[Drake] TR4C weird xmit trouble

[Al Parker]

hi Dick, and Herman,
	I think Herman's right, I think I've seen the same thing on a Drake 
transmitter, don't remember if it was a TR-3/4 or a T-4xxx (besides, 
Herman knows these sorts of things).  Ck neutralization first off, that 
might well be it.
	Borrow a spectrum analyzer or a service monitor, or befriend a 2-way 
service tech & take it to his shop.  Sorry both Herman & I are too far 
away.  But neutralize first, might save a trip.
	Also, have you at least replaced the bias supply's filter cap(s)?
	Herman, don't expect to see you at Maysville, but will at Benson I imagine?
73,

Al, W8UT
www.boatanchors.org
www.hammarlund.info

"There is nothing -- absolutely nothing -- half so much
worth doing as simply messing about in boats"
Ratty, to Mole

On 10/4/2010 7:46 PM, N4ch at aol.com wrote:
> Sounds like a parasitic oscillation (possibly in the TR-4C's  PA) to me.
> Check neutralization.   If that doesn't fix  things, something like a bad
> bypass cap or other defective component, bad solder  joint, or other fault may
> be causing an unwanted feedback path somewhere,  possibly involving another
> stage, and not just the PA by  itself.   If U can borrow a spectrum
> analyzer from someone, try  connecting a couple feet of wire to its input, and let
> it run within a few feet  of the radio chassis so that U can loosely "see"
> what the radio might be  spraying out, and see what's going on.   DO NOT
> connect the analyzer  to the transceiver directly, as U will fry it.   If U can
> find a 40-50  dB power attenuator pad, then U could run the output of the
> TR-4C thru that into  the analyzer, though.   Set the sweep on the analyzer to
> cover from as  low in frequency as it goes all the way up to 30-50 MHz or
> so.   Bet  you will see some ragged RF on a different frequency than what the
>   transceiver is tuned to.   It might be that an earlier stage is flying  on
> some frequency removed from what the PA is tuned to, and this could explain
>   the high plate current.   Good luck and 73, Herman,  N4CH.
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