[Antennas] Checking 3-500 tubes

[David W Sher]

With regard to disconnecting the B+ power supply before checking for
grid-plate shorts:

An Icelandic YL named Inger
Did not in this vale of tears linger
     Her final blew out,
     She started to pout -
And checked the B+ with her finger

Dave          W9LYA
What wrought doG hath?

On Sun, 09 Jun 2002 10:25:52 -0500 "George, W5YR" <w5yr@att.net> writes:
> 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 ohmmeter 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 ohmmeter 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
> dc 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 ohmmeter. 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 output 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
> >
> - - - 
> 
> Your moderator for this list is:
> Larry Wilson KE1HZ antennas-owner@mailman.qth.net
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