DX-100 Quirky Grid Drive Problem

[W3NP]

Heres the deal. My newly rebuilt and modified DX-100 has gobs of grid drive on all bands except 80 meters. 15 and 10 are down somewhat as is the norm so we can forget about them.
The rig was this way when I got it, but now that I changed the LV supply to choke input and dropped the voltage to the driver stage it has become an issue. On 160 and 40 the drive control sits at about 10 o'clock for 6ma of drive. On 80 I have to crank it wide open to just make 5 to 6 ma.
The RF voltage to the grid of the 5763 is about the same on all 3 bands so the problem seems to be related to the driver stage. Since all the bands share all of the circuitry except for the bandswitch contacts, wiring,  and the non-shorted out portion(s) of the driver tank coil, this should be a simple thing to solve. The wiring is correct, the contacts are good, solder joints redone. The coil "looks" ok - no burnt or damaged spots to indicate shorted turns. There is a nice sharp peak on 80 when the driver cap is adjusted, just as on the  other bands....just low grid drive on that band only. The unit works fine and even tho the drive control is maxed out, it does make enough drive to modulate well, etc. I just don't like having an unsolved issue lurking in this FB wireless set.
One other thing - the driver capacitor setting for 80 meters is about 20 while 160 and 40 are somewhere around 45. Not that that may mean anything but maybe you other DX-100 guys can check yours out.

Has anyone experienced anything similar to this?

I will be awaiting the "answer" to my woe....what have I overlooked?

[WA1HZK]

Mine is at 13 for 80 meters. My drive control opened up on me & gave me intermittant fits but that does not sound like your problem.
Keith
WA1HZK

[N8ECR]

I would touch all the solder connections on the driver coil with  a fresh bit of solder. as well inspect the connection from the driver thru the sheild  to the 6146's( see if the feed thru insulator  connections are tight.)  And last but not least, the band switch wafers for the driver.  I speculate some thing is dirty!!!  Good luck!!!

Mike/N8ECR

[W3NP]

Thanks Mark. While I was home I quickly checked the inductance of my driver tank coil and it looks to be pretty much in line with yours. I measured from where the bottom of the coil connects to the bandswitch and the feedthrough to the grids of the 6146's. My test lead adapter wouldn't allow me to duplicate your points of measurment without clip leads and that might account for my lower reading on 160. At any rate, my coil is pretty much the same as yours

Yours:

160M:  184 uH
80M  :   52 uH
40M  :   12 uH
20M  :   3.7 uH
15M  :   1.5 uH
10M  :   0.9 uH

Mine:

160M:   206 uH
80M  :   53.5 uH
40M  :   12.3 uH
20M  :   3.65 uH
15M  :   1.37 uH
10M  :   0.63 uH

I was able to get the drive up somewhat...more on that when I have the time...gotta get to work!!!!