Bush SRG91 - UK Vintage Radio Repair and Restoration Discussion Forum

Michael Maurice · 7th Apr 2018, 11:52 pm

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.

jmedley · 13th Apr 2018, 2:23 pm

I remember this model very well, we sold quite a few in the early days.
it was always a favourite and performed very well.
Wish I had house room for one.
The only problem we had were the coupling capacitors to the output stage.
(that capacitor)
Hope all works out well for you
Jim

7th Apr 2018, 11:52 pm	#1
Michael Maurice Moderator Join Date: Feb 2006 Location: Wembley, Middlesex Posts: 7,223	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. __________________ Forum Moderator http://www.michaelmauricerepairs.co.uk/

13th Apr 2018, 2:23 pm	#2
jmedley Rest in Peace Join Date: Jun 2012 Location: Milton Keynes, Buckinghamshire, UK. Posts: 109	Re: Bush SRG91 I remember this model very well, we sold quite a few in the early days. it was always a favourite and performed very well. Wish I had house room for one. The only problem we had were the coupling capacitors to the output stage. (that capacitor) Hope all works out well for you Jim