[Boatanchors] Re: [Hallicrafters] SX-42, Band 4 Progress

[Bill]

Several suggestions - assuming you have an oscilloscope....

Check the RF level by injecting into another Rx, e.g. a modern one
  but first: 
	check level with oscilloscope to make sure its not too strong
	couple with high voltage cap, just to block any dc that might be
cause
 	by a leaky cap on the old sig gen.

Turn the RX OFF:
 set the sig gen to a a level that can be easily observed with
oscilloscope
 for each stage in the receiver, you can inject the signal at the input
to
	the tuned filters and check the output of the tuned filters for
coupling
	e.g. set RX frequency to (pick one) 15.0 MHz and RF sig gen to
15.0 MHz,

	For the 1st RF amp, connect sig gen to antenna, and check input
to tube with scope
	For for any other RF amp, connect sig gen to tube plate (RX is
OFF!!), and check
	  input to next stage with scope.

	While doing this, play with the tuning to see if signal peaks.

You can check effectiveness of by-pass caps by putting a 500 ohm
resistor in series
  with signal gen lead, and scope probe on other end of resistor.  Touch
the scope end
  of resistor to non-grounded end of cap and scope signal should
disappear.

Good luck  (My time is coming, I have 3 to work on, after a few sp-600's
etc)

Bill, ve3jhu

-----Original Message-----
From: hallicrafters-bounces at mailman.qth.net
[mailto:hallicrafters-bounces at mailman.qth.net] On Behalf Of Carole
White-Connor
Sent: Saturday, October 14, 2006 5:49 PM
Cc: boatanchors at mailman.qth.net; hallicrafters at mailman.qth.net
Subject: Re: [Boatanchors] Re: [Hallicrafters] SX-42, Band 4 Progress


Thanks, guys.

1. I did check antenna to ground (with the link closed). It read short
on each band. (By the way, I recently installed a knife switch on my
long-wire antenna lead in so I can easily disconnect the antenna when
I'm done listening. I've heard too many horror stories about lightning
strikes or static build-ups frying antenna coils).

2. I don't know how much I'm injecting. I'm using a Supreme signal
generator that is older than the hills but works well. When I get back
to the SX-42, I'll probably inject a signal into Band 3 and find the
setting that is barely audible. I'll then inject a signal of that level
into Band 4 and see what happens.

3. Band 4 was weak before the recapping of the RF section. I usually
check the receiver out on all bands before recapping so I can easily
determine if something I did made matters worse. (Yes, I have been known
to make matters worse!).


Joe Connor

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