Marconi 702 transportation - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

dtvmcdonald · 9th May 2017, 2:25 am

The set is now at home sitting in the back of my SUV. The movers are coming
tomorrow afternoon. I will remove the side panels in the morning. Among
all the prewar British sets at the ETF museum is a plaque comparing the
prices to a car. The price, in numerical pounds converted to dollars at the current rate, of a cheap car in 1936 England is less than I'm paying the movers.

The set has been partially recapped and may have at least one rewound
transformer (hard to tell which one from just seeing some yellow vinyl
leads around the power unit.)

After my recent unexpected difficulties with a WWII iconoscope
camera for a B-17 "kamikaze" drone caused by (very high quality) oil HV caps,
I will investigate carefully.

peter_scott · 9th May 2017, 7:40 am

Hi Doug,

It sounds like you may have a working set there. It would be great to see some photos.

Peter

dtvmcdonald · 9th May 2017, 2:44 pm

I have the side panels off and it examined as best I can in the large SUV.

Its been seriously worked on, if not a total restoration. Lots of Japanese
blue electrolytics and brown radial film caps. I can't tell in brand or age in the car.
Also, lots of dust on said parts.

An X41 was not in its socket, but safely held by its top cap and
has a nice shiny getter. BUT ... what on EARTH is the tiny wire sticking up
out of the (very slightly loose) base?

I will take photos. One lettered plate on the back is visible ... maybe the serial number?

This set may be recognizable by one or more of you folks.

high_vacuum_house · 9th May 2017, 3:24 pm

Good afternoon,
The X41 is a triode hexode with a metalised coating which acts as a screen.
The wire sticking out of the base is most likely to be the connection to the valve envelope metalising. This would be connected to ground or chassis by pin 6. These wires do become detached very easily as the metalising is not held to the glass very strongly.

Christopher Capener

Ed_Dinning · 9th May 2017, 8:29 pm

Hi, the wire should be reconnected to the metallising if at all possible or the valve may start oscillating at frequencies where it is not wanted!
A wrap of Cu or Al tape with conductive adhesive often works.

If you have problems with the EHT transformer mail me as I believe I have the winding specs for this unit.

Ed

dtvmcdonald · 9th May 2017, 9:11 pm

The tube is not metallized. It looks like it has an internal graphite coating.

I think we should close this thread, since the title is obsolete.
I started a new one about the set itself.

9th May 2017, 2:25 am	#21
dtvmcdonald Pentode Join Date: Mar 2016 Location: Champaign, Illinois, USA. Posts: 227	Re: Marconi 702 transportation The set is now at home sitting in the back of my SUV. The movers are coming tomorrow afternoon. I will remove the side panels in the morning. Among all the prewar British sets at the ETF museum is a plaque comparing the prices to a car. The price, in numerical pounds converted to dollars at the current rate, of a cheap car in 1936 England is less than I'm paying the movers. The set has been partially recapped and may have at least one rewound transformer (hard to tell which one from just seeing some yellow vinyl leads around the power unit.) After my recent unexpected difficulties with a WWII iconoscope camera for a B-17 "kamikaze" drone caused by (very high quality) oil HV caps, I will investigate carefully.

9th May 2017, 7:40 am	#22
peter_scott Dekatron Join Date: May 2003 Location: Edinburgh, UK. Posts: 3,274	Re: Marconi 702 transportation Hi Doug, It sounds like you may have a working set there. It would be great to see some photos. Peter __________________ http://www.nostalgiatech.co.uk https://www.youtube.com/c/PeterScott/videos

9th May 2017, 2:44 pm	#23
dtvmcdonald Pentode Join Date: Mar 2016 Location: Champaign, Illinois, USA. Posts: 227	Re: Marconi 702 transportation I have the side panels off and it examined as best I can in the large SUV. Its been seriously worked on, if not a total restoration. Lots of Japanese blue electrolytics and brown radial film caps. I can't tell in brand or age in the car. Also, lots of dust on said parts. An X41 was not in its socket, but safely held by its top cap and has a nice shiny getter. BUT ... what on EARTH is the tiny wire sticking up out of the (very slightly loose) base? I will take photos. One lettered plate on the back is visible ... maybe the serial number? This set may be recognizable by one or more of you folks.

9th May 2017, 3:24 pm	#24
high_vacuum_house Octode Join Date: May 2003 Location: Belper Derbyshire Posts: 1,935	Re: Marconi 702 transportation Good afternoon, The X41 is a triode hexode with a metalised coating which acts as a screen. The wire sticking out of the base is most likely to be the connection to the valve envelope metalising. This would be connected to ground or chassis by pin 6. These wires do become detached very easily as the metalising is not held to the glass very strongly. Christopher Capener __________________ Interests in the collection and restoration of Tefifon players and 405 line television

9th May 2017, 8:29 pm	#25
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: Marconi 702 transportation Hi, the wire should be reconnected to the metallising if at all possible or the valve may start oscillating at frequencies where it is not wanted! A wrap of Cu or Al tape with conductive adhesive often works. If you have problems with the EHT transformer mail me as I believe I have the winding specs for this unit. Ed

9th May 2017, 9:11 pm	#26
dtvmcdonald Pentode Join Date: Mar 2016 Location: Champaign, Illinois, USA. Posts: 227	Re: Marconi 702 transportation The tube is not metallized. It looks like it has an internal graphite coating. I think we should close this thread, since the title is obsolete. I started a new one about the set itself.