Hacker RV14 Mayflower hum problems - UK Vintage Radio Repair and Restoration Discussion Forum

jim_beacon · 1st Nov 2005, 9:07 pm

Hi,

I've been working on a Mayflower over the last couple of weeks, and have it working nicely, except for one thing - there is a low level of mains hum audible when the set is off tune. The best way to hear it, is to turn the "sensitivity" control to minimum, and it appears, but doesn't seem to be particularly effected by the volume control.

Is this normal for one of these? I've changed the main smoothing caps, the ouput stage bypass and coupling caps, and the detector load cap, but everything else is original. I though I had altered the wiring a little, but have checked it, and it made no difference.

Any ideas?

Thanks

Jim.

Nickthedentist · 1st Nov 2005, 9:17 pm

Hi Jim,

Quote:

Originally Posted by jim_beacon

Is this normal for one of these?

No, I'm afraid not. Mine produces no discernable mains hum at all, whatever the setting of the controls. And mine's even running on its original smoothing electrolytics.

I did replace quite a few other caps though, plus LOADS of resistors which were way out-of-spec (>>50%

).

Sorry, I'm not clever enough to offer you any suggestions, but I'm sure someone here is

BTW, the manual (RV20, can't find my RV14 one today

) advises to check/replace: Valves (heater-cathode leakage, esp. EB91), and C27, 28, 35, 36.

Good luck,
Nick.

ukcol · 1st Nov 2005, 9:49 pm

Hi Jim

I haven’t got an answer for you, just thinking out loud really. There seems to be some confusion in the manual between the numbering of the gain pot in the cct and in the parts list, but if the fault is worse at the minimum setting of the sensitivity control (10k pot in cathode cct of V2?) Then perhaps V2 has a H/K leak. This is consistent with the pot in the minimum gain (maximum resistance) position. The only problem with that thought is that you’d expect the hum to reduce to nothing when the volume is turned down to zero.

Is the hum 100Hz (sorry CPS J) or 50Hz? That could indicate whether it is smoothing or perhaps modulation hum. Lastly, is the bridge rectifier OK? (One diode O/C?)

Knowing your technical abilities and the fact you have not tracked it down yet, probably means it’s going to be a B.

jim_beacon · 1st Nov 2005, 9:56 pm

Nick,

I was afraid of that.......

Colin,

I haven't really put much effort into it yet

The reason for asking is a lack of familiarity with Hacker valve sets - I didn't want to spend hours tracking down a "normal" condition!

The original HT smoothing caps were changed as the can had vented, though they still measured OK, I think it was only a matter of time.

I think the fault must be in the audio stages, as the volume control has little effect. I'll check the bridge rectifier, and if thats not the culprit, I'll get the scope out and see if I can trace the fault.

I suppose I could take the easy way out and turn the volume up...... (but this set is SERIOUSLY LOUD!)

Thanks

Jim.

hotbulb · 2nd Nov 2005, 8:47 am

FWIW my RV14 also suffers from a hum problem which I've never managed to track down. It's had the main smoothing electrolytics replaced, plus all the other usual C's and R's, and a new set of valves, except for the ECL86's.
It's definitely 50Hz, and it's there all the time , not just when off tune. It doesn't vary with the volume setting, but as Jim says, this a loud radio, and turning up the wick is not...erm...domestically acceptable. Maybe I ought to check the bridge rectifier, must admit I hadn't thought of that one. Neither of my two RV20's hum at all of course......

Regards

Philip

Ed_Dinning · 2nd Nov 2005, 9:08 am

Hi Gents, this definitely sounds like a time to get the scope out. I've had similar problems on other chassis and traced it to poor earth connections to the chassis. In one case it had probabply been there since manufacture as the offending earth bolt was sealed down with factory applied varnish.
It may be that people expected a certain level of hum in those days.

HTH Ed

Paul_RK · 2nd Nov 2005, 1:36 pm

Quote:

Originally Posted by Ed_Dinning

...It may be that people expected a certain level of hum in those days.

HTH Ed

Hi all.

Ed's comment prompted me to dig out Geoffrey Horn's "Gramophone" review of the RV14, from May 1962.

"Over 6 watts are available from 40c/s to 15kc/s, distortion, hum and noise are very low...

A good quality radio for anyone of taste, simple enough for granny, good enough for the Hi-Fi fan (he can even run his electrostatic speaker from it), loud enough for anyone...

[but] hum becomes audible at high volume levels with a better loudspeaker connected..."

Doesn't sound as though there should be a problem near minimum volume, but there's no shortage of plausible possibilities for its cause.

Paul

Hunts smoothing bomb · 2nd Nov 2005, 1:47 pm

Hi all,

Phillip also stated he has hum problems, could this be down to those ECL86's?
I have had trouble with these valves in amplifiers before causing hum, do the anodes produce a just visible red glow in a darkened room? because they shouldn't. I once had an amp that used these tubes and one of them developed an internal short which inturn fried the the EZ81 and took out the mains transformer!

Lee

hotbulb · 2nd Nov 2005, 3:25 pm

I suppose its possible that oneof the ECL86's may have developed a heater/cathode leak, but all the voltages check out fine. I do have another pair of new ones somewhere which may be worth trying.
BTW, if one of the diodes had gone down in the bridge rectifier, would it cause a reduction in the HT voltage?

Regards

Philip

Hunts smoothing bomb · 2nd Nov 2005, 3:57 pm

I could be wrong ( I'm someone will put me right if I am) but I believe if you have a diode gone open circuit on the bridge then you should be expecting roughly half HT voltage not sure what would happen if one diode had gone short though...

Probably cause hum though because of the strong AC content.

Regards Lee

ppppenguin · 2nd Nov 2005, 4:04 pm

Quote:

Originally Posted by Hunts smoothing bomb

I could be wrong ( I'm someone will put me right if I am) but I believe if you have a diode gone open circuit on the bridge then you should be expecting roughly half HT voltage not sure what would happen if one diode had gone short though...

Probably cause hum though because of the strong AC content

An o/c diode will cause slightly reduced voltage but cetainly nothing like as bad as half. The hum will be worse, and 50Hz rather than 100Hz. The mains transformer may also get rather hot.

G0PKH - Pete · 2nd Nov 2005, 4:20 pm

My RV14 does not suffer from any hum whatsoever.

All I notice when the volume is right down is just a very slight "Mechanical" Buzz from the transformer laminations.

I would certainly be interested in the outcome of this.
I think I would be tempted to head straight for the bridge rect myself.

I notice that the rectifier in my set does get rather hot in use, much more than I would expect from a modern unit.

I am very tempted to replace the rectifier in my set just for this reason.
I am thinking about using 4 1N5407's (rather overkill but I have them in stock)and a series resistor mounted neatly on piece of tag board.

I will also be fitting a fuse on the secondary side of the transformer, to prevent any damage, been meaning to do this for some time, ever since I saw the picture of Nick's which had had a nasty burnup.

I really must get round to this soon.

Pete

hotbulb · 2nd Nov 2005, 4:40 pm

I can more or less quantify the hum levels in the RV14 as follows...I also have a Ecko U319 set in room, which gets listened to regularly. This has the standard UCC85, UCH81, UF89, UABC80, UL84, UY85 valve lineup. The hum level on the Hacker is higher than the hum level on the Ecko, which definitely can't be right

Of course I don't have any sand state diodes in stock, so do I order a bridge rectifier or go for Peter's elegant approach and buy some 1N5407's. Actually that would probably be a better idea as the tag board would fill the space vacated by the big contact cooled metal rectifier.
I still they should have used an good old fashiond EZ81 in the Mayflower anyway

Regards

Philip

paulsherwin · 2nd Nov 2005, 4:50 pm

Hi Philip. I would use a bridge rectifier for this since I have them in stock and it makes a neater job with less hassle. They're easy enough to make up with diodes though, and as you don't have any diodes *or* bridges I suggest you buy some diodes as they're more versatile. These should be OK:

http://cgi.ebay.co.uk/Diode-Rectifie...QQcmdZViewItem

These are even cheaper if you need a lot:

http://cgi.ebay.co.uk/200-x-1n4005-M...QQcmdZViewItem

These are 3A rated, though you don't need that for this application:

http://cgi.ebay.co.uk/50-x-1N5408-3A...QQcmdZViewItem

No connection with any of the sellers.

Best regards, Paul

jim_beacon · 2nd Nov 2005, 4:57 pm

Well, I found it!

The hum was 50Hz, which immediatly ruled out HT smoothing.

I tried new ECL86's incase of heater/cathode leakage, and that made no difference.

Then I systematically poked around all the wiring in the audio stages, the outcome being a poorly soldered joint on the volume control (an old repair). After re-soldering this, and carefully re-routing the audio cables away from the mains cables on the switch, all the hum has disappeared.

Jim.

G0PKH - Pete · 2nd Nov 2005, 5:12 pm

Excellent news.

Well done Jim.

Now you can get on with enjoying this wonderful radio.

Pete

mickjjo · 2nd Nov 2005, 5:13 pm

Well Done Jim ! , I was just about to suggest poking around the volume control , since an RV20 I was recently working on had intermittent hum caused by bad earthing due to a loose nut on the control.....

.
The simplest faults take longer to track down.

Regards, Mick.

Hunts smoothing bomb · 2nd Nov 2005, 5:26 pm

Nice one Jim.

There's nothing more satisfying than getting a good old bit of valve kit working properly again

Regards
Lee

Nickthedentist · 2nd Nov 2005, 9:14 pm

Quote:

Originally Posted by jim_beacon

Well, I found it!

Well done, Jim, hope you enjoy what is definitely my favourite radio ever

As Pete said, do fit an HT fuse (just like the RV20 has). My RV14 has obviously had a new rectifier, HT wiring and transformer fitted at some point in its life (mid-70s, judging by the date codes), which might well have been avoided if a fuse had been present

Nick.

hotbulb · 3rd Nov 2005, 9:33 am

[QUOTE=paulsherwin]Hi Philip. I would use a bridge rectifier for this since I have them in stock and it makes a neater job with less hassle. They're easy enough to make up with diodes though, and as you don't have any diodes *or* bridges I suggest you buy some diodes as they're more versatile. These should be OK:

http://cgi.ebay.co.uk/Diode-Rectifie...QQcmdZViewItem

These are even cheaper if you need a lot:

http://cgi.ebay.co.uk/200-x-1n4005-M...QQcmdZViewItem

These are 3A rated, though you don't need that for this application:

http://cgi.ebay.co.uk/50-x-1N5408-3A...QQcmdZViewItem

Thanks for the info. Paul.

I've now bought a lifetimes supply of diodes

When they arrive, and when I get a round tuit, I'll investigate the Hacker throughly, and report back on what the problem is...assuming I can ever find it!

Regards

Philip

1st Nov 2005, 9:07 pm	#1
jim_beacon Retired Dormant Member Join Date: Mar 2003 Location: Bishop's Waltham, Hants, UK. Posts: 939	Hacker RV14 Mayflower hum problems Hi, I've been working on a Mayflower over the last couple of weeks, and have it working nicely, except for one thing - there is a low level of mains hum audible when the set is off tune. The best way to hear it, is to turn the "sensitivity" control to minimum, and it appears, but doesn't seem to be particularly effected by the volume control. Is this normal for one of these? I've changed the main smoothing caps, the ouput stage bypass and coupling caps, and the detector load cap, but everything else is original. I though I had altered the wiring a little, but have checked it, and it made no difference. Any ideas? Thanks Jim.

1st Nov 2005, 9:49 pm	#3
ukcol Rest in Peace Join Date: May 2003 Location: Harlaxton, Lincolnshire, UK. Posts: 3,944	Re: Hacker RV14 Mayflower hum problems Hi Jim I haven’t got an answer for you, just thinking out loud really. There seems to be some confusion in the manual between the numbering of the gain pot in the cct and in the parts list, but if the fault is worse at the minimum setting of the sensitivity control (10k pot in cathode cct of V2?) Then perhaps V2 has a H/K leak. This is consistent with the pot in the minimum gain (maximum resistance) position. The only problem with that thought is that you’d expect the hum to reduce to nothing when the volume is turned down to zero. Is the hum 100Hz (sorry CPS J) or 50Hz? That could indicate whether it is smoothing or perhaps modulation hum. Lastly, is the bridge rectifier OK? (One diode O/C?) Knowing your technical abilities and the fact you have not tracked it down yet, probably means it’s going to be a B.

1st Nov 2005, 9:56 pm	#4
jim_beacon Retired Dormant Member Join Date: Mar 2003 Location: Bishop's Waltham, Hants, UK. Posts: 939	Re: Hacker RV14 Mayflower hum problems Nick, I was afraid of that....... Colin, I haven't really put much effort into it yet The reason for asking is a lack of familiarity with Hacker valve sets - I didn't want to spend hours tracking down a "normal" condition! The original HT smoothing caps were changed as the can had vented, though they still measured OK, I think it was only a matter of time. I think the fault must be in the audio stages, as the volume control has little effect. I'll check the bridge rectifier, and if thats not the culprit, I'll get the scope out and see if I can trace the fault. I suppose I could take the easy way out and turn the volume up...... (but this set is SERIOUSLY LOUD!) Thanks Jim.

2nd Nov 2005, 8:47 am	#5
hotbulb Tetrode Join Date: Apr 2003 Location: Wantage, Oxfordshire, UK. Posts: 93	Re: Hacker RV14 Mayflower hum problems FWIW my RV14 also suffers from a hum problem which I've never managed to track down. It's had the main smoothing electrolytics replaced, plus all the other usual C's and R's, and a new set of valves, except for the ECL86's. It's definitely 50Hz, and it's there all the time , not just when off tune. It doesn't vary with the volume setting, but as Jim says, this a loud radio, and turning up the wick is not...erm...domestically acceptable. Maybe I ought to check the bridge rectifier, must admit I hadn't thought of that one. Neither of my two RV20's hum at all of course...... Regards Philip

2nd Nov 2005, 9:08 am	#6
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: Hacker RV14 Mayflower hum problems Hi Gents, this definitely sounds like a time to get the scope out. I've had similar problems on other chassis and traced it to poor earth connections to the chassis. In one case it had probabply been there since manufacture as the offending earth bolt was sealed down with factory applied varnish. It may be that people expected a certain level of hum in those days. HTH Ed

2nd Nov 2005, 1:47 pm	#8
Hunts smoothing bomb Octode Join Date: Oct 2005 Location: Wimborne, Dorset, UK. Posts: 1,407	Re: Hacker RV14 Mayflower hum problems Hi all, Phillip also stated he has hum problems, could this be down to those ECL86's? I have had trouble with these valves in amplifiers before causing hum, do the anodes produce a just visible red glow in a darkened room? because they shouldn't. I once had an amp that used these tubes and one of them developed an internal short which inturn fried the the EZ81 and took out the mains transformer! Lee

2nd Nov 2005, 3:25 pm	#9
hotbulb Tetrode Join Date: Apr 2003 Location: Wantage, Oxfordshire, UK. Posts: 93	Re: Hacker RV14 Mayflower hum problems I suppose its possible that oneof the ECL86's may have developed a heater/cathode leak, but all the voltages check out fine. I do have another pair of new ones somewhere which may be worth trying. BTW, if one of the diodes had gone down in the bridge rectifier, would it cause a reduction in the HT voltage? Regards Philip

2nd Nov 2005, 3:57 pm	#10
Hunts smoothing bomb Octode Join Date: Oct 2005 Location: Wimborne, Dorset, UK. Posts: 1,407	Re: Hacker RV14 Mayflower hum problems I could be wrong ( I'm someone will put me right if I am) but I believe if you have a diode gone open circuit on the bridge then you should be expecting roughly half HT voltage not sure what would happen if one diode had gone short though... Probably cause hum though because of the strong AC content. Regards Lee

2nd Nov 2005, 4:20 pm	#12
G0PKH - Pete Retired Dormant Member Join Date: Aug 2003 Location: Stansted Essex Posts: 263	Re: Hacker RV14 Mayflower hum problems My RV14 does not suffer from any hum whatsoever. All I notice when the volume is right down is just a very slight "Mechanical" Buzz from the transformer laminations. I would certainly be interested in the outcome of this. I think I would be tempted to head straight for the bridge rect myself. I notice that the rectifier in my set does get rather hot in use, much more than I would expect from a modern unit. I am very tempted to replace the rectifier in my set just for this reason. I am thinking about using 4 1N5407's (rather overkill but I have them in stock)and a series resistor mounted neatly on piece of tag board. I will also be fitting a fuse on the secondary side of the transformer, to prevent any damage, been meaning to do this for some time, ever since I saw the picture of Nick's which had had a nasty burnup. I really must get round to this soon. Pete

2nd Nov 2005, 4:40 pm	#13
hotbulb Tetrode Join Date: Apr 2003 Location: Wantage, Oxfordshire, UK. Posts: 93	Re: Hacker RV14 Mayflower hum problems I can more or less quantify the hum levels in the RV14 as follows...I also have a Ecko U319 set in room, which gets listened to regularly. This has the standard UCC85, UCH81, UF89, UABC80, UL84, UY85 valve lineup. The hum level on the Hacker is higher than the hum level on the Ecko, which definitely can't be right Of course I don't have any sand state diodes in stock, so do I order a bridge rectifier or go for Peter's elegant approach and buy some 1N5407's. Actually that would probably be a better idea as the tag board would fill the space vacated by the big contact cooled metal rectifier. I still they should have used an good old fashiond EZ81 in the Mayflower anyway Regards Philip

2nd Nov 2005, 4:50 pm	#14
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,944	Re: Hacker RV14 Mayflower hum problems Hi Philip. I would use a bridge rectifier for this since I have them in stock and it makes a neater job with less hassle. They're easy enough to make up with diodes though, and as you don't have any diodes or bridges I suggest you buy some diodes as they're more versatile. These should be OK: http://cgi.ebay.co.uk/Diode-Rectifie...QQcmdZViewItem These are even cheaper if you need a lot: http://cgi.ebay.co.uk/200-x-1n4005-M...QQcmdZViewItem These are 3A rated, though you don't need that for this application: http://cgi.ebay.co.uk/50-x-1N5408-3A...QQcmdZViewItem No connection with any of the sellers. Best regards, Paul

2nd Nov 2005, 4:57 pm	#15
jim_beacon Retired Dormant Member Join Date: Mar 2003 Location: Bishop's Waltham, Hants, UK. Posts: 939	Re: Hacker RV14 Mayflower hum problems Well, I found it! The hum was 50Hz, which immediatly ruled out HT smoothing. I tried new ECL86's incase of heater/cathode leakage, and that made no difference. Then I systematically poked around all the wiring in the audio stages, the outcome being a poorly soldered joint on the volume control (an old repair). After re-soldering this, and carefully re-routing the audio cables away from the mains cables on the switch, all the hum has disappeared. Jim.

2nd Nov 2005, 5:12 pm	#16
G0PKH - Pete Retired Dormant Member Join Date: Aug 2003 Location: Stansted Essex Posts: 263	Re: Hacker RV14 Mayflower hum problems Excellent news. Well done Jim. Now you can get on with enjoying this wonderful radio. Pete

2nd Nov 2005, 5:13 pm	#17
mickjjo Rest in Peace Join Date: Jul 2004 Location: Dartford, Kent, UK. Posts: 1,661	Re: Hacker RV14 Mayflower hum problems Well Done Jim ! , I was just about to suggest poking around the volume control , since an RV20 I was recently working on had intermittent hum caused by bad earthing due to a loose nut on the control...... The simplest faults take longer to track down. Regards, Mick.

2nd Nov 2005, 5:26 pm	#18
Hunts smoothing bomb Octode Join Date: Oct 2005 Location: Wimborne, Dorset, UK. Posts: 1,407	Re: Hacker RV14 Mayflower hum problems Nice one Jim. There's nothing more satisfying than getting a good old bit of valve kit working properly again Regards Lee

3rd Nov 2005, 9:33 am	#20
hotbulb Tetrode Join Date: Apr 2003 Location: Wantage, Oxfordshire, UK. Posts: 93	Re: Hacker RV14 Mayflower hum problems [QUOTE=paulsherwin]Hi Philip. I would use a bridge rectifier for this since I have them in stock and it makes a neater job with less hassle. They're easy enough to make up with diodes though, and as you don't have any diodes or bridges I suggest you buy some diodes as they're more versatile. These should be OK: http://cgi.ebay.co.uk/Diode-Rectifie...QQcmdZViewItem These are even cheaper if you need a lot: http://cgi.ebay.co.uk/200-x-1n4005-M...QQcmdZViewItem These are 3A rated, though you don't need that for this application: http://cgi.ebay.co.uk/50-x-1N5408-3A...QQcmdZViewItem Thanks for the info. Paul. I've now bought a lifetimes supply of diodes When they arrive, and when I get a round tuit, I'll investigate the Hacker throughly, and report back on what the problem is...assuming I can ever find it! Regards Philip