Removing a Cyldon turret tuner conversion, or not? - UK Vintage Radio Repair and Restoration Discussion Forum

Ghostuser · 11th Sep 2006, 9:33 pm

I have a Decca 1000 which has been converted to 13 channels by adding a turret tuner. The conversion plugs into the RF and Mixer/oscillator valve sockets and I assume that it steals HT and heater supplies and routes its output to the first IF transformer.
I have the circuit diagrams for both the double sideband (Alexanrda Palace) and vestigial sideband (all others) versions of the receiver. My RF chassis and input attenuator are coded black which means it was an Alexandra Palace set. Circuit tracing however shows the vision IF amp to be a vestigial sideband circuit whereas the RF and Mixer/oscillator circuits are a mixture of the two published versions. I am assuming that later Alexandra Palace sets used vestigial sideband receivers, which would have had more gain than the double sideband sets, worked fine on double sideband and anyway, why bother making two versions if one would do? My other guess is that the circuit evolved during production.
It looks as if I can simply pull out the turret tuner plugs from the valveholders, substitute the missing valves and get back to a single channel, unless anyone knows better. After all, who needs more than one channel now, given Auroras as standards converters?
The only snag I can think of is that the IF may have had to be trimmed to match the IF from the turret tuner. Has anybody any experience of these sorts of mods and are there traps for the unwary?
Cheers
Nigel

Heatercathodeshort · 12th Sep 2006, 9:17 am

Hello Nigel,
It sounds as if your DECCA 1000 was converted to band 3 using a CYLDON tuner. These usually had a small panel containing the aerial sockets and twin RF gain controls for band 1/3. Conversion was simple by removing the RF valve and inserting the 'power' plug from the tuner. In a similar way the mixer valve was removed and the i.f. plug inserted in its place. That was all that was usually required and it was a good conversion. In weak signal areas the I.F. plug was removed and wired direct to the mixer valve which then acted as an additional i.f. amplifier. The local oscillator coil was disconnected in this case. Simply reinstating the valves should return the set to band 1 operation but some front end tuning may be required. Do not touch the i.f. alignment Regards John.

Ghostuser · 14th Sep 2006, 8:55 am

Dear John,
That is just the information that I wanted and I will take your advice about leaving the IF alignment alone. I will probably leave the tuner in place, otherwise I will have a hole to fill in the side of the cabinet. That way I will be able to run either single channel or 13 channel according to my whims! Thanks very much for you help.
Regards
Nigel

Heatercathodeshort · 14th Sep 2006, 7:56 pm

Hello again Nigel,
I think you have made the right decision. After all conversion was all part of televison history. Regards John.

stephanie · 14th Sep 2006, 8:11 pm

Yeah. Best to leave it in place. Probably makes for easier use of the set anyway (tune to best channel for picture and sound).

11th Sep 2006, 9:33 pm	#1
Ghostuser Pentode Join Date: Oct 2003 Location: Alton, Hampshire, UK. Posts: 137	Removing a Cyldon turret tuner conversion, or not? I have a Decca 1000 which has been converted to 13 channels by adding a turret tuner. The conversion plugs into the RF and Mixer/oscillator valve sockets and I assume that it steals HT and heater supplies and routes its output to the first IF transformer. I have the circuit diagrams for both the double sideband (Alexanrda Palace) and vestigial sideband (all others) versions of the receiver. My RF chassis and input attenuator are coded black which means it was an Alexandra Palace set. Circuit tracing however shows the vision IF amp to be a vestigial sideband circuit whereas the RF and Mixer/oscillator circuits are a mixture of the two published versions. I am assuming that later Alexandra Palace sets used vestigial sideband receivers, which would have had more gain than the double sideband sets, worked fine on double sideband and anyway, why bother making two versions if one would do? My other guess is that the circuit evolved during production. It looks as if I can simply pull out the turret tuner plugs from the valveholders, substitute the missing valves and get back to a single channel, unless anyone knows better. After all, who needs more than one channel now, given Auroras as standards converters? The only snag I can think of is that the IF may have had to be trimmed to match the IF from the turret tuner. Has anybody any experience of these sorts of mods and are there traps for the unwary? Cheers Nigel

12th Sep 2006, 9:17 am	#2
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Removing a turret tuner conversion Hello Nigel, It sounds as if your DECCA 1000 was converted to band 3 using a CYLDON tuner. These usually had a small panel containing the aerial sockets and twin RF gain controls for band 1/3. Conversion was simple by removing the RF valve and inserting the 'power' plug from the tuner. In a similar way the mixer valve was removed and the i.f. plug inserted in its place. That was all that was usually required and it was a good conversion. In weak signal areas the I.F. plug was removed and wired direct to the mixer valve which then acted as an additional i.f. amplifier. The local oscillator coil was disconnected in this case. Simply reinstating the valves should return the set to band 1 operation but some front end tuning may be required. Do not touch the i.f. alignment Regards John.

14th Sep 2006, 8:55 am	#3
Ghostuser Pentode Join Date: Oct 2003 Location: Alton, Hampshire, UK. Posts: 137	Re: Removing a turret tuner conversion Dear John, That is just the information that I wanted and I will take your advice about leaving the IF alignment alone. I will probably leave the tuner in place, otherwise I will have a hole to fill in the side of the cabinet. That way I will be able to run either single channel or 13 channel according to my whims! Thanks very much for you help. Regards Nigel

14th Sep 2006, 7:56 pm	#4
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Removing a turret tuner conversion Hello again Nigel, I think you have made the right decision. After all conversion was all part of televison history. Regards John.

14th Sep 2006, 8:11 pm	#5
stephanie Retired Dormant Member Join Date: Jul 2005 Location: New Bern, North Carolina, USA Posts: 346	Re: Removing a turret tuner conversion Yeah. Best to leave it in place. Probably makes for easier use of the set anyway (tune to best channel for picture and sound).