Some tube questions

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Sam Laming

Sam Laming

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Thinking of getting some new tubes as I'm out of spares so a few things I'd like to learn follow:

1. Why are tubes paired? What happens if you don't?

2. Can you put any amp tubes in a Herbert?

3. What are 'power' tubes as opposed to tubes?

4. Is there any difference in each pair's function? (1&6, 2&5, 3&4)

5. Can you have 3 different pairs?

Many thanks guys. I wish to experiment as much as possible :thumbsup:
 
Sam Laming":z7euknha said:
Thinking of getting some new tubes as I'm out of spares so a few things I'd like to learn follow:

1. Why are tubes paired? What happens if you don't?

4 tube or 6 tube amps can be biased in 3 different ways - singles (Fortin), Pairs (Herbert and many others), Quads (VH4 and Uberschall). Tubes are thus sold as a matched pair or quad or even sextests because of the variety of biasing designs that amp manufacturers make. Most do bias in pairs. A matched pair (or quad or sextet) have the same properties for output and current draw. As there is only one bias trim pot for the pair, having tubes with different properties would not output power efficiently. They could almost be opposing each other. One thing on ordering tubes is that a tube dealer will have no upcharge for a quad over a pair (other than 2x the price). So, I sometimes buy in matched quads for pair options, as in a pinch, you could drop another tube in without having to bias, in a gig situation.

2. Can you put any amp tubes in a Herbert?

Damn near anything that biases from 50mA a pair up to 100mA per pair. This goes from 5881's - KT88's. Anything in between would work.

3. What are 'power' tubes as opposed to tubes?

Power tubes are what provides the analog output in terms of sound. Preamp tubes provide the tonal characteristics of the amp and provide driver functions (loop, verb, etc). Preamp tubes have no power output.

4. Is there any difference in each pair's function? (1&6, 2&5, 3&4)

No. Power should be distributed equally.

5. Can you have 3 different pairs?

Sure.

Many thanks guys. I wish to experiment as much as possible :thumbsup:
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That is excellent. Thank you so much :thumbsup:

Only thing that puzzled me a tad = power tubes/pre amp tubes, what are the EL34 type tubes? Are the other type the little nodules that sit infront of the tubes on a Herbert?
 
Power tubes are the larger tubes, EL34/6550/KT88/6L6GC... ect

Pre amp tubes are the smaller ones, 12ax7/12at7/12au7...ect
 
Anything inside the amp's chassis that looks as though it's made of glass in more than likely a "tube" also known as a "valve".

Bigger tubes take care of output and sonically, have a tremendous effect on the sound of an amp. EL34 is vintage and thick, 6L6 is sharp and wailin' with greater thickness in the mid-to-highs, 6550's are high-output "balanced" tubes, etc. These are gross generalizations but probably not far off in most people's opinions here on the board. Sound/tone is so subjective.

Pre-amp tubes shape the various channels' tone and also buffer FX loops et al. Oddly enough, sometimes the no-name Chinese variants are the best for making an amp kick serious ass in the gain department. As with everything, prices vary. I use Tung Sol 12AX7's in all my amp's preamp sections...all of 'em. I have 4 amps using 4 different types of tubes - 6L6, EL34, 6550, and EL38. All unique, all for different sounds in the studio. And I love everyone of them :thumbsup:

V.
 
Excellent, that's brilliant, thanks for your help guys.

How does one change the pre-amp tubes? I can do power tubes easily but not so sure of the others. Do the pre amp tubes ever blow?
 
Pre-amp tubes are changed in the exact same manner as power tubes. Line the pins up in the socket, and gently push them in. NOTE: Newbie mistake when removing any tube is to "twist" them out - DO NOT TWIST!! With any tube, preamp or power, just pull straight out. Job is made 100% easy by removing the chassis from the amp box.

Preamp tubes tend to last a lot longer than power tubes. Hard to say how long, but a lot longer. When things start sounding squishy - not as crisp - or your getting weird hums, feedback, microphonics, etc. it's time to change your preamp tubes.

Cheers,
V.
 
Excellent. That's utterly brilliant again, thanks for sharing your knowledge :thumbsup:
 
Sam Laming":jlij0etn said:
Excellent, that's brilliant, thanks for your help guys.

How does one change the pre-amp tubes? I can do power tubes easily but not so sure of the others. Do the pre amp tubes ever blow?
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Just out of curiosity, you do know the amp has to be biased when you put new power tubes in it, right? Steve K mentioned it in his post earlier, but your knowledge of tubes seems limited, but yet you seem quite confident you can swap the power section without any trouble. I am not trying to demean you in any way, just simply trying to help you keep from harming yourself or your amplifier. There is more to it than just taking out the old tubes and plugging in the new ones.
 
That's kind of you and thus thanks :thumbsup: I am indeed aware, however, I'm replacing my EL34s with likewise thus I don't think a bias is necessary until I try something different when these blow. I've biased my amp before :yes:
 
Sam Laming":353tj6t1 said:
That's kind of you and thus thanks :thumbsup: I am indeed aware, however, I'm replacing my EL34s with likewise thus I don't think a bias is necessary until I try something different when these blow. I've biased my amp before :yes:
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You will still be required to bias new, likewise tubes, regardless of how close they are in model and manufacture. The only way this is avoided is if all tube-sets are matched at the time they're acquired (ie 8 tubes all purchased at once from the dealer, completely matched). Just a heads up, perhaps you won't kill your amp with not doing this, but you won't get the real meat out of it without it.

V.
 
Ventura":3507a0be said:
Sam Laming":3507a0be said:
That's kind of you and thus thanks :thumbsup: I am indeed aware, however, I'm replacing my EL34s with likewise thus I don't think a bias is necessary until I try something different when these blow. I've biased my amp before :yes:
Click to expand...

You will still be required to bias new, likewise tubes, regardless of how close they are in model and manufacture. The only way this is avoided is if all tube-sets are matched at the time they're acquired (ie 8 tubes all purchased at once from the dealer, completely matched). Just a heads up, perhaps you won't kill your amp with not doing this, but you won't get the real meat out of it without it.

V.
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+1 to V's post above. Not only will you not get the real meat out of it, your bias values could drift even further apart. This isn't a good thing and while not necessarily damaging to the amp, isn't really recommended. I'd STRONGLY suggest you bias the new tubes and also to have the task performed by a reputable and experienced technician (if not Diezel). It's too easy to flub things if you don't know what you're doing. Just my .2 cents, and congrats on owning one of the best amps ever made!
 
I can bias an amp - my bro's an electrician and helped me do so. I was under the impression that where you have 3 'different' pairs of tubes that they aren't dependant on each others correspondance + Doug of Diezel UK once explained to me that you can get a really great sound out of biasing the tubes slightly more than what is recommended - they won't last so long but it'll give a better sound.

I've got fuses/tubes done now just not biased so I shall ask my bro to bring his multi meter home :thumbsup:
 
Just to double check:
biasm.jpg

'Diezel's suggestions for pairwise plate biasing are (Einstein, Herbert):
5881: 50 mA
6L6: 60 to 70 mA
EL34 60 to 70 mA '<<<

0.70 = correct like what it reads on the meter of mine yes?
 
Sam Laming":x7m9zf8a said:
Just to double check:
biasm.jpg

'Diezel's suggestions for pairwise plate biasing are (Einstein, Herbert):
5881: 50 mA
6L6: 60 to 70 mA
EL34 60 to 70 mA '<<<

0.70 = correct like what it reads on the meter of mine yes?
Click to expand...

yes
 
That was it without fuse, turned on fully. Should it be 70.00 as opposed to 00.70? I has been making funny noises and being a bit weird, only played it once or twice since biasing...
 
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