Yaqin MC-10L bias voltage too low
- Thread starter 20minc
- Start date
Yes adjust to the recommended, I suggest somewhere between between 0.25vdc and 0.40vdc depending on what you like better, lower will stress the tubes less and give a more relaxed presentation, while higher will give a tighter presentation.
The driver used is Torx type of suitable size, insulate the shaft with shrink wrap.
The bias pot in these can be very touchy, so just slight pressure on turning, sometimes just a fraction of 1mm will move the bias amount very noticeably.
Edit: If you get a set of torx drivers one will fit snug, and don't let the tip wander around in there, look for the bias pot before inserting so you only contact it with the tip
The driver used is Torx type of suitable size, insulate the shaft with shrink wrap.
The bias pot in these can be very touchy, so just slight pressure on turning, sometimes just a fraction of 1mm will move the bias amount very noticeably.
Edit: If you get a set of torx drivers one will fit snug, and don't let the tip wander around in there, look for the bias pot before inserting so you only contact it with the tip
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I have the 13s which I think I have the newer version of the 10L and you will definitely want at least 0.35 on EL34's.
I have reissue Tung Sol EL34's that seem to sound best at the higher end 0.38-0.40 on the bias.
If you get a chance, you might try the JJ KT77's. I'm currently using a set adjusted to around 0.45 and think they are best sounding tubes I've used in this amp.
I have reissue Tung Sol EL34's that seem to sound best at the higher end 0.38-0.40 on the bias.
If you get a chance, you might try the JJ KT77's. I'm currently using a set adjusted to around 0.45 and think they are best sounding tubes I've used in this amp.
You are the one to judge what sounds best to you.
Just go for somewhere in the recommended range, that is why It's a range and not a single figure. Everything else is just what an individual prefers in his system with his preferences.
Edit: and example is i know some that prefer a setting of 0.25vdc, some prefer a setting of around 0.30vdc and so on, you might prefer 0.335vdc, only you will know.
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Hi ya'
Was just thinking and thought to ask you something if I may?
When you measured the bias, did you measure each of all 4 output tubes? Where they all reading 0.08vdc?
The reason i ask is that it would be very strange if it had been set correctly and drifted down the same on all 4 tubes. So if they measured all the same for you I would think they set them at this level before selling, then I would wonder why so low as It's not a logical level to bias EL34's at. It makes me wonder if they set it at those levels for a reason and I can only think of bad reasons to do this, maybe it wouldn't set higher for some reason...worn tubes maybe or wouldn't run stable at higher settings
BUT, before we look at that, you were measuring correctly weren't you, 20minc?
The meter works correctly? and these were DC voltage measurements?
Sorry for the questions but I think they need to be asked in order for you to proceed at this point.
primosounds
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I thought if the tubes are drawing that much current they would be in "cut off" or almost there . That is the bias voltage is too low (too much negative voltage) to allow the el34 to conduct, with the grid blocking the electrons from moving to the plate. The sound quality would be much improved if you put the right bias voltage on the tubes. It maybe that at the correct voltage the tubes were red plating hence the previous user turned down the bias to allow the tubes to operate safely. So watch your el34 tubes carefully when you adjust the bias to its proper level.
Amp can work even with ZERO bias. Sound quality will suck though.
