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Hi all. I have a pair of Jolida JD3000 monoblock amps that use two 211 tubes each. The manual says to bias them to 235-265mv, but only one of them will go that low. The rest will only go as low as 325 to 425mv. I've been running them at the lowest setting each one would go above 265mv, i.e. to 265mv, 325mv, 370mv, and 425mv respectively. Last night I re-biased them all to the highest setting of 425mv, and everything sounds much better. I'd appreciate some feedback on this, particularly whether I'm going to damage anything, or shorten the tube life. Thanks.
Follow Ups:
Hi Sturmey,
425mV is far too high for the Jolida 3000A amps. This could cause problems with the amp and/or tubes.
There are a few reasons why you may not be able to get the proper bias. The first thing could be the wrong location of the tubes. Did you put them in the proper locations as marked by Jolida? Other things that can cause high bias is the driver tubes. Did you replace the EL34s or use the stock pieces? Jolida uses an EL34B and some other EL34s will not bias in these amps. Also, the speaker cable can cause a problem with bias on these particular amps (no kidding). What speaker cable are you running. You have to watch the capacitance of the cable.Feel free to email to discuss these amps further if you find the need.
Happy Listening,
Response34
Build your system for yourself, not the critics!
Bill,Ok, I found the old EL34B's that came with the units, put everything back to stock, and it still would not bias properly. The manual says that you do not have to rebias when changing the EL34's or 12AT7's. I tried three different quads of 12AT7s', and thee different quads of EL34's, and none of them changed the bias setting at all. Only one of the four 211 tubes would go as low as 250mv. I have some new 211's that I bought, so I'll try them next.
HI Jeff,
When replacing the EL34's, I have found that the bias should at least be checked as they can vary as a driver tube causing fluctuations in the bias.
Here is another thing to try. Swap the 211 with another one in one of the amps to see if it will bias in a different location. It could justbe a bad power tube. If you getthe same result for this tube in another socket, replace that tube. Also check to see if the tube you installed in this socket you took the tube from will bias.
Process of elimination.
Let me know your findings. You can also email me and I can give you my number if you would like to discuss this in person over the phone rather than on the board.
Happy Listening,
Response34
Build your system for yourself, not the critics!
Thanks Bill.I talked with a teck(Shawn) at Jolida, who said they are having problems with this, but thought they had it solved. I've got an early pair I guess. Anyway, he said that as long as the tubes are not "cherrying up", then I should be OK. They look fine to me.
I have done the tube swap thing already, to no avail. I have a new set of tubes by a different manufacturer that I'll try tonight, and will let you know what happens.
Thanks for the "response". I'm using some cryovaced Electro-harmonics EL34's, and cryovaced Chinese 12AT7's, as well as the original 211's. I did not notice any sequence requred when I first installed the tubes. The cables are Synergistic Research Resoltion Reference, internally biwired cables. Speakers are Aerial 10T's, running as called for on the 4 ohm taps, which sound better then the 8 ohm taps. I have no idea where the original EL34B's are, but I'll look for them. Any suggestions? Thanks again.
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