Kb 425 - UK Vintage Radio Repair and Restoration Discussion Forum

Glowsindark · 22nd Dec 2011, 1:10 pm

I'm in need of some advice again guys/gals.

When I got this radio I didn't turn it on because some of the wiring looked bad, plus I didn't know what it was like under the chassis.

So I have replaced a few wires, but while the chassis was out I replaced a few resistors as some where way out of tolerance. All caps apart from two mica looking caps had been changed already.

Now for the problem. When it's turned on there is no stations or static.

It's not all bad, some parts are working OK.

When the valves warm up the volume control does change the volume coming from the speaker, you need to put your ear to the speaker to hear it. The tone control also changes the tone. A loud pop comes from the speaker when the band switch is changed. When turning the tuner control it did tune in the power supply of a Apple mac sat next to it.

My dad was the last owner of this radio, he said it worked but didn't work well. He said LW was OK but on MW half of the tuning was dead, no stations or static.

So does this sound like the radio just needs realigning?

PJL · 22nd Dec 2011, 7:00 pm

Hi, are you working off trader 102? You need to measure the valve voltages and compare with the trader but make sure you have a thoroughly clean wavechange switch first.

Glowsindark · 22nd Dec 2011, 8:03 pm

Hi PJL.

Yes Trader sheet 102 is what I have here. Band switch was cleaned with Servisol and a cotton bud when the chassis was out.

I'll check the voltages tonight.

Since I posted I have connected an AVO signal generator up to the antenna socket as in part 2 of the alignment on the trader sheet just to see what would happen. I get a loud tone from the speaker if it helps.

Cobaltblue · 22nd Dec 2011, 8:07 pm

Hi Glows

As I don't know how much experience you have please don't feel offended but have you got an Aerial plugged in?

10 feet or so of wire should get the stronger stations.

Enjoy

Mike T

Tractorfan · 22nd Dec 2011, 8:51 pm

Hi,
Yes, I forgot an aerial once. I was given a Murphy A122 when I was but a kid. Although it seemed to be OK with valves glowing merrily (the ones that the metallising had fallen off anyway), it stubbornly refused to pull in any stations. After a while, the penny dropped and I attached an old length of flex then hung it out of the window (the flex, not the radio

). Et voila! most of the world's languages were suddenly vying for room in my loudspeaker! Aye, 'tis an easy thing to forget.
Cheers, Pete

Glowsindark · 4th Jan 2012, 9:43 pm

Sorry for late reply, been to busy to do any work on the radio.

This radio has a frame aerial but I did try some wire, still no stations

Will post back when I have checked the voltages.

Don't worry about offending me, I don't know much about fault finding. I'm just starting out in the hobby really.

Thanks for the advice so far

Steve_P · 5th Jan 2012, 1:00 am

The service sheet for this set is available on this very site. The cost keeps the forum running...

http://www.service-data.com/product.php/3161/4060

Anyway, if it's doing something when the wavechange switch is turned, then the IF's are doing something and going off what your dad said, it's probably all linked to the first stage, V1 or Frequency Changer V2.

Start by cleaning the wavechange switch fully and make sure the tuning capacitors are not shorting out. Meter on Ohms range, Negative to earth, disconnect L2, L6 and then red on the junction of C4 and C5, then on L2 at the valve end, or on the valve itself, Follow the wiring through. There are trimmers attached to the tuning cap, check these too. Especially if they have been touched...

Check each section and don't forget to put the wires back!

If these are OK, with the radio on and warmed up, use another set to try and pick up the local oscillator. If you tune the faulty set to 200 Metres (About 1.5 Mhz) you should be able to pick up the IF on 218 Metres (1.370 Mhz) on the test set.

(130 kHz IF)

If it's not there, try measuring the volts on V2. You should get HT on the Anode, G5 and 3 (One Pin) and G2. Also the cathode.

If it is, try connecting your Aerial to either side of C5 and see if you get anything. If you do, go to V1 and check for volts on the anode, screen and cathode.

V2 is here: http://www.radiomuseum.org/tubes/tube_15d1.html
V1 is here: http://www.radiomuseum.org/tubes/tube_9d2.html

Voltages are DC and the negative lead of the meter stays on the chassis.

I hope the coils are OK.

Cheers,

Steve P.

22nd Dec 2011, 1:10 pm	#1
Glowsindark Retired Dormant Member Join Date: Aug 2011 Location: Andover Posts: 6	Kb 425 I'm in need of some advice again guys/gals. When I got this radio I didn't turn it on because some of the wiring looked bad, plus I didn't know what it was like under the chassis. So I have replaced a few wires, but while the chassis was out I replaced a few resistors as some where way out of tolerance. All caps apart from two mica looking caps had been changed already. Now for the problem. When it's turned on there is no stations or static. It's not all bad, some parts are working OK. When the valves warm up the volume control does change the volume coming from the speaker, you need to put your ear to the speaker to hear it. The tone control also changes the tone. A loud pop comes from the speaker when the band switch is changed. When turning the tuner control it did tune in the power supply of a Apple mac sat next to it. My dad was the last owner of this radio, he said it worked but didn't work well. He said LW was OK but on MW half of the tuning was dead, no stations or static. So does this sound like the radio just needs realigning?

22nd Dec 2011, 7:00 pm	#2
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: Kb 425 Hi, are you working off trader 102? You need to measure the valve voltages and compare with the trader but make sure you have a thoroughly clean wavechange switch first.

22nd Dec 2011, 8:03 pm	#3
Glowsindark Retired Dormant Member Join Date: Aug 2011 Location: Andover Posts: 6	Re: Kb 425 Hi PJL. Yes Trader sheet 102 is what I have here. Band switch was cleaned with Servisol and a cotton bud when the chassis was out. I'll check the voltages tonight. Since I posted I have connected an AVO signal generator up to the antenna socket as in part 2 of the alignment on the trader sheet just to see what would happen. I get a loud tone from the speaker if it helps.

22nd Dec 2011, 8:07 pm	#4
Cobaltblue Moderator Join Date: Dec 2010 Location: Exeter, Devon and Poole, Dorset UK. Posts: 6,878	Re: Kb 425 Hi Glows As I don't know how much experience you have please don't feel offended but have you got an Aerial plugged in? 10 feet or so of wire should get the stronger stations. Enjoy Mike T __________________ Invisible airwaves crackle with life or at least they used to Mike T BVWS member. www.cossor.co.uk

22nd Dec 2011, 8:51 pm	#5
Tractorfan Dekatron Join Date: Mar 2008 Location: St. Frajou, l'Isle en Dodon, Haute Garonne, France.(Previously: Ellesmere Port, Cheshire, UK.) Posts: 3,184	Re: Kb 425 Hi, Yes, I forgot an aerial once. I was given a Murphy A122 when I was but a kid. Although it seemed to be OK with valves glowing merrily (the ones that the metallising had fallen off anyway), it stubbornly refused to pull in any stations. After a while, the penny dropped and I attached an old length of flex then hung it out of the window (the flex, not the radio). Et voila! most of the world's languages were suddenly vying for room in my loudspeaker! Aye, 'tis an easy thing to forget. Cheers, Pete __________________ "Hello?, Yes, I'm on the train, I might lose the signal soon as we're just going into a tunn..."

4th Jan 2012, 9:43 pm	#6
Glowsindark Retired Dormant Member Join Date: Aug 2011 Location: Andover Posts: 6	Re: Kb 425 Sorry for late reply, been to busy to do any work on the radio. This radio has a frame aerial but I did try some wire, still no stations Will post back when I have checked the voltages. Don't worry about offending me, I don't know much about fault finding. I'm just starting out in the hobby really. Thanks for the advice so far

5th Jan 2012, 1:00 am	#7
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Kb 425 The service sheet for this set is available on this very site. The cost keeps the forum running... http://www.service-data.com/product.php/3161/4060 Anyway, if it's doing something when the wavechange switch is turned, then the IF's are doing something and going off what your dad said, it's probably all linked to the first stage, V1 or Frequency Changer V2. Start by cleaning the wavechange switch fully and make sure the tuning capacitors are not shorting out. Meter on Ohms range, Negative to earth, disconnect L2, L6 and then red on the junction of C4 and C5, then on L2 at the valve end, or on the valve itself, Follow the wiring through. There are trimmers attached to the tuning cap, check these too. Especially if they have been touched... Check each section and don't forget to put the wires back! If these are OK, with the radio on and warmed up, use another set to try and pick up the local oscillator. If you tune the faulty set to 200 Metres (About 1.5 Mhz) you should be able to pick up the IF on 218 Metres (1.370 Mhz) on the test set. (130 kHz IF) If it's not there, try measuring the volts on V2. You should get HT on the Anode, G5 and 3 (One Pin) and G2. Also the cathode. If it is, try connecting your Aerial to either side of C5 and see if you get anything. If you do, go to V1 and check for volts on the anode, screen and cathode. V2 is here: http://www.radiomuseum.org/tubes/tube_15d1.html V1 is here: http://www.radiomuseum.org/tubes/tube_9d2.html Voltages are DC and the negative lead of the meter stays on the chassis. I hope the coils are OK. 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...? Last edited by Steve_P; 5th Jan 2012 at 1:14 am.