mwl168

Table updated.

Ok. This is making more sense now. @MartinC700 : It is a good idea if you pre-adjust the CCS using what JoaMat and steefdebrijn described, there are other variables will come into play when you actually power up the amp. You still need to fine-tune the CCS once you actually power up the amp and allow it to warm up. Again, be careful when you make adjustments with the amp on. These HV applications are not forgiving and it’s easy to accidentally short something or get electrocuted. Many of us had that unpleasant experience, myself included.

Hmm, I am confused by your question. What do you mean by “using the LV supply to adjust the current”? The bias current of the amp is set by the CCS. You use the trim pots in the CCS while measuring the voltage drop of the test points to set the bias current. Glad to know that you fixed the HV supply.

Thanks Chris! I do have MPSW parts on hand but would like to save them in case I need them for other applications. The differences in spec are that MPSA parts are rated for .650W dissipation (vs 1W for MPSW parts) and .25V collector-emitter saturation voltage ( vs .4V for MPSW parts).

For the off board version can I safely use the following substitute parts? MPSA06/56 for MPSW06/56 MJF15030/15031 for MJE15030/15031

Thanks Jose. And, yes, I will be building an "off board" version and most likely with a dual-mono GRLV power supply.

Thanks guys! I’ll need to do some more research. There are plenty of v1.43 boards available on eBay but I really don’t want to buy them because I consider those pirated products. I do have enough MPSW06 and MPSW56 on hand.

I am thinking about building this amp. Is V1.43 that uses MJE15030/15031 the latest board? Anyone has boards for sale? I have 2SJ109/2SK389 on hand so I may be able to build older versions that use JFET input too.

Quick update on the status of the GB - we are in the process of testing the boards before sending them to the fab house for estimates. Will provide another update as progress is made.

You can try do a simple diode test of those transistors and compare the results between the two boards to see if one or more are out of ordinary. Make sure the capacitors are completely drained before you perform the tests though.

I would try replacing the correct value resistor first and test the board again before swapping out the LT1021.

My Blue Hawaii without servo takes about 90 minutes for the offset/balance to stabilize. Although after 60 minutes or so they do not drift more than a few volts. I adjust offset/balance after two hours running and leave them be from there on. From power on to power on these voltage will vary a bit but usually within a volt or two once stabilized. There shouldn't be need to readjust on power-on unless the ambient temperature changes a lot or new tubes are inserted. Does the balance, measured between L+ and L-, R+ and R-, also varies significant from power-on to power-on?

It was not clear to me reading your posts if the -27V is the DC offset from one phase of the outputs and if it occurs to both channels? If it only occurs with one channel you can rule out if the tubes are the culprit or not by swapping the tubes around.

Table updated.

It’s better you clearly list which boards and quantities you need.