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Old 3rd Nov 2020, 4:10 pm   #1
alanjam
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Default Pye RF Power Amp

I have a Pye AT27324 RF amp and would like to know what it is out of and anything about it. The final transistor is a 2N5642 which gives 20W at 175Mhz FM from 28V supply or can also be used for low band AM.
Any ideas?
Alan
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Old 3rd Nov 2020, 4:39 pm   #2
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Default Re: Pye RF Power Amp

Hi Alan,

Well it's definitely Pye and probably 1970's era. I think it could possibly be one of two things:

Either the driver unit out of a T470; this is a UHF fixed station transmitter. If so, the unit is designed to generate 10-15 watts (?) on 150MHz which is then tripled to the final frequency around 450MHz in a varactor multiplier unit. Difficult to say for certain, its many years since I've seen one!

Or, it could also be the PA unit from a T150 VHF link Tx in which case it will output about 25W at VHF. A lot of these would have been liberated by the police/fire VHF systems being decommissioned in the 2000's.

There are several other ex-Pye people on here who may be able to offer more accurate information.

Cheers
Alan G0NFY
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Old 3rd Nov 2020, 4:41 pm   #3
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Default Re: Pye RF Power Amp

Just seen this thread on the T470.

https://www.vintage-radio.net/forum/...d.php?t=155810

Looks very similar but is only 2 stage so I'd go for the T150 PA unit theory!

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Old 5th Nov 2020, 12:46 pm   #4
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Default Re: Pye RF Power Amp

If I remember correctly the T150 used on police/fire links was 10W out. Some which had been in service 24/7/365 for 20 years struggled to produce even that. They were highly reliable. Could you post a pic showing the lid fitted as well please Alan, that might jog a few brain cells.

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Old 5th Nov 2020, 3:29 pm   #5
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Default Re: Pye RF Power Amp

I'm wondering about T30FM...didn't that have such an amp box feeding another squarer one with a pair of parallel devices inside it? Long time since I have been in one.
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Old 6th Nov 2020, 5:53 pm   #6
alanjam
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Default Re: Pye RF Power Amp

Thank you for your replies Alan, Martin and Jon. I'm attaching a picture of the cover as requested - or I will if I can work out how to do so.

My amp has the number 2 marked on it. Similar looking PAs on the T470 and Whitehall have nos 3 and 4 respectively so it looks like they were of the same era. Information on the T30FM seems to be hard to find.

I rather like putting old bits and pieces to work. Maybe you can suggest some characteristics of the unit? The transistors are likely to be tripler, preamp and PA I think. Coils are 5 turns and about 1/4" diameter. Frequency? The left hand coax will be RF in and the right hand RF out. Could the one in between be modulation or is this always done at the oscillator stage? 12V DC to left end, unknown purple and white wires exit at bottom, unknown blue at right end. The last could be separate supply for the final??

As an aside, I worked for Farmers Radio in the 1970s in Adelaide, mostly repairing AM radios in the 70-85Mcs band. Mr Farmer was very keen on saving the customers from Pye (read Big Brother). If people came in for Pye repairs he would send them away but if he was out we would accept them because we wanted to have a look inside. We mostly encountered Pye Cambridge and Leader. The Leader seems to have been forgotten. It was very like our own sets and in a case almost the size of the old Reporter. On one occasion someone brought in an enormous Pye from a truck (24V) but I forget the name on it.

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Old 6th Nov 2020, 7:53 pm   #7
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Default Re: Pye RF Power Amp

It's almost certainly from an FM transmitter, the AM units of the era e.g T30AM tended to use valve driver and PA stages- QQV03-10 and QQV06-40 respectively. They were high-level modulated by a solid state modulator with (IIRC) 2N3055 output transistors. The first all solid-state AM fixed-station Tx that I saw was the T401 and that was totally different in construction.

It's possible that the first stage is a double or tripler but Pye generally used a phase modulator/multiplier assembly that had a lot of stages, in order to get the required deviation with reasonable linearly. I forget the exact figures (it is 30-odd years ago when I last worked on this kit!) but the crystal oscillator might be on as low as 4Mhz and be followed by a total multiplication of 36 in the case of highband. This unit would provide a few 10's of milliwatts drive at final frequency to the PA unit. If each stage in the PA unit has an average of 10dB power gain that would give 10 watts out for 10 milliwatts in.

The fact that some stages have a different supply connection is probably for power control purposes. There might also be points for metering.

As far as band is concerned, it's difficult to tell. The part number would tell you that if you could look it up! Here in the UK, the main PMR bands were 'low band' 70-88 MHz, with base Tx on 85 or 87MHz, the old 'mid-band' with base TX on 139-141MHz and mobile Tx on 105-108 (yes- in the FM broadcast band! They did away with that following the 1979 WARC conference; the police had to shift off it too) and 'high-band' with base Tx usually around 165-167Mhz. There was also band 3 but that used a later generation of equipment.

If it was from an ex-police or fire L150 link Tx it would have been on 146-147 or 154-155 MHz. But I have to say that my gut feeling, looking at the number of turns on the coils and the use of compression trimmers, is that it's lower in frequency than this.

I think Jon has a good point that it might be T30FM- I remember something of the sort too. There's a picture of the insides of one here, if you scroll down the page: https://www.pye-story.org/companies/...s-in-the-1960s
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Old 6th Nov 2020, 8:13 pm   #8
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Default Re: Pye RF Power Amp

I had (maybe still have) a T30FM High Band.

When 1200 Baud Packet came along I discovered it could do 45 Watts out provided the duty cycle was very short. The first digi-peater (remember them?) was at RSGB HQ in Potters Bar, rather a long way from Cambridge.

It did fine service though I doubt the mechanical TX/RX relay liked it much!

Actually now I remember it went off to long term storage at a QTH now on the route of HS2. I'm not expecting to see it again soon HI!

I'm sure my shed might have some T30FM info in paper format. The computer has nothing unfortunately.

alanjam you are making me wonder about the Pye Leader, a slightly familiar name and yet not. What was that please?
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Old 14th Nov 2020, 11:38 pm   #9
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Default Re: Pye RF Power Amp

Hello Alan & Jon
I think that you are probably correct Alan C in that there is no multiplier in this unit. My next move is probably to apply 12v and a 2m signal and see if I can tune it to 2m. A bit of a concern is that there are more trimmers than coils. Some are probably for coupling adjustment to get a specified output - hopefully none are for neutralisation.

Jon, I don't remember too much about the Pye Leader. It was in a nice blue case, almost as big as the Pye Reporter, with ventilation slots and was lighter than Farmers sets, especially our older ones with vibrators. Light weight was a bonus when trying to screw these things under a dashboard while lying in a contorted position. Inside the Leader was all valves except the power supply. It seems that the Leader was one of several models produced by Pye Australia and not released in the UK. Until the mid 1970s Pye Australia dominated the am market and Philips the FM market.
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Old 15th Nov 2020, 4:36 am   #10
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Default Re: Pye RF Power Amp

If the final transistor is a 2N5847 (hard to tell from the pic), then the module is a low VHF type.

The 2N5847 is only rated to 80MHz & ~ 15W.
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Old 15th Nov 2020, 1:19 pm   #11
alanjam
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Default Re: Pye RF Power Amp

Hi Terry. No it's a 2N5642 fed by a 2N5641. Should be good to 175Mhz

I see your callsign around the place. In my youth 5TM was, if I recall correctly, Trevor Marshall who was building amplifiers the last time I saw him.

I also see that you are in the great city of Tintinara. When I was at Farmers Radio we had customers there, I think in the fire service. In addition to the VHF range, Farmers made hf 2-ways for rural services. The all valve MRT9A was quite successful but its successor 9B had the receiver valves replaced with germanium transistors on long leads, and was inclined to be unstable and insensitive.

Regards
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Old 15th Nov 2020, 1:41 pm   #12
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Default Re: Pye RF Power Amp

I'll have to dig through the call books, but in 1962 it belonged to an R D Martin out in Elizabeth.

There was a lot of stuff in HRT magazine on converting/modding PMR stuff, but your amp doesn't show up in the few I've looked at.

Should make a nice PA for 2m, assuming it is working of course (I have a few out of the old Philips 828's, both VHF and UHF).
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Old 15th Nov 2020, 5:29 pm   #13
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Default Re: Pye RF Power Amp

I'd love to see some more details of the Pye Leader - searching the web brings only pages about Pye being a leader in technology, even the Pye Museum Vehicle Mounted Mobiles page only has a couple of 'Team leaders', but I'm sure I encountered one in a Leeds surplus dealers in the 70s, under the railway arches iirc. I'm sure it had a sloping grille front, but looked very like the Front-mounted Ranger of 1955-62. Inside the chassis looked just like them. I also think the one I saw was an HF (25MHz) version, and I wanted it but couldn't contemplate an outlay of £15.

The suggestion that these were only available in Australia and maybe S Africa would explain their obscurity. Does anyone have any pictures? New thread perhaps?
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Old 16th Nov 2020, 7:54 pm   #14
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Default Re: Pye RF Power Amp

Quote:
A bit of a concern is that there are more trimmers than coils.
That's pretty normal for solid state transmitters, and yes you're right- there are different configurations but essentially you're tuning for best match from the impedance of one stage into the next. Two trimmers forming a capacitive tap on the tuned circuit is a common arrangement- you adjust them as a pair for max output. The Q of these tuned circuits is quite low, being heavily damped by the low impedances that transistor stages run at, so don't expect super sharp peaks on all the trimmers. Its very rare indeed to see neutralising networks on this kind of kit.

Yes by all means try giving it some RF at 2 metres- use a rig with variable power to drive it, and a power supply with current metering. It won't need much drive power, too much and you risk frying that first stage. We don't have the manual so we don't know the exact procedure but you are probably okay just tuning for maximum RF output. It will likely all run in class C so it won't take any current from the supply until you feed it some RF, but it will take a few amps at max output. You can tune the inter-stage couplings initially for maximum current.

Alan
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Old 16th Nov 2020, 8:21 pm   #15
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Default Re: Pye RF Power Amp

If trying a tuneup-without-the-manuals, beware of inadvertent parasitics; I recall a 1970s VHF transistor PA strip used by a Danish company that were big in the business back then, where if bench-testing the thing you needed to feed it from a drive-source that had rather specific impedance characteristics across a surprisingly-wide bandwidth. Get this wrong and the input-stage would achieve its lifetime-ambition of becoming an oscillator - for a few seconds before the transistor self-destructed.

We used to do any 'bench-test' tests of these with a 6dB resistive-pad between the drive-source and the amplifier.

Also - things can be complicated if you don't have the covers on! VHF Pye Westminsters had a piece of PCB cut as a cover over the entire PA strip, with holes for access to the trimmers. The copper on the cover was etched in a particular pattern WRT the stages and the screws that held [and grounded] the cover to the chassis. Trying to resurrect a 'scrap' Westminster - which came without the official Pye cover, I cut a slice of PCB, drilled holes, and then spent a futile morning trying to stop the damned PA from oscillating.

Fitting a 'proper' Pye cover all was calm. Eventually I cottoned-on, sliced a couple of strips of copper out from my replacement cover, and all was joy once again.

Transistor VHF amplifiers in the real-world are much more an occult-art than a science.
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Old 16th Nov 2020, 8:26 pm   #16
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Default Re: Pye RF Power Amp

I wonder if all they did was stop a few induced current loops. That Wezzy cover wasn't much more than a coil diameter away after all and I have been to the same place as you for the same reasons!

The PA Boxes from base stations have much more depth. Still haven't been to see if I still have a T30FM - sorry.
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Old 17th Nov 2020, 12:10 pm   #17
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Default Re: Pye RF Power Amp

Early Westminster had an aluminium sheet cover, painted black with white lettering. This fm pa module probably needs around 200 or so mW drive, as was produced from the original long fm mod- driver strip with about a dozen coils in screened compartments.
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