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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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3rd Jun 2018, 12:10 pm | #1 |
Heptode
Join Date: May 2015
Location: Bradford, West Yorkshire, UK.
Posts: 512
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Junk sale linear amplifier
I picked this little toy up yesterday at an amateur junk sale, it appears to be a well constructed linear amplifier, it has 3 PL509's along with all the power supplies inside the case. I need to do a bit of "reverse engineering"to trace out the grid configurationon, it but judging by the quantity of transformers inside (6) 1 for each of the 40v heaters, a whopping great HT transformer 612-0-612 and a large unkown transformer for (screens?) it's probably set up in an AB class which should provide a large amount of gain, possibly built for a 50mW SSB exciter.
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worried about the electrons entering the circuit and the smoke leaving Andrew Last edited by Andrew B; 3rd Jun 2018 at 12:26 pm. |
3rd Jun 2018, 2:37 pm | #2 |
Dekatron
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Re: Junk sale amplifier
I don't know much about amateur transmitting gear as I was only ever an SWL. However I do appreciate good construction. The builder certainly went to town on the construction.
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3rd Jun 2018, 2:50 pm | #3 |
Heptode
Join Date: May 2015
Location: Bradford, West Yorkshire, UK.
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Re: Junk sale amplifier
Just wish he had posted a circuit diagram inside
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worried about the electrons entering the circuit and the smoke leaving Andrew |
3rd Jun 2018, 4:07 pm | #4 |
Dekatron
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Re: Junk sale amplifier
Could it be the PA0FRI Frinear?
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3rd Jun 2018, 6:35 pm | #5 |
Heptode
Join Date: May 2015
Location: Bradford, West Yorkshire, UK.
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Re: Junk sale amplifier
Not sure but I fired it up !!!
There's 450V HT on the anodes, which seems a bit low. There's a push button for testing the standing anode current and ~I got the following readings, TX readings are in ( ) Anode 480v (390v) sagging HT? G2 272v (269v) G1 -246v (-65v) K 0v (0.475v) has 10 ohm resistor to ground, tied to G3 Main HT transformer 612-0-612 @ 450Ma (CT GND) is putting 1240v AC into bridge/smoothing caps.
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3rd Jun 2018, 6:51 pm | #6 |
Dekatron
Join Date: Nov 2011
Location: Surrey, UK.
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Re: Junk sale linear amplifier
Could it currently be in some sort of tune-up mode with reduced/ballasted HT, something maybe to do with the relays etc. that are discernible? I see what appear to be transistors on the underneath tag-strips- they must feel a bit like the rabbits next to the lions' enclosure with all that HT around!
It certainly looks competently put together (as one would hope with something of that nature....)- must weigh a ton. Good luck with what I would find a rather intimidating beastie. |
3rd Jun 2018, 7:29 pm | #7 |
Heptode
Join Date: May 2015
Location: Bradford, West Yorkshire, UK.
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Re: Junk sale linear amplifier
There are 3 Sockets on the thing, there's a SO259, a Belling Lee and an RCA phono, which I suspect is for TX/RX switching. There's a panel meter on the front which is scaled 0 to 100 micro amps (will look for a shunt). There are 3 relays in it, 1 is a large Omron and 2 smaller GPO type change over. These are in the in/out circuit and change the antenna over between RX/TX and switch the bias, I can find nothing that "up's" the HT. Weight is 20+ Kg
Grounding the RCA does nothing and there's no voltage on it. The transistors appear to be screen voltage regulation and seem to be holding up well, just a puzzle why the HT is low.
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worried about the electrons entering the circuit and the smoke leaving Andrew Last edited by Andrew B; 3rd Jun 2018 at 7:37 pm. |
3rd Jun 2018, 8:56 pm | #8 |
Heptode
Join Date: May 2015
Location: Bradford, West Yorkshire, UK.
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Re: Junk sale linear amplifier
I've wrapped it up for tonight, just need to calibrate the Ik standing cathode current meter, as I mentioned before each valve has a 10 ohm cathode resistor, measuring each cathode in turn I got 0.478v, 0.267v and 0.505v, look like valve 2 could be low in comparison but total current for the 3 is about 125mA, a bit high (the meter read 200 microamps, so a dabble with the shunt should sort that, along with a wind down of the standing current to 80 or 90 mA hopefully should be a ball park figure. Does that seem right for 3 PL509's ?
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worried about the electrons entering the circuit and the smoke leaving Andrew |
3rd Jun 2018, 9:06 pm | #9 |
Dekatron
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Re: Junk sale linear amplifier
Hi Andrew, I think we were at the same sale, we were talking outside about that amplifier, and also microwave oven transformers etc. The linear looks different with the covers off, but certainly looks well made. You were hoping it was going to contain a single specialized valve with a bespoke chimney and cooling system rather than TV line output valves. However, there's nothing wrong with 'sweep tube' in linear amplifiers for non-continuous use. Have you checked whether the valves are conducting hard dragging the HT down?
I think that amplifier was the bargain of the day - I certainly missed that one! |
4th Jun 2018, 12:48 am | #10 |
Heptode
Join Date: May 2015
Location: Bradford, West Yorkshire, UK.
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Re: Junk sale linear amplifier
aha, we certainly were Techman, I was with Fuzz and Jim (knew him from the 11m days).
Basically I turned the knobs (thought it had a rollercoaster), lifted it up and thought hernia, I just knew it was an amplifier., pot luck it had 3 X PL509's instead of a 2CX/3CX or an 813. HT is too low for an 813 mod but it's extremely well made. Has regulation on G2 screens, hard switched G1 bias and choke smoothed anode HT with 700 volts, it's a well made item. I'm looking for a low power HF transceiver to hook up to it, maybe test a CB (into a dummy load). It's hard switched, so need a TRX with a relay output or incorporate an RF switch, Should be good for 100+ W output, wonder if 509's will work on 6M ?. For £9 it was a good buy.
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worried about the electrons entering the circuit and the smoke leaving Andrew Last edited by Andrew B; 4th Jun 2018 at 1:06 am. |
4th Jun 2018, 1:50 am | #11 |
Nonode
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
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Re: Junk sale linear amplifier
Something about that amp is tickling a bell and Radcom magazine comes to mind, can't quite put my finger on it.
If you do a 'net search of PL509 rf amps, most are running in the region of 1100V HT and 3 valves should safely give you around 300W, even more with forced air cooling. It looks (in one pic) that you have at least one cooked resistor in there (left hand side under valve socket). |
4th Jun 2018, 2:05 am | #12 |
Nonode
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
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Re: Junk sale linear amplifier
I don't think this is your amp from your description of some of the components, but may be helpful.
Radcom February 1990 page 30. It uses PL519's but other articles mention PL509's and 519's as being interchangeable. And there are mentions on the net of PL509's being used on 6m. |
4th Jun 2018, 10:29 am | #13 |
Dekatron
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Re: Junk sale linear amplifier
The PL519 was a later version of the PL509 used as a colour TV line output valve. I have a box of them I saved from the last scrappers, they are complete with bases and top cap connectors.
Peter |
4th Jun 2018, 10:39 am | #14 |
Dekatron
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Re: Junk sale linear amplifier
At that price it was a steal, let alone a good buy.
Just the transformers..........
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4th Jun 2018, 12:17 pm | #15 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
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Re: Junk sale linear amplifier
HT does sound low: check that you haven't got an O/C rectifier diode.
Also you say it's got various relays: one trick I've seen in amplifiers is to have the screen-supply from the centre-tap of the HT transformer and to switch the "HT" for the valves to the same point for tuneup (so screens and anodes are at the same voltage) so reducing output power and the risk of doing something nasty to the valves/PA network if the antenna-matching is way out of kilter. The "Tune" switch which does this is bypassed and full HT hits the anodes when operating normally. You may find that you get full HT with the right relays closed! |
4th Jun 2018, 1:15 pm | #16 |
Dekatron
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Re: Junk sale linear amplifier
Interesting bit of kit! Nicely constructed as well.
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4th Jun 2018, 8:03 pm | #17 |
Heptode
Join Date: May 2015
Location: Bradford, West Yorkshire, UK.
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Re: Junk sale linear amplifier
I'm going to post a bit of the HT diagram using "pencil and paper" MK1 scanned. the rectifier circuit IS full wave with an 8H choke in the centre tap to ground. so the "700 and a bit volts" HT is all that I have. The screens have a separate transformer and regulator, hence the transistors. The slightly "cooked" looking resistor is a 1K 3 Watt and it's in the common screen supply rail, with a max rating of 7W per screen then maybe a 10W WW would serve better?
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worried about the electrons entering the circuit and the smoke leaving Andrew |
6th Jul 2018, 7:36 pm | #18 |
Octode
Join Date: Nov 2005
Location: Ayrshire, UK.
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Re: Junk sale linear amplifier
The gettering looks a bit 'skinny' on the PL5x9 closest to the camera in the first photo. This may or may not have a bearing on the operation/performance.
HTH TimR
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