Push-Pull tube amp. Importance of matched tubes?

[Keith_W]

EDIT: But do note the fuses! Safety First!

Stupid question here: why do people use fuses instead of circuit breakers?

 

[wwenze]

I wanted to say "of course match them", but then I remembered, the whole point of selecting old amplifier designs i.e. where matching would actually make a difference is because people do not want to use newer designs which already solved most of the matching issue to the point that you can have different op-amps on different channels and not even hear or measure a difference.

Which means, the whole point of buying these older designs is because you want to hear the problem of matching issues. In which case you should leave the tubes unmatched. Heck, two tubes for pull-up and one tube for pulldown and reap all that second-order harmonics!

Stupid question here: why do people use fuses instead of circuit breakers?

They cost a few cents each in bulk and not much of a dollar individually, and can be spammed anyhow, solder them straight onto wires (with heatshrink) or the PCB and at the end of the build you can just toss them away instead of recovering 4 expensive CBs.

 

[wwenze]

Hey all, I have a Muzishare x7 integrated tube amplifier. See on Amazon. I've had the amp for about two years and not long ago I noticed a substantial channel imbalance. (about 5 db). I started replacing the front tubes as these were the cheapest and it improved things to where now there's about a 2db difference.

My question. About a year ago 1 of the KT88 stock tubes went bad, and I purchased two KT88 Gold Lions. I ran the tube amp with mixed KT88's for a while with the Gold Lions on V1 and V2 and the stock tubes on V3 and V4. Could this have caused the imbalance? With a push-pull amp like the Muzishare, what is the best practice with nonlike tubes? If this is ok? Does it matter if they are both on one side or should I run one set on V1 and V3 with the others on V2 and V4? I hope this will be ok as I just replaced all the other tubs and two more KT88's would be a couple hundred bucks. At this point, I'm almost scared to use it in fear that I had messed things up with the non-matched tubes.

Thanks!

This is... honestly a very hard question to answer

Ideally you want all 4 tubes (2 x 2 channels) to be the same... I think the left-right imbalance is easy to understand. For tube amp in push-pull however, essentially you have one tube conducting during the signal's positive phase and the other tube conducting during the signal's negative phase... (but for the other tube we flip the incoming signal and then we also flip the output connection, hooray for transformers) so ideally you want both tubes to have identical performance.

But see my previous post regarding if matching top/bottom is actually necessary...

So if the GL have one set of performance and the stock tubes have another set of performance, perhaps you can put the GL in the top or non-inverting socket and the stock tubes in the inverting socket per channel.

 

[Keith_W]

They cost a few cents each in bulk and not much of a dollar individually, and can be spammed anyhow, solder them straight onto wires (with heatshrink) or the PCB and at the end of the build you can just toss them away instead of recovering 4 expensive CBs.

That is fair, but it is different for the end user. I have an amplifier that has a fuse. When it blew, I had to wait until the electronics store opened before I could replace it - which meant no music for my friends and I that night. It was a one-off, if I had to keep replacing fuses I would have taken the amp to the tech. I asked the question because I would like to know if there is some kind of advantage for using fuses instead of a circuit breaker in an amp that is ready for production.

 

[wwenze]

Fuses do not blow 99% of the time. Makes no sense to use expensive CB for protection.