New to me amp. I am used to repairing ss gear, not familiar with tubes.
When I first turn on the amp, one of the 12AT7 tubes flashes like a light bulb, then dims down to about normal. Once the amp has been on and warmed up, I get a popping sound thru one of my speakers, looked at the tubes and the 4 EL34's that are on the same side as the 12AT7 that lights up are arcing.
I replaced the 12AT7 with a different one and it still does the exact same thing.
I swapped out the EL34 tubes to the other side - it still does the same thing.
Curious if anyone had any ideas on what I should be checking.
Thanks
When I first turn on the amp, one of the 12AT7 tubes flashes like a light bulb, then dims down to about normal. Once the amp has been on and warmed up, I get a popping sound thru one of my speakers, looked at the tubes and the 4 EL34's that are on the same side as the 12AT7 that lights up are arcing.
I replaced the 12AT7 with a different one and it still does the exact same thing.
I swapped out the EL34 tubes to the other side - it still does the same thing.
Curious if anyone had any ideas on what I should be checking.
Thanks
Just a thought,
The first thing I would check is the voltage set to the correct voltage for your mains? It says it is switchable!
If its under waranty send it back before you loose it!
The EL34's arcing is very dangerous it can stuff the output Tx if it hasn't already! Also it can damage the EL34's.
You need to remember that you are talking high voltages and your amp may hold charge after power off. Test before you touch!
The first thing you need is a schematic, do you have one?
Then check the bias on the tubes. Do any of the tubes plates glow red? This is not the heater. the black metal plates inside the tubes.
The pre-amp / driver tube is unlikly to be the cause!
Could be B+ is to high.
It could be the connections on the tube grids are wrong.
It could be a bad coupling cap.
Is this a new amp or second hand?
The thing to do is compare the two sides of the amp (connections to the tubes) if the fault does not follow the tubes then its in the circuit on that side!
Hope this helps!
Regards
M. Gregg
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Initial brightness from a 12AT7 (or other types) is not unusual and does no harm. It is common in valves based on Philips designs. However, worth checking that the heater voltage is correct.
I would concentrate on the other problems, which sound more serious.
I would concentrate on the other problems, which sound more serious.
thanks for the information - is appreciated. Just kind of bummed. I tried to save a few pennies and bought a used one - I knew I should have bought new 🙂
Going to open her up tomorrow and check the bias and see if any caps have failed.
I do not have schematics, can't seem to find any. Will compare readings with the good side.
I have been told how to set the bias
Going to open her up tomorrow and check the bias and see if any caps have failed.
I do not have schematics, can't seem to find any. Will compare readings with the good side.
I have been told how to set the bias
hmmmmm, On a whim, I tried it out as an integrated amp - there was still a feint "pop" sound in both speakers, but I played it for a good 15 minutes at fairly high volume and the EL34's did not arc........
so - as a power amp , one side arcs after about 5 minutes, as an integrated it does not......
so - as a power amp , one side arcs after about 5 minutes, as an integrated it does not......
Excuse my ignorance, but what exactly do you do to it to convert it between 'integrated' and 'power' modes?
This amp apparently has different input. Presumably, the power amp input couples the signal directly to the phase inverter, while the integrated inputs run the signal through the preamp as well. I don't have a schematic though, so I'm going off what I could find using Google.
Does it make any difference if you switch from UL to Triode?
Can you take a photo of the inside at a resonable size so we can have a close look? (Keeping to limits)
Or maybe a few covering each part.
Regards
M. Gregg
Can you take a photo of the inside at a resonable size so we can have a close look? (Keeping to limits)
Or maybe a few covering each part.
Regards
M. Gregg
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I think it is the blue glass. EL34s were designed for clear glass, so blue glass will modify the photon absoption by the anodes and tilt the balance towards shorter wavelengths. 😎
Believe I got it - I just adjusted the bias sort of (not sure what Mingda says it should be so I guessed) Nary a pop let alone any arcing....
Thanks for everyone's help, is deeply appreciated.
Thanks for everyone's help, is deeply appreciated.
no, the blue glass tale actually goes on.....
turns out it still does it if I crank it up fairly loud for a bit. At normal listening volumes, which is probably a tad louder then most people listen to their music - it does fine.
Crank it and after about 15 minutes or so, it starts popping rhythmically - BUT, none of the tubes are arcing.......
I am going to just have to wait until next month when I get paid and get some new tubes (winged c). I just bought the ML SL3 speakers and of course now the amp (used), so my audio budget is shot to heck for now
turns out it still does it if I crank it up fairly loud for a bit. At normal listening volumes, which is probably a tad louder then most people listen to their music - it does fine.
Crank it and after about 15 minutes or so, it starts popping rhythmically - BUT, none of the tubes are arcing.......
I am going to just have to wait until next month when I get paid and get some new tubes (winged c). I just bought the ML SL3 speakers and of course now the amp (used), so my audio budget is shot to heck for now
When you adjusted the bias did you make the valves run a bit cooler? If so, it could be that they are a bit gassy and don't like being too hot.
I somehow suspect an arc-over somewhere on the pcb, which happens at higher instantaneous voltages, so it may well be in the anode/ output transformer primary.
it is all point to point wiring. Thing of beauty actually with quite a few nice multicaps in it.
well, not really - apparently bias should be set anywhere from .3 - .4.
Yesterday I had them all running pretty much right at .3 - today I did it again but bumped them all up to about .38 to see if the extra voltage would make it worse. Didn't really. I listened to it for about 40 minutes after I re-adjusted the bias and it never started arcing but still had the popping between songs or if I turn off the music. The first time I checked the bias, they were all over the place - anywhere from .7 to .3, most of them up there around .5
I really do not want to go in and start checking all of the individual components, even tho point to point will make it easier. For now I am just going to keep an eye on it and make sure it doesn't start arcing.
I only get "paid" once a month (disabled vet) so will get a new set of tubes then and see what happens. I was going to get the winged c, but I have pretty much shot my audio allowance for a while, so will probably just get some electroharmonix etc, just to see if a tube is the problem.
After I try new tubes, if it still does it, I guess I will have no choice but to go in and start checking individual components.
I am guessing here, but if it is a component, my guess would be a capacitor.
They did not cheap out on them, but is possible for anything to go bad I guess.
I am just going to hope it is a tube
I appreciate everyone's help, thank you. I will report back after I try some new tubes or happen to find something in the meantime.
Thanks
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Yeah, I know, I have a Ming-Da too. It still arced over when I turned it up with no speakers connected :/
you could try checking the resistance of your output transformer, my music angel had a similar problem to yours and as it turned out, i had an open circuit in the output transformer... it could be a capacitor, but at least checking the transformers is pretty quick and easy.
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