[Boatanchors] KWM2A

[Gary Schafer]

Hi Bill,

First thing I would do is loosen and retighten all of the shield cans for
the driver coil sections. A bad ground will give you all sorts of fits in
there.

The next thing is to try turning the neutralizing capacitors slightly. This
includes the feedback neutralizing cap. They can stick and or become flakey.
When the transmitter is neutralized properly you will have less drive than
when it is not. You may have low drive and the neutralization may be off and
drifts in and out. Check that the grid current decreases when the plate
current dips. This is opposite of a normal transmitter. The feedback circuit
causes this and is normal when everything is adjusted properly.

73
Gary  K4FMX

> -----Original Message-----
> From: Boatanchors [mailto:boatanchors-bounces at mailman.qth.net] On Behalf
> Of Bill and Liz
> Sent: Monday, January 05, 2015 3:08 PM
> To: boatanchors at mailman.qth.net
> Subject: [Boatanchors] KWM2A
> 
> I'm playing with a KWM2-A which has intermittent drive problems.  After
> turn-on, it may or may not produce grid current and, if it does, after a
> few cycles the drive disappears "until next time".  Drive is always
> available up to the grid of the driver tube-the intermittent condition
> is after that.  I can find no blown or damaged components.  The only
> clue is that when drive is available it starts with a decent reading and
> then declines fairly quickly to about 1/3 of the initial meter reading.
> I have tested the driver tube ; screen and plate voltages are always the
> proper value.  It is possible that it is a relay problem (driver tube is
> biased off in receive and switched by K2) but I inspected the relay,
> cleaned the contacts with paper and NuTrol and even rapped the relay
> with a screwdriver when drive disappeared, all to no avail.
> 
> I'd hate to recommend to my friend that he replace the relay if the
> problem may lie elsewhere.  So, until I do that I wonder if anyone may
> have encountered this problem before or has any suggestion where else to
> look.
> 
> Bill VE3NH
> 
> PS-I posted some weeks ago about the oscillating regenerative IF in a
> homebrew receiver.  There was some coupling between input and
> output...poor building practice (parts laid across the tube socket-I
> should have seen that before I posted!)....but the real culprit seems to
> be that the tube has considerably more gain than is necessary and is
> sensitive to screen voltage (regeneration is in the cathode).  Right now
> I have the stage working but it still does not go into and out of
> oscillation as smoothly as I think it should .  So, still working on
> that one.
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