Marconi VT161: local distant control repair. - UK Vintage Radio Repair and Restoration Discussion Forum

FERNSEH · 22nd Apr 2014, 11:18 pm

The local distant control in my Marconi VT161 has fallen to pieces. There's is no chance of course of finding an exact replacement so a conventional 2Meg pot will have to be used instead. This will involve using my favourite device, the adaptor plate.
The local distant control sets the delay voltage to the AGC supplied to the RF amplifier. When receiving very weak signals it is desirable to remove or delay the AGC voltage supplied to the PCC84 RF amplifier. Doing this can improve the signal to noise ratio. On strong signals no AGC delay is required and the full AGC voltage is fed to the RF valve.

There are few other jobs to do the set before the chassis is installed into the cabinet.

DFWB.

Tazman1966 · 23rd Apr 2014, 8:36 am

Nice job (as always). It looks like it was there from new.

Hybrid tellies · 23rd Apr 2014, 11:36 am

A very nice tidy job.

Peter.N. · 23rd Apr 2014, 12:09 pm

Yep very neat, looks like an RS pot.

FERNSEH · 23rd Apr 2014, 12:42 pm

The original component was a Morganite make and the replacement is a Welwyn. It does have a RS look about.
I've turned my attention to the sound. The original PCL82 was low emission and has been replaced. Also the 0.01mfd Hunts coupling capacitor to the grid of the triode section needed replacement.
Much more sound now.
The Marconi VT161 has direct line sync. This set is always prone to slightly ragged verticals, something I must look into to later.
TV sets with blocking oscillators do seem less prone to ragged verticals than those with multivibrator line oscillators.
Focus Diode (Brian) called around today and he noticed another adaptor plate, this one was fitted by the manufacturer. The metalwork allows the fitment of an octal line output valve, say a PL36, and as this set uses the PL81 which has the smaller B9A base an adaptor plate is called for.

DFWB.

Focus Diode · 23rd Apr 2014, 2:10 pm

Lovely set and a great performer. David's done a great adaptor for the dropper too as can be seen in the photo below, a brilliant piece of work the manufacturer would've been proud of.

Cheers,
Brian

22nd Apr 2014, 11:18 pm	#1
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Marconi VT161: local distant control repair. The local distant control in my Marconi VT161 has fallen to pieces. There's is no chance of course of finding an exact replacement so a conventional 2Meg pot will have to be used instead. This will involve using my favourite device, the adaptor plate. The local distant control sets the delay voltage to the AGC supplied to the RF amplifier. When receiving very weak signals it is desirable to remove or delay the AGC voltage supplied to the PCC84 RF amplifier. Doing this can improve the signal to noise ratio. On strong signals no AGC delay is required and the full AGC voltage is fed to the RF valve. There are few other jobs to do the set before the chassis is installed into the cabinet. DFWB. Attached Thumbnails

23rd Apr 2014, 8:36 am	#2
Tazman1966 Nonode Join Date: May 2006 Location: St Albans, Herts, UK. Posts: 2,193	Re: Marconi VT161: local distant control repair. Nice job (as always). It looks like it was there from new. __________________ All the very best, Tas

23rd Apr 2014, 11:36 am	#3
Hybrid tellies Nonode Join Date: Jan 2004 Location: 1966-1976 Coverack in Cornwall and Helston Cornwall. 1976-present Bristol/Bath area. Posts: 2,965	Re: Marconi VT161: local distant control repair. A very nice tidy job. __________________ Simon BVWS member

23rd Apr 2014, 12:09 pm	#4
Peter.N. Dekatron Join Date: Jul 2008 Location: Charmouth, Dorset, UK. Posts: 3,601	Re: Marconi VT161: local distant control repair. Yep very neat, looks like an RS pot.

23rd Apr 2014, 12:42 pm	#5
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Marconi VT161: local distant control repair. The original component was a Morganite make and the replacement is a Welwyn. It does have a RS look about. I've turned my attention to the sound. The original PCL82 was low emission and has been replaced. Also the 0.01mfd Hunts coupling capacitor to the grid of the triode section needed replacement. Much more sound now. The Marconi VT161 has direct line sync. This set is always prone to slightly ragged verticals, something I must look into to later. TV sets with blocking oscillators do seem less prone to ragged verticals than those with multivibrator line oscillators. Focus Diode (Brian) called around today and he noticed another adaptor plate, this one was fitted by the manufacturer. The metalwork allows the fitment of an octal line output valve, say a PL36, and as this set uses the PL81 which has the smaller B9A base an adaptor plate is called for. DFWB. Attached Thumbnails Last edited by FERNSEH; 23rd Apr 2014 at 12:57 pm.

23rd Apr 2014, 2:10 pm	#6
Focus Diode Octode Join Date: Jan 2006 Location: Borough of Gateshead, UK. Posts: 1,420	Re: Marconi VT161: local distant control repair. Lovely set and a great performer. David's done a great adaptor for the dropper too as can be seen in the photo below, a brilliant piece of work the manufacturer would've been proud of. Cheers, Brian Attached Thumbnails