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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 15th Sep 2020, 9:58 am   #1
electronicskip
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Default Transmitter Tuning unit TU-5B WW2 Find

Another unit rescued from the closed down workshop is a US Army signal corps transmitter unit for a BC375 Aircraft transmitter used in WW2.

I've no idea how it came to be there of course, but obviously it's been there decades due to the amount of dust and grime I cleaned off it to reveal what was underneath.

It's missing the tuning knobs but otherwise seems to be all there .

Probably has no use now but an interesting piece of US Airforce WW2 history.
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Old 15th Sep 2020, 10:16 am   #2
ronbryan
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Default Re: Transmitter Tuning unit TU-5B WW2 Find

I remember that the interior of the TU5-B rack contained lovely (possibly silver) plated coils wound on large ceramic formers, with variable tuning capacitors with large spacings between the plates and also some impressive rotary switches. I was given one once when I was a schoolboy. All that is left of it now is a pair of rack handles.

Ron
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Old 15th Sep 2020, 10:57 am   #3
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Default Re: Transmitter Tuning unit TU-5B WW2 Find

Lots and lots of these appeared on the surplus market. Almost all got boiled down for the power RF components. I've got quite a variety of ex-TU-5B bits in my junk boxes and in a couple of ATUs

That sideways knob reduction drive at top left was pure torture to tune very far!

David
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Old 15th Sep 2020, 11:47 am   #4
G3VKM_Roger
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Default Re: Transmitter Tuning unit TU-5B WW2 Find

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Originally Posted by electronicskip View Post
Another unit rescued from the closed down workshop is a US Army signal corps transmitter unit for a BC375 Aircraft transmitter used in WW2.

I've no idea how it came to be there of course, but obviously it's been there decades due to the amount of dust and grime I cleaned off it to reveal what was underneath.

It's missing the tuning knobs but otherwise seems to be all there .

Probably has no use now but an interesting piece of US Airforce WW2 history.
The BC-375 transmitter that your TU fitted into is now a sought-after collectors item. Unfortunately, the bright-emitter valves the radio uses are triodes and so are in great demand by audio fans.

I think your TU looks like it covers the 80 metre band and if so is more likely to be of interest to BC-375 owners than other TUs which don't cover an amateur band.

Cheers

Roger

Last edited by G3VKM_Roger; 15th Sep 2020 at 11:49 am. Reason: Incorrect type number
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Old 15th Sep 2020, 4:47 pm   #5
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Default Re: Transmitter Tuning unit TU-5B WW2 Find

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That sideways knob reduction drive at top left was pure torture to tune very far!

David
TU5B units - including the sideways-tuning reduction-gear - were popular for converting into VFOs in the 1950s - the components were all of really high quality, massively proportioned too - so RF losses were low and 'self-heating' of the tuned-circuit - always an issue in VFOs - was minimised.
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Old 19th Sep 2020, 10:40 pm   #6
WB6NVH-GEOFF
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Default Re: Transmitter Tuning unit TU-5B WW2 Find

TU-5 is the 160 Meter tuning unit.

I too acquired many as a schoolboy and tore them apart. This was not easy because of that purple "glypt" varnish GE put all over the threads of every screw in the thing, and then to add insult to injury, the screw heads were unusually shallow and wide. We eventually learned to heat any fasteners with a soldering iron to soften the glypt before attempting to turn them.

I am sure my junkboxes are still stocked with massive variable capacitors, refugees from these things.
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Old 20th Sep 2020, 9:15 am   #7
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Default Re: Transmitter Tuning unit TU-5B WW2 Find

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Originally Posted by ronbryan View Post
I remember that the interior of the TU5-B rack contained lovely (possibly silver) plated coils wound on large ceramic formers, with variable tuning capacitors with large spacings between the plates and also some impressive rotary switches. I was given one once when I was a schoolboy. All that is left of it now is a pair of rack handles.

Ron
Hi Ron at least you have something to hold onto! Mick.
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Old 20th Sep 2020, 9:48 am   #8
Hans PE1KWH
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Default Re: Transmitter Tuning unit TU-5B WW2 Find

These TU's are used for the mentioned BC375 but also for the BC191 transmitter.

The first was mainly used in large aircraft ( multi engined bombers ) and powered with the board voltage of 28 Volt DV.

The BC191 was the 14V version of the same transmitter.
The only difference is al large resistor in the top which regulates the heater voltages.
The BC191 is not that scarce because it could be run from a car battery on charge so pretty easy to use as a ham or pirat. The BC375 is much less found.

If anyone like to swap a BC375 for my BC191F please let me know.
It could come with the right dynamotor.
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Old 20th Sep 2020, 5:41 pm   #9
turretslug
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Default Re: Transmitter Tuning unit TU-5B WW2 Find

It's something of an eye-opener to those like me who grew up with increasingly miniaturised solid-state electronics as to just how much "clobber" even a base-line aircraft radio fit of the WW2 era constituted with its dynamotor packs, remote control boxes with long mechanical control cables wending around the fuselage, aerial coupling/changeover units and so on. I realise this isn't an aviation forum but this overview of a basic installation shows how it was dotted around wherever it could be fitted in even in a large and relatively capacious aircraft like the B-24, with TU-x tuning unit racks to span the spectrum used taking up a fair amount of space behind wing centre-section and notoriously cramped radio operator's position ahead of the intrusive high-mounted wing featuring bulky BC-375 at his knees under the table on which the BC-348 was fitted. And this is before aircraft became ever more crammed with electronics as the war progressed.

http://jproc.ca/ve3fab/b24.html

I have heard the BC-191/-375 described as produced en-masse in the early '40s to a design from the early '30s with valves from the early '20s! Possibly a bit of poetic licence there but maybe not so far of the mark.
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Old 21st Sep 2020, 5:22 am   #10
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Default Re: Transmitter Tuning unit TU-5B WW2 Find

There was a series of articles in RCA Ham News and I think QST for making monobanders out of those TU's.
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Old 21st Sep 2020, 11:08 am   #11
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Default Re: Transmitter Tuning unit TU-5B WW2 Find

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Originally Posted by turretslug View Post
I have heard the BC-191/-375 described as produced en-masse in the early '40s to a design from the early '30s with valves from the early '20s! Possibly a bit of poetic licence there but maybe not so far of the mark.

Certainly the design of the BC-375 is starkly crude, with VFO feeding directly into 4 PA valves in parallel. The so-called MOPA layout. The performance is correspondingly crude, these sets being known for terrible chirp on CW. All one can say about them is that they were "good enough" most of the time. And we won't know about the times when they weren't good enough - those sets were probably lost along with the plane and crew.

The T1154 equivalent transmitter used by the RAF is similarly crude - and again is a 1930s design rushed into production for the war effort.

The truth about wartime production is that money might be no object but there is no time to invent wondrous improvements when solutions already exist. So famously the WS19 prototypes were knocked up in 6 weeks, and though they then had to be greatly improved over the next few years, the basic design - along with a myriad of flaws - stayed in use for the next couple of decades.

One area where there was true innovation was RADAR, and that was because there was nothing pre-existing to fall back on. It all had to be invented from scratch.
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Old 23rd Sep 2020, 5:47 pm   #12
Hans PE1KWH
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Default Re: Transmitter Tuning unit TU-5B WW2 Find

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Originally Posted by trh01uk View Post
Certainly the design of the BC-375 is starkly crude, with VFO feeding directly into 4 PA valves in parallel. The so-called MOPA layout. The performance is correspondingly crude, these sets being known for terrible chirp on CW. All one can say about them is that they were "good enough" most of the time. And we won't know about the times when they weren't good enough - those sets were probably lost along with the plane and crew.
Not quite, One VT4C was used as oscillator and another as PA.
The other 2 VT4C's are used as modulator amp's.
A VT25 was the LF pre-amp or modulating tone oscillator ( MCW ).

The transmitter was capable of CW, MCW and AM putting out something like 35 Watts carrier depending on which band it was used.

Indeed a early 30's design but with a correct power suppy stable enough for the purpose it was used in, short messages from aircraft to ground.
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Old 23rd Sep 2020, 9:59 pm   #13
trh01uk
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Default Re: Transmitter Tuning unit TU-5B WW2 Find

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Originally Posted by Hans PE1KWH View Post
Not quite, One VT4C was used as oscillator and another as PA.
The other 2 VT4C's are used as modulator amp's.
A VT25 was the LF pre-amp or modulating tone oscillator ( MCW ).

The transmitter was capable of CW, MCW and AM putting out something like 35 Watts carrier depending on which band it was used.

Indeed a early 30's design but with a correct power suppy stable enough for the purpose it was used in, short messages from aircraft to ground.

Hans - yes indeed, sorry for posting about the line-up relying on my memory, which is now getting a bit rusty - I was putting one of these brutes on the air over ten years ago. For some reason I was thinking of the Command sets which have a separate modulator.

As you rightly say - it was good enough for air to ground comms.

Richard
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Old 24th Sep 2020, 6:14 pm   #14
Hans PE1KWH
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Default Re: Transmitter Tuning unit TU-5B WW2 Find

As you say Richard, those where very crude transmitters which for some reason where used during a large part of WW2.
They must have swapped tons and tons of those fragile VT4C's as the vibrations and shocks on those large airplanes are terribly.

Nice to hear you had one on the air !

They do definitely deserve respect after all their history, just like all the equipment from the warriors and of course the warriors too.
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