Can anyone help me biasing a Jadis Defy 7?

Matt,

Not sure what all that adds up to, but the following questions seem to suggest themselves:

1)Can you discern what the two ends of the resistor are connected to (i.e., which pin(s) of the 6550, and/or chassis ground, or some other circuit point)? And are the resistors marked as 1.5 ohms, or if not do they have color-coded bands encircling them, and if so what are the colors (from which we could determine the resistor value).

2)What range of voltages CAN you get across the resistors?

3)Have you checked the fuses with an ohmmeter or multimeter?

4)I would strongly suggest that you ignore the instruction that it is ok to have the speakers not connected. As you probably know it is certainly not ok to have no speaker load present while a music signal is being processed through a tube amp (other than an otl, possibly). However, even with no music or other signal present, if you were to turn the amp off with no speaker load present, it seems to me that an internally generated turn-off transient could lead to an inductive kickback effect that would damage the output transformers, just as might happen if a music signal were being processed with no load.

Regards,
-- Al

Thanks Al...
Speakers are attached.

Tracing the connections of the resistor might require some help. The colors on the resistor are next to impossible to see.... very brown looking. But the voltage readings of other neighboring resistors is much higher than 33mv, so I am feeling that these are the correct resistors that Brooks told me to measure.

Fuses are all good.

All voltages are much higher than 33mv.

The tubes are Gold Lion KT88.

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