[Amps] Henry amp problem

[Joe Isabella]

Hi Tim,
I have a Henry 3K-A Console and recently (two days ago) installed a new blower.  The original one ran pretty slow and was much quieter, but the added cooling makes the extra noise worth it.  
 
It sounds to me like you are on the right track regarding the idle plate current.  One thing to try is pull one tube, then the other after putting the first back in, and see what happens.  If only one tube causes the current to flow, then you'll know something's up with that tube.  Mine draws 120mA when keyed on the low tap (2.9kV) and about 200mA on the high tap (3.9kV).
 
Joe, N3JI
 

Tim <N6DRA at nc.rr.com> wrote:
Hello all:

I recently acquired a beautiful Henry 2KD Classic desktop amplifier. It works fine and makes good power- but... It is drawing idling current while sitting in standby. Henry told me that I probably have a shorted tube but I haven't been able to confirm that fact. I did an ohmmeter check and the tubes seem fine at DC. They are late Amperex 3-500Zs with the plates that look like stacked coins as opposed to the Eimac zigzag folded plate.

Anyone seen this type of problem in this chassis before? I didn't have time to really get into it today but I did put an ohmmeter probe on the cathode pins and it read 10K to ground. The print shows a 10K resistor in series with the zener (in parallel with a 220 Ohm 2W). The 10K is shorted out when the relay pulls in for bias. One would think that 10K would develop enough voltage drop to clamp the tube pretty hard, but the tubes continue to produce quite a bit of heat- enough to make the top of the case quite warm over a little while. I can't see any color to the plates during this stage. The plate current meter does show about 120mA at this point (unkeyed) and increases to about 130-140mA when keyed.

My reading about this amp indicated that many people disliked the blower noise. This one seems to have a decent airflow through the chimneys and out the top, but is not overly loud. How loud is loud in this case? It's really not much louder (if any) than my SB-220 which runs cool even during use.

I will look deeper this weekend, but would appreciate any insight that might be offered.

' 73

Tim
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