Bugera guitar amp question (Bad tubes?)

[Falkner]

Alright, I have another guitar related question since you guys are so knowledgeable about them too.

Earlier this year I bought one of those 5 watt Bugera guitar amps as my first tube amp, and I love it. I decided to replace the stock tubes since the consensus seems to be that they are lacking. I bought a replacement EL84 and 12AX7, and just installed them today. The amp sounds amazing with them, far better than stock. Unfortunately, after 30 seconds to a minute the amp starts popping like a popcorn machine. Sometimes it doesn’t happen, sometimes it’s barely there, and sometimes it’s a constant barrage of noise.

After making sure the tubes were secure and replacing them each one at a time with the originals and trying the other replacement tube (I bought a matched pair, only need one), it seems that something is up with the EL84 power tubes. They both seem to run hotter than the stock Bugera tube, one so much that the EH brand painted on the outside melted off. The stock tubes and the new preamp tube work perfectly.

Before I send these back for replacement, I am wondering if I somehow got two bad tubes, or is it more likely something wrong with the amp itself?

[T-Bird]

Hi.

My vote would go for bad tubes.

In a class A (SE) operation the tube is biased so the operating point is in the middle of the curve, and it conducts fully for the entire duration of the cycle (as opposed to class B & A/B, PP). Nothing that I know of can be done will make it conduct more.

What is the stock tube? Bugera?

Disclaimer: This is an opinion based on personal experience only, but I wouldn't buy EH tubes, for any price, even though one of my amps had 'em as stock and there's still two of them there.

Regards
Sam

[Falkner]

Thanks, with my limited knowledge of amps that's what I assumed was the case with class A amps like this. They weren't packed all too well, as typical from MF, so they might have been damaged in transit. If MF will eat the return shipping on that I might try another set, but if not I'm not paying half of of their cost to return these to them if it might happen again.

Yes, the stock tubes are Bugera branded, whether they make them themselves or if they're rebranded I don't know. They don't sound horrible, but these new ones sounded much better fro the 30 seconds they worked.

I admit I know nothing when it comes to tube brands and bought these blind, just relying on the few reviews I could find. What are some of the more reputable brands?