Issues with driverboard testing [resolved]

[Paul Joppa]

Yes it's an issue. That's why PB asked for the voltages at the DC board, which should be 6.3v +/- a percent or two. You'll get a better measurement on a 20v scale compared with measuring voltage to ground on each tube pin (on a 200v scale) and subtracting.

If those voltages are correct, then the series resistors at the tube socket may need to be adjusted for non-standard heater current. If they are greater than 6.3v, there may be an error on the DC board.

The point of the Kaiju DC board is to make the filament voltage both correct and  independent of the power line voltage.

[ericoto]

I honestly didn't see that part, I was looking on my phone and it was cutoff.  I will recheck tomorrow, I have it working now, sounds great, the DC supply an improvement. No audible hum. Thank you for pointing that out. I noted  that the 300b on the BeePre are cooler than the Kaiju, and with an infrared non contact thermometer  by about 100F, is that normal? The 300b are from different manufacturers

[Paul Birkeland]

It is possible to connect the filaments of the 300Bs to the unregulated output of the DC filament supply, which are the pads on the side of the board facing the front of the amp, and that will provide more filament voltage than is desired to the 300B.

Yes, the Kaiju runs the 300Bs at about 27W of plate dissipation and the BeePre runs the 300Bs at about 5-6W, so the temperature difference is certainly expected.

[ericoto]

Well, you figured it out I had the output miswired, corrected and now voltages fine 4.53 VDC Thanks.

[Paul Birkeland]

4.53 also isn't desirable, but what I am remembering is that the 300B will draw a fair amount of startup current which tapers off over time, so you may see 4.5V after a few seconds of operation, then it slowly should come up closer to 5V as the amp is allowed to run for a few minutes.

[ericoto]

Yes, recheck when I returned from work today, it reads 4.86 VDC on both sides and 6.3 VDC at the reg+ and reg- terminals after running for about 3 minutes. So now all seems fine. Thanks again,