Marconi Generator Help - UK Vintage Radio Repair and Restoration Discussion Forum

Valvewhiz1 · 26th Feb 2021, 9:51 pm

Hi all,
More lockdown fun, I’ve just dug out a long dormant Signal Generator No. 18 Mk2 CT402 Marconi /TF995A/3/S.
Partially working except for the 54 to 108MHz band and the 108 to 220MHz band.

The question is does anyone have manual / circuit diagram for this, I have the standard TF995A/5 but this one has a different circuit and an add on IF amplifier and supply panel TM5347.

Regards
Amanda M0DZO

Julesomega · 26th Feb 2021, 11:40 pm

I have the front panel and a few remains of a TF995A/2 if you are looking for any bits. 0n the sub-assemly for the modulator and crystal calibrator there are big differences from the schematic shown on Radiomuseum - I'm hanging on to the crystal unit and I'd like to know what's inside it.

Julesomega · 27th Feb 2021, 12:12 am

Nice coincidence that you asked as I currently have this on the floor awaiting assessment and recovery of most of the bits. Haven't yet got round to opening up the calibrator osc unit, but have been wondering why it needs 3 wires going into it when it already uses the chassis gnd

Terry_VK5TM · 27th Feb 2021, 12:29 am

This will take some digging around on the internet - the US Air Force have these listed as amongst equipment they used to have - plant number 6625 6340 5103.

There is/was a site or public access portal that carried a lot of the US forces service manuals, but I can't find it at the moment, hopefully someone else will remember it.

geeoboeh2s · 27th Feb 2021, 11:50 am

Have you looked at the Marconi Instruments group on .io. There are ex-Marconi people on there.

Chris

geeoboeh2s · 27th Feb 2021, 12:06 pm

Sorry, I should have provided a link.

https://groups.io/g/Marconi-Test-Instruments

Chris

Valvewhiz1 · 27th Feb 2021, 6:14 pm

Hi all,
Thanks for the info so far, I’ve joined the Marconi group, with perseverance the top two bands are working now, most of the valvebases in the rf stage had a brown goo on them, cleaned this off which helped a lot, then looked at the underside of the rf chassis, sticky brown goo around the valve pins of the vhf frequency stages which appears to be resin flux.

I will report further on it as I progress.

Regards
Amanda M0DZO

vintage_8bit · 27th Feb 2021, 8:22 pm

I have a 995B/2 this also has flux all over, all of the valve bases. I have also changed numerous high value resistors in mine.

Colin

David Simpson · 28th Feb 2021, 11:48 am

Amanda, there is also the massive VMARS online military archive. Well worth a visit.
If the inside of the 995's cabinet smells a bit like old fly spray, then the "brown goo" might well be the pan-climatic fungicide which many items of military test equipment were sprayed with internally. Some brylcreme boy, pongo or matelot might have been a bit heavy with a spray can back in the 60's.
As I have an A/5 & an A/2, like many other Marconi enthusiasts, will find your thread excellent reading.

Regards, David

26th Feb 2021, 9:51 pm	#1
Valvewhiz1 Triode Join Date: May 2008 Location: Birmingham, West Midlands, UK. Posts: 38	Marconi Generator Help Hi all, More lockdown fun, I’ve just dug out a long dormant Signal Generator No. 18 Mk2 CT402 Marconi /TF995A/3/S. Partially working except for the 54 to 108MHz band and the 108 to 220MHz band. The question is does anyone have manual / circuit diagram for this, I have the standard TF995A/5 but this one has a different circuit and an add on IF amplifier and supply panel TM5347. Regards Amanda M0DZO __________________ Check out My Website www.meazzi.org.uk

26th Feb 2021, 11:40 pm	#2
Julesomega Nonode Join Date: Dec 2012 Location: Stockport, Greater Manchester, UK. Posts: 2,102	Re: Marconi Generator Help I have the front panel and a few remains of a TF995A/2 if you are looking for any bits. 0n the sub-assemly for the modulator and crystal calibrator there are big differences from the schematic shown on Radiomuseum - I'm hanging on to the crystal unit and I'd like to know what's inside it. __________________ - Julian It's good here

27th Feb 2021, 12:12 am	#3
Julesomega Nonode Join Date: Dec 2012 Location: Stockport, Greater Manchester, UK. Posts: 2,102	Re: Marconi Generator Help Nice coincidence that you asked as I currently have this on the floor awaiting assessment and recovery of most of the bits. Haven't yet got round to opening up the calibrator osc unit, but have been wondering why it needs 3 wires going into it when it already uses the chassis gnd Attached Thumbnails __________________ - Julian It's good here

27th Feb 2021, 12:29 am	#4
Terry_VK5TM Nonode Join Date: Oct 2010 Location: Tintinara, South Australia, Australia Posts: 2,339	Re: Marconi Generator Help This will take some digging around on the internet - the US Air Force have these listed as amongst equipment they used to have - plant number 6625 6340 5103. There is/was a site or public access portal that carried a lot of the US forces service manuals, but I can't find it at the moment, hopefully someone else will remember it. __________________ Terry VK5TM https://www.vk5tm.com/

27th Feb 2021, 11:50 am	#5
geeoboeh2s Rest in Peace Join Date: Mar 2010 Location: Berkshire, UK. Posts: 72	Re: Marconi Generator Help Have you looked at the Marconi Instruments group on .io. There are ex-Marconi people on there. Chris

27th Feb 2021, 12:06 pm	#6
geeoboeh2s Rest in Peace Join Date: Mar 2010 Location: Berkshire, UK. Posts: 72	Re: Marconi Generator Help Sorry, I should have provided a link. https://groups.io/g/Marconi-Test-Instruments Chris

27th Feb 2021, 6:14 pm	#7
Valvewhiz1 Triode Join Date: May 2008 Location: Birmingham, West Midlands, UK. Posts: 38	Re: Marconi Generator Help Hi all, Thanks for the info so far, I’ve joined the Marconi group, with perseverance the top two bands are working now, most of the valvebases in the rf stage had a brown goo on them, cleaned this off which helped a lot, then looked at the underside of the rf chassis, sticky brown goo around the valve pins of the vhf frequency stages which appears to be resin flux. I will report further on it as I progress. Regards Amanda M0DZO __________________ Check out My Website www.meazzi.org.uk

27th Feb 2021, 8:22 pm	#8
vintage_8bit Heptode Join Date: Feb 2013 Location: Rainham, Kent, UK. Posts: 525	Re: Marconi Generator Help I have a 995B/2 this also has flux all over, all of the valve bases. I have also changed numerous high value resistors in mine. Colin

28th Feb 2021, 11:48 am	#9
David Simpson Nonode Join Date: Mar 2008 Location: Aberdeen, UK. Posts: 2,852	Re: Marconi Generator Help Amanda, there is also the massive VMARS online military archive. Well worth a visit. If the inside of the 995's cabinet smells a bit like old fly spray, then the "brown goo" might well be the pan-climatic fungicide which many items of military test equipment were sprayed with internally. Some brylcreme boy, pongo or matelot might have been a bit heavy with a spray can back in the 60's. As I have an A/5 & an A/2, like many other Marconi enthusiasts, will find your thread excellent reading. Regards, David