Mixing power tubes JCM900 SLX

[booradley]

Greetings,

I recently did a 2 hour show with my 100 watt SLX. No issues. A week later I put the amp on its side setting up for band practice and when powered it up…poof. Turns out the V8 EHX EL34LS died. I replaced it with a JJ EL34L and amp seems fine. Where to go from here? Is there any issues with mixing power tubes like this? I haven’t rebiased yet. Not sure I can get a full set of new ones. I retubed and biased the power tubes in 2015 I think. This is the 2100 model.

 

[junk notes]

Yes, the replacement tube will have a different current draw, just rebias as you mentioned. Happy to hear it is up and ruining.

 

[Chris-in-LA]

Yes, the replacement tube will have a different current draw, just rebias as you mentioned. Happy to hear it is up and ruining.

Up and ruining? LOL

 

[Chris-in-LA]

Actually a good question in these times of tube shortages. On an amp with 4 mixed power tubes, would the goal be to get each side as close to each other as possible?

 

[Rokinroller]

I've done it . With 2 different pairs of EL34's . One pair GT EL34M and one pair Mesa STR440 as a quad in a TSL100 . No problems at all . Amp sounded great . Both sides biased up evenly 70ma no problem . As long as you dont see any red-plating or get hum , all should be good .

 

[Pete Farrington]

Electrons react the same whatever the branding / origin of the circuit devices

Provided they’re idling at roughly similar currents, any functional EL34 can be used. That’s kinda the point of them being labelled ‘EL34’.

 

[Pete Farrington]

On an amp with 4 mixed power tubes, would the goal be to get each side as close to each other as possible?

Pretty much, but I suggest not to obsess about it.
Even if they idle the same, no 4 valves are likely to behave identically over the full range, and peak current may be 10x idle.

 

[booradley]

70ma seems like a lot. Should they be around 37ma?

 

[rockgod212]

did you change the output transformer for el34's. thought the 900's used 5881's?

 

[Rokinroller]

70ma seems like a lot. Should they be around 37ma?

Thats 70ma per pair . Not per tube .