answers to questions about matched tubes.

[crazyzeke]

Brad, how about that thing where you run the outer pair with EL34s and the inner pair with 6L6s? Is that as bad an idea as it sounds, assuming seperate bias pots for each pair?

[crazyzeke]

Bob over at Eurotubes. Personally I wouldn't trust an amp running like that, even with really tough transformers.

[Jay]

I don't see why you couldn't do that given the tubes were each biased independently or the entire thing was cathode biased. If the latter you'd have to have a cathode resistor that got the bias into a range amicable for both types but it's certainly doable.

[Jay]

I do believe there are commercial amps available that run a variety of power tubes at the same time. The Egnater Rebel comes to mind as one but I've no idea what the circuit is actually doing.

[budda12ax7]

Brad, how about that thing where you run the outer pair with EL34s and the inner pair with 6L6s? Is that as bad an idea as it sounds, assuming seperate bias pots for each pair?

This is the setup on the Mesa Boggie Mark 3 amps....I run two EL 34's and two 6L6s....I can also run the amp on just the EL 34's with a flip of the switch...

It sounds great...

[case_dizzle]

I've always wanted to try a mismatched set because I've heard it can produce some lovely sounds, but I've been afraid to. I think I am going to go for it.

[blacktiger]

'K, then I am mistaken...

You weren't mistaken. Your original question mentioned doubt about the function of a hum balance control on a BF Fender and Jay confirmed it. Perhaps it's an aftermarket modification added by an end user?

No, there was definitely a "hum balance" control on some Fenders at some point. IIRC, it was a post-CBS thing.

[46346]

I've always wanted to try a mismatched set because I've heard it can produce some lovely sounds, but I've been afraid to. I think I am going to go for it.

i've had my eye out for affordable single power tubes (of good quality manufacture) in good shape for this kind of experimentation.
seems they're way cheaper than half of a matched pair.


does anyone have something of a strategy toward 'semi-matching', i.e. pairing up disparate power tubes?

[jorri]

I heard it was still needed in cathode-biasing amps, at least for longevity ( i know little, but i just was persuaded to pay for some matched quad!), and headroom was also explained to be better.

I tried to replace w/ a matched pair on the ac30 primarily to save money knowing two were gone...i think i got the positions wrong even after switching them about a bit into their pairs-sounded awesome then the new tubes blew in 6 months. Is it still the xyyx position? it will be usefull to remember for next time.

[øøøøøøø]

xyyx, or yxxy.

not xyxy, and definitely not xxyy

[aRoseisaRoseis]

Figured this might be the best thread to ask this.
I have a Vox TB35 which is running 4 6v6s.
The stock power tubes gave out and I've started looking into replacements.
Could I swap the quad 6v6s for one pair of 6L6(G)s?
The amp being cathode biased, it it a direct swap or am I missing something?

[budda12ax7]

xyyx, or yxxy.

not xyxy, and definitely not xxyy

Just to ask.....I am redoing my Ampeg VT-22...I could just buy two pairs of 7027a's instead of a matched quartet? AND would this run on 6l6gc's?

[øøøøøøø]

xyyx, or yxxy.

not xyxy, and definitely not xxyy

Just to ask.....I am redoing my Ampeg VT-22...I could just buy two pairs of 7027a's instead of a matched quartet? AND would this run on 6l6gc's?

question 1: definitely yes
question 2: most likely yes, depending on the individual 6L6GC. I believe JJ sells a 7027a that appears to be identical to their 6L6GC. No guarantees on that info, though.

[Larsongs]

I'm not a Tech... But, in my experience different Tubes have different Sound... JJ 12AX7's sound different than Tung Sol, Groove Tubes or whatever.. Same with all other Tubes I've tried...

Then depending on the what kind of Amp a Tung Sol might sound better whereas on another brand of similar type Amp the same size JJ may sound better or some other Brand of Tube..

It does seem, usually, better Tubes are more expensive... I usually wait for a Sale 10-20% off to buy Tubes that I need or might need.. Paying the extra $4-5.00 for a matched Set isn't a make or break deal for me. So I buy the matched Set.. Whether it's hooey I can't say? If it might help me avoid performance issues that's what matters.. $5.00 isn't that big of a deal....

[DeathJag]

Doesn’t RobRob make the case that close-matching tubes are completely unnecessary?