Bush SRG91
I've just finished repairing the radio chassis from this radiogram and had some very off faults.
When I got it the ECC83 had gone to air, so after a recap and replacing of some resistors, I found R50 was smoking, this was because one of the EL84's was taking grid current, ie the grid voltage was positive and the cathode was at 14 volts rather than 6-7 volts.
Next I couldn't get FM, and I found a hunts capacitor C39 lurking around the switch bank, I replaced it and I got FM.
The most surprising thing I found was that the grid of the ECH81 was also positive, so I removed it and the grid voltage dropped to 0V, so I replaced it and the grid voltage remained at 0V.
I supposed any valve can run into grid current though I thought it only power valves that this happened to.
|