[Heath] DX100 Question

[Glen Zook]

Heath never really publicized the voltage chart for the DX-100!  However, I grew up 35-miles from the Heath plant in St. Joseph, Michigan (the mailing address was Benton Harbor but the plant was on Hilltop Road In St. Joseph).  In high school, I used to drive up to the plant to "drool over" the latest kits.  There was a showroom to the left after immediately entering the building where you could purchase a kit and take it home with you.

If one had any questions about any kit that Heath ever made, or had any problems with a kit, the attendant would call back, into the plant, and an engineer, almost always someone from the design team, would come out and answer your questions.  Often, that person would draw a schematic about improving the equipment.  Then, he would go back, into the plant, and come out with a bag of parts to make the modification.  No charge!

Several times, I had questions about my original DX-100 and one time the engineer gave me a copy of an internal Heath document giving the voltages at each tube pin in the transmitter as well as other documents on the DX-100.  I have comprised a PDF containing all of those documents and that is available at:

http://nebula.wsimg.com/de13bc22f82b797942847fbbafb6e51f?AccessKeyId=D1250C433DB440D6B60D&disposition=0&alloworigin=1 

Glen, K9STH 

Website:  http://k9sth.net


________________________________
From: T. David Cohen <tdavid at eatel.net>
To: Heath at puck.nether.net 
Sent: Tuesday, April 10, 2018 5:44 PM
Subject: [Heath] DX100 Question



For some of y’all who remember DX100’s…
 
I picked up an old DX100 at a ham fest a couple of years ago and just got around to trying to get ‘er going.  Have had to handle several issues:  The HV filter caps had to be changed and the upper half of the HV bleeder resistor was open.  I thought the low voltage filter was OK and then it blew up (spectacularly) so that had to be changed as well.  As the cap died, it took out the 5V4 low voltage rectifier.  Not having a 5V4, I replaced it with a 5T4 and now here’s the question, what should the low voltage B+ be?   Since there was no audio, in checking the modulator section, I found an open driver transformer primary (fortunately I had a suitable replacement).   Also the cathode resistor for the 12BH7 driver looked toasted.  I replaced it with a 1 watt of proper value and it’s getting very hot too.   I’m getting very nearly 400 volts B+ and there’s no reference in the manual to what the correct value should be.  I can’t think of any other cause except for excessive voltage.  Any help would be appreciated.