V2 / V3 Voltages Off

[JammyDodger]

Hey All,

There's something nasty in the woodshed here.... I am tweaking up my 100W HRM with BM Pi based on ODS-101 values. I am getting some screwy voltages on V2 and V3. Heres what I have.

Measured at 124V Line
V1a 185.7 / 1.91
V1b 185.5 / 1.76

V2a 187.7 / 1.523
V2b 247.8 / 2.082 ****

V3a 277.1 / 76.9 ****
V3b 283.8 / 76.9 ****

Dropping String is 441 / 439 / 413 / 334 / 302

Bias is -49VDC ! 40mA

Any sugestions?


Cheers, Mike

[Bob-I]

One of 2 things come to mind immediatly.

1) The plate/cathode values are incorrect, double check with a meter.

B) V2 is bad. Swap it out.

V1 may sort itself out when you get V2 fixed.

[greiswig]

I agree about swapping tubes: that can make a big difference. But...

That looks like an unusual dropping string. How did you arrive at those values?

[JammyDodger]

Hey All,

I'll swap the tubes....

The dropping string is straight from ODS-101.

B+1 - choke - B+2 - 3k/5W - B+3 - 15k/2W - B+4 - 10k/2W

Cheers, MIke

[greiswig]

Hey All,

I'll swap the tubes....

The dropping string is straight from ODS-101.

B+1 - choke - B+2 - 3k/5W - B+3 - 15k/2W - B+4 - 10k/2W

Cheers, MIke

My bad: I read your original before coffee, and I read those values as ohms, not volts.

[JammyDodger]

To All,

It was a bad (out of spec) tube. This was an EH 12AX7. Very strange. I have had two bad tubes in this build, a Winged C 6L6GC and this one. Bought from the same company at the same time. I've never had a bad tube in my life, now I have two!

Oh well, it's fired up and now time to start tweaking

Cheers, Mike