[Heathkit] SB-102 Very little drive - Update

[Glen Zook]

Before you do anything else, check the 10 ohm resistors that go from the cathode connections of the 6146 tubes.  There are a total of 6 in parallel that form the meter shunt for the "plate" meter (actually reads cathode current).  These are 1/2 watt and in virtually every SB-Line transmitter / transceiver that I have worked on these have changed value significantly and thus the meter reading is "way off".  New 1 watt resistors are about the size of the original 1/2 watt resistors and I always change these out to 1 watt.

Glen, K9STH

Website:  http://k9sth.com


--- On Mon, 4/6/09, Carlos A. Archilla <caab at libertypr.net> wrote:

After working on and off for about a week on the low drive problem here are some comments on my findings. I discovered many off value resistors in the driver board, but the real challenge is changing them; the foil side of the Driver Board is covered with the band switch wafers, shaft, driver and grid coil boards and a couple of shields. There is no way to get in there short of unassembling half the radio so I had to work out from the top side of the board with "surface mounting" the new resistors to the remaining studs of the old ones.  If anyone knows of a different way, without taking the radio apart, please let me know.
 
The low drive improved some with the resistor's change, but the real improvement came about after tightening the nut on the neutralizing capacitor mounted on the RF cage.  Still not 100% but much better.  200ma on 80m I will keep looking.