A 1950s 1930s Marconi oddity - UK Vintage Radio Repair and Restoration Discussion Forum

JoshWard · 26th Jun 2022, 5:30 pm

Hi folks,
After working on a series of 1960s transistor sets over the past couple of weeks today I fancied working on something a bit older, so I pulled an innocent looking Marconi 857 off the to-do pile with visions of chain tuning drives, top caps, 8 pin valve bases and leaky boxes of electrolytics.
I was very surprised when I took the back off. Somebody appears to have built a new radio onto the chassis! It looks to have been done with some skill- the plates adapting the old valve base holes to take the miniature valves are all very uniform. Whilst there are plenty of solder joints in mid-air, it's all been done to a decent enough standard. The appearance of an EL84 output valve must date it to the second half of the 1950s so the question is why?
An ambitious home constructor who didn't mind having an old fashioned cabinet which was rather ugly even when it was first made? A treasured item which was beyond repair but somebody wanted to keep? Somebody wanting to fool with a radio enthusiast in 70 years' time?

It's clear some parts are original. The tuning capacitor and possibly the mains transformer. The output transformer is branded as a Goodmans and the loudspeaker is also a Goodmans. The IF cans look different to those on the 857 service sheet. One electrolytic has a 1949 date code so some components were old, but not as old as the chassis/cabinet, when it was constructed. As you can see, all the other components seem to be 1950s with wax capacitors and Hunts mouldseals.

Has anybody else come across something like this? I have seen plenty of homemade radios but nothing where somebody has so skilfully constructed their own radio around an existing chassis and case!
It works surprisingly well and I'm pleased to say after recapping it I was able to spend the rest of the afternoon working on an HMV 499. I was slightly nervous about that as it came from the same sale as the Marconi but, other than some replacement smoothing capacitors, it proved to be all original!

Radio Wrangler · 26th Jun 2022, 5:40 pm

The socket adaptor plates are not only uniform, they are cut with curved sides... elliptical by the look. This is a lot more work with hand tools, could they have been commercial items at some time?

And that looks like meccano chain, also used in Racal's RA17 family.

David

Silicon · 26th Jun 2022, 7:21 pm

EMI were using that chain in the late thirties.

There are a number of 'shadows' on the top surface of the chassis that suggests that the IF transformers were changed.

It looks like the RF stage was simplified or radically changed.

Magazines such as 'The Radio Constructor' sometimes featured radical modifications to scrap radios.

These projects are understandable when you are faced with yet another dull, dreary wet Sunday in the 1950s.

Ed_Dinning · 26th Jun 2022, 7:24 pm

Hi Josh, there have been threads about chassis with adaptor plates before.
If a company used a common size chassis for production reasons, it would make sense to use up old stock by fitting adaptor plates when smaller based valves were used in the next series of sets.
Chassis were often seen with additional holes that appeared to have no use; this cost very little extra to do in the press shop and if it increased volumes could actually reduce costs and ease production

Ed

emeritus · 26th Jun 2022, 10:21 pm

The chassis of dad's mid-1950's RGD radiogram, which has a single valve 3W class A output stage, has a few unpopulated stamped valve-holder-sized holes. They would probably have been used for a different (export) version which had a more powerful push-pull output stage.

JoshWard · 27th Jun 2022, 8:52 am

Yes, the tuning chain is standard EMI. Interesting to hear about the adaptor plates. Perhaps they were bought for the job which explains why they are so well made. I think this probably hits the nail on the head:

Quote:

Originally Posted by Silicon

These projects are understandable when you are faced with yet another dull, dreary wet Sunday in the 1950s.

After all, a dull Sunday afternoon is why I pulled it off my 'to-do' pile!

turretslug · 27th Jun 2022, 10:21 am

There were a few post-war sets where a change of valve series was instituted during the production run (Loktal/B8B going to B7g miniatures was one option encountered) and existing punched chassis stock had adapter plates fitted to suit. Also, it seems to be a feature with post-war thermionic Eddystones with cast coilboxes that adapter plates of IO/Loktal-type footprint were used for B7g/B8a/B9a valve sockets, in this case I suspect that it was a production convenience so that the sockets could be pre-loaded with passive components before assembly into the tightly-packed coilboxes.

As mentioned, it's entirely possible that someone passed some dreary '50s rainy days by updating the set as a pastime.

Heatercathodeshort · 28th Jun 2022, 8:29 am

That looks like a Plessey chassis. Marconiphone did use Plessey chassis, autochangers and television chassis in some models.

Valve manufacturers classified valves as Current, Replacement and Obsolete. They were very keen on manufacturers using the current range of valves rather than the earlier designs in NEW equipment. Adaptor plates were often used to convert various bases to current production in a well tried popular chassis.

An exception is the BusH DAC90A using rimlock valves when the B9A series would have been the current range in the later models. UCH81 etc. I have never seen a DAC90A with adaptor plates. Maybe Mullard did a special deal to dispose of thousands of excess stock! John.

26th Jun 2022, 5:30 pm	#1
JoshWard Octode Join Date: Dec 2005 Location: Near Stowmarket, Suffolk, UK. Posts: 1,962	A 1950s 1930s Marconi oddity Hi folks, After working on a series of 1960s transistor sets over the past couple of weeks today I fancied working on something a bit older, so I pulled an innocent looking Marconi 857 off the to-do pile with visions of chain tuning drives, top caps, 8 pin valve bases and leaky boxes of electrolytics. I was very surprised when I took the back off. Somebody appears to have built a new radio onto the chassis! It looks to have been done with some skill- the plates adapting the old valve base holes to take the miniature valves are all very uniform. Whilst there are plenty of solder joints in mid-air, it's all been done to a decent enough standard. The appearance of an EL84 output valve must date it to the second half of the 1950s so the question is why? An ambitious home constructor who didn't mind having an old fashioned cabinet which was rather ugly even when it was first made? A treasured item which was beyond repair but somebody wanted to keep? Somebody wanting to fool with a radio enthusiast in 70 years' time? It's clear some parts are original. The tuning capacitor and possibly the mains transformer. The output transformer is branded as a Goodmans and the loudspeaker is also a Goodmans. The IF cans look different to those on the 857 service sheet. One electrolytic has a 1949 date code so some components were old, but not as old as the chassis/cabinet, when it was constructed. As you can see, all the other components seem to be 1950s with wax capacitors and Hunts mouldseals. Has anybody else come across something like this? I have seen plenty of homemade radios but nothing where somebody has so skilfully constructed their own radio around an existing chassis and case! It works surprisingly well and I'm pleased to say after recapping it I was able to spend the rest of the afternoon working on an HMV 499. I was slightly nervous about that as it came from the same sale as the Marconi but, other than some replacement smoothing capacitors, it proved to be all original! Attached Thumbnails

26th Jun 2022, 5:40 pm	#2
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,872	Re: A 1950s 1930s Marconi oddity The socket adaptor plates are not only uniform, they are cut with curved sides... elliptical by the look. This is a lot more work with hand tools, could they have been commercial items at some time? And that looks like meccano chain, also used in Racal's RA17 family. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

26th Jun 2022, 7:21 pm	#3
Silicon Nonode Join Date: Jun 2007 Location: Coulsdon, London, UK. Posts: 2,163	Re: A 1950s 1930s Marconi oddity EMI were using that chain in the late thirties. There are a number of 'shadows' on the top surface of the chassis that suggests that the IF transformers were changed. It looks like the RF stage was simplified or radically changed. Magazines such as 'The Radio Constructor' sometimes featured radical modifications to scrap radios. These projects are understandable when you are faced with yet another dull, dreary wet Sunday in the 1950s.

26th Jun 2022, 7:24 pm	#4
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: A 1950s 1930s Marconi oddity Hi Josh, there have been threads about chassis with adaptor plates before. If a company used a common size chassis for production reasons, it would make sense to use up old stock by fitting adaptor plates when smaller based valves were used in the next series of sets. Chassis were often seen with additional holes that appeared to have no use; this cost very little extra to do in the press shop and if it increased volumes could actually reduce costs and ease production Ed

26th Jun 2022, 10:21 pm	#5
emeritus Dekatron Join Date: Jan 2012 Location: Brentwood, Essex, UK. Posts: 5,339	Re: A 1950s 1930s Marconi oddity The chassis of dad's mid-1950's RGD radiogram, which has a single valve 3W class A output stage, has a few unpopulated stamped valve-holder-sized holes. They would probably have been used for a different (export) version which had a more powerful push-pull output stage.

27th Jun 2022, 10:21 am	#7
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,395	Re: A 1950s 1930s Marconi oddity There were a few post-war sets where a change of valve series was instituted during the production run (Loktal/B8B going to B7g miniatures was one option encountered) and existing punched chassis stock had adapter plates fitted to suit. Also, it seems to be a feature with post-war thermionic Eddystones with cast coilboxes that adapter plates of IO/Loktal-type footprint were used for B7g/B8a/B9a valve sockets, in this case I suspect that it was a production convenience so that the sockets could be pre-loaded with passive components before assembly into the tightly-packed coilboxes. As mentioned, it's entirely possible that someone passed some dreary '50s rainy days by updating the set as a pastime.

28th Jun 2022, 8:29 am	#8
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: A 1950s 1930s Marconi oddity That looks like a Plessey chassis. Marconiphone did use Plessey chassis, autochangers and television chassis in some models. Valve manufacturers classified valves as Current, Replacement and Obsolete. They were very keen on manufacturers using the current range of valves rather than the earlier designs in NEW equipment. Adaptor plates were often used to convert various bases to current production in a well tried popular chassis. An exception is the BusH DAC90A using rimlock valves when the B9A series would have been the current range in the later models. UCH81 etc. I have never seen a DAC90A with adaptor plates. Maybe Mullard did a special deal to dispose of thousands of excess stock! John.