Bush VHF61/62: tuning issues on FM - UK Vintage Radio Repair and Restoration Discussion Forum

Nickthedentist · 1st Dec 2008, 1:03 pm

Hello everyone,

I've nearly finished restoring a well-worn example. This mainly involved replacing all of the horrible 20 wax/paper caps, plus the ECC85 in the VHF front end.

Results are now very respectable, though there's quite a lot of 50/100Hz hum between stations on VHF. It requires very careful tuning indeed to completely eliminate this.

I have not fiddled with the alignment at all, and nor has anyone else as far as I can tell.

The "new" ECC85 was something I fished out of my spares box, and presumably came from a radio I scrapped years ago.

Is this a fault? If so, what might it be?

Cheers,
Nick.

paulsherwin · 1st Dec 2008, 2:28 pm

I would try swapping the ECC85 before trying anything else. It may have a h-k short.

Paul

ronbryan · 1st Dec 2008, 3:04 pm

Nick

Apart from Paul's suggestion, I wonder if you have swapped C56, the 5uF FM discriminator stabilising electrolytic? This is supposed to reject AM on the FM signal and may have dried out.

You could also try swapping the EABC80 if you have a known good one, or parallel the smoothing electrolytics with 32uF to see if that has any effect.

Ron

Nickthedentist · 1st Dec 2008, 3:10 pm

Hi Ron,

Quote:

Originally Posted by ronbryan

I wonder if you have swapped the FM discriminator stabilising electrolytic?

I have actually done that already - should have said so.

Quote:

Originally Posted by ronbryan

You could also try swapping the EABC80 if you have a known good one, or parallel the smoothing electrolytics with 32uF to see if that has any effect.

Good idea. I will try both of your suggestions.

The canned electrolytics are the originals, but were re-formed. HT volts are correct and there's no hum on gram.

Thanks

Nickthedentist · 1st Dec 2008, 3:11 pm

Quote:

Originally Posted by paulsherwin

I would try swapping the ECC85 before trying anything else. It may have a h-k short.

Thanks Paul, will do.

Nick.

georgesgiralt · 1st Dec 2008, 3:38 pm

Hi !
Just my 2 cents, here...
I own a nice NOS ECC85 which cause tremendous tuning drift on my Grundig set, and no drift at all on a Blaupunkt set.
So they are not born equal ! And worth swapping before pulling out hairs ;-)

Steve_P · 1st Dec 2008, 3:59 pm

Now that's true. Gerry Wells said 'try several and find one that works' to me once about these lovely little valves. I've had them work in one set but not in another.

EABC80's can be a bit hummy. Try that too.

Clean the wavechange buttons again and try repositioning a few wires.

Cheers,

Steve P.

paulsherwin · 1st Dec 2008, 5:47 pm

If the set doesn't hum with the volume turned right down, it's very unlikely to have a problem with the smoothers.

Paul

kalee20 · 1st Dec 2008, 6:42 pm

I had a little Philips Philetta radio which hummed madly between stations on FM. Changing the UABC80 cured that. I'd certainly try a new EABC80. If you haven't got one, buy one - it's used in probably 90% of AC-only AM/FM radios, so very useful to have as a spare in any case!

Following on from this - and it's not going OT - can anyone put in a plausible explanation of what internal fault in the xABC80 can cause this? Leakage from the heater, obviously - but to what, and why does it not matter when the radio's exactly on-tune?

paulsherwin · 1st Dec 2008, 7:47 pm

Quote:

Originally Posted by kalee20

can anyone put in a plausible explanation of what internal fault in the xABC80 can cause this? Leakage from the heater, obviously - but to what, and why does it not matter when the radio's exactly on-tune?

I suspect it's a leak to the separate diode cathode. This is normally used as half of the ratio detector so a bit of 50Hz here would cause all sorts of problems for FM reception, while not affecting AM.

Paul

Nickthedentist · 1st Dec 2008, 11:30 pm

Solved (well almost!).

A diffferent ECC85 from the depths of the junk box made the world of difference.

Thanks everyone

Nick.

Nickthedentist · 2nd Dec 2008, 12:09 am

POSTSRCIPT...

And a new EABC80 as well has made it PERFECT!!

This poor old set now only has a mere 3 of its 8 original valves left. It must have had a lot of use over the years

Thanks again to all you helpful experts

Nick.

Nickthedentist · 12th Dec 2008, 6:25 pm

P.P.S.

The hum's back again

Silent on gram, perfect on AM, nasty hum when tuned-in on VHF though silent (except for healthy interstation hiss) between stations.

Interestingly, the hum goes when the dipole mounted on the set's card back is moved away from the cabinet and chassis. Very puzzling (to me).

Will report back later when I've done more valve swapping (

), but all suggestions welcome.

Nick.

Steve_P · 12th Dec 2008, 8:11 pm

Have you swapped the caps on the heater line : C18, C30, C61. Also in the VHF can, C11, C5, C6 - all in the heater chain Also C4.

Cheers,

Steve P.

Nickthedentist · 12th Dec 2008, 8:21 pm

Hi Steve,

Thanks for replying

BTW, Steve's using the manufacturer's datasheet.

Quote:

Originally Posted by Steve_P

Have you swapped the caps on the heater line : C18, C30, C61.

Yes, all the Hunts and TCC waxies on the main chassis and OP transformer were replaced with nice little yellow axial Vishays, rather like the ones from the BVWS. About 20 in all

Quote:

Originally Posted by Steve_P

Also in the VHF can, C11, C5, C6 - all in the heater chain. Also C4.

Er, nope. I didn't go inside the VHF front end. These are all 560pF so I assumed they wouldn't be wax/paper and so might be OK left. I will definitely change them if I can't find anything else wrong though. Do you think 1nF would be OK for replacements?

Cheers,
Nick.

paulsherwin · 12th Dec 2008, 8:27 pm

I think you should investigate the relationship between the FM aerial and the hum. Try connecting a bit of wire to the FM aerial socket and moving it around the chassis while listening to a station.

Can you confirm there is no hum when using an external aerial?

Paul

Nickthedentist · 12th Dec 2008, 8:41 pm

Thanks Paul, I'll report back later.

One thing I've noticed is that when it's misbehaving, a hand placed near the top of the set restores normal operation... but maybe that's just because it's helping out the aerial slightly.

I'm in a strong signal area, and my 1950s valve sets never have problems pulling in all the main stations with excellent S/N ratio using just their internal aerials.

Nick.

Steve_P · 12th Dec 2008, 9:19 pm

Try it in one or two different places in the house. It may be picking something up. Have you re-aligned it?

Cheers,

Steve P.

Nickthedentist · 12th Dec 2008, 9:31 pm

Quote:

Originally Posted by Steve_P

Try it in one or two different places in the house.

Good point, I will.

Quote:

Originally Posted by Steve_P

Have you re-aligned it?

No, other than sliding the windings on the ferrite rod around a bit, because nothing seemed to have been disturbed. Sensitivity and selectivity is excellent, as is the sound quality... when the back's offf

Nick.

Nickthedentist · 8th Jan 2009, 1:56 pm

Sorry for the long delay.

After weeks of enjoying the set with the back off (and hence the aerial further away from the chassis), I had several guests staying over the New Year period, some of whom had young and inquistive children. So the back had to be replaced, and the hum returned.

But a simple external aerial connected in addition to the internal dipole, (i.e. 3 feet of insulated wire with the stripped end poked into one of the aerial socket's pins and then the internal aerial's plug rammed home to secure it), has solved the problem, making me wonder whether it's really a fault at all, or merely a manifestation of a slightly marginal signal

Either way, it works so well that I think I'll leave well alone.

Thanks to everyone who's helped.

Nick.

1st Dec 2008, 1:03 pm	#1
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,837	Bush VHF61/62: tuning issues on FM Hello everyone, I've nearly finished restoring a well-worn example. This mainly involved replacing all of the horrible 20 wax/paper caps, plus the ECC85 in the VHF front end. Results are now very respectable, though there's quite a lot of 50/100Hz hum between stations on VHF. It requires very careful tuning indeed to completely eliminate this. I have not fiddled with the alignment at all, and nor has anyone else as far as I can tell. The "new" ECC85 was something I fished out of my spares box, and presumably came from a radio I scrapped years ago. Is this a fault? If so, what might it be? Cheers, Nick. Last edited by Nickthedentist; 1st Dec 2008 at 1:27 pm.

1st Dec 2008, 2:28 pm	#2
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,927	Re: Bush VHF61/62: tuning issues on FM I would try swapping the ECC85 before trying anything else. It may have a h-k short. Paul

1st Dec 2008, 3:04 pm	#3
ronbryan Octode Join Date: Jan 2003 Location: Guildford, Surrey, UK. Posts: 1,959	Re: Bush VHF61/62: tuning issues on FM Nick Apart from Paul's suggestion, I wonder if you have swapped C56, the 5uF FM discriminator stabilising electrolytic? This is supposed to reject AM on the FM signal and may have dried out. You could also try swapping the EABC80 if you have a known good one, or parallel the smoothing electrolytics with 32uF to see if that has any effect. Ron Last edited by ronbryan; 1st Dec 2008 at 3:16 pm.

1st Dec 2008, 3:38 pm	#6
georgesgiralt Hexode Join Date: Jul 2008 Location: Toulouse, France Posts: 406	Re: Bush VHF61/62: tuning issues on FM Hi ! Just my 2 cents, here... I own a nice NOS ECC85 which cause tremendous tuning drift on my Grundig set, and no drift at all on a Blaupunkt set. So they are not born equal ! And worth swapping before pulling out hairs ;-)

1st Dec 2008, 3:59 pm	#7
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Bush VHF61/62: tuning issues on FM Now that's true. Gerry Wells said 'try several and find one that works' to me once about these lovely little valves. I've had them work in one set but not in another. EABC80's can be a bit hummy. Try that too. Clean the wavechange buttons again and try repositioning a few wires. Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

1st Dec 2008, 5:47 pm	#8
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,927	Re: Bush VHF61/62: tuning issues on FM If the set doesn't hum with the volume turned right down, it's very unlikely to have a problem with the smoothers. Paul

1st Dec 2008, 6:42 pm	#9
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,077	Re: Bush VHF61/62: tuning issues on FM I had a little Philips Philetta radio which hummed madly between stations on FM. Changing the UABC80 cured that. I'd certainly try a new EABC80. If you haven't got one, buy one - it's used in probably 90% of AC-only AM/FM radios, so very useful to have as a spare in any case! Following on from this - and it's not going OT - can anyone put in a plausible explanation of what internal fault in the xABC80 can cause this? Leakage from the heater, obviously - but to what, and why does it not matter when the radio's exactly on-tune?

1st Dec 2008, 11:30 pm	#11
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,837	Re: Bush VHF61/62: tuning issues on FM Solved (well almost!). A diffferent ECC85 from the depths of the junk box made the world of difference. Thanks everyone Nick.

2nd Dec 2008, 12:09 am	#12
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,837	Re: Bush VHF61/62: tuning issues on FM POSTSRCIPT... And a new EABC80 as well has made it PERFECT!! This poor old set now only has a mere 3 of its 8 original valves left. It must have had a lot of use over the years Thanks again to all you helpful experts Nick.

12th Dec 2008, 6:25 pm	#13
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,837	Re: Bush VHF61/62: tuning issues on FM P.P.S. The hum's back again Silent on gram, perfect on AM, nasty hum when tuned-in on VHF though silent (except for healthy interstation hiss) between stations. Interestingly, the hum goes when the dipole mounted on the set's card back is moved away from the cabinet and chassis. Very puzzling (to me). Will report back later when I've done more valve swapping (), but all suggestions welcome. Nick.

12th Dec 2008, 8:11 pm	#14
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Bush VHF61/62: tuning issues on FM Have you swapped the caps on the heater line : C18, C30, C61. Also in the VHF can, C11, C5, C6 - all in the heater chain Also C4. Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

12th Dec 2008, 8:27 pm	#16
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,927	Re: Bush VHF61/62: tuning issues on FM I think you should investigate the relationship between the FM aerial and the hum. Try connecting a bit of wire to the FM aerial socket and moving it around the chassis while listening to a station. Can you confirm there is no hum when using an external aerial? Paul

12th Dec 2008, 8:41 pm	#17
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,837	Re: Bush VHF61/62: tuning issues on FM Thanks Paul, I'll report back later. One thing I've noticed is that when it's misbehaving, a hand placed near the top of the set restores normal operation... but maybe that's just because it's helping out the aerial slightly. I'm in a strong signal area, and my 1950s valve sets never have problems pulling in all the main stations with excellent S/N ratio using just their internal aerials. Nick.

12th Dec 2008, 9:19 pm	#18
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Bush VHF61/62: tuning issues on FM Try it in one or two different places in the house. It may be picking something up. Have you re-aligned it? Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

8th Jan 2009, 1:56 pm	#20
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,837	Re: Bush VHF61/62: tuning issues on FM Sorry for the long delay. After weeks of enjoying the set with the back off (and hence the aerial further away from the chassis), I had several guests staying over the New Year period, some of whom had young and inquistive children. So the back had to be replaced, and the hum returned. But a simple external aerial connected in addition to the internal dipole, (i.e. 3 feet of insulated wire with the stripped end poked into one of the aerial socket's pins and then the internal aerial's plug rammed home to secure it), has solved the problem, making me wonder whether it's really a fault at all, or merely a manifestation of a slightly marginal signal Either way, it works so well that I think I'll leave well alone. Thanks to everyone who's helped. Nick.