Baird 664 Dual Standard Monochrome TV - UK Vintage Radio Repair and Restoration Discussion Forum

molochkartovski · 1st Oct 2006, 4:57 pm

I bought this some time ago.
Today I've resurrected it, or tried to. Can anyone tell me any known faults of this set? It's on page 228 of 69/70 radio and TV Servicing - Baird 660 chassis all valve IF.
Although everything's date stamped 1966!

it is basically working!
I can get a picture on 405; very good picture in fact but no sound.
On 625 I can't get a picture or sound. There is power at the UHF tuner and everything seems to be connected correctly.
The AF amplifier's working; I can get a good loud buzz out of it by touching the grid of the triode and further back at the system switch on 405 or 625.
I've given the system switch a good clean, which has made it switch over more smoothly but still no sound!
I've replaced the EF80 and EF183 Sound IF valves; still nothing.
Replaced a couple of dodgy looking Hunts caps - the rest are Mullard "mustards".

Anyone got any suggestions where to look next ?

Thanks
Richard

dazzlevision · 2nd Oct 2006, 9:01 am

Hello,

The 405 sound detector diode could be u/s, but as you are getting neither sound nor vision signals on UHF, it might be the (common to both 405 & 625) sound IF amplifier itself (625 sound uses a separate ratio detector - with two diodes).

On 625, if you turn up the volume and connect a test lead to the video amplifier's control grid, you should hear some short wave radio signal breakthrough - if the 625 6MHZ intercarrier sound take-off and sound IF stages are working correctly.

Is the UHF tuner valve (PC86 & PC88) or transistor? If it's a valve type, you'll almost certainly need to replace them both to get reasonable UHF sensitivity. If it's a transistor type, the LT supply could be missing - typically 12-20Vdc.

Note that, on UHF, the UHF tuner's IF output passes through the VHF tuner's mixer stage, for additional IF gain. It might be worth cleaning the VHF tuner's turret coil contacts and the fixed leaf spring that make contact with them. I have found that, on the longer UHF coild "biscuit" - if fitted, the extra studs don't reach the springs, so a little gentle bending might be required.

Regards,

Dazzlevision

molochkartovski · 2nd Oct 2006, 6:16 pm

Hi Dazzlevision

I did wonder about the detector diode myself, but as you say UHF being FM has a different arrangement anyway.

It could be 2 different faults I suppose?
The UHF tuner is transistorised and it has a 12V supply to it. There is no biscuit in the turret tuner for UHF I assumed this was normal although now you come to mention it the channel 6 biscuit is missing too so it could be "someone" has taken it out!
It certainly works on channels 1 & 9 - (vision anyway). I'll have a poke about with the signal generator this evening if I get time and see if that sheds any light.

Thanks
Richard

dazzlevision · 2nd Oct 2006, 6:22 pm

Hello again,

Looking at my Baird service manual for these sets, I now see that the UHF tuner IF output is injected into the VHF tuner mixed control grid by way of a bridge arrangement, rendering a special UHF coil biscuit unnecessary.

The 6MHz intercarrier sound signal is taken off to the sound IF stages via C116, a 3.3pF capacitor in the vision detector stage, en route to the video amplifier. According to the circuit, there is a 9" run of "coax" linking the video detector and sound If input stage on 625.

I'd certainly see if you can get any signals into the VHF tuner (on 625), from the UHF tuner's IF connection to it
Good luck,

Dazzlevision

1st Oct 2006, 4:57 pm	#1
molochkartovski Tetrode Join Date: Jun 2005 Location: Wilton, Salisbury, Wiltshire, UK. Posts: 66	Baird 664 Dual Standard Monochrome TV I bought this some time ago. Today I've resurrected it, or tried to. Can anyone tell me any known faults of this set? It's on page 228 of 69/70 radio and TV Servicing - Baird 660 chassis all valve IF. Although everything's date stamped 1966! it is basically working! I can get a picture on 405; very good picture in fact but no sound. On 625 I can't get a picture or sound. There is power at the UHF tuner and everything seems to be connected correctly. The AF amplifier's working; I can get a good loud buzz out of it by touching the grid of the triode and further back at the system switch on 405 or 625. I've given the system switch a good clean, which has made it switch over more smoothly but still no sound! I've replaced the EF80 and EF183 Sound IF valves; still nothing. Replaced a couple of dodgy looking Hunts caps - the rest are Mullard "mustards". Anyone got any suggestions where to look next ? Thanks Richard

2nd Oct 2006, 9:01 am	#2
dazzlevision Dekatron Join Date: Sep 2003 Location: Near Swindon, North Wiltshire, UK. Posts: 3,622	Re: Baird 664 Dual Standard Monocrome TV Hello, The 405 sound detector diode could be u/s, but as you are getting neither sound nor vision signals on UHF, it might be the (common to both 405 & 625) sound IF amplifier itself (625 sound uses a separate ratio detector - with two diodes). On 625, if you turn up the volume and connect a test lead to the video amplifier's control grid, you should hear some short wave radio signal breakthrough - if the 625 6MHZ intercarrier sound take-off and sound IF stages are working correctly. Is the UHF tuner valve (PC86 & PC88) or transistor? If it's a valve type, you'll almost certainly need to replace them both to get reasonable UHF sensitivity. If it's a transistor type, the LT supply could be missing - typically 12-20Vdc. Note that, on UHF, the UHF tuner's IF output passes through the VHF tuner's mixer stage, for additional IF gain. It might be worth cleaning the VHF tuner's turret coil contacts and the fixed leaf spring that make contact with them. I have found that, on the longer UHF coild "biscuit" - if fitted, the extra studs don't reach the springs, so a little gentle bending might be required. Regards, Dazzlevision

2nd Oct 2006, 6:16 pm	#3
molochkartovski Tetrode Join Date: Jun 2005 Location: Wilton, Salisbury, Wiltshire, UK. Posts: 66	Re: Baird 664 Dual Standard Monocrome TV Hi Dazzlevision I did wonder about the detector diode myself, but as you say UHF being FM has a different arrangement anyway. It could be 2 different faults I suppose? The UHF tuner is transistorised and it has a 12V supply to it. There is no biscuit in the turret tuner for UHF I assumed this was normal although now you come to mention it the channel 6 biscuit is missing too so it could be "someone" has taken it out! It certainly works on channels 1 & 9 - (vision anyway). I'll have a poke about with the signal generator this evening if I get time and see if that sheds any light. Thanks Richard

2nd Oct 2006, 6:22 pm	#4
dazzlevision Dekatron Join Date: Sep 2003 Location: Near Swindon, North Wiltshire, UK. Posts: 3,622	Re: Baird 664 Dual Standard Monocrome TV Hello again, Looking at my Baird service manual for these sets, I now see that the UHF tuner IF output is injected into the VHF tuner mixed control grid by way of a bridge arrangement, rendering a special UHF coil biscuit unnecessary. The 6MHz intercarrier sound signal is taken off to the sound IF stages via C116, a 3.3pF capacitor in the vision detector stage, en route to the video amplifier. According to the circuit, there is a 9" run of "coax" linking the video detector and sound If input stage on 625. I'd certainly see if you can get any signals into the VHF tuner (on 625), from the UHF tuner's IF connection to it Good luck, Dazzlevision