[Boatanchors] DX-100 RF delay

[Glen Zook]

There was an official Heath modification kit, MK-3, which changed the step antenna loading switch and 150 pf variable capacitor to a continuously variable loading capacitor.  Transmitters with that modification were "unofficially" called DX-100A transmitters and that is one of the reasons that the next production model was the DX-100B.  You can find the official Heath instructions for this kit, as well as a number of other service information, at

http://k9sth.com/uploads/Heathkit_DX-100_mods-1.pdf


If you are getting 140-watts out of the DX-100 you are definitely over-driving the final amplifier.  You really shouldn't get more than 120-watts out and even then that is really "pushing" the final amplifier tubes.  If you run about 100-watts output on CW the station on the other end of the QSO will not be able to tell the difference and your final amplifier tubes will last a LOT longer!

On phone, Heath rated the DX-100 at 160-watts input.  However, that is definitely considerably more input power than the maximum ratings on the 6146 and 6146A/8298 tubes used in the final.  The maximum RCA ratings for AM operation is 67.5-watts input per tube or 135-watts input for the pair.  However, one should not run the transmitter at more than 120-watts input and more like 110-watts input will allow the final amplifier tubes to last a LOT longer.  That means no more than 80-watts output on AM and running 70-watts output will result in MUCH longer tube life.

As for the power problem:  Check the 12BY7 driver tube as well as the 6AQ5 clamp tube.  Both can be problematic where power output is concerned.
 
Glen, K9STH


Website:  http://k9sth.com


________________________________
 From: Bob <hoopmonk at snet.net>
To: heathkit at yahoogroups.com 
Cc: Boatanchors <Boatanchors at mailman.qth.net> 
Sent: Monday, February 4, 2013 7:19 PM
Subject: [Boatanchors] DX-100 RF delay
 
I recently purchased a DX-100 that is mostly stock except for the fact that someone has removed the coarse loading function and no I don't think it is a B model.I have it putting out about 140 watts after some cleaning and tube replacement. At this point the only thing that is a problem is that there is between a two and six second delay before it puts out any RF when the plate switch is thrown. I thought it might be the plate switch and I paralleled the switch with a good one but no luck.It also exhibits the same delay when switching from CW to phone. At times after the set has been off for a while and I turn it on again I will have to readjust the driver before it will produce RF,maybe this is related to the delay problem.. Does anyone have any thoughts on where the problem lies?