Pye washboard set (VT4) no picture - UK Vintage Radio Repair and Restoration Discussion Forum

retroaudio · 3rd Aug 2006, 8:39 pm

Hi,

I would appreciate some help from forum members with this as I don't have a circuit diagram and even if I did it might not direct me to the problem given my limited technical knowledge.
It was working fine until last night. It's the version of the washboard set with the tuner on the side and the rectangular CRT.

I was watching a film when the image went leaving audio only. When I took the back off it had blown the topmost 250 mA fuse. and there was a smell of burning coming from the metal box where the lopty is. When I looked at it properly it would appear that there are two coils on a metal former which sits behind the lopty assembly on the rear edge of the chassis. They control linearity and amplitude.

Three wires go into the linearity one and the red one had the insulation blown out the side of it. I have carefully opened the black rubberised jacket that covers the coil and the three wires that go into it have the last few millimetres turned over tinned and the fine wire of the coil soldered into them.

The coil appears to be intact, the coil has original been bound with a clear/amber tape or lacquer to hold the three wires to the side of the coil and presumable stop them moving around, the amber coloured coating has decomposed.

1) Is the fault which has occurred in the set likely to have occurred elsewhere in the circuitry and is this red wire with the insulation burned out merely a symptom of another problem ?

2) If the coil is intact and its feasible to replace the red wire which goes from the coil to the top cap of PY81 what would be a suitable medium to wrap round the coil when putting it back ?

thanks in anticipation

Alex

Brian R Pateman · 3rd Aug 2006, 11:19 pm

Hi Alex,

I have an original manual for the V4 (Issue 2 - April 1953) and I could let you have a photocopy if you like. I can't scan it as I don't have a working scanner!

PM me if you are interested.

Regards,

Ghostuser · 4th Aug 2006, 5:25 pm

Hi Alex,
The circuit diagram of the V4 shows that the HT supply to the line O/P valve goes through the 250mA fuse through the booster diode and through the linearity coil before going through the LOPT primary to the Line O/P anode. The fuse should have protected the circuit, but maybe the fuse had been replaced with one with a higher rating? You need to discover whether the linearity control wiring itself was the cause of a short or whether grossly excessive current was being taken by the line O/P valve. The latter case can arise when the line oscillator fails. If the line oscillator is running OK, there should be a negative voltage of maybe 15 to 30 volts on the grid of the line O/P valve. Also, check for continuity of the LOPT primary coil, which may have suffered.
I have a thread on the V4 currently running. The V4 is a Band 1 set whereas the VT4 has a turret tuner for Bands 1 and 3. Otherwise they are similar.
Cheers
Nigel

3rd Aug 2006, 8:39 pm	#1
retroaudio Pentode Join Date: Mar 2005 Location: Cairneyhill, Fife, UK. Posts: 135	Pye washboard set (VT4) no picture Hi, I would appreciate some help from forum members with this as I don't have a circuit diagram and even if I did it might not direct me to the problem given my limited technical knowledge. It was working fine until last night. It's the version of the washboard set with the tuner on the side and the rectangular CRT. I was watching a film when the image went leaving audio only. When I took the back off it had blown the topmost 250 mA fuse. and there was a smell of burning coming from the metal box where the lopty is. When I looked at it properly it would appear that there are two coils on a metal former which sits behind the lopty assembly on the rear edge of the chassis. They control linearity and amplitude. Three wires go into the linearity one and the red one had the insulation blown out the side of it. I have carefully opened the black rubberised jacket that covers the coil and the three wires that go into it have the last few millimetres turned over tinned and the fine wire of the coil soldered into them. The coil appears to be intact, the coil has original been bound with a clear/amber tape or lacquer to hold the three wires to the side of the coil and presumable stop them moving around, the amber coloured coating has decomposed. 1) Is the fault which has occurred in the set likely to have occurred elsewhere in the circuitry and is this red wire with the insulation burned out merely a symptom of another problem ? 2) If the coil is intact and its feasible to replace the red wire which goes from the coil to the top cap of PY81 what would be a suitable medium to wrap round the coil when putting it back ? thanks in anticipation Alex Last edited by Mike Phelan; 24th Aug 2007 at 10:56 am.

3rd Aug 2006, 11:19 pm	#2
Brian R Pateman Nonode Join Date: Jun 2005 Location: Western Lake District, Cumbria (CA20) - UK Posts: 2,136	Re: pye washboard set Hi Alex, I have an original manual for the V4 (Issue 2 - April 1953) and I could let you have a photocopy if you like. I can't scan it as I don't have a working scanner! PM me if you are interested. Regards, __________________ Brian

4th Aug 2006, 5:25 pm	#3
Ghostuser Pentode Join Date: Oct 2003 Location: Alton, Hampshire, UK. Posts: 137	Re: pye washboard set Hi Alex, The circuit diagram of the V4 shows that the HT supply to the line O/P valve goes through the 250mA fuse through the booster diode and through the linearity coil before going through the LOPT primary to the Line O/P anode. The fuse should have protected the circuit, but maybe the fuse had been replaced with one with a higher rating? You need to discover whether the linearity control wiring itself was the cause of a short or whether grossly excessive current was being taken by the line O/P valve. The latter case can arise when the line oscillator fails. If the line oscillator is running OK, there should be a negative voltage of maybe 15 to 30 volts on the grid of the line O/P valve. Also, check for continuity of the LOPT primary coil, which may have suffered. I have a thread on the V4 currently running. The V4 is a Band 1 set whereas the VT4 has a turret tuner for Bands 1 and 3. Otherwise they are similar. Cheers Nigel