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Old 25th Apr 2019, 3:46 pm   #1
QWENIX
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Default Wavemeter T.F.724A.

For a fellow collector user of old vintage measuring equipment I am looking for info about a wavemeter T.F.724A. We think it's Marconi but don't know anything about this piece. So any info welcomed.

See the pics in the Dutch vintage radio forum:

https://nfor.nl/index.php?id=267213

Valves: UU5, EA50, Y63, L63, VR137 and 2 x VR65. It's WW2 equipment.

Kind regards, Qwenix.

Last edited by QWENIX; 25th Apr 2019 at 3:50 pm. Reason: pics attach
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Old 25th Apr 2019, 8:46 pm   #2
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Default Re: Wavemeter T.F.724A.

Hi
The number does sound very "Marconi" and the construction is Marconi like. However it is not in my 1953 Marconi Instruments catalogue.

Sorry to be negative.
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Old 25th Apr 2019, 9:09 pm   #3
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Default Re: Wavemeter T.F.724A.

Definitely Marconi Instruments. The sketchy information I have suggests it started as a TF724 in 1941 and ended as a TF724A in 1952. I'll try and dig around to see if there's anything more to be had.
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Old 26th Apr 2019, 12:55 pm   #4
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Default Re: Wavemeter T.F.724A.

The colour looks like R.A.F. as my first thought. Somebody in the Netherlands thinks this could be part of the Rebecca system.

In which after 5 flights the planes channels (transmitter) were adjusted to the beacon. So any info is welcome.
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Old 26th Apr 2019, 3:47 pm   #5
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Default Re: Wavemeter T.F.724A.

I had one in my youth, they were on sale in Hurst St or Moor St, Birmingham. They came in a large strong wooden crate with Admiralty markings and included, from what little I can remember, a length of thick co-ax with a "Pye Plug" at one end, and the outer conductor stripped back to leave a quarter-wave of polythene insulation and the inner conductor as a 'sniffer' antenna. I think there was also a set or spare valves, and an instruction booklet.

Can't think how I got it home on the bus, but the case was eventually re-used for something domestic. I had no conceivable use for the meter and I eventually disposed of it.
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Old 26th Apr 2019, 4:26 pm   #6
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Default Re: Wavemeter T.F.724A.

Thinking again, it had a strong lid over the front panel, held by toggle catches. I think the antenna was clipped inside the lid, and the operating procedure or schematic was pasted in the lid.
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Old 26th Apr 2019, 8:14 pm   #7
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Default Re: Wavemeter T.F.724A.

If it were an RAF test set I would expect to see Air Ministry Section Reference numbers in evidence on at least some of the parts, if not an AM label identifying the equipment, and I can't see any. Indeed the 'flag' labelled EA50 counts against it being specifically a military item. I think it is an item of civilian test equipment, made by Marconi.

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Old 29th Apr 2019, 12:11 pm   #8
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Default Re: Wavemeter T.F.724A.

Here's some stock library images we've found. They don't add much I'm afraid. Still looking for schematics etc.
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Old 29th Apr 2019, 12:55 pm   #9
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Default Re: Wavemeter T.F.724A.

What connects to where?

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Old 29th Apr 2019, 1:47 pm   #10
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Default Re: Wavemeter T.F.724A.

Apart from what I assume to be the mains lead, at the moment it's anyone's guess. I can't see any other input or output connector.
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Old 29th Apr 2019, 4:57 pm   #11
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Default Re: Wavemeter T.F.724A.

I've had a closer look at the photo's, there appears to be an opening or something on the LH side of the case in the first of the black and white photo's, it seems to be in line with something that's just above the RH side edge of the chassis shown in the second photo, that something (socket?) appears to be fixed at least in one place to the front panel by a right angle bracket which can also be seen in the second photo, it all seems to head into the VR137 circuit.

So far as I can make out, the L63 valve seems to be configured as a crystal oscillator.

Lawrence.

Last edited by ms660; 29th Apr 2019 at 5:22 pm. Reason: addition
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Old 30th Apr 2019, 3:26 pm   #12
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Default Re: Wavemeter T.F.724A.

I am still reading the info you share here kind regards in the name of my friend collector. Keep it coming.
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Old 23rd May 2019, 2:05 pm   #13
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Default Re: Wavemeter T.F.724A.

It's amazing what you find when you're looking for something else (Elliptical speakers, anyone?)

Slightly different but related instrument. The folding arm used to hold aloft the 1/4-wave probe antenna. Note the unusually high-cycle mains requirement. Must have a look what's inside...
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Old 23rd May 2019, 5:16 pm   #14
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Default Re: Wavemeter T.F.724A.

Quote:
Originally Posted by Julesomega View Post
It's amazing what you find when you're looking for something else (Elliptical speakers, anyone?)

Slightly different but related instrument. The folding arm used to hold aloft the 1/4-wave probe antenna. Note the unusually high-cycle mains requirement. Must have a look what's inside...

Nothing unusual about the power supply. Absolutely standard for airborne (RAF) kit during WWII. While it says "2000c/s", it actually means somewhere between 800c/s and roughly 2000c/s, since the alternator in question was driven off the aircraft engine, and obviously engine could speed could vary.

The higher than usual mains frequency (i.e. 50/60c/s) means that all the iron cored components were far smaller and lighter than normal, which is a critical matter when you have to haul loads of heavy electronics into the air. And of course, on an aircraft the higher capacitive losses from the higher frequency hardly matter because long cable runs are impossible on any known aircraft.


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Old 23rd May 2019, 5:18 pm   #15
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Default Re: Wavemeter T.F.724A.

As a general comment on this thread, I am not sure what the fascination is with yet another wavemeter made by the Air Ministry - or in this case, more likely Marconi for the Air Ministry?

They were so numerous drawing up a full list would be a very tedious matter. And they varied by miniscule amounts. Perhaps a more interesting question is why they needed so many variations on a theme......?


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Old 23rd May 2019, 5:51 pm   #16
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Default Re: Wavemeter T.F.724A.

Quote:
Originally Posted by trh01uk View Post
... a more interesting question is why they needed so many variations on a theme......?

Richard
Indeed. My Wavemeter No,1 has a marginally different freq range, possibly both types met the prevailing spec.
Looking inside, there seem to be a couple of date codes from '47, and it seems to have been made in a hurry, judging by the little wooden tag post.

I wonder who made my unit, would it be Plessey or Pye? Several components are identical on both, including the tuning mechanism and capacitor. The style of valve-type tags is the same on both though different valve types were used, and mine looks as though it has a lot less gain with only one LF type. Missing from my remains are an RF type and a detector diode. I do remember having the small 3-pin diode and base which can be seen on the underside of the Nederlands Forum unit.

The 'why' of the freq range is addressed in the reply https://nfor.nl/index.php?id=267262 where it is pointed out that the Eureka-Rebecca system was used by the RAF from 1942 tot 1958
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