[Amps] SB 200 negative grid current on 15 and 10 meters

[Alton McConnell]

Hello everyone!

I am working on a friends SB 200 amp.  Works on 75, 40 and 20m.  Has a slightly negative grid current on 15 m and low output.  A very negative grid current and lower output on 10 meters.

Tubes are new ebay units.  Unknown quality.  The SB 200 uses a pair of 572Bs.


  1.
 My tube tester will not test 572Bs  but I can test 811As.  Can I use the same tube tester set up to test the 572Bs?
  2.
What is likely causing the negative grid current?

Thanks!

Alton, NU8L