does this sound like perhaps a tube going south ?

[popthree]

i recently picked up a 2nd hand Blues Junior. The seller has done a couple of the BillM mods to it.. twin mod, and some tone stack stuff. The amp sounds very good...however... occasionally.... after running for an hour or longer... it sometimes experiences a volume loss.. i'd say almost in half.. ..its a brief occurrence.. usually lasting 3-10 seconds then recovering to the previous level. possibly a tube fading ?

[popthree]

bumpage

[scoots]

i wonder if it's a solder issue to one of your power tubes. my deville did that fade in/fade out thing for a while then it did the permanent half fade out and this is what it was with mine. when it fades out like that, maybe flip it around and see if all your power tubes are glowing

[popthree]

hey scoots, by solder issue with a tube.. you mean like where the tube socket is soldered onto the board.. like a cold solder joint ?

i may have to wait for the problem to worsen before i can properly diagnose it. it fades and then restores pretty quickly... thats why i thought maybe a tube was just going bad.

[scoots]

yeah, that's what it was with my hr deville, cold solder joint to the board. haven't had a problem again. if it's going in and out fast like that, man i dunno. early stages of a cold solder joint? mid stages of a tube going? hey, someone chime in on this that knows this sh...stuff...

[Wally]

THat's a hard one to diagnose if it won't 'stay broken'....it could be any heat related problem. I would suggest touching up the solder jonits.
That said, the initial question led me to this.....best 'tubes goin' south' sound I know of....
http://www.youtube.com/watch?v=C8hSNbB1X9k

[popthree]

ok, today i caught the amp acting up again. the volume dropped and stayed at a low level. i turned the amp around and noticed that one of the EL84's was very very bright, the other was lit but not as brilliantly. i poked both tubes with a toothpick but noticed no differences. finally i turned the amp off and waited a minute or so, then powered it back up. volume went back to normal, and both tubes glowed the same... neither glowed with extreme brilliance. what ya think.. bad tube ?

[woodman]

i've got a brown Pro ('62) that's doing the half-power thing too, only it's not recovering ...

when it started doing this, i took it to my tech, he checked it out and everything seemed fine. brought it home, tested it, no problem. took it to a gig, and yep, the power had dropped ... as i was testing it, once it popped back to full power for a second, then dropped again. i changed out all the tubes except the recto (didn't have one in my spare tube kit), no change. it's driving me outa my gourd.

[jefrs]

Swap the EL84 valves around and see if the issue reverses itself. If the same valve goes dim then it's the valve, if the same socket goes dim then it's the socket or components around it. It could be a dry solder joint or a poor valve pin connection in the socket. It is easy to damage a socket when inserting a valve.

[Wally]

popthree, "very, very bright"......here's the question relating to the 'brilliance' of that tube glow. IF you look at those tubes, you will see some long,dark elements that run from the bottom to the top of the assembly inside that glass envelope. These are the plates. What you don't want to see a tube do is 'redplate'. When the current draw is excessive in a tube, those plates will glow first orange and then red as the amount of excessive current draw increases. IF you take the time to look closely and observe, you will see that this red glow is due to the metal of the plate overheating....it looks kind of like some metal that is being brazed or welded. Note: do not let a tube redplate for any significant amount of time. Study that effect for about 1 second, right? Then shut the amp down. The life of a redplating tube is measured in very short periods of time. Minutes maybe, depending on the amount of current draw and the heat to which the tube is subjected. IF this is what that one tube is doing, shut the amp down and don't play it any more until a tech goes in and finds out what the problem is. You could have a bad tube, a resistor could be bad or the output transformer could be shot. IF you play the amp in this condition and the transformer is not yet bad, it may well soon be.
IF the tube is not redplating...plates glowing some color from light orange to fiery red; could yo uplease describe exactly what type of glow that the tube is exhibiting.

[popthree]

i was actually suspecting that the tube that flares more brightly was probably the one going bad..

[Wally]

Jefrs point about swapping the tubes' positions is a good one to determine if the problem is in the tube or in the circuit somewhere.

[popthree]

yeah, i just tried it...swapped the power tubes around. while doing the swap i noticed that the tube sockets are just a hair wiggly.. probably not a good thing eh?

anyway after swapping them, i turned the amp on and played a bit. it sounds perhaps slightly different in tone.. maybe this is just me imaging things.. but i dunno.. anyway, i'm not imagining the next thing.. a smell.. faint smell.. almost like the smell of hair burning.. its very faint.. the amp seems to be working, but i suspect something is amiss..

[Wally]

popthree, imho that amp needs to see a tech. I would not use the fellow from whom you bought the amp. I would not turn the amp on again until someone who understands thigns has a look at it.
Tube sockets do not 'lock' a tube in. They all move around a bit. IF you hear noises pop up while you move the tube around....amplified noises....then there is a problem with things in that area.
The one thing that makes me think that you had an amp that was not compromised regarding the OT when you bought it was the fact that it you reported in the OP that it sounded 'very good' until things went south. That buring smell is not good....resistor, cap? or the OT....again, just my 25 cents that won't even buy a coffee.....don't play the amp until it gets proper service. Playing an amp with excessive current draw can compromise the soemwhat expensive transformer/s. Cross your fingers, pop3. HOpe that you have a resistor and/or power tube gone bad, but it is tech time. NOW! IF NOT NOW, DON'T PLAY THE AMP.
Excuse the yelling. LOL I have the best of intentions.....saving your tranformer/s.

[popthree]

yeah, you are probably right Wally. I can't decide for sure if the smell is new or something i haven't noticed before. its really faint. may just be the way the bugger smells.. i'm ultra sensitive to everything at the moment and possibly over compensating /obsessing about possible issues. i did turn the amp back on one more time after my last post and played thru it a bit. it didn't do the power drop thing, but i can definitely smell a faint odor coming from the amp... a heat smell.. could be normal..but i'm just not sure. i already emailed a guy i know who can fix these things. hopefully he'll have the bandwidth to take it in... otherwise, the only other local place will have the amp from now til january, and probably really stick it to me.

[popthree]

Originally Posted by Wally

Tube sockets do not 'lock' a tube in. They all move around a bit. IF you hear noises pop up while you move the tube around....amplified noises....then there is a problem with things in that area.

its the tube sockets themselves that are wiggly.. only the power tube sockets are like that. the 3 preamp sockets are more solid. i did wiggle them just a bit..by poking them with a toothpick, but it didn't cause any static or popping sounds.

i heard from my guy and he's going to take on the project.

[Wally]

pop, now you are learning about one of the things about this type of amp construction that I cdon't care for. The tube sockets are mounted directly into the board. Yes, that board flexes when tubes are pushed in and pulled out, and the board takes all of the heat from the tube/tube socket area.
I hope you get that amp up and running for a small bit of money.

[popthree]

yeah i knew that about the tube sockets being mounted to the PCB going in on this deal.. been reading the tdpri for a few years now.. ha. i just didn't realize they'd be wiggly to boot. anyway, thanks for the help. great forum, great people.

[popthree]

Originally Posted by Wally

popthree, "very, very bright"......here's the question relating to the 'brilliance' of that tube glow. IF you look at those tubes, you will see some long,dark elements that run from the bottom to the top of the assembly inside that glass envelope. These are the plates. What you don't want to see a tube do is 'redplate'. When the current draw is excessive in a tube, those plates will glow first orange and then red as the amount of excessive current draw increases.

after re-reading this excellent description.. i'm sure this is what's happening.. the plates were glowing bigtime. i'm dropping the amp off tonight... guess i'll just sit back now and await diagnosis.

[Scott S]

Originally Posted by woodman

i've got a brown Pro ('62) that's doing the half-power thing too, only it's not recovering ...

when it started doing this, i took it to my tech, he checked it out and everything seemed fine. brought it home, tested it, no problem. took it to a gig, and yep, the power had dropped ... as i was testing it, once it popped back to full power for a second, then dropped again. i changed out all the tubes except the recto (didn't have one in my spare tube kit), no change. it's driving me outa my gourd.

Hmm, that's sad! How long did the tech have it on? Perhaps he could borrow it, leave it on for a while with a signal generator into a dummy load, and smack it around to see if something is making intermittent contact when warm.

[Wally]

Originally Posted by Scott S

Hmm, that's sad! How long did the tech have it on? Perhaps he could borrow it, leave it on for a while with a signal generator into a dummy load, and smack it around to see if something is making intermittent contact when warm.

Lol SCott. Who did that old song about playing the doghouse bass...
"Slapping my Baby around!"
Re: the '62 Pro.....yep, it needs closer attention from a tech. IF it came to me, the first qusetion is 'Does it have original electrolytics?" But, then, ya'll knew that woudl be my first qeustion, right? LOL
The fact that this amp's production comes and goes does indeed lead one to look for a bad connection. I would maybe not even worry about the heat relationship since it will come on strong even when hot, go away, come back. Usually heat related problems are constant once the heat causes the problem to come up. I would smack it around the instant it was making good volume...and I would think that one would hear the results quickly. IF the volume wasn't there in the beginning, then smacking it around might bring the volume up. ONCe again, I could be wrong.

[patrickhowell]

It sounds like an issue with one of your power tubes. Does this sound like the issue you're having? (From the Billm FAQ):

Ron says:
February 10, 2009 at 7:47 pm
My Blues Junior started to crackle and then lost about half of its volume. It now has a distorted sound if I turn up the master and or volume. This has happend before, but came back. But now its gone. It is less than 3 months old. Ruled out instrument cable and guitar problems. Your view on what the problem could possibly be. I’m sure there are a few. Thank you for your time. Ron

Ron says:
February 10, 2009 at 8:22 pm
Bill…disregard the question on my Blues Junior. The tube pins on V3 were not making a good contact. Thanks again for your time. Ron

The more times you turn on your amp before having this issue fixed, the greater the chance that it won't turn on the next time. Get it to a tech ASAP.

[woodman]

sounds like pop's on the way to solving his problem, so i don't feel so bad about hijacking the thread ... the old Pro sounded fine when i got it home from the shop. i had suspected the power tubes, so my tech (very trustworthy) sold me a set of ANOS 6L6GCs at a bargain, though he said the 6L6WGBs i took out tested good. (i figure you can't have too many spare tubes!) so i took it home, played it awhile and thought the problem was solved.

i didn't have another big-amp gig for several weeks, then we played a high-profile festival gig where i needed the Pro ... at setup, i fired it up and it had gone back to that half-power situation i described. (sounds about like a Princeton cranked up to 10, breaking up and not much punch). i played it some and after a minute, it went to full power for about a second, then dropped again.

so i changed all the preamp and power tubes — still the same. never could get it back to full power, so i had to use the 5E3 (not ideal for a big-stage gig).

this afternoon, i had some free time so i checked it out. when i turned it on, it was still half-power. put an entirely different set of tubes in, after cleaning the pins thoroughly. still half-power. i jiggled the tube sockets and speaker cord, no change. played it for a few minutes, then suddenly it busted into full power! jiggled everything again to see if it would cut out, but it wouldn't. so i'm baffled.

i've got a big-bucks gig on the 17th where i really need it to be dependable. do you think i should try reflowing the tube-socket solder joints?

[Wally]

Woodman, there is no telling where that problem is. IN these situations, I go to the trusty chopstick 'guerilla' method of amp repair. The chassis has to be on a bench and hooked up to an appropriate speaker. ONe goes to tapping everyhwere to see if a physical connection problem can be found. Regular warning here....CAution: dangerous current flowing with a live amp. ONe nad behind the back, please. Don't attempt if not experienced.
ONE cannot discount the possibility of a bad speaker cable/connection, either. Do you run a trem control footswitch. Disconnect that and check things there, too. I have found reverb/trem cable connections that would kill an amp's production in the manner you are describing. Somewhere between the input and the speaker there is a problem....lol...that is all one can know looking at the amp as it is, imho.

[patrickhowell]

Originally Posted by woodman

i fired it up and it had gone back to that half-power situation i described. (sounds about like a Princeton cranked up to 10, breaking up and not much punch).

Crossover distortion ?

[popthree]

i dropped off my BJ tonight and my friend gave it a quick look. he had an extra set of el84's handy and so dropped them in there and turned the amp on... observing it, after a few minutes, the plates on those tubes started to heat up and glow a bit.. looked like it was well on its way to the same condition. also the faint heated electronic smell was creeping back... so he turned it back off and said he'd have to start checking voltages, etc. there's something definitely not right going on there.

also, while looking at the original el84's he noticed that they both had black charred marks on the glass, and the silk screening was burnt in a couple of spots... this bugger is getting hot and bothered about something.

ah well. such is life.