800B Trial Today

[Joseph W Strickland]

Today I took time to check throughout both chassis of my 800B for any B+ shorts and did not find any. So, I hooked the unit up to my Variac and advanced power and at a little over 40% I was able to activate the On relay. I left it there a while and seeing no evidence of smoke I eventually raised it to 50% and then 60%. I began to hear stations but there was a loud hum. I also noticed that the volume control had no effect on volume. After checking with power off, I found the shield to the center tap lead of the audio from the volume control had broken away from the bottom lug of the volume control. I trimmed back the jacket until there was enough shield wires visible to solder an extension lead to the shield. Then I covered the repair with a piece of black heat-shrink tubing. Attaching the shield to the bottom lug of the volume control solved the loud hum I was hearing.

It played with good volume and then all of a sudden it developed weak sound and sounded really thin with no bass response. I looked and discovered that V-20 the 6L6G nearest the power transformer was red plating. I took time to check the coupling capacitor and it was still a .05 wax paper foil type. I pulled it out and changed it to a new Panasonic .1uF@630VDC inside the bathtub enclosure. I had failed to change that one because its companion part to the grid of V-21 I had opened up and it had already been changed to a .1uF@600VDC Sprague Orange Drop type, so at the time I assumed the one feeding V20 had been changed. I never should have trusted that. However, after changing the capacitor and re-installing I also had to replace the 1A fuse to the remote control power transformer - not sure what happened there. In any case I replaced the fuse and gave it another go. It came up and V20 began to red plate again. I had checked it for shorts on my tube tester, and it showed no shorts.

For the short period earlier that it worked the, reception was good using the Philco AM loop antenna from a model 40-201. I have two of these loop antennas plus one that is functioning in my restored Philco 40-201. It made a good antenna for testing the Scott.

Time to order a new set of 6L6G output tubes. I checked for tight socket contacts in the tube socket for V20 pin 5 (the signal grid). They were OK, but I tightened them slightly and tried it again - same thing, red plating.

Joe