[Amps] bad 572B's

[kingwood]

Greetings to all,

        Last week, I received a case (10 tubes) of new Chinese 572B tubes 
from a distributor that I have bought tubes from for over ten years.  These 
tubes were new, from the latest production.  I plugged two into a SB-200 and 
was disappointed to see a bit less than 50 % of the expected power.  I tried 
another pair and got the same results.  I went through the entire case and 
found them all to be way, way, down in emission, but, I must say, they were 
extremely well balanced.  HI Hi

        I had a pair of 572B's, from the same source, that I bought about 
two years ago, in another amp.  I plugged them into the test amp and got the 
normal, expected, output.  The entire case of new 572B's went back to the 
distributor.  I wonder if they mixed up some low Mu tubes with their Hi Mu, 
572B's at the factory.

        There was some discussion about the Svetlana the 572-160, in one 
post. They are excellent tubes for audio work.  They have, basically, the 
same internal structure (large graphite anode) as the 572B, but, without a 
plate cap, they would not be an simple job to install them in an SB-200, 
FL-2100, or Ameritron amp.  But, for the AM'ers,  they make a great 
modulator tube.

73 de Lon, K5JV

Lon W. Cottingham

1110 Golden Bear Ln.
Kingwood, TX 77339

281-358-4207
281-795-1335 Cell