.

I was initially thinking about the yellow jackets in the inner slots, because of the way they work, I think the cold bias of the slots doesn't matter, they block the bias anyway with a capacitor.

 

[gummx97]

guys,

i recently retubed my mark 4 from JJ's, high gain option 6L6, how does the 6V6 sound with all four of them in the sockets? thinking of trying 6v6 on the mark 4.

 

[dkiss4ck]

I just noticed the recommendation in the manual for simulclass only with the 6V6s and would have 'warned' you.
You're ahead of me technically if you've measured the bias - though I was aware of the cold biassing in the inner pair.

With the fixed bias issue I've always just specified the amp to suppliers to get correctly rated valves - 6L6/12AX7.
So how would that work in selecting the EL84s in YJs ? I think as you're saying that they configure the bias independently of what was in-circuit so the tube would need to be a match for the YJ and not the amp ?

For the (inner) 6V6s maybe you have alternatives to JJ in mind now (they would have been my first thought) ?

BTW A reputable valve supplier gave me the general advice not to 'mix' YJs with larger tubes but he may not have picked up on the exact configuration here.

Is the primary risk only to the tubes themselves ?
Thanks