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Old 14th Jan 2023, 5:49 pm   #1
Jon_G4MDC
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Default Pye T4001 AM TX Modulator

The recent thread about AM made me think of the this Pye transistorised VHF AM TX.

It modulates the RF driver and output transistor using a series pass transistor arrangement. It has an audio compressor with a JFET as a Voltage controlled attenuator. There is an active filter with circuit as the attached.

Unfortunately they have failed to put the type number of IC1 and I only have the circuit diagrams not the parts list.

It doesn't appear to be any common op-amp since many of the circuit nodes use 2pins of the IC. I'm wondering if it could be a transistor array e.g CA3046 or some such?

Does anyone have the parts list or have an inkling what IC1 might be please?
(No T4001 here to look at in the flesh so to speak, it's up on a hilltop site)
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Last edited by Jon_G4MDC; 14th Jan 2023 at 5:59 pm. Reason: added modulator amp circuit and pass TRs
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Old 18th Jan 2023, 9:37 pm   #2
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Default Re: Pye T4001 AM TX Modulator

Jon

I have dug out a Pye T4001 manual IC1 on Tx board AT27777 is listed as a thick film active filter FU00521 although been shown as a 14 pin dil package IC on the circuit board layout see attached pdf
If there is any other info that would help let me know
Paul
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Old 19th Jan 2023, 10:24 am   #3
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Default Re: Pye T4001 AM TX Modulator

Hello Paul, very many thanks for that.

It's a mystery isn't it? FU00521 is a number that would be decoded by the microfilm fiche if only it was still in existence.

Interesting they call it a thick film. It certainly looks more like an off the shelf 14 PIN DIL IC. I wonder if they stole the circuit description wording from the Olympic M201 mobile which also used this modulator arrangement. That one definitely used thick film circuits covered by red blue or yellow epoxy coating.

I will continue to try and figure out what the IC could be. CA3046 doesn't seem to match.
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Old 19th Jan 2023, 11:55 am   #4
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Default Re: Pye T4001 AM TX Modulator

Later model Olympic tx audio used discrete components. Far more reliable I found.
Whether a later M201 Olympic manual has the actual circuit?
I will have a look around, but not holding my breath.
Got rid of most of my Pye handbooks when I retired 10 years ago.
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Old 19th Jan 2023, 12:37 pm   #5
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Default Re: Pye T4001 AM TX Modulator

Thanks Rob, that will be interesting.
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Old 20th Jan 2023, 10:33 pm   #6
Mascot-22
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Default Re: Pye T4001 AM TX Modulator

Hi Jon

I had a another dig through a pile of Pye manuals today and found the T4002 VHF FM
T4004 VHF link Tx and the UHF T4012 manuals. In their Tx audio circuit they all use a
similar active filter circuit all referenced as IC 1 in the parts list and all FU00521 as in the T4001 manual. I was worth a look.
Paul
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Old 20th Jan 2023, 11:09 pm   #7
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Default Re: Pye T4001 AM TX Modulator

Did the MF6AM mobile not have a series modulator, the later PYE small black box reporter. My Pye manuals went over 20 years ago. But that may be worth a look at, I can not remember any thick film units in that but could be wrong.

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Old 21st Jan 2023, 12:50 pm   #8
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Default Re: Pye T4001 AM TX Modulator

It will have had. I have no manuals for that but it could be searched.

You have reminded me that the MX293 used the same technique and there the audio circuits employ 4 sections of an NE5514. Very annoying that my scan of the circuit has been done in 2 stages and they have left a gap in the middle where you have to guess what is missing.

I might see if I can fill it in. It has a compressor so might lend itself to copying for homebrew.

The crystal controlled version M293 uses all transistors with no op-amps.

What all these lack, that the T4001 has, is the loosely coupled detector at the PA output which is used for envelope feedback. Essentially I have always though of it as a crystal set on the output and they are using it's output to cancel modulator distortion. I can get my T4001 to 95% and it is perfectly symmetrical + & -. I have never measured distortion but I reckon it will be good.

Last edited by Jon_G4MDC; 21st Jan 2023 at 12:57 pm.
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Old 21st Jan 2023, 7:12 pm   #9
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Default Re: Pye T4001 AM TX Modulator

That IC1 in the original active filter circuit is still being tricky.

The 3046 transistor array doesn't seem to work for it.
The 3096 is a different transistor array but it has 16 pins so that is ruled out.
LM324 quad OpAmp was around from 1972 but it doesn't match.
uA757 was in use then for IF Amps. I don't think they repurposed that.

I found these arrays of transistors which I had not seen before but I think they are quite recent devices. So far I can't see how they might suit.

Still stumped so far. Ticker-om as they say in Sweden.
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Old 21st Jan 2023, 7:29 pm   #10
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Default Re: Pye T4001 AM TX Modulator

I have no longer any 400/4000 series manuals. I did find my M201 am Olympic manaul. It has the 3 thick film module tx audio board, plus the supplement with the circuit for the later discrete component board.
My Epson scanner printer is currently playing up so will scan when it is ok again. The tx module does take a feedback from near the pa RF output pin.
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Old 21st Jan 2023, 7:59 pm   #11
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Default Re: Pye T4001 AM TX Modulator

Thanks Rob! I downloaded the M201 manual today. I missed the TX PA diode detector but, now you mention it, I really should not have.

In my days as a Student Engineer they sent me on a programme of time in the various production departments. They didn't care much about the order in which you did things.

I went first to mobile test where M201s were the thing of the day. This one has crap TX modulation, change the PA, now it passes. I rejected a good number of them.

A few months later I got sent to module test. Ah, well here we are, some of my own rejects. Pass, Pass, Pass etc, just as the previous bloke in my seat must have found. But their tickets show they have been through here time and again... I wasn't happy.

I knew these were rubbish when put in sets so why? That's when I realised they had no test on the detector and the diodes HP5082-2800 were blown.

It got me a trip upstairs of Site 1 to the mobile lab to say - er... I think you have an issue with your test spec.

I had completely forgotten this. I still like the technique
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Old 22nd Jan 2023, 6:29 pm   #12
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Default Re: Pye T4001 AM TX Modulator

Jon, I have scanned the M201 amendment doc plus the M201 circuit with the original thick film pcb and PA circuit, plus interconnections.
Just emailed it to you.

Available for anyone else if they message me with your email address.

From this, it would be possible to make a modulator with compression along the lines of that in the M201, using discrete components
.
I also found the sheet with circuit, components and connections for am and fm use of the "ladyshave" microphone. This was discussed in another thread, but don't know which one.
It is included in the pdf above.
I will attach as an image now, not sure how it will display on the forum though?
Rob
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Last edited by CambridgeWorks; 22nd Jan 2023 at 6:32 pm. Reason: added third line ref email
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Old 22nd Jan 2023, 6:41 pm   #13
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Default Re: Pye T4001 AM TX Modulator

I remember the coming of the 'Ladyshave' mic; I had a load of Westminsters/Europas out on weekly-rental with the old square olive-green-yellowish bar-of-soap mics, as well as a bunch of Olympics [which came with the shaver-mics as standard].

Minicabbers being at heart deeply status-seeking creatures, being seen with an old-style mic damaged their egos, and it was surprising how many of the bar-of-soap mics got creatively 'damaged cables' or 'it got caught in the door' so they could get a replacement shaver-mic and look modern.

The AM-optimised Pye mics [including the 'Tulip' types - see my thread here - https://www.vintage-radio.net/forum/...d.php?t=192282 ] are really good for use with amateur-band SSB transceivers.
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Old 22nd Jan 2023, 6:49 pm   #14
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Default Re: Pye T4001 AM TX Modulator

Was there much difference between the 401 and the 4001?
I have a feeling I have the 401 manual somewhere
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Old 22nd Jan 2023, 8:07 pm   #15
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Default Re: Pye T4001 AM TX Modulator

Thanks Rob. I'll check my mail!

I like the Westminster square mic with white button (or I have black and orange button, I think for Met Police). The AM inserts are very nice for SSB. I would put one up against a Shure 444 and in a blind test I reckon it might win.
They go like a bomb on Icom IC202s.

The shaver mic was indeed a style thing. That came from something called The Concern Design Center in Eindhoven. So did the PF8 Bodie-fone. Piggyback on the Philishave & Ladyshave popularity. They also gave us edge mounted controls driven by tortuous gear chains to meet the requirements of that style council. Late Philips Cassette Recorders I'm looking at you! There was nothing wrong with the EL3302 method.

No not much between T401 and T4001. I think some tweaks to decoupling and screening gaskets to pass stricter type approval regs. Basically I think they are the same circuitry.

Last edited by Jon_G4MDC; 22nd Jan 2023 at 8:16 pm.
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Old 22nd Jan 2023, 9:59 pm   #16
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Default Re: Pye T4001 AM TX Modulator

T401 and T4001 not a lot different?
R401 and R4001 two entirely different beasts!
R401 was a designer's ultimate 1970s fantasy. PLL for fm demodulation. AM/FM by changing a few links. PCB was hard to discern as a proper rx. Rubbish die cast box front end prone to faulty feedthrough decouplers and instability.
R4001 internally actually looked like a proper rx. You could almost tune it up without a handbook. I exaggerate, but it looked the part, just like a proper rx and worked well.
Rob
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Old 23rd Jan 2023, 12:42 am   #17
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Default Re: Pye T4001 AM TX Modulator

Quite right Rob - very big differences in the RXs.
The R401 & R402 were very strange beasts indeed. I still reckon for the TXs not a lot in it.
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Old 23rd Jan 2023, 10:40 pm   #18
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Default Re: Pye T4001 AM TX Modulator

I looked again at the MX293 AM modulator. I can see no diode detector at the end of the TX chain.

Unlike the M201 and T401/4001 arrangement I suppose they abandoned envelope detection for feedback of a modulation error component. It might only be worth a few % of mod depth, which in a Base could be valuable, in a mobile much less so.
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