Read quite a few threads of over bright red (orange) plate glow. Can't quite know what to make of this.
Have 4 JJ EL84's on my Yaqin MC-84L. Bought new and matched very well with about 200 hours on them now. Amp on about 4 hours a day with no short on/off's.
All of a sudden with amp on for about 15 minutes, front left tube is glowing twice as bright. Jumped up and shut it down, let it cool for about five minutes and switched two front tubes. Everything normal with an hour of use so far. No audio distortion or anything else. Clean white tube socket scorched a little bit. Amp has no manual bias.
Have 4 JJ EL84's on my Yaqin MC-84L. Bought new and matched very well with about 200 hours on them now. Amp on about 4 hours a day with no short on/off's.
All of a sudden with amp on for about 15 minutes, front left tube is glowing twice as bright. Jumped up and shut it down, let it cool for about five minutes and switched two front tubes. Everything normal with an hour of use so far. No audio distortion or anything else. Clean white tube socket scorched a little bit. Amp has no manual bias.
Are you saying that in normal use the plates glow orange? That certainly would explain why one failed after only a 200 hours. I surprised they lasted that long.
Pardon? Nothing failed (yet). As stated, the front left tube all of a sudden is glowing 2 to 3 times brighter (plate is all bright orange). Again, shut it down quick and let them cool and switched front two.
Everything normal with an hour of use so far. No audio distortion or anything else. Clean white tube socket scorched a little bit. Amp has no manual bias.
Everything normal with an hour of use so far. No audio distortion or anything else. Clean white tube socket scorched a little bit. Amp has no manual bias.
Are you saying that the anode was glowing brighter than normal? EL84 anodes should not glow at all. Only the heater and cathode should glow, and most of that is hidden.
Hmmm....
There should be NO Plate Glow At All.....
(Although a VERY SLIGHT redness could be seen in a fully dark room on the plate--the outside grey/black bit-- of a tube running at its absolute limit....)
ONLY the Heaters and Cathodes, (The bit in the middle...) should glow orange....
The Plates of an EL84--no matter What Make-- should Never heat to an Orange-colour, unless there's some severe overload or faults!
I think this amp has a shared cathode resistor for the output stage. If one tube loses its cathode connection (poor pin connection?), the other tube will conduct much more to make up the loss.
BTW, it's considerate to post a schematic if you are asking for free help.
Sheldon
BTW, it's considerate to post a schematic if you are asking for free help.
Sheldon
Here's the schematic: http://www.diyaudio.com/forums/tubes-valves/127048-transistor-phase-splitter-yaqin-mc-84l.html
I realize there should be no plate glow...... Never had a problem or this happen before.
Have not been able to duplicate this problem after switching the two front's. The obvious problem (to start) was possible "poor pin connection" even though the tubes and sockets on the amp itself are all fairly new.
Let me repeat again that the entire plate in the said left front tube was 2 to 3 times brighter than normal and glowing bright orange. If I hadn't caught it quickly, I'm sure it would of burned.
I realize there should be no plate glow...... Never had a problem or this happen before.
Have not been able to duplicate this problem after switching the two front's. The obvious problem (to start) was possible "poor pin connection" even though the tubes and sockets on the amp itself are all fairly new.
Let me repeat again that the entire plate in the said left front tube was 2 to 3 times brighter than normal and glowing bright orange. If I hadn't caught it quickly, I'm sure it would of burned.
I mentioned pin connection, because the problem was at least temporarily resolved by taking the tubes in and out. You might get some wire the same diameter as the tube pins, and check each connection for tightness. Another possibility along the same lines, is a loose connection at the grid pin. In that case the grid can drift positive and cause the tube to conduct more.
Were you listening at the time. If so, did you hear any change?
Sheldon
Were you listening at the time. If so, did you hear any change?
Sheldon
Hey there,
let me repeat again that there is no "2 times brighter than normal" if we're talking about EL84 plates. The plate should *not* glow at all, not red, not orange, simply *no* light.
As long as you're talking about "brighter than normal" you imply that it has always glowed in what you consider a "normal" operating mode. This surely isn't a normal operating mode for an EL84.
Greetings,
Andreas
Yes. I could not understand the "2 times brighter than normal" either because "normal" is dead-on black. Only the heaters should glow.
If these plates had even a HINT of "glow" it means something is wrong and that alone could explain the root cause of the problem.
It's like if I said, "I was driving to work and noticed the flames and smoke coming out the engine was twice as much as normal."
Ya... the plate was bright orange. I mean the WHOLE plate.
Was listening to classical music at the time at medium volume, and didn't notice anything audibly, just visually. What got me was only waited five minutes to swap them across, and it was cool enough to handle that fast...
I did the loose wire pin tightens on the socket- all seems tight and normal as the sockets are as new as the amp....
Sheldon- the lose connection at the grid pin is sounding more like the problem now. Will have to take the MC-84L apart again and take a look (it's a pain in the butt to do that...).
Thanks again fellas- will let you know if I can find anything. It's been running for about 14 hours since, with no visual or audible problems at all...
(I hate intermittent electronic problems..)
Was listening to classical music at the time at medium volume, and didn't notice anything audibly, just visually. What got me was only waited five minutes to swap them across, and it was cool enough to handle that fast...
I did the loose wire pin tightens on the socket- all seems tight and normal as the sockets are as new as the amp....
Sheldon- the lose connection at the grid pin is sounding more like the problem now. Will have to take the MC-84L apart again and take a look (it's a pain in the butt to do that...).
Thanks again fellas- will let you know if I can find anything. It's been running for about 14 hours since, with no visual or audible problems at all...
(I hate intermittent electronic problems..)
If it has Chinese tube sockets keep in mind that after each tube replacement their contacts need to be re-formed.
By the way, I am impressed by your infra-red vision and ability to measure brightness!
By the way, I am impressed by your infra-red vision and ability to measure brightness!
An externally hosted image should be here but it was not working when we last tested it.
Which proves again: people hear different cables, capacitors and resistors but a tube sucking at least twice the current, completely knocking out the symmetry of the push pull circuit can't be distinguished 😀
Hi,
A lot of modern(manufactured today) EL84 tubes cannot handle high B+, to be safe side some designers suggest the B+ should not exceed 300Vdc for both anode and screen. Actually the the screen voltage should not exceed this and anode can.
Looking at the Yaqin cct diagram the B+ is about 345Vdc, sometimes the main voltage increases by 5-10% that way it will further increase the B+, this may cause the tube to glow.
A lot of modern(manufactured today) EL84 tubes cannot handle high B+, to be safe side some designers suggest the B+ should not exceed 300Vdc for both anode and screen. Actually the the screen voltage should not exceed this and anode can.
Looking at the Yaqin cct diagram the B+ is about 345Vdc, sometimes the main voltage increases by 5-10% that way it will further increase the B+, this may cause the tube to glow.
Some may say that is because the rest of his system lacks sufficient 'discrimination', or he hasn't spent enough on room treatment, magic crystals, handmade cables etc. On the other hand, the gross assymetry will re-introduce second-order products so it will sound like an SE output!the_manta said:
Could be he need those quantum purifier thingies, or jitter removers. Or, given that the system is on for four hours a day, maybe he just wasn't listening very closely at the time. I've connected a section of my multiamped system out of phase before. Only when I sat down did I notice some strange imaging.
Sheldon
Sheldon
Sheesh... you guys.... If you saw the tube to the common man's laymans eyes, ANYONE would of noticed the problem. I look at the amp a lot when it's powered up for it's astethic glow,
and a JJ thats glowing completely orange with the plate bright orange really stands out.
As I stated, I shut the amp down almost immediately after I noticed it, and regardless of all the banter and blah discussion in the last 5 posts, there was no noticeable change in audio to my tuned system and hand built efficient speakers.
Now, back to topic, since I havent noticed an visual or audible problems since:
-Think the tube is damaged?
- Need to tear the amp apart merely to inspect and/or fix the underneath of the tube socket?
Obviously, it didnt blow a cap or fry a resistor or anything else. Again, only thing I've noticed is a slight brown small burn mark on the top of the socket itself. Very micro small.
Valves are surprisingly tough, so a short period of overload might not have done any harm apart from using up a little life. I can't remember whether you swapped it over, but this would let you check whether the fault follows the valve or the circuit. If it does what my orange EL34 did it will then work OK for months - I'm still waiting for it to fail again. For the first few weeks I would not leave it switched on but unattended for more than a few minutes.
It is certainly worth inspecting the socket, just in case there is something obviously wrong there. Modern sockets don't seem to be as reliable as NOS ones.
It is certainly worth inspecting the socket, just in case there is something obviously wrong there. Modern sockets don't seem to be as reliable as NOS ones.
Not anyone would notice that it is 2-3 times brighter than the normal infra-red glow!
So funny! To perceive what you hear is mostly a subjective matter. Really like this comment!
I've had a redplating Dynaco ST70 twice, while the music wasn't playing very loud, I could hear a very audible hum... meaning the power supply was in trouble supplying power!
The ST70 wasn't in my view, the television stood in front of it back then...
When I heard the hum, I checked on the amp. Normally all the plates on those EL34s look grey so I immediately noticed 2 of them were glowing orange. Also when I turned the amplifier off, the ticking (and other 'glassy' noises) lasted much longer then normal, meaning the tubes were more 'deformed' due to overheating.I just didn't want this to happen again so I restored and upgraded the amplifier, and it never happened ever since.
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