[Antennas] Checking 3-500 tubes

[George, W5YR]

GT,

Briefly there are a few things that I can think of that can or should be
checked:

1. Filaments - are they intact? Check with an ohmeter and/or apply the
proper voltage and observe the brightness, if any.

2. Internal short-circuits - a major failure mode of these tubes is
internal shorting of the grid to the plate (if I remember correctly). If a
short exists and is permanent, an ohmeter check will show it. But it may
appear only after the tube has heated up, so a better test is to run the
filament at rated voltage, let it cook for a bit, and then check for "hot"
shorts to the other elements.

3. Emission - can the tube deliver the rated current at the rated plate
voltage with the rated grid voltage? This requires at least setting up a
d-c test arrangement and metering the voltages and currents. But you can
use your SB-220 for this . . .

I would start by putting the ?? tubes one at a time into your 220 and
seeing how the filaments look. You should have a known good tube in the
other socket for comparison of brightness. Then after the tube is warmed
up, check for shorts with an ohmeter. MAKE SURE THAT YOU HAVE DISABLED THE
HV POWER SUPPLY WHILE YOU ARE DOING THIS.

If no shorts are indicated, put the plate connector on and apply the HV and
observe the plate and grid meter readings with no r-f drive. If they are
normal, I would apply a bit of r-f drive and observe the meters again. If
they seem to be behaving as usual, go ahead and set your normal operating
conditions and check the output r-f power. 

All that is with one known good tube and one questionable tube. Repeat with
each of the other ?? tubes. If at least two of the ?? tubes seem to be OK,
then run the amp with both ?? tubes and check the operating currents and
r-f ouput level.

This is far from a complete routine for evaluating these tubes, but it
should pick up the usual faults and allow you to decide whether or not they
can be used.

You are fortunate to have a 220 to check them in . . .

73/72/oo, George W5YR - the Yellow Rose of Texas         
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe   
Amateur Radio W5YR, in the 56th year and it just keeps getting better!
QRP-L 1373 NETXQRP 6 SOC 262 COG 8 FPQRP 404 TEN-X 11771 I-LINK 11735
Icom IC-756PRO #02121  Kachina 505 DSP  #91900556  Icom IC-765 #02437


KK5VR@ARN.NET wrote:
> 
> To all:
>   I ran across 3, 3-500 tubes made for the SB-220 (and other) amps. I need to
> check these tubes the easiest way. Is there a way of checking these tubes for
> worthiness with a VOM meter or would I have to put them in an amp under a load? I
> do have an SB-220. Any comments would be useful. Thanks for your for your help.
>    GT
>