Bush VHF-54. Working but no FM - UK Vintage Radio Repair and Restoration Discussion Forum

MeanDumpsterCat · 29th Apr 2021, 12:27 pm

Hello everyone. A while ago I got hold of a very lovely Bush VHF-54. It's in generally good condition although I took a few knocks in transit (thanks, Hermes). Luckily nothing was seriously broken.

It was generally quite clean and a little work with a toothbrush on the chassis bought it up quite nicely. It had the wonderful smell of what seemed like fireplace soot and cannabis.... lovely.

I havent yet replaced a single thing on it as I wanted to see what I had to work with and the seller had already tested it. Even passed a PAT test! I gave it a small amount of power on the current limited variac supply and much to my surprise it started receiving stations on the MW band. The sensitivity wasnt great but given it's still on all it's original components I was impressed.

As a matter of fact everything seems to work fine with the exception of the FM. I can hear some quiet static and some small changes in sound when it passes certain frequencies which I presume are strong local stations.

I havent yet looked under the FM chassis but I would be willing to bet there are some Hunts capacitors that would need replacing. Is there anything else that could lead to non working FM discriminator other than the obvious things like a bad cap or open / high resistor? I hear these sets can be tricky when it comes to FM.

I will be replacing all the old wax and hunts capacitors as everything on this set is very accessible. One of the main reasons I like Bush designs.

I'll start by checking all the caps and resistors in the FM sub chassis and if that brings no joy i'll start voltage checking.

Also the magic eye isnt working but that's a pretty minor thing. I think that will be the last thing to do.

Any pointers would be much appreciated. I'll keep this thread updated as work progresses.

cathoderay57 · 29th Apr 2021, 12:55 pm

You'll need a pair of very good EF80s in the VHF front end. Get them tested for gain if poss. Also check or replace the 5uF electrolytic across two of the diodes in the EABC80. On the Trader sheet it is listed as C47 and on the Manufacturer's data sheet C50. A 4.7uF will do but make sure the positive terminal is soldered to chassis. Interestingly (or not) I note in passing that the Bush Manufacturer's data sheet, page 1 (specifications) says that the EM80 or EM81 magic eye tuning indicator is octal-based which it definitely isn't. You can get Russian new replacements for the ME. Cheers, Jerry

Sideband · 29th Apr 2021, 2:08 pm

Quote:

Originally Posted by cathoderay57

You'll need a pair of very good EF80s in the VHF front end. Get them tested for gain if poss.

Absolutely must do that! The EF80's are being pushed to their limits in terms of frequency response and it's likely that one or both are well below par. As an experiment, you could try swapping them over since the one used as RF amp doesn't work quite as hard as the self-oscillating mixer so it might bring FM to life even if not properly.

There are literally thousands of EF80's about and a couple of brand new ones from Langrex won't break the bank.

MeanDumpsterCat · 30th Apr 2021, 12:50 pm

Quote:

Originally Posted by Sideband

Quote:

Originally Posted by cathoderay57

You'll need a pair of very good EF80s in the VHF front end. Get them tested for gain if poss.

Absolutely must do that! The EF80's are being pushed to their limits in terms of frequency response and it's likely that one or both are well below par. As an experiment, you could try swapping them over since the one used as RF amp doesn't work quite as hard as the self-oscillating mixer so it might bring FM to life even if not properly.

There are literally thousands of EF80's about and a couple of brand new ones from Langrex won't break the bank.

I think i'll try that. I think I might have some new old stock ones going spare somewhere too.

PYE 405 · 30th Apr 2021, 1:33 pm

Hi MDC, a handsome set indeed is the VHF54.
I have one too, and I found it also was dead on FM to begin with. Replacement EF80's sorted the problem along with the usual capacitor replacement.
Later, I put back the old EF80's and after some minutes, they sprung into life. My theory is that if the set is used on AM only for long periods, the EF80's have no HT and the cathodes may suffer from interface resistance. I think I fitted a bleed resistor of about 100k on mine to keep a small amount of current passing through them when the set is switched to AM.

MeanDumpsterCat · 30th Apr 2021, 1:42 pm

Okay so I just had another little play with it. I swapped the two EF80's and no joy. Just some faint hiss and a few pops and crackles. I think what i'm going to do is re-cap as much of the set as I can seeing as the sensitivity even on the medium wave band is pretty poor and I would presume the FM section requires the rest of the radio to be operating at a good level of sensitivity.

Sideband · 30th Apr 2021, 6:13 pm

I could test the EF80's for you but it hardly seems worth it....the cost of postage would probably buy you a couple of brand new ones....!

29th Apr 2021, 12:27 pm	#1
MeanDumpsterCat Pentode Join Date: Oct 2014 Location: Selsey, West Sussex, UK. Posts: 204	Bush VHF-54. Working but no FM Hello everyone. A while ago I got hold of a very lovely Bush VHF-54. It's in generally good condition although I took a few knocks in transit (thanks, Hermes). Luckily nothing was seriously broken. It was generally quite clean and a little work with a toothbrush on the chassis bought it up quite nicely. It had the wonderful smell of what seemed like fireplace soot and cannabis.... lovely. I havent yet replaced a single thing on it as I wanted to see what I had to work with and the seller had already tested it. Even passed a PAT test! I gave it a small amount of power on the current limited variac supply and much to my surprise it started receiving stations on the MW band. The sensitivity wasnt great but given it's still on all it's original components I was impressed. As a matter of fact everything seems to work fine with the exception of the FM. I can hear some quiet static and some small changes in sound when it passes certain frequencies which I presume are strong local stations. I havent yet looked under the FM chassis but I would be willing to bet there are some Hunts capacitors that would need replacing. Is there anything else that could lead to non working FM discriminator other than the obvious things like a bad cap or open / high resistor? I hear these sets can be tricky when it comes to FM. I will be replacing all the old wax and hunts capacitors as everything on this set is very accessible. One of the main reasons I like Bush designs. I'll start by checking all the caps and resistors in the FM sub chassis and if that brings no joy i'll start voltage checking. Also the magic eye isnt working but that's a pretty minor thing. I think that will be the last thing to do. Any pointers would be much appreciated. I'll keep this thread updated as work progresses. Attached Thumbnails

29th Apr 2021, 12:55 pm	#2
cathoderay57 Nonode Join Date: Oct 2017 Location: Bristol, UK. Posts: 2,388	Re: Bush VHF-54. Working but no FM You'll need a pair of very good EF80s in the VHF front end. Get them tested for gain if poss. Also check or replace the 5uF electrolytic across two of the diodes in the EABC80. On the Trader sheet it is listed as C47 and on the Manufacturer's data sheet C50. A 4.7uF will do but make sure the positive terminal is soldered to chassis. Interestingly (or not) I note in passing that the Bush Manufacturer's data sheet, page 1 (specifications) says that the EM80 or EM81 magic eye tuning indicator is octal-based which it definitely isn't. You can get Russian new replacements for the ME. Cheers, Jerry

30th Apr 2021, 1:33 pm	#5
PYE 405 Pentode Join Date: Dec 2009 Location: Chatteris, Cambridgeshire, UK. Posts: 176	Re: Bush VHF-54. Working but no FM Hi MDC, a handsome set indeed is the VHF54. I have one too, and I found it also was dead on FM to begin with. Replacement EF80's sorted the problem along with the usual capacitor replacement. Later, I put back the old EF80's and after some minutes, they sprung into life. My theory is that if the set is used on AM only for long periods, the EF80's have no HT and the cathodes may suffer from interface resistance. I think I fitted a bleed resistor of about 100k on mine to keep a small amount of current passing through them when the set is switched to AM. __________________ Andrew

30th Apr 2021, 1:42 pm	#6
MeanDumpsterCat Pentode Join Date: Oct 2014 Location: Selsey, West Sussex, UK. Posts: 204	Re: Bush VHF-54. Working but no FM Okay so I just had another little play with it. I swapped the two EF80's and no joy. Just some faint hiss and a few pops and crackles. I think what i'm going to do is re-cap as much of the set as I can seeing as the sensitivity even on the medium wave band is pretty poor and I would presume the FM section requires the rest of the radio to be operating at a good level of sensitivity.

30th Apr 2021, 6:13 pm	#7
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,580	Re: Bush VHF-54. Working but no FM I could test the EF80's for you but it hardly seems worth it....the cost of postage would probably buy you a couple of brand new ones....! __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....