No GRID current on my Heathkit DX-100 NEED HELP!!

[KF4IZE]

I recently inherited a restorable Heath DX-100. Apparently, I cannot achieve any GRID drive on my DX-100. I've tried in both VFO and crystal modes, but no success. I did notice a bare wire coming from the bottom of the stator of the DRIVE variable cap going through a grommet in the final shield where it was apparently cut off from a previous owner. It appeared to heading to the top of the 6146 RF choke at one time. I've attached a photo of this with this posting. I don't recall seeing this in the Heath DX-100 assembly manual. Perhaps I may have an early version of the DX-100.  Would this have anything to do with my inability to achieve GRID drive? Also, the rig does not have the COARSE loading feature, but has the FINE. Can the rig be used without the COARSE loading? I did a total recap of the HV, LV and BIAS capacitors and it has good HV of about 875V and all filaments light up, but no GRID. Does anyone have any suggestions for me? It would be greatly appreciated. Will, KF4IZE

[Pete, WA2CWA]

The wire is probably an added neutralizing "gimmick" capacitor to improve stability on 10 meters. It was used on the Apache and maybe even the DX-100B.
The coarse loading stuff was removed in a documented DX-100 modification.
Read all this info: Heathkit DX-100 “Official” Modifications and Other Info

Can you hear the VFO or crystal oscillator in a receiver?
Is the low voltage negative supply working?
Have you checked all the voltages on the various tubes in the RF section of the transmitter?
Are the meter shunts good?

[K9DXL]

As Pete noted, you should be able to hear the oscillator in your receiver. One maybe far-fetched possibility: my DX-100 has a flaky meter switch. Jiggle it around a bit and see if you get an indication. If the meter jumps around you should clean the switch contacts, and check solder connections. Also, your function switch on the right hand side of the panel has to be on CW.

[KF4IZE]

I was not able to hear any signals on my receiver in both VFO and crystal modes. I performed resistance checks per the manual and found the LV filter points showing infinite resistance when it should read about 32k-ohm according to the manual. LV displayed about 470 VDC with my VTVM when it should have read 360 VDC according to the manual. Seems a little high to me. My bias and HV check good per specs. Does this mean I have a bad LV choke? Guessing this could be the source of my problem with non-existent grid drive. Any help is greatly appreciated.

[Pete, WA2CWA]

Check the voltages on the tube pins for the VFO, oscillator, and driver tubes. Use the link I provided, page 6, to see the typical tube pin voltages. Check all the power supply voltages.

[KF4IZE]

Performed all the voltage checks and found zero plate voltage on Pin 6 of the 5763 per the DX-100 Modifications manual (BTW, thanks for the file). This pin is connected to the middle terminal of the 25K-ohm driver pot. Also, voltages were a little low on Pins 8 and 9. Should be -70, but I measured about -25. Was wondering about the 47pF capacitor coming off of Pin 7 of the 12BY7 to Pin 9 of the 5763. The schematic and assembly pictorals has the cap going to Pin 8 of the 5763 instead of Pin 9. My unit has it wired to Pin 9. Which is correct? Thanks for any help.

[Pete, WA2CWA]

Performed all the voltage checks and found zero plate voltage on Pin 6 of the 5763 per the DX-100 Modifications manual (BTW, thanks for the file). This pin is connected to the middle terminal of the 25K-ohm driver pot. Also, voltages were a little low on Pins 8 and 9. Should be -70, but I measured about -25. Was wondering about the 47pF capacitor coming off of Pin 7 of the 12BY7 to Pin 9 of the 5763. The schematic and assembly pictorals has the cap going to Pin 8 of the 5763 instead of Pin 9. My unit has it wired to Pin 9. Which is correct? Thanks for any help.

Have to learn to use a tube manual to help verify tube pin connections. In a 5763, pin 8 and pin 9 are internally wired together: http://www.mif.pg.gda.pl/homepages/frank/sheets/049/5/5763.pdf

[N8ETQ]

  Will,



     The VFO itself only operates on 160
and 40m. And some goofy frequecies for 11m
coverage if your into that sort of thing.

     Does your 0A2 glow? If so the LV sup.
is OK.  You can't hear anything on 160 or
40M ?


     You mentioned it doesn't work with XTAL's
either, The VFO Is out of circuit then and the
12BY7 is the XTAL OSC.

     Do you have the manual? Grid current
won't read if the 6146's are pulled.

GL

73

/Dan