Can anyone help me biasing a Jadis Defy 7?

I keep swapping and tweaking.... the sound is improving, but I still have not reached the magic.

I am going to bed soon, but I thought that it might be the combination of 12au7 and 12ax7 tubes that might be causing some of the difficulties.

Is anyone else using Gold Lions in a Defy7 and is so, what 12ax7 and 12au7 tubes seem to work for you?

All voltages are much higher than 33mv.

Do the voltages vary as you turn the bias pots? And how much higher than 33mv are the readings? I would imagine that if they were WAY higher than 33mv, and the circuit is presently wired such that the voltage across them represents bias current, and if you are measuring correctly, then the plates of the tubes would be glowing red or orange (they aren't, are they?).

Also, just to make sure nothing simple is being overlooked, are you using the dc (not ac) voltage function on the meter, and are you connecting the meter leads to the two ends of the resistor, and not for instance between one end of the resistor and chassis?

Beyond those things, I'm not sure what to suggest.

Best regards,
-- Al

Almarg -

I found something... possible the root cause of my biasing problem.

I found a bad resistor labeled 5w150 ohm j under one of the tubes. I measure the othe 11 and they have ground on one side and 150 ohms on the other. It looks like this one resistor is open.

The resistors look like small white boxes. I have not been able to source them yet. I am going to try Brooks in California to see if he has any. I have a good tech here in Chicago that I trust to install it.

Then, I hope that I can get this sounding like it should. Thanks for hanging in there with me.

Matt

Sounds like an extremely promising discovery, Matt! The "5w" undoubtedly refers to the wattage that the resistor is rated to handle, which is consistent with the shape you are describing (a power resistor).

If Brooks can't readily supply them, any major electronics distributor should have suitable equivalents. Digikey.com is one such place.

Good luck!
-- Al

I replaced all 12 resistors with Jadis supplied 180 ohm resistors that came with the amp.

The Gold Lions still do not bias properly and measure differently from each other by more than double in some cases when the pots are set for minimum.

I put the original JJ kt88 tubes back in and had the amp biased to 4.5 volts in less than 5 minutes.

Should any brand kt88 be biasable in my amp? It seems that the gain in the Gold Lions I received is much higher than the JJ tubes.