[AMRadio] Johnson Valiant output capacitors

[Morris]

Good advice.  When I finally studied how these emission checkers worked I
realized that lumping all the elements besides the cathode together as an
anode and checking the emission is not a very practical circuit to test for
real situations. More useful for a short/leakage tester between elements but
even then ...

Morris 



> -----Original Message-----
> From: amradio-bounces at mailman.qth.net 
> [mailto:amradio-bounces at mailman.qth.net] On Behalf Of Lawrence Steeno
> Sent: Saturday, May 14, 2011 3:32 PM
> To: AMRadio at mailman.qth.net
> Subject: [AMRadio] Johnson Valiant output capacitors
> 
> 
> A while back I posted about where I could find output caps 
> for several Valiant transmitters I have here. One said I 
> should get "snubber" caps from Mouser. Well I did that and 
> they worked. I had several problems with this unit. First, 
> the 300mmf -big square brown one--showed very leaky on my 
> Heathkit capacitor checker starting at only 25 volts! After 
> changing the caps all seemed well for a few minutes--then at 
> times when going to transmit the plate current was pinning 
> the meter and output fell way off. I rechecked the 6146's on 
> my Hickok 800 tube checker, they check great. Back to 
> transmitter, I made a loop of copper wire thru the cathode 
> pins and put a fresh lug to the chassis. No change, check 
> voltages and resistances-no change,loosen and tighten all 
> screws. Then I pulled out my Hickok 539B and checked the 
> 6146's still show good, Looked and scratched my head, 
> rechecked everything--no change, still at times the plate 
> current was pegging the meter. Then I  pulled out from under 
> the bench the TV2C/U (too much setup to use most times) 
> checker and the tubes still check great. Damn, I pulled out 
> from case the chassis of another Valiant and swapped the 
> 6146's. All is now good!!!!! This goes to show me that one 
> cannot always trust a tube checker no matter how good it is. 
> They check tubes at DC and 60 cycles, not at RF frequencies. 
> Now all seems good. Should get it on 40 this weekend I hope, 
> maybe even of 15 or 10 if open. Thanks for the responses and 
> NEVER fully trust any tube checker as the final check. 
> Substitution is the final check. Hard lesson learned but all 
> in all great brain work. Larry K9LWI
> 
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