Wireless Set No. 52 Canadian - Project

[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 couple of Sunday morning observations.

It appears these receiver chassis were inspected at a standard inspection station that used a steel stamp punch to verify the inspection. I have found this 5/16 inch stamp on the outer left and right chassis side panels on both the main set receiver and the remote receiver. these two units are roughly 2,000 apart by serial number in Marconi's 1944 production.

The other interesting discovery relates to the Crystal Calibrator chassis in the upper left corner of the receiver. If you check back at the photo in Post #4, you will see a large daub of blue paint on the calibrator chassis at the left end of it. I found the remains of a similar daub on the Remote Receiver calibrator chassis.

This mark was applied at the factory to denote that all the valves in the calibrator have been 'aged'. That means they have been run for 12 hours to ensure the electrons will feel right at home in the valves when they are put to work. In addition, the receiver manual notes that Marconi has aged all essential and spare calibrator valves issued with the set. These valves have also been marked with a blue dot of paint on the end of the locating pin.

Whenever a valve has been replaced in the calibrator, the calibration test needs to be performed. With an aged replacement valve, this test can be done straight away. If the valve has not been aged, the calibrator needs to be run for 12 hours before the test can be performed.

David

[Chris Suslowicz]

Originally Posted by David Dunlop

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.
David

Consider it done.

Looking at the photo of the broken screw, I suspect the culprit attempted to undo it using a screwdriver. This is a mistake, as all the screw slots are in-line with the contact slot (twisting the screwdriver would deform the contacts) and the obvious assembly/disassembly method is with a box spanner or nut spinner on the rear of the connector. (Also the nuts are sealed with varnish, so may be very hard to undo without applying a suitable solvent (or heat) first.)

Chris.

[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

[David Dunlop]

While giving a closer look to the Remote Receiver today, a piece of beige paper revealed itself trough a circular hole on the left side of the chassis. While looking at it, I noticed a pattern of four screws, above and bracketing this hole. I had seen that pattern before and it took a while to register exactly where. It was on either the side, or rear B-Set chassis plate on my 19-Sets. It was a Modification Card Holder and this one on my Remote Receiver clearly held a card.

I was delighted when I removed the card to find it confirmed the Serial Number of the Remote Receiver as being '7746'. Three modifications were done to the receiver on 10/03/61 (I can never remember the Military Day/Month sequence on these things but interesting the work was done in 1961).

'F257' is probably the reference code for the 52-Set Cdn, and if that is correct, at least six modifications exist and the three noted relate to the receiver.

This prompted another look at the Main Set receiver. Sure enough, the Modification Card Holder was there, but I could not see a card initially. However, when I shone a flashlight down into the top of the holder, I could see something was there. This resulted in a quick raid of my lovely wife's sewing room. A possible tool was found. A return to the receiver and an insertion of the tool pulled out a modification card. (Who knew a crochet hook could be so handy!) A different pattern mod card than the other one. Much stiffer paper and when folded over in the holder it stayed put. Interestingly it shows the chassis Serial Number to be '8356', as opposed to the plate on the front of the receiver being '8349'. At the moment, my gut is going with the Mod card. It was firmly in place in its holder and invisible. More likely the data plate was replaced or the entire upper front panel of the receiver.

Only one modification was performed on this receiver on 01/12/52 - F257/#1.

Be interesting to find a record of these modifications.


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

[David Dunlop]

Hello John.

I am not sure how much help I can be for you and your friend, but I have copied your post into a new topic on the M170 in the Post-war Military Vehicles Thread where there are a lot more knowledgable people on this particular topic.

You might also want to look at the M38A1CDN2 Antenna Mast Assembly Thread under the same section of the Forum. It deals with some of the issues you raised as well.

David