Joe,I have a H/W T-90 The mod driver shows 400 Ohms one side and 390
other side. On these older rigs it is not uncommon to find un-balance
in the windings and many have had the driver xfmr replaced,,windings
are extremely small. gauge wire..I know the people that built them
never expected us to be using them over 50 years later...hi..A great
little rig... 73 Harold W4PQW
Joe L. wrote:
Hello. I'm fixing up a Harvey Wells T-90 transmitter and have a
question. Perhaps another T-90 owner would be so kind as to help.

The tube socket resistance table in the instruction manual states that
the resistance from V9 pin 8 to ground should be 400 ohms. Same for V10
pin 8 to ground. These are the grids of the modulator tubes, fed in
push-pull from the secondary of driver transformer T1 which has a center
tap to ground. In my unit, the resistances are only half that much (211
ohms and 223 ohms). I'm suspicious that the 400 ohm value in the
resistance table might have been meant to pertain to the *total*
resistance between the two grids.

It would seem an unlikely coincidence for the transformer to have failed
with shorted turns and end up with exactly half the specified resistance
in both halves of the secondary. Of course, that's always a possibility.

Would someone else with a T-90 please help by checking these resistances
for me? I would appreciate it very much. (Disconnect the transmitter
from the power supply while making this measurement.)

73 & TIA,
Joe K9LY