popping, sizzling when amp first warms up

[Tonegeek]

Shortly after taking my Dclone off standby, it pops and sizzles for a few seconds. The amp works normally and the noise does not seem to return after that first go round. If I let it cool down for a while, it will do the same thing next time it starts up. So far I have observed the behavior with all masters on zero, and the loop bypassed so i am thinking it is probably somewhere between the PI input forward. I have also replaced the PI tube and wiggled it in the socket as the noise was occurring to no effect so I think the socket and tube are OK. I just replaced power tubes a few days before this started happening and can't rule them out as the culprit. I will check them next with replacements from another amp I have. I am thinking more likely bad cap coupler or plate resistor somewhere or cold solder joint. Could the supply caps do this? Any ideas before I open her up? Thanks

[skyboltone]

Shortly after taking my Dclone off standby, it pops and sizzles for a few seconds. The amp works normally and the noise does not seem to return after that first go round. If I let it cool down for a while, it will do the same thing next time it starts up. So far I have observed the behavior with all masters on zero, and the loop bypassed so i am thinking it is probably somewhere between the PI input forward. I have also replaced the PI tube and wiggled it in the socket as the noise was occurring to no effect so I think the socket and tube are OK. I just replaced power tubes a few days before this started happening and can't rule them out as the culprit. I will check them next with replacements from another amp I have. I am thinking more likely bad cap coupler or plate resistor somewhere or cold solder joint. Could the supply caps do this? Any ideas before I open her up? Thanks

Yes supply caps could, and everything else you mentioned too. You're on the right track. Interesting that it was ok before the tube change. I also wonder, why did you change the power tubes already? A good set should last years maybe?

[Tonegeek]

Yes supply caps could, and everything else you mentioned too. You're on the right track. Interesting that it was ok before the tube change. I also wonder, why did you change the power tubes already? A good set should last years maybe?

I agree, tubes should last years. I have 20+ years on some Sylvania's (granted, they really do need changing, but hey, they still work to some degree) in my Twin but only 18 months on the JJ EL-34s in the Dclone. What happened is one of them got microphic. Low end from the speaker cab would cause it to feedback. You could tap it and get a bunch of noise so I replaced both of them, again with JJ's. I hope it was just a fluke because I like the sound of these.

I also started thinking that just because my masters are down and I still get noise might not mean that the other pre's could not be the problem. If a plate or plate resistor was causing an issue upstream I suppose it could bouce back thru the PS so I think I will replace all the tubes momentarily just to eliminate the tubes as an issue. Wont cost anything cause I have an amp I just finished for a friend sitting here so I will just borrow his brand new tubes. Wish I could swap the whole amp as I think his amp sounds a tad better than mine! Not to change the subject, but I am sure some of you have built 2 identical amps except that they just don't sound identical. Anyway I am glad his turned out so good since he decided to spring for it based on hearing mine! would hate for it to go the other way...

[skyboltone]

I hear you on different outcomes with same or near same procedure. Who knows? This electronical stuff is all about electrons and they're tiny and self willed I think.

Like you said there's nothing to say the new tubes aren't clinkers too. You've got one good one of your previous pair......see how it matches up in idle current with one of the new ones. Not to say that idle current alone is a match but I don't think most of what passes for "matched pair" is truely matched anyway.

Anyway, before you start tearing stuff up I'd check out some more tubes. I bought two pair of Sovtek 6L6GC and got exactly two good tubes out of the four. They're not bad though. I hear good things about winged C. I don't think they can build great tubes for $8.95....even in Russia.

[Tonegeek]

Yep - its another bad JJ tube! I swapped em twice becuase I couldn't beleive it. This tube lasted all of 2 weeks. Wonder if AES will swap me another but then it would have to be 2 because they are matched. I run my bias on the conservative side so can't blame it on over heating. My plate voltage is ~455 so pretty normal there too. I think I may try some SEDS next time although Mat says he heard a loss of bass response when he tried them vs. the JJ.

I hate to start saying "they don't make em like they used to", but they really don't. It has only been recently that I have had this much trouble with tubes. On this same amp I had an EH preamp tube go bad. Like you inplied, it is hard to beat the low price. I guess buying $10 tubes and getting one bad one every now and then still beats buying the more expensive ones, and whose to say those won't have quality issues as well?

[rfgordon]

I have a pair of generic Chinese 6V6s that do the snap-crackle-pop for about 5 seconds after the HT hits them. The thing is, though, they are the most marvelously sweet sounding tubes after that. So they stay, and I put up with their misbehavior because they play and record so nicely.

As for JJ tubes, I've had two of their 5AR4s go "fireworks in a bottle" at first powerup. No more for me.

[drz400]

Yep - its another bad JJ tube! I swapped em twice becuase I couldn't beleive it. This tube lasted all of 2 weeks. Wonder if AES will swap me another but then it would have to be 2 because they are matched. I run my bias on the conservative side so can't blame it on over heating. My plate voltage is ~455 so pretty normal there too. I think I may try some SEDS next time although Mat says he heard a loss of bass response when he tried them vs. the JJ.

I hate to start saying "they don't make em like they used to", but they really don't. It has only been recently that I have had this much trouble with tubes. On this same amp I had an EH preamp tube go bad. Like you inplied, it is hard to beat the low price. I guess buying $10 tubes and getting one bad one every now and then still beats buying the more expensive ones, and whose to say those won't have quality issues as well?

Check your heater voltage is at 6.3 or under
Make sure none of the cathodes is over 180VDC in respect to heater
Probably not unless you have some cathode follower in a loop or something

[Structo]

Current production tubes are a crap shoot.
I had a TAD 6L6 redplate with less than 10 hours on it.
If you like JJ's, buy them from Bob at www.Eurotubes.com
That's all he sells.
He checks them out real good before selling them and will replace any defective ones.

[skyboltone]

Check your heater voltage is at 6.3 or under
Make sure none of the cathodes is over 180VDC in respect to heater
Probably not unless you have some cathode follower in a loop or something

An excellent recommendation mister. How come all filament transformers are wound for 115V primary? If you have 123V at the wall you're over 7V at the pins. With 3 12AX7s and two 6L6s a .22ohm resistor in series with one filament lead will bring things back to normal. Pain in the whatzit.

[FUCHSAUDIO]

Shortly after taking my Dclone off standby, it pops and sizzles for a few seconds. The amp works normally and the noise does not seem to return after that first go round. If I let it cool down for a while, it will do the same thing next time it starts up. So far I have observed the behavior with all masters on zero, and the loop bypassed so i am thinking it is probably somewhere between the PI input forward. I have also replaced the PI tube and wiggled it in the socket as the noise was occurring to no effect so I think the socket and tube are OK. I just replaced power tubes a few days before this started happening and can't rule them out as the culprit. I will check them next with replacements from another amp I have. I am thinking more likely bad cap coupler or plate resistor somewhere or cold solder joint. Could the supply caps do this? Any ideas before I open her up? Thanks

Try starting up the amp without a PI tube. Some TAD 6L6's do exactly what you mention. Crackle when starting up. If that doesn't show it, then remove tubes one at a time till you hit the bad one. Perhaps bad solder joint(s) or a noisy resistor, but tubes most likely...

[Tonegeek]

All good advice. My earlier msg was unclear I guess because I HAVE FOUND THE PROBLEM and it is in one of the output tubes. From reading some of the other posts it appears other tube brands do this same thing and it may not mean the tube is bad. My experience with this sort of thing though is that once a tube starts making noice, it only gets worse. Since this is my amp, and I don't play out much, I may just keep an eye on it, unless AES will send me a replacement set. I will also be checking my heater supply voltage. Thanks guys...