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Hello, i turned on ella just a while back - went to work on my pc while it warmed up and heard a fairly loud thud [even with the vol pot turned all the way down]. i turned around to see the first right tube turn a bright orange. quickly switched it off.
the ella has been with me for a long time [7 maybe 8 years] and sometime last year i think, with brian's help [thank you again brian], i gutted the amp and reworked it with point to point wiring.
i am a bit wary of turning it on again.
could anybody pls tell me what could have gone wrong and what i should be doing to fix it?
a caveat - i am not technically competent in any way so diagnosing the amp on my own is out unless i am guided on this. my soldering skills and ability to read a schematic is fairly ok i think. what i am essentially trying to say is that i would really appreciate a dummies' guide to fixing it. thanks very much.
i finally got around to checking the voltages. following brian's manual - chapter 10, these are what i got:
1. checked power tubes pin 5 - brought each up to -50v.
2. checked heaters on power tubes - from left to right - 6.44, 6.45, 6.44 and 6.46
3. middle tunes 6.5v and 9 pin tubes the same as well.
4. B+ is 441v
5. checked output caps at the point where the 10k resistor meets the bias pcb board - from left to right -50v, -50.3v, -50.8v, and -50.4v [Rasim: im not supposed to get any dc so these figures are not good?]
6. popped the power tubes back in and this is where the 1st tube started getting weird. i could bias the other tubes to .4vdc [el 34s] but the first tube had the numbers in my dmm skittering all over the place. i could not get a fix on this. swapped tubes, same problem.
Edit: found out it was a grounding problem - the rca ground for the probe was not in tight contact with chassis. fixed this and it the bias readings are find now.
what should i be doing next? thanks very much for any help in diagnosing this anomaly.
Edit: i popped in some 6550 tubes and the amp is working fine but would still appreciate any insights.
Usually caused by:
1. coupling caps
2. bias control pot
3. tube pin not gripping
anything that could cause loss of bias. Maybe remove power tubes and measure the bias voltage at the socket on each tube.
DIY - Done Right!
hi brian, thanks very much for the suggestions. i will check it out and revert.
btw, the pec pot has turned scratchy. i like the pec but i think a replacement will over time develop the same problem - how does the stepped attenuator that you have compare to the pec and would that be suitable for the ella?
Could be that the coupling cap went bad and passed thru some DC to power tubes (KT88 etc). Very easy to dignose. Be careful V is high. With no input, measure DC on the power tube side of the respective cap. Place the black probe in the 0 of the speaker output at the back, use only one hand, dont touch anywhere else and with the red probe of voltmeter check the cap. If you cant figure out which side of the cap, check both, one side should not show any DC volt.
Hope this helps.
thanks very much rasim for the suggestion. i hope to test the amp out this weekend. i will be very careful. i try wherever possible to use alligator clips. thanks again - any other tips from you, brian d. or anyone else will be appreciated.
I think your version is something like this one. If so, I tried to show you where to check for faulty coupling cap.
Also pay attention to Brians comments if you have automatic bias control
Yes its the same version. Last weekend turned out to be a working one so I couldnt check out the amp. Hopefully this weekend if all goes well.
Thanks very much again Rasim for the help. I will post my findings.
thanks brian d. for the suggestion - i will check out the sockets. could be arcing (??) any other suggestions and tips will be appreciated.
i'm thinking of running the basic tests found in the ella manual. would this be a good place to start as well ?
the volume pot has gone scratchy on me. its a pec carbon pot. would be good to know what pots ella owners have in their amps. recommendations appreciated. i might as well get this sorted out if i have to pop the hood.
I've used a DACT Stepped Attenuator an Alps Blue and a TKD. The TKD didn't work in my amp in so far as there was a hiss I couldn't get rid of, sounded good though if you could ignore the hiss between tracks. The Alps came with the amp when I bought and is good too though the DACT was the best by far until I bought a Django last year.
Hi BrianD, thank you for the suggestions. The Dact sounds like a good idea. I havent paid much attention to Django and I think I should look into that.
I've had this before with my Ella, which I bought about 6 years ago now.
On inspection I found a bad connection to the socket that had the runaway valve. I did some trimming of wire and resoldering and it was ok for a long time, though it did happen again once since then. I think there is a possibility the pins on the socket are just not tight enough so I bought some new sockets from Brian. I haven't installed them yet because it's working fine.
I'm not an expert so I don't know if this is the only potential cause of this kind of fault, but that's certainly where I'd start looking.
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