[TMC] Part needed

[Richard Knoppow]

     Do you have access to any sort of impedance bridge?  You could use 
it to check the capacitors and coils. An RF bridge could measure the 
impedance at the tube plates (power off of course) but even an audio 
frequency bridge would check the components. A cap checker of the sort 
used for power supply caps might indicate if the caps are going short 
with voltage applied. I think this is unlikely but can't be ignored.
     The intermittent nature of the problem suggests something on the 
order of a cold solder joint. Might change with voltage applied. A very 
careful visual inspection might turn something up.  You may be able to 
find something by poking at the wiring while making ohm meter checks. I 
would not suggest it with power applied.
     I am not very familiar with this transmitter but the instruction 
books are available (I probably have them) and will have a look to see 
if there is anything inspirational there.

On 10/28/2016 3:45 PM, Larry wrote:
> I've been having trouble with my PAL-500 loading.  I've replaced the
> finals, checked various voltages in the bottom, done continuity checks
> and other things that have been suggested.  NO success.  Funny thing was
> that it worked one day a couple weeks back flawlessly generating 40M
> (7293 Kc) AM with excellent reports from Arizona, Idaho and central
> Texas.  Then the next day it would not take a load at all.
>
> The one thing i've yet to try is to replace the .002 4KV plate blocking
> cap.  While it checks good with power off, i'm wondering if maybe it's
> really open or mostly open.  If you happen to have a PAL-500 or possibly
> a PAL-350 it is C217.  I have no idea where someone would find something
> like this on the market but possibly there are a junker or parts units
> laying around that might have one inside it.  I'd like to do a shotgun
> replacement to see if that really is the problem.  Not knowing where
> else to check with the symptoms i have which are:
>
> Plate voltage normal, screen current normal, drive varies with input.  I
> cannot get the final to dip, like there is no tank circuit attached.  I
> can vary the plate tuning and the plate current varies but it will never
> dip indicating that it's seeing a load. Power output when the plate
> current peaks will be a couple of watts never going higher.
>
> Anyone have something like this around that i could borrow for a test
> and purchase if it works out?
>
> Thanks and lets hope this is indeed the culprit as this is indeed a fine
> piece of equipment.
>
> Larry
> W0OGH
>
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-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL