[Heathkit] DX-100 Capacitor Question

[Glen Zook]

As I mentioned earlier, the 3 capacitors were changed to improve the grid drive on the 6146 tubes on the 10-meter band.  There was a short article in QST telling which capacitors were changed for those who had problems with low drive on 10-meters.

Heath did not make the voltage chart on the original DX-100 widely available.  When I was in high school, I had an original DX-100 and lived about 35-miles from the Heath plant in St. Joseph, Michigan (the mailing address was Benton Harbor but the actual plant was on Hilltop Road in St. Joseph), and used to drive up to the plant to "drool over" their latest kits (there was a sales/showroom just to the left as you went in the front door of the building).  If someone had a question about a product that Heath had produced the person in the showroom would telephone back to the engineering department and someone, often the lead engineer on the design team of the product, would come out and talk with you.  I usually left with a hand-drawn schematic and a bag with the parts to make the changes (no charge).  One one of these trips, I was given a one-page document with all of the voltages in the DX-100.  This was an "official" document but was not really
 distributed outside of Heath.  I also got information on the various modification kits for the DX-100 and the DX-100B during various trips to St. Joseph.

That information is on my website at the following URL:

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

 
Glen, K9STH


Website:  http://k9sth.com


________________________________
 From: L L bahr <pulsarxp at embarqmail.com>
To: Heathkit Reflector <heathkit at mailman.qth.net> 
Sent: Thursday, April 12, 2012 1:04 PM
Subject: Re: [Heathkit] DX-100 Capacitor Question
 
Well, I pulled out a later DX-100B manual then the one I was looking at earlier and now noticed they made one later or third change in this area:

1st version (DX-100): blocking cap on pin 1 of the 5763 was a .001, no cap to ground on pin 8 of the 12BY7, and the blocking cap on pin 7 of the 12BY7 was 47 pf.

2nd version (Early DX-100B):  blocking cap on pin 1 of the 5763 was changed to 68 pf, a 150 pf cap to ground was added on pin 8 of the 12BY7, and the blocking cap on pin 7 of the 12BY7 was still 47 pf.

3rd version (Late DX-100B):  blocking cap on pin 1 of the 5763 was 68pf, there was a 150 pf cap to ground on pin 8 of the 12BY7, and the blocking cap on pin 7 of the 12BY7 was changed from 47 pf to 200 pf.

So when all was said and done there were three cap changes from the earliest to latest variant.  What is interesting is the late DX-100B manual also gives tube pin voltages and also lists R and C labels next to all the resistors and caps such as R1 and C1 and so forth.  The cap to ground on the 12BY7 is C32, the blocking cap on pin 7 of the 12BY7 is C37, and the blocking cap on pin 1 of the 5763 is C39