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About power tubes

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dawgkeeper51

Active Member
I would like to get some feedback from end users before I ask the manufacture this question.
All your comments are very much appreciated.

Since this is my first tube amp...........
TAD 60 (Tube Audio Design) I would like to ask a question. Would it hurt to mix the type of power tubes one uses in their amp. Like my TAD-60, it uses 4 power tubes and I can use any of the following tubes......
6L6GC, EL-34, 6CA7, KT-77, 6550, KT-88 & KT-90 tubes. Would it hurt the amp if I were to put in 2 6550 and 2 EL34 tubes. I would put one each in a 6550 tube into the 1st & 3rd socket the a EL34 into the 2nd and 4th socket. This would give me one of each type of tube in the right and left channel.
I have only been using tube equipment for about a year and my tube amp for about 6 months. I like the high and mid range of the EL 34 and the bass of the 6550.
Thanks
Ron
 
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I would not mix tubes in any manner.

I assume you bought your amp from Paul Grzybek. I would email him and ask directly. He's very quick about responding to email.
 
Just wanted to hear the feedback

Yes Paul answers very quickly and I will ask him later on this month. He is on vaca right now. I just wanted to get a few opinions from other tube users. I will not do anything to void the warranty of the amp but the thought crossed my mine. I did get one TAD60 owner saying he thought it would not hurt the amp. But, like I said I will ask Paul the same question that I asked hear. If the answer is different I will post Paul's reply.
Thanks for the input
Ron


Still I would like to know why you can't mix tubes? There has to be so other reason besides the numbers on the tubes.
 
You want a pair of tubes to have matched transconductance (gain). More specifically, you want the family of transconductance curves of one tube to be very close to the family of curves for the other. This yields a state of symmetry and balance, which equates to low distortion and clean sound.

It is very hard, if not impossible, for a 6550 to have the same transconductance curves as an EL34.

Fred Longworth
 
dawgkeeper51 said:
I would like to get some feedback from end users before I ask the manufacture this question.
All your comments are very much appreciated.

Since this is my first tube amp...........
TAD 60 (Tube Audio Design) I would like to ask a question. Would it hurt to mix the type of power tubes one uses in their amp. Like my TAD-60, it uses 4 power tubes and I can use any of the following tubes......
6L6GC, EL-34, 6CA7, KT-77, 6550, KT-88 & KT-90 tubes. Would it hurt the amp if I were to put in 2 6550 and 2 EL34 tubes. I would put one each in a 6550 tube into the 1st & 3rd socket the a EL34 into the 2nd and 4th socket. This would give me one of each type of tube in the right and left channel.
I have only been using tube equipment for about a year and my tube amp for about 6 months. I like the high and mid range of the EL 34 and the bass of the 6550.
Thanks
Ron
Click to expand...

NO NO NO! :nono: Do NOT mix tube models, with the following exceptions from your list. It's likely that the sockets are paired V1 & V2 and V3 & V4. Mixing a 6L6GC and 6550 or EL34 and 6550 or 6L6GC and EL34 together is like hitching up a horse and mule in the same team. Mixing tubes as you mentioned will wreak havoc on the amp, plus you'd never get their bias set correctly.

Give the tech support folks at TAD a call and run your question past them. It'll make their day... :D

EL34 = 6CA7
6CA7 is the American designation for the EL34. Same internal power pentode construction.
Standard in Marshall music amps and the ever lovable Dynaco ST-70. The KT77 is a rarer direct substitute for the EL34, but differs in it's beam-power rather than power pentode construction. KT77s now come out of China (many times under the Gold Dragon or Gold Lion name.)

6L6CG, EL37, KT66, 7581
Same family, with the KT66 (British) and 7581 (American) having slightly higher plate voltages and about 5 watts stronger than a 6L6GC. Considered the "industrial strength" version of the 6L6GC.
Do NOT substitute in any recent 5881 or 6L6WGB which are lower voltage (and wattage) and will likely meltdown both themselves and other components as well. Same goes for the older 6L6, 6L6GA, and 6L6GB versions.

6550 and KT88
Same family with the KT88 being the British and the 6550 being the American designation. 6550s were standard in Ampeg music equipment and account for the bottom end you like.


Although not suggested, it's typically safe to mix models from the same family as long as it's done in pairs (e.g. 2 x EL34 and 2 x 6CA7) Most folks will recommend you get power tubes in "matched pairs" or "matched quads" so that their measured specs are nearly identical when placed in the circuit together.

If nothing else, try different brands of preamp tubes to vary the overall sound with each model of power tube to see if you can strike a happy medium with the right combination that suits your listening.
 
The best way to go on power tubes is to replace all of the power tubes in a suspect channel together as a matched set. Part of the design of a push pull output stage is the ability to cancel noise.
Both tubes amplify the same noise out of phase it cancels in the transformer an you don't hear noise. If one tube doesn't match it will cancel either more or less hum than it's partner leaving you with more noise in the output than an amplifier with matched tubes.
Same thing happens at full power when one tube runs out of "steam" and the other is still conducting it can cause asymmetrical clipping, limiting full power and introducing even more distortion.
Matched tubes are always best.
Unfortunately owning the best is rarely cheap.
 
dawgkeeper51 said:
I would like to get some feedback from end users before I ask the manufacture this question.
All your comments are very much appreciated.

Since this is my first tube amp...........
TAD 60 (Tube Audio Design) I would like to ask a question. Would it hurt to mix the type of power tubes one uses in their amp. Like my TAD-60, it uses 4 power tubes and I can use any of the following tubes......
6L6GC, EL-34, 6CA7, KT-77, 6550, KT-88 & KT-90 tubes. Would it hurt the amp if I were to put in 2 6550 and 2 EL34 tubes. I would put one each in a 6550 tube into the 1st & 3rd socket the a EL34 into the 2nd and 4th socket. This would give me one of each type of tube in the right and left channel.
I have only been using tube equipment for about a year and my tube amp for about 6 months. I like the high and mid range of the EL 34 and the bass of the 6550.
Thanks
Ron
Click to expand...
Not recommended. If you bias the 6550 correctly in a mixed setup like that, the EL34 will be in cutoff (not conducting significant plate current at all). If you bias the EL34 correctly, the 6550 will red-plate and suffer a miserable death. Stick to the tube type recommended by the amp manufacturer in all sockets calling for the tube.
 
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