UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Radio (domestic)

Notices

Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

Closed Thread
 
Thread Tools
Old 12th May 2006, 8:44 am   #1
David G4EBT
Dekatron
 
David G4EBT's Avatar
 
Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 3,588
Default Ekco A22 - Hum at various points on dial. Huh?

Hi all,

I've just finished renovating an Ekco A22 which was in a very sorry state.

Most of what I've had to do has been to replace perished wiring, and I've routinely replaced all the paper caps with new polypropylene ones.

I've replaced a few of the resistors which had gone high, but left in place the ones which measured OK. I haven't replaced any of the mica caps in the RF or IF stages, (they check out OK anyway) and the cores of the IFTs and RF coils are sealed with wax, and seem not to have been disturbed at any time (nor the trimmers).

Using about 20 ft of wire strung round the workshop for an aerial, the set pulls in several stations on medium and short waves, but on some stations there's a background heterodyne.

Also, at various points on the dial, there's a strong hum as though there should be a station heard, but no signals are there. Otherwise, when not tuned to a station, there's very little background hum, even with the volume turned up high.

When local stations (and distant ones on short waves) are tuned in, the set is very sweet, with no distortion.

On long waves, there only the occasional loud hum at various points on the dial, but then I don't think there's much on long waves anyway (except R4).

Any thoughts on the hum at various points, and what I might do to improve matters? I'm reluctant to start fiddling with the alignment if the symptoms I've describe point to other problems, (EG: AGC?), albeit as a first step, I should of course check the alignment.

I've given the wavechange switch a shot of servisol.

(By the way, the valves are all new/old stock, just supplied. All the voltages seem OK).

Very easy set to work on - most of the components are on a tagstrip around the outside of the rim of the circular chassis. Some nice design features too, such as the dial light travelling around the circular dial in keeping with the tuning.

Many thanks in advance for any thoughts.

David.
G4EBT
David G4EBT is offline  
Old 12th May 2006, 9:04 am   #2
BassoonBloke
Pentode
 
BassoonBloke's Avatar
 
Join Date: Feb 2006
Location: East London, UK.
Posts: 221
Question Re: Ekco A22 - Hum at various points on dial. Huh?

Hello David,

As you seem to have done everything right and there's no reason for the hum to come from your set i wonder if you have strip lighting in your workshop. I have come across strip lighting fittings that emit RF at certain frequencies and maybe your large piece of wire as an aerial is picking this up?
Try turning all your lighting off and see if it still happens.

All the best,
Alan.
BassoonBloke is offline  
Old 12th May 2006, 12:15 pm   #3
Ed_Dinning
Dekatron
 
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 5,454
Default Re: Ekco A22 - Hum at various points on dial. Huh?

Hi David, it could be modulation hum. Try adding additional 0.1uF caps on the HT rail to improve the decoupling at HF. Older e-caps can have quite high impedance at RF.
You should also add an X rated cap across the mains input.

HTH Ed
Ed_Dinning is offline  
Old 12th May 2006, 2:40 pm   #4
Sideband
Dekatron
 
Sideband's Avatar
 
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
Posts: 5,281
Default Re: Ekco A22 - Hum at various points on dial. Huh?

Quote:
Originally Posted by G4EBT
Using about 20 ft of wire strung round the workshop for an aerial, the set pulls in several stations on medium and short waves, but on some stations there's a background heterodyne.

Ok to everything said previously. The heterodynes however, could be caused by second-channel interference. This may point to badly aligned aerial trimmers or O/C caps in the aerial circuit. I don't have info on the I F frequency to hand but if it has a low I F (120khz or so) there is probably an I F filter which may need a tweak, but check general alignment first.


Rich.
__________________
On Spike Milligan's headstone......I told you I was ill...
Sideband is offline  
Old 13th May 2006, 4:57 pm   #5
PaulR
Octode
 
PaulR's Avatar
 
Join Date: Oct 2003
Location: Southport Lancashire, UK.
Posts: 1,963
Default Re: Ekco A22 - Hum at various points on dial. Huh?

David - have you tried switching your computer off at the mains? It sounds very similar to interference I get on AM sets when one of the several PCs in the house is switched on. I think it is caused partly by a poor quality, badly shielded hard drive and by the power supply. It is better when the computer is switched off but only completely disappears when the mains switch at the socket is off.

My son is a computer buff and has built himself a computer from good quality, expensive components and I get no interference from that, but my daughter and I have off-the-shelf PCs bought from a local dealer and they both cause interference of varying amounts.

Hope that helps

Regards

Paul
PaulR is offline  
Old 17th May 2006, 4:55 pm   #6
David G4EBT
Dekatron
 
David G4EBT's Avatar
 
Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 3,588
Default Re: Ekco A22 - Hum at various points on dial. Huh?

Hi guys,

Thanks for all the advice and encouragement, on which I'd comment as follows:

As to the PC, mine's situated in the house about 15 yards from the workshop, so it never occured to me that it could cause hash. However, it does indeed, so it must be coming down the mains rather than radiating RF. Much better when switched off.

As to the flourescent light, yes, I have two twin tubes, but it only makes a slight difference whether they're on or off. I also have a circular flourescent magnifying lamp which plays havoc!

I've replaced a decoupling cap which had gone OC, fitted an additional 0.1uF to improve the HT decoupling and aligned the set. This has much improved things on Medium and Short waves. The whisltles have disappeared.

However, despite crawling all over the front end switchery, coil continuity, caps trimmers etc, I can't pull in any long-wave stations, albeit I can peak up the coils with a sig genny. (EG, on 1500M). All I get without the genny one is a loud hum where the stations should be.

Something obscure going on, but I'm going to quit while I'm winning -the alternative would be to pull out the front-end coil and switch unit to have a better poke around for any shorts, which is a step too far when there's not much on Long wave anyway.

(BTW, I'm impressed with the short wave performance - very lively!)

(Not sure if I mentioned it before, but I'd bought a new old stock EBL31 which turned out to have a diode to screen short. When replaced with another, the set burst into life big style!).

So thanks once more for the help fellas - much appreciated.

David
G4EBT
David G4EBT is offline  
Old 18th May 2006, 10:29 am   #7
Sideband
Dekatron
 
Sideband's Avatar
 
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
Posts: 5,281
Default Re: Ekco A22 - Hum at various points on dial. Huh?

Quote:
Originally Posted by G4EBT
As to the PC, mine's situated in the house about 15 yards from the workshop, so it never occured to me that it could cause hash. However, it does indeed, so it must be coming down the mains rather than radiating RF. Much better when switched off.

As to the flourescent light, yes, I have two twin tubes, but it only makes a slight difference whether they're on or off. I also have a circular flourescent magnifying lamp which plays havoc!
This has been discussed on these forums before. It can apply to anything with a switched mode power supply. I once had a (Canon) printer that sent loads of mush up the mains...took me ages to isolate the strange pulsing noise and I only noticed it changing frequency when someone else was using the printer.

As to flourecent lights...these also. Some low energy lamps are dreadful. You need to experiment with these. Good branded ones are usually OK but some budget types are very bad.



Rich.
__________________
On Spike Milligan's headstone......I told you I was ill...
Sideband is offline  
Old 19th May 2006, 12:17 pm   #8
Jim - G4MEZ
Tetrode
 
Jim - G4MEZ's Avatar
 
Join Date: Feb 2006
Location: Newport Pagnell, Buckinghamshire, UK.
Posts: 85
Default Re: Ekco A22 - Hum at various points on dial. Huh?

Quote:
Originally Posted by Richard_Newman
Good branded ones are usually OK but some budget types are very bad.



Rich.
Huh... My Hewlett Packard Colour LaserJet 4550 radiates in the 2M Band. It almost needs its own transmitting licence...
__________________
Jim

G4MEZ
Jim - G4MEZ is offline  
Old 23rd May 2006, 8:12 am   #9
Ghostuser
Pentode
 
Join Date: Oct 2003
Location: Cheltenham, Gloucestershire, UK.
Posts: 133
Default Re: Ekco A22 - Hum at various points on dial. Huh?

Another major source of hum and interference in my home is a Pioneer plasma screen. It completely wipes out medium wave radio.
Nigel
Ghostuser is offline  
Old 23rd May 2006, 9:21 am   #10
David G4EBT
Dekatron
 
David G4EBT's Avatar
 
Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 3,588
Default Re: Ekco A22 - Hum at various points on dial. Huh?

I've come to the conclusion that the local oscillator stops working on long wave. Why, I don't know. I've checked out all the coils and switchery for continuity, and the associated Rs and Cs.

All seems to be OK, but clearly something isn't, and logic would point to it being soemething such as a duff switch contact. It isn't a major job to remove the whole front end coil unit and band switchery on this set - just unsolder a few wires and it comes out in one chunk for close exmination, switch cleaning etc.

However, as the set is so lively on MW and SW and there's not much on LW anyway, I'm going to leave it as it is. It was in a poor state when I started fettling it up - all the rubber wiring had perished and was bare in places, a replacement transformer was dangling on two screws supported on car wheel nuts for spacers.

Several wires had just been tacked on with dry joints ready to drop off.

The volume control/mains switch was duff and needed replacing.

The dial was cracked and speaker fabric torn - I've replaced both (dial from Clive Mason).

The dial cord needed replacing.

I've replaced all the waxies, but only a few of the Rs had changed in value.

Judging by the pics, many Ekcos have non-original mains and output trannies, so I suppose they're a weakness. One presently on offer has nasty score marks around the perimeter of the dial where the travelling cursor has rubbed it. It's such a focal point that it really mars the appearance and will need replacing to look anything like.

If I could find another A22 at a sensible price in a poor state, so long as the cabinet, knobs and back were intact, I'd gladly have another go at one - a total strip down, chassis de-rust and spray etc.

Sad, isn't it. Maybe I need to get out more?

David.

Last edited by Darren-UK; 20th Apr 2008 at 8:20 pm. Reason: To comply with forum rules.
David G4EBT is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 2:36 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Copyright ©2002 - 2019, Paul Stenning.