[Heathkit] DX-100 Capacitor Question

[L L bahr]

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

Lee, w0vt
"No charge for consultations lasting less then 30 seconds"  




----- Original Message -----
I've been studying the DX-100 and DX-100B schematics.  The B model used a 68 pf cap as a blocking cap off the 5763 plate pin 1 and the DX-100 used a .001.  At the same time they added a 150 pf cap off of pin 8 of the 12BY7 on the B model. No cap was there on the DX-100.  I can't see any other changes in the drive circuits or power supply feeding these circuits.  (Discussion is not taking into account the crystal/VFO switching circuit differences).

Lee, w0vt

----- Original Message -----

On some versions the capacitor in question IS a 68pf, as listed in the parts list.

Bill - K5MIL

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