High Voltage testing reading high

[gort]

Hi All,

just finished attaching and soldering the PCB and ran the high voltage test. The "B" side is coming in a little hot, above the recommended threshold in the upgrade manual. the "A" side is within spec. Also the B+ reading is coming in high. All solder joints look good to me, well flowed. The low voltage test was right on the money. Are these reading acceptable?

6U: 138.3v DC
16U: 144.5v DC
4U: 7.93v DC
14U: 8.08v DC
B+: 185.9v DC

Mains: 122.3v AC

Should be noted I'm testing with some 6k6g tubes, not sure if that would throw off any of the readings.

Thanks!

 

[Paul Birkeland]

It would be a very good idea to put 6V6 tubes back in for testing, as what might be a small difference in plate voltage with plate loading resistors can sometimes be magnified by swapping to a CCS.

Given that your cathode voltages are both around 8V, that indicates that the C4S is working properly. You may need to go down to a lower value of cathode bias resistor to bring the plate voltage down, but keep in mind that there are a lot of balls in the air to balance in that upgrade module, so there may end up being more changes necessary if you run into unforeseen issues.

 

[gort]

Thank you Paul, I'll switch out my tubes to the stock 6v6 and remeasure later on this afternoon.

If the tube swap has no effect on the the test voltages would it be safe to continue the build with my current values?

 

[Paul Birkeland]

The other possibility to look for if that doesn't have any influence would be reflowing the solder on the center leg of the MJE5731A transistors feeding the output terminals of the C4S section.

 

[gort]

Thank you Paul,

Fired up the Moreplay with the stock 6v6 tubes this afternoon. The 6U/16U voltage dropped down to within spec, both around 127-128 V DC. B+ still a little high at 183.5 V DC, 4U/14U reading 8.01/8.09 V DC. The solder on the transistors looked good but reflowed them just to check the box.

Finished the build and gave it a listen, WOW it sounds good! Anyone reading this, the upgrade is worth every dollar and can be done in a couple of evenings.

 

[Paul Birkeland]

Well, it looks like you'll just have to drop those cathode bias resistor values a little bit for the alternate tubes.