Bush VHF81 dead FM - UK Vintage Radio Repair and Restoration Discussion Forum

crusher19860138 · 20th Mar 2017, 12:27 am

I have just finished recapping a Bush VHF81,it ran really well for a couple of hours when the FM died on me, just a crackling sound, MW and LW work fine, I have tried another UCC85 to no avail, voltages seem ok, could anyone offer some guidance on what may have gone wrong?

Boater Sam · 20th Mar 2017, 1:40 am

I have had one of the ceramic trimmer caps in the FM tuner head go short on more than one occasion, can't remember which one, probably TC1 (Bush Manf sheet), puts triode "B" anode volts on the grid.
If you move the adjusting screw by a very small amount it may clear the short for a while, mark where it started out, you can't re-adjust without some very special gear.

crusher19860138 · 22nd Mar 2017, 12:23 am

I turned TC1 clockwise by about 1/8th and the FM has come back to life,also I have found that it now tunes up to 102.5 which is where my local community station is located without loosing R2 at the other end of the dial.

Boater Sam · 22nd Mar 2017, 6:56 pm

Well done, its an odd fault this but its occured several times to me. Glad it worked for you.
Sam.

20th Mar 2017, 12:27 am	#1
crusher19860138 Hexode Join Date: Sep 2010 Location: Stourbridge, West Midlands, UK. Posts: 434	Bush VHF81 dead FM I have just finished recapping a Bush VHF81,it ran really well for a couple of hours when the FM died on me, just a crackling sound, MW and LW work fine, I have tried another UCC85 to no avail, voltages seem ok, could anyone offer some guidance on what may have gone wrong?

20th Mar 2017, 1:40 am	#2
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Re: Bush VHF81 dead FM I have had one of the ceramic trimmer caps in the FM tuner head go short on more than one occasion, can't remember which one, probably TC1 (Bush Manf sheet), puts triode "B" anode volts on the grid. If you move the adjusting screw by a very small amount it may clear the short for a while, mark where it started out, you can't re-adjust without some very special gear.

22nd Mar 2017, 12:23 am	#3
crusher19860138 Hexode Join Date: Sep 2010 Location: Stourbridge, West Midlands, UK. Posts: 434	Re: Bush VHF81 dead FM I turned TC1 clockwise by about 1/8th and the FM has come back to life,also I have found that it now tunes up to 102.5 which is where my local community station is located without loosing R2 at the other end of the dial.

22nd Mar 2017, 6:56 pm	#4
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Re: Bush VHF81 dead FM Well done, its an odd fault this but its occured several times to me. Glad it worked for you. Sam.