Can anyone help me biasing a Jadis Defy 7?

Well... I spoke with Brooks Berdan and he shed a whole new light on the particular Defy. It has the s/n 213 and it turns out that Jadis built all defy-7 amps from something like s/n 200 to s/n 399 a little bit different.
On these amps, you do not bias by measuring voltage between chassis and fuse. You measure across a greenish brown 1.5 ohm resister that sits under the power tubes.
You have to aim for 33 mv.
You also have to swap tubes around to try to get the best match while biasing. I am glad to have read the previous posts and hear that the lengthy biasing procedure will be worth the effort.
Thanks folks.

Still having a rough time shifting these tube around and trying to find some balance. The voltages are ranging from in the 3 volt range up to the 7 volt range..... it seems that when I finally get 6 tubes close to 5 volts, the remaining tubes I have left are (at this point in time), not going to be able to get to being close to 5 volts.

My feeling is that I may not have a matched full set of 12 and instead have 3 matched quads (plus a couple of spares).

If this is the case, am I chasing my tail?

Yes.... it should be irrelevant. I cannot get any of the tubes to read at 33 mv. So at this point, I am thinking that the tech notes that I have from Da-Hong Seetoo may reveal that the modification he performed on 3/7/91 updated the amp to be biased to the chassis and fuse readings.
He wrote his report to include the following:

1 - installed new 6550a tubes.
2 - modified bias power supply.
3 - updated protection circuit.
4 - removed cathode follower.
5 - replaced output cables. (stated he used Furakawa cable)
6 - installed new power caps.
7 - modified pre-drive circuit.
8 - adjusted bias.
9 - burn in tested.
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I also received an envelope containing a bunch of Jadis 180 ohm resistors and a box of quarter amp Littlefuses. Not sure what to do with the resistors.
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I also have an email from Jadis@jadis-electronics.com dated 5/19/03 suggesting setting the bias voltage between 4.5 and 5.5 volts.
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I have a typewritten letter than came from the seller with everything else I have mentioned. I am not sure of the origin, but it has what look to be biasing instructions and reads as follows:

Here are the instructions to bias the Defy-7 II power amp.

1 Check all 12 160mA slo-blo fuses on the board. Very often some of the fuses are broken. When ever one tube goes it also takes out its fuse with it.

2 After you put the new tube in the amp, make sure you turn all 4 trim pots all the way up clockwise before turning on the amp. (Turn to right)

3 Make sure there is no input signal. Speakers could either be connected or disconnected to the amp. (No load is necessary)

4 After letting the amp warm up for 10 minutes, use a DC voltage meter to measure between the ground and the fuse holders. The target reading should be about 4 volts.

5 There are 4 rows of tubes and 4 trim pots respectively. each trim pot controls one row of tubes. (3 tubes) Turn the trim pot slowly counter clockwise to bring up the bias reading. You will find that changing the bias of any given row will effect the other 3 rows. Therefore, you must repeat the biasing process many times until they all read 4 volts.

6 Since it is a tube power amp, the tolerance of the tubes will greatly effect the bias reading. Even when you use super matched tubes, the readings still could be as far away from each other as 20%. (From 3.2 - 4.8 volts) Don't go nuts over it if you can't get them to be within couple of % of each other. Try to swap the tubes amount (sic) 12 of them so within each row all 3 will have a relatively close bias setting after it is done.

7 Recheck the bias again after about an hour of usage. The better the tube, the closer the 2nd reading will be against the first one.

8 As usual, when everything fails, call the guy who knows what he is talking about. (718-xxx-xxxx and ask for you know who!

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I tried that number and it has been disconnected.

My thoughts are that Da-Hong Seetoo performed a mod to this amp that brought it back to the regular way of biasing between chassis and fuses.

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?

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

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.