[Heathkit] DX-40 Keying trouble

[Bill Stewart]

Hi Curt,
What I'm suggesting probably doesn't make good sense, but once I was using a DMM to make measurements on a HW-16 osc. ckt..never could get the correct readings and seemed to load the ckt or at least have an effect, making me think there was a problem...then chg'd to the old V-6 VTVM and everything started working and measuring right & no more problems. Found no pblms with the DMM.
73, Bill K4JYS 

----- Original Message -----
From: "Curt" <rhulett1 at comcast.net>
To: heathkit at mailman.qth.net
Sent: Monday, August 30, 2010 6:46:47 PM GMT -05:00 US/Canada Eastern
Subject: Re: [Heathkit] DX-40 Keying trouble

I'm aware that any electronic component, including a ceramic disc cap, can 
fail.  However would expect either a fail short or fail open, not 
intermittent.  Intermittents in my experience are active device problems ( 
tube or transistor ) or poor connections or shorts.  This problem doesn't 
exhibit with vibration or movement of the transmitter.

The behavior of the transmitter is that sometimes (but not every time) the 
keyline stays low enough to continue to turn on the oscillator / PA after 
key-up.  The chirp is always there, but the failure of the oscillator to 
turn off surfaced during a prolonged CW rag chew, so may be temperature 
related.  Swapping oscillator/buffer tubes and crystals makes no difference 
in behavior.  With a DVM connected accoss the key ( to measure the voltage 
on key-up ) the problem disappears.  Disconnecting the DVM causes the 
oscillator to hang up again.

I've ordered the caps, but plan some more voltage measurements and further 
testing before wholesale change of the disc caps.

Thanks for all the advice, am surely happy this is a simple rig.

73, Curt KB5JO 

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