1940s Radio Sub-Unit for what? - UK Vintage Radio Repair and Restoration Discussion Forum

OldBoffin · 28th Feb 2007, 7:23 pm

does any one recognize this sub-unit?
3 switched bands, twin gang tuning C with slow mkotion drive and logging scale.
Was a Loctal frequency changer valve (I changed V/H to Octal for 6K8 but never finished job!) Fitted transistors instead much later.
470kcs IF txfr -I fed O/P to cheap transistor radio and got 27mhz on one range of the 3 - 27M rubbish! that finished me! But interested to know what it was for?
Any interest to any one?
OldBoffin

Station X · 28th Feb 2007, 7:45 pm

It looks like part of the receiver unit from a B2 Spyset.

I'll have a look inside one of mine later and confirm.

jim_beacon · 28th Feb 2007, 10:54 pm

it's not B2 - that has a single chassis for the whole set.

Jim

Station X · 28th Feb 2007, 11:01 pm

Oh yes it is Jim! The receiver section has two sub chassis and this is one of them. I know because I had to seperate the sub chassis to repair one example.

I have a receiver opened up beside me at the moment and will try to post a scan of it shortly. I'm afraid my digital camera has given up the ghost.

jim_beacon · 28th Feb 2007, 11:06 pm

I stand corrected!
It's a long time since I had one in bits, and it had been heavily modified - Loktal Valves for a start!

Jim.

Station X · 28th Feb 2007, 11:32 pm

Here's some pictures which should allow Old Boffin to confirm the identity of the unit. Sorry about the poor quality, but they're actually scans, as my digital camera is bust.

What OB has is the RF/Mixer Unit. The IF and AF unit is on the other sub chassis.

I've removed one of the valves to make things clearer.

I have several complete units and don't need any spares.

The unit might fetch something on eBay if the Spy Set aspect is stressed. People pay over the odds for these sort of things nowadays, which is why I've stopped collecting them.

OldBoffin · 1st Mar 2007, 2:04 pm

Thanks to everyone for the information, including interesting circuit diagram.
Looks like a double superhet?
Any further information on the actual frequencies covered?
Seems strange to use Loctal valves in wartime - were they British units or USA as they had loctals first I understand.
I have Cossor 7B7 and Cossor 7S7 in my store for disposal if any interest to anyone.
Thanks again,
OldBoffin.

Station X · 1st Mar 2007, 2:18 pm

These units were British built at The Frythe in Hertfordshire.

Not a double superhet. It has a Beat Frequency Oscillator (BFO) for reception of morse signals. The BFO tuning capacitor has specially bent vanes which short circuit it the BFO off position.

Receiver coverage is 3.1 to 15.5 Mhz in three bands.

Grid bias is obtained by feeding the HT though a resistor in the PSU.

The so called volume control is actually a sort of manual agc which varies the bias on the variable mu valves preceding the AF Amp. This doesn't work very well and the output is either loud or very loud.

After the war the French built some almost identical sets using a different valve series. I can't remember which at present. I've never seen one of these French sets the flesh.

28th Feb 2007, 7:23 pm	#1
OldBoffin Retired Dormant Member Join Date: Jan 2007 Location: Rugeley, Staffordshire, UK. Posts: 54	1940s Radio Sub-Unit for what? does any one recognize this sub-unit? 3 switched bands, twin gang tuning C with slow mkotion drive and logging scale. Was a Loctal frequency changer valve (I changed V/H to Octal for 6K8 but never finished job!) Fitted transistors instead much later. 470kcs IF txfr -I fed O/P to cheap transistor radio and got 27mhz on one range of the 3 - 27M rubbish! that finished me! But interested to know what it was for? Any interest to any one? OldBoffin Attached Thumbnails

28th Feb 2007, 7:45 pm	#2
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,287	Re: 1940s Radio Sub-Unit for what? It looks like part of the receiver unit from a B2 Spyset. I'll have a look inside one of mine later and confirm. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

28th Feb 2007, 10:54 pm	#3
jim_beacon Retired Dormant Member Join Date: Mar 2003 Location: Bishop's Waltham, Hants, UK. Posts: 939	Re: 1940s Radio Sub-Unit for what? it's not B2 - that has a single chassis for the whole set. Jim

28th Feb 2007, 11:01 pm	#4
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,287	Re: 1940s Radio Sub-Unit for what? Oh yes it is Jim! The receiver section has two sub chassis and this is one of them. I know because I had to seperate the sub chassis to repair one example. I have a receiver opened up beside me at the moment and will try to post a scan of it shortly. I'm afraid my digital camera has given up the ghost. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

28th Feb 2007, 11:06 pm	#5
jim_beacon Retired Dormant Member Join Date: Mar 2003 Location: Bishop's Waltham, Hants, UK. Posts: 939	Re: 1940s Radio Sub-Unit for what? I stand corrected! It's a long time since I had one in bits, and it had been heavily modified - Loktal Valves for a start! Jim.

28th Feb 2007, 11:32 pm	#6
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,287	Re: 1940s Radio Sub-Unit for what? Here's some pictures which should allow Old Boffin to confirm the identity of the unit. Sorry about the poor quality, but they're actually scans, as my digital camera is bust. What OB has is the RF/Mixer Unit. The IF and AF unit is on the other sub chassis. I've removed one of the valves to make things clearer. I have several complete units and don't need any spares. The unit might fetch something on eBay if the Spy Set aspect is stressed. People pay over the odds for these sort of things nowadays, which is why I've stopped collecting them. Attached Thumbnails __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

1st Mar 2007, 2:04 pm	#7
OldBoffin Retired Dormant Member Join Date: Jan 2007 Location: Rugeley, Staffordshire, UK. Posts: 54	Re: 1940s Radio Sub-Unit for what? Thanks to everyone for the information, including interesting circuit diagram. Looks like a double superhet? Any further information on the actual frequencies covered? Seems strange to use Loctal valves in wartime - were they British units or USA as they had loctals first I understand. I have Cossor 7B7 and Cossor 7S7 in my store for disposal if any interest to anyone. Thanks again, OldBoffin.

1st Mar 2007, 2:18 pm	#8
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,287	Re: 1940s Radio Sub-Unit for what? These units were British built at The Frythe in Hertfordshire. Not a double superhet. It has a Beat Frequency Oscillator (BFO) for reception of morse signals. The BFO tuning capacitor has specially bent vanes which short circuit it the BFO off position. Receiver coverage is 3.1 to 15.5 Mhz in three bands. Grid bias is obtained by feeding the HT though a resistor in the PSU. The so called volume control is actually a sort of manual agc which varies the bias on the variable mu valves preceding the AF Amp. This doesn't work very well and the output is either loud or very loud. After the war the French built some almost identical sets using a different valve series. I can't remember which at present. I've never seen one of these French sets the flesh. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.