Just a thought about matched output tubes

[iknowjohnny]

Not that i'm telling you guys anything you don't know already, but another reason matching is foolish is that tubes will drift soon after you put them in anyways. I would typically watch them drift as much as 8 or 10 ma apart in no time.

[selloutrr]

Not that i'm telling you guys anything you don't know already, but another reason matching is foolish is that tubes will drift soon after you put them in anyways. I would typically watch them drift as much as 8 or 10 ma apart in no time.

you should use a higher quality bias pot maybe one that locks.
is the drift because your tubes were matched before they were burned in? or was the phase inverter not balanced and your push / pull voltages were off?

I'll agree with you to a point on this but the same "magic" you claim also has the potential to not sound good, cause damage, to the tubes and other parts of the amp. IMHO i'm guessing you got lucky and the tubes you are using were close enough they complimented your playing. but the bias does matter. think of it as an oil change for your sports car you, get it changed on a regular schedule the car runs smooth, reliable, perfect. you miss a few and start getting into higher mileage, the sports car stops being so sporty. keep it up you blow the transmission or the engine goes. just saying it all has reason. consider yourselves lucky if you've owned amps you didn't properly bias. fender amps are pretty forgiving, newer hi gain amps not so much.

[iknowjohnny]

you should use a higher quality bias pot maybe one that locks.

I'm talking about any amp and matched tunes. You buy a pair thats matched and they read that they are. Then a while later, be it a few hours or weeks of play and they then measure different from each other. I have yet to see tubes that don't drift. In my home brew they stay put once they're burned in well. Can match them or mismatch them and they won't drift except over long periods. It has nothing to do with bias pots. Also, i don't bias them hot at all. If i use two totally different tubes i still have each one biased correctly. whether the OT has issues with that or not i don't know. But in any case now i'm back to the 6l6 pair and i think i'm keeping it there. It's not quite as rich, but close, and the high end is smoother. I'm still reeling tho over the sozos. Those things are fantastic. Wish i had tried them long ago.

[Jana]

Just wait until the Sozo's break in! It takes a while but once they do it is like a blanket is lifted from the amp.

As for bias--I have my amps set with a fixed resistor--no pot. I have a stash of EL34's that will last me for the rest of my life and I have the bias set on my amps so that they can just be plugged in and played.

[iknowjohnny]

You're the second person who said that. (wait till sozos break in) I asked elsewhere about breaking in caps and most of the replies were "thats just internet BS". For the record, i trust you people here more than most other forums so i'll take your word, and i can't wait to see how they mature. How long does it usually take, and will leaving the amp on w/o playing it contribute to break in?

[Jana]

Will leaving the amp on without playing it help? I don't know. I think it contributes to the break in but not sure.

How long will it take? I don't know. It takes about 80 to 100 hours for me. I don't know for sure though since I don't record times, I just play it. I left the amp on as much as possible and played it when I had a chance.

[selloutrr]

It takes about as long to tonally form caps as it does to break in a speaker 40 -100 hours. Leaving it on helps form the cap similar to using a variac at power up from zero voltage for the first time or after a long break of not being powered on, but physically playing it does the real break in.

The drift you are experiencing in your tubes is probably the fact they are matched but not burned in prior to matching. You will find greater stability from a 24 hr burn in matched set. Most tubes are pulled from the production line stuck on a test rig for 1-5 minutes maybe less, tested and labeled.

If you want better stability in your matching you could use a test rig like the Maxiburn before you match your tubes. Keep in mind you run the risk of your matched set no longer being matched.

[Super_Reverb]

Honestly theres no hum at all. I just biased them like i would normally bias each type. I biased the 34 at about 33ma and the 6l6 about 10 higher. No hum, just killer tone.

Another factor in the push-pull output hum equation that we all know is that you can reduce/eliminate 120 Hz hum in an AB output stage at idle and low signal levels (while both tubes in PP pair are conducting). But, once one of the tubes goes into cutoff, while it's partner is conducting, the output signal be amplitude modulated with 120 Hz AC (hum). It's always been that way with Bassmans, Marshalls and other AB push-pull output stages.

You could always bias the outputs up into class A - and reduce the effect. I guess it matters how much hum bothers you.

cheers,

rob

[iknowjohnny]

Ouch....gonna be a long time till i get to hear them at thier best. I don't play much at all. Maybe a couple hours a week. Guess i'll know by 2012. But thats ok, they're great as is.

[rp]

IKJ which Sozoz are you using - the normal ones? I don't really care for any of the modern ubiquitous types, 150, 6PS etc. I will try the Sosoz even though I hate companies like them and Mercury that provide no specs whatsoever. If you do engineering you provide complete specs or you are wanker in my book. I emailed Sozo looking only for dimensions and never heard back. My stash of old moldeds is almost gone so I might just have to turn off my BS detector, down a stiff drink, and try the Sozos.

[iknowjohnny]

Well, the fact is they sound great unless you are one of very few that i have heard say they weren't impressed. And i mean VERY few. I really don't think in those terms, IE: "I hate companies like them and Mercury that provide no specs whatsoever". I now have my amp sounding better than ever and i'm digging the heck out of it for about $15. I could probably find something to hate about them if i dug deep enough. But unless the company rips people off or some such thing, then assuming their product does what i want at a price thats worth it, i'm in. Put your feeling aside and just try them. Maybe your stash of vintage caps will be better, i dunno. But if you find them as good as i did you'll be happy you did.

Speaking of sozos, can anyone tell me whether they think the .1uf on the PI's unused side and the .1uf NFB cap (both are still mallory) would benefit from sozos? I spaced when ordering and forgot those.

[iknowjohnny]

Anyone? On that last question that is...

Speaking of sozos, can anyone tell me whether they think the .1uf on the PI's unused side and the .1uf NFB cap (both are still mallory) would benefit from sozos? I spaced when ordering and forgot those.

It's going to cost me the $4 for the caps then 5 or 6 bucks for shipping so i don't want to waste that on 2 caps if it's not going to matter.

[Firestorm]

There isn't really an "unused" side of the PI, so if caps make a difference anywhere in the power amp, it would make a difference there, too. The nfb cap (you mean the presence cap, right?), maybe not. But I would think -- and I am just talking off the top of head -- that the benefits of different caps would be most pronounced earlier in the signal path, so if it were me, I wouldn't place a special order just for two caps. Wait until the next build.

[iknowjohnny]

Thanks, i will, tho it may be a long while.