Wireless Set No. 52 Canadian - Project

[David Dunlop]

While doing a visual inspection of the chassis a little earlier, I spotted what I initially assumed was an old style solid fuse and clips assembly linked between the two Aerial Terminals and Ground. It seemed like a very odd place for a fuse initially but I didn't think much more of it, other than to make note to get back to it later and clean it off to see what rating information it was marked with. It was about 2.25 inches long and .375 inches wide. Standard fuse end caps and a brownish tan central body.

Well this afternoon I went back in to clean it up and have a closer look. Started wiping away the crude on the main body and was very surprised to discover a mirrored glass cylinder staring back at me, as per attached photo. I also became very reluctant to attempt removal of the item in case it broke.

My first thought was since it was glass, perhaps it had markings on it similar to those on glass valves, so I carefully applied some downward pressure to the nearest end cap in its clip. The oxidation accumulation between the clip and the end caps broke free and the cylinder could be slowly rotated in the clips. No markings to be found on the glass or anywhere on either end cap.

Next stop…the Circuit Diagram. A quick look at the Aerial Circuit finds a pair of small outlined half circles, curved sides facing each other across a small gap, and the words "DISCHARGE GAP" written next to it. A look at the components listed on the diagram shows no part identified as such.

So off to the main components listing in the 52-Set Manual. Nothing listed there either. Last possibility was to read through the Receiver section of the manual. And there it is, a very cryptic comment that a "gas filled discharge gap will be found linking the two aerial posts to ground".

All very well and good, but I cannot find much at all online about them, or there use in radio aerial circuits in receivers. More importantly, if one of these happens to break or stop working, how will one find a replacement? I am assuming two possibilities: (a) this item was simply missed in the components listings for the Wireless Set No. 52, or, (b) these things are tougher than God's Toenails and nobody at Marconi ever expected them to fail or break.

Can anyone shed any light on them? It might also be part of the WS No. 9 design and covered in those manuals (I'm hoping) or it was entirely new to the 52-Set design.


David

[Bruce MacMillan]

The Canadian Marconi CSR5 receiver also uses this device. It's purpose is to protect the receiver front end from damage by HV static. The one used in that receiver is described as:
antenna discharge gap Admiralty Pattern Type 8431 C.G.E.

It breaks down at 100V. It has no effect on the operation of the set. I suspect that as both sets were made by Marconi it could be the same part number.

I would guess that unlike a fuse it is a reusable part.

[Chris Suslowicz]

Originally Posted by Bruce MacMillan

The Canadian Marconi CSR5 receiver also uses this device. It's purpose is to protect the receiver front end from damage by HV static. The one used in that receiver is described as:
antenna discharge gap Admiralty Pattern Type 8431 C.G.E.

It breaks down at 100V. It has no effect on the operation of the set. I suspect that as both sets were made by Marconi it could be the same part number.

I would guess that unlike a fuse it is a reusable part.

Having noticed it on the circuit diagram while rummaging for the connector details further up the thread, it appears on the circuit diagram as "Spark Gap" and is noted in FZ522:

RECEIVER

R.F. Amplifier V1A (ARP3)

30. The input to the tuned R.F. amplifier is
taken from the P.A. tank circuit in the
sender. When the sender tank circuit is
tuned to the receiver frequency its resonant
characteristics contribute to the image
frequency attennuation and slightly to the
sensitivity. A gas-filled discharge gap,
SG1, is connected across the input terminals.

Under "Miscellaneous" in the receiver parts list it's described as:

"SG1 100W. neon discharge gap".

(I assume the 100W is a typo for 100V.)

Chris.

[David Dunlop]

Chris.

It seems a number of USAAF Command Set Receivers also used these Neon Tubes in their Aerial circuits as protection from 'external static discharge from either the aircraft or atmospheric sources". They were rated at about 60V.

David

[David Dunlop]

Rummaging in a 19-Set Parts Bin the other day and found an NOS Microphone, Hand, No. C3 I had forgotten about. It is now in the bits pile for any future Sender for the 52-Set.

A Remote Receiver and Case also arrived in the mail. Serial Number on the ID Plate is 7746 built in 1944.

A UHF Socket was added to the rear of the case, below the Connector Socket and a small hole drilled into the case to the right of the Connector Socket. I have since removed the UHF bit and its half of three feet of wire. The other half is still attached to the upper Aerial Terminal inside the set. Interestingly, the Gas Filled Discharge Gap is missing from its clips in this receiver.

The clip at the "R" position inside the Connector Socket at the rear of the receiver is missing. The broken screw shaft is still visible in the bakelite.

A small dent exists in the lower front edge of the case, just to the right of the Pull Knob below the Speaker.

The other interesting thing is the presence of a white "NON-LUMINOUS DIAL" decal centered between the Speaker and the Meter.

Sure nice to have two receiver chassis available for detailed comparisons now.

More on this Remote Receiver as the project unfolds.


David

[Chris Suslowicz]

Originally Posted by David Dunlop

The clip at the "R" position inside the Connector Socket at the rear of the receiver is missing. The broken screw shaft is still visible in the bakelite.

The 'R' position is not needed for the Remote Receiver - it's the transmit/receive relay line and the relay grounds the aerial input in the receiver and mutes the audio amplifier (via the -1200V line that provides cathode bias to the PA stage.) (It doesn't have -1200 volts on it, just the 813 cathode bias voltage, I assume.)

If you need a spare connector I can post you the ones I have here as a source for spare contacts - the contacts are retained by a screw and nut so should be easy to swap out.

Chris.
(Who will eventually get to the Post Office - honest!)

[David Dunlop]

Hi Chris.

Downloading the 2/4 EMER for the 52-Set is on my Must Do list Monday evening when my 2 week probation is up. I have the equivalent 19-Set publication which also covers the same Flick Assy and I know I have disassembled quite a few on the 19’s years ago. I used that publication as my reference and ‘I think’ it covers reassembly, but it has been a while.

With regards to the Connector on the rear of the receiver missing its R-Clip, if you have spares to spare that would be a big help. Thanks.

I must revisit my parts bins again soon. I am sure I have other items tucked away, but cannot recall what. Never know what common items from the 19-Set might fall out of a bin and be shared with the 52-Set.

David

[David Dunlop]

A nice surprise today. I was giving the innards of the Remote Receiver a closer look and a bright, shiny object suddenly caught my attention. It was the Gas Filled Discharge Gap that was missing from its clips at the Aerial terminals, stuck between two of the calibrator valves.

Cleaned it off and took the attached photo before clipping it back into its proper place. It measures 2-5/16 inches long and 7/16 inch diameter at the caps. The only markings on it are "PATT. 3841" stamped into the sides of each end cap.

David

[John Hooper]

David:
As it is apparent that you have some radio background I have a question.
What would be the correct radio for an M38A1 M170 1955.
A chum has picked this up and wants to go radio vehicle not ambulance.
TNX
John