HMV 1125 trouble - UK Vintage Radio Repair and Restoration Discussion Forum

SGT.Pepper · 28th Dec 2008, 11:40 pm

Hi all, it's me again...
When I tune this radio all the way to the left there's loud radio static, and when I tune it to the right, it gets gradually quieter. Sometimes I can pick up stations, but they aren't very loud. Putting my soldering iron on the earth terminal doesn't make much difference. Also, the radio makes no noise whatsoever until I plug something into the aerial socket. I've already replaced the speaker transformer, but it is by no means an exact replacement. There is a 12K resistor in there that measures nothing, but when replaced with a close enough replacement it makes no difference.

Any ideas on how to get this one working?

Steve_P · 29th Dec 2008, 12:19 am

I tend to think about the L.O. if the IF is OK. IF is 470 kHz.

Clean the wavechange switch.

I would first try the voltage to V1 - X78. Then I would go for C8, C9, C6 and R22.

ERT sheet covers this, available up top.

Cheers,

Steve P.

yestertech · 29th Dec 2008, 3:47 pm

sounds like the HT volts could be low - Have you checked all the voltages as per service sheet ?
As Steve has mentioned, the oscillator section of the frequency changer looks to be failing. If the voltages are OK ,or more importantly if they are high, then the X78 could be tired.

As to the 12K, it would appear to be part of the potential divider supplying volts to g2,g4 of the X78 and as such may make only a small difference. You should see around 88 volts on the non earthed end of this component - much less would point to the source of the trouble relating to either the HT volts or other resisitor(s).
More troubleshooting needed methinks !

Andy

Top Cap · 29th Dec 2008, 4:48 pm

Check the vanes of the tuning gang are not giving partial shorts down at the crackly end of the tuning scale. Does the crackling appear at the end of the scale where the vanes get more meshed?
Les

SGT.Pepper · 29th Dec 2008, 9:11 pm

Well, actually I've just found out that the increased amount of static down one end of the scale is due to mains interference from somewhere. Another radio of mine in full working order is having the same problem. It's just that on the 1125 the stations are quiet and faint, and the radio can't isolate them from the static. Hope that makes sense...

Steve_P · 29th Dec 2008, 9:16 pm

Yes, it does. Makes things a bit easier, perhaps. If the IF is OK, try a large aerial. or C10.

What's causing the Interference?

Cheers,

Steve P.

SGT.Pepper · 30th Dec 2008, 11:27 am

Unfortunately I don't know what's causing the interference, as the set is in a block of flats and it seems to be coming from one of the rooms above or below me. I've tried the best aerial I've got and it still isn't working, and also I've found that the gram input is really quiet, too. I've got to go to Maplin's sometime today anyway, so do you think that changing all the caps in it would get it working?

Steve_P · 30th Dec 2008, 2:34 pm

Measure a few voltages and lets see what they are.

HT on the anode of the output valve (Pin 5), HT on the screen grid (Pin 7), volts on the cathode (Pins 2 and 6). Output valve is V4, N78.

HT on the Cathode of V5 - Pin 7 and on the pins of the smoothing block.

Replace C21 if you haven't done already.

Cheers,

Steve P.

Boom · 30th Dec 2008, 2:58 pm

Quote:

Originally Posted by SGT.Pepper

Unfortunately I don't know what's causing the interference, as the set is in a block of flats and it seems to be coming from one of the rooms above or below me.

Oh dear. I traced the same interference symptoms that you mention to a router here. Luckily it was my own router so I was able to do something to cure it (bought another make) but if that is what it is and it is coming from a router in another flat you might be out of luck.

If you get on with the other occupants it might well be worth asking them to switch their routers off for 2 minutes to narrow it down.

28th Dec 2008, 11:40 pm	#1
SGT.Pepper Retired Dormant Member Join Date: May 2008 Location: Bath, Somerset, UK. Posts: 37	HMV 1125 trouble Hi all, it's me again... When I tune this radio all the way to the left there's loud radio static, and when I tune it to the right, it gets gradually quieter. Sometimes I can pick up stations, but they aren't very loud. Putting my soldering iron on the earth terminal doesn't make much difference. Also, the radio makes no noise whatsoever until I plug something into the aerial socket. I've already replaced the speaker transformer, but it is by no means an exact replacement. There is a 12K resistor in there that measures nothing, but when replaced with a close enough replacement it makes no difference. Any ideas on how to get this one working?

29th Dec 2008, 12:19 am	#2
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: HMV 1125 trouble I tend to think about the L.O. if the IF is OK. IF is 470 kHz. Clean the wavechange switch. I would first try the voltage to V1 - X78. Then I would go for C8, C9, C6 and R22. ERT sheet covers this, available up top. 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...?

29th Dec 2008, 3:47 pm	#3
yestertech Nonode Join Date: Dec 2002 Location: Coulsdon, Surrey, UK. Posts: 2,135	Re: HMV 1125 trouble sounds like the HT volts could be low - Have you checked all the voltages as per service sheet ? As Steve has mentioned, the oscillator section of the frequency changer looks to be failing. If the voltages are OK ,or more importantly if they are high, then the X78 could be tired. As to the 12K, it would appear to be part of the potential divider supplying volts to g2,g4 of the X78 and as such may make only a small difference. You should see around 88 volts on the non earthed end of this component - much less would point to the source of the trouble relating to either the HT volts or other resisitor(s). More troubleshooting needed methinks ! Andy

29th Dec 2008, 4:48 pm	#4
Top Cap Octode Join Date: Mar 2006 Location: Watford, Hertfordshire, UK. Posts: 1,270	Re: HMV 1125 trouble Check the vanes of the tuning gang are not giving partial shorts down at the crackly end of the tuning scale. Does the crackling appear at the end of the scale where the vanes get more meshed? Les __________________ Whether the Top Cap is Grid or Anode - touching it will give you a buzz either way!

29th Dec 2008, 9:11 pm	#5
SGT.Pepper Retired Dormant Member Join Date: May 2008 Location: Bath, Somerset, UK. Posts: 37	Re: HMV 1125 trouble Well, actually I've just found out that the increased amount of static down one end of the scale is due to mains interference from somewhere. Another radio of mine in full working order is having the same problem. It's just that on the 1125 the stations are quiet and faint, and the radio can't isolate them from the static. Hope that makes sense...

29th Dec 2008, 9:16 pm	#6
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: HMV 1125 trouble Yes, it does. Makes things a bit easier, perhaps. If the IF is OK, try a large aerial. or C10. What's causing the Interference? 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...?

30th Dec 2008, 11:27 am	#7
SGT.Pepper Retired Dormant Member Join Date: May 2008 Location: Bath, Somerset, UK. Posts: 37	Re: HMV 1125 trouble Unfortunately I don't know what's causing the interference, as the set is in a block of flats and it seems to be coming from one of the rooms above or below me. I've tried the best aerial I've got and it still isn't working, and also I've found that the gram input is really quiet, too. I've got to go to Maplin's sometime today anyway, so do you think that changing all the caps in it would get it working?

30th Dec 2008, 2:34 pm	#8
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: HMV 1125 trouble Measure a few voltages and lets see what they are. HT on the anode of the output valve (Pin 5), HT on the screen grid (Pin 7), volts on the cathode (Pins 2 and 6). Output valve is V4, N78. HT on the Cathode of V5 - Pin 7 and on the pins of the smoothing block. Replace C21 if you haven't done already. 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...?