Can i mix tubes?

[foliver]

Hello,
one of my 4 valvo el84 tubes is gone due to electrical fealure.

The ones my amp uses are a KM4 production.
My question is, can i use another production number Valvo el84 along with the 3 i have now working?

Does different prod number have diferent sound that can make an audible change if i mix them?

Just to confirm, logic says all matched 4 tubes, but i din;t find a MK4 valve..

Thanks for your opinions

Fabian

 

[knockbill]

Push-Pull amps should have at least, matched pairs of output tubes,,, some requiring matched quads... What amp are we talking about?

Regards,
John

 

[nashvillebill]

It's preferred to have matched pairs, but in the real world, amps were produced for decades without installing "matching" tubes. The manufacturer would reach into a big box of tubes, grab some, and install them. Even today, big-name guitar tube amp manufacturers follow this same practice. "Matching" output tubes is a relatively recent concept.

Again, it's ideal to have matched pairs, but as long as one isn't terribly out of whack, the world won't end. Some amps have individual bias adjustments to allow for minor tube mismatches.

 

[sony6060]

No damage will result. Matched tubes are great, but not absolutely necessary. An experiment with a DIY PP amp testing 36 NOS power tubes of same manufacture and year for matched and unmatched resulted in matched tubes being a little cleaner sonically per a group of four listeners. YMMV.

 

[nashvillebill]

To further "stir the pot" on the tube matching concept: it's important to question how the tubes were matched?

Did the vendor (ahem, typically from a certain auction site) just stick them in a Hickok tube tester and look for the same transconductance? Bear in mind a tube tester measures tubes at relatively low voltage, not the same plate and screen voltages they will actually be running in your amp. Or did the vendor use a different setup? And exactly what parameters were matched? There are several operating characteristics for a tube, transconductance being only one of them. Furthermore, how many hours were the tubes operated at before measuring these parameters? A tube at 2 hours will read slightly different from a tube at 20 hours life...or 200 hours.

Bottom line: in theory it's great if the pairs are exactly matched, in all respects, no matter where (under what operating condition) they are measured or what parameter is measured. But that's likely not going to be achieved. Many folks think they've gotten "matched" tubes when in reality the tubes were only "matched" with respect to one parameter, at one given set of operating conditions. Which means the rest of the time the tubes are no more "matched" than tubes randomly pulled from a box.

 

[mpholland]

Was electrical failure do to old age? If all tubes are getting aged and running close to minimum spec then I would replace with a whole new quad of your liking. They shouldn't have to be perfectly matched, but put the closest pairs in each channel. If it was just a single bad tube and the other 3 are still in good shape, you can probably find another Valvo that is close for about 30-40 bucks. If you don't care about such things, any other EL84 will work in a pinch, but as I stated before, your best results will come from taking your two closest pairs and putting them in each channel.

 

[gadget73]

It wasn't even remotely uncommon to see things with 2 totally different output tubes installed. When I got my Magnavox amp, it had 4 EL84 outputs, no two were the same brand. They were pretty grossly mismatched, and it still made sound.

 

[foliver]

thanks for your repplies.
It;s a Grundig NF2 amp (original, not upgraded yet). It runs with original valvo's EL84, all 4 the same KM4 code.
I think i;;l look for another used valvo, then recap the beast, and then...

I'm surpised on how well it worked (until yesterday) comparing to my sansui qrx 8500.
I was having fun building oppen baffles with the original console speakers.
The smoke ( fire really, it was scarry) problem happens at the same time of a big thunder, a change in speakers connections to test the open baffles and a pluged unpluged test source, doh!

 

[sKiZo]

Big thunder, as in storm?

Short cycling will kill a tube amp. Power blips, and the capacitors aren't allowed to discharge properly, power comes back on, and you have a heavy overload. Owch!

You can fix that by adding a NON-LATCHING GFCI adapter between the wall and power cord.

If the weather does interrupt power, the internal breaker will trip and require a manual restart. Leave the amp off till the weather settles down, and then hit the reset button. You should in any case allow at least a couple minutes before resetting.

Not sure what you got for power down there, but I expect you could find something similar. The "non-latching" is the important part, and different from what you find in a standard GFCI breaker like you'd find in a power panel. Those will reset automatically and not do much good in this case.

 

[foliver]

I got it.
Thanks for the tip Skyzo