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Old 22nd Jul 2021, 1:53 pm   #21
Bazz4CQJ
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Default Re: HT for a car radio

Yes, but I'm thinking more about what a receiver might be be affected by.

I'm now at 220V 65mA, and my thermal camera shows that the transformer is winning the heat stakes at @48'C, whereas the FET on its heat sink does not seem bothered. So any improved cooling needs to be of the whole module, not just the FET.

B
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Old 22nd Jul 2021, 1:57 pm   #22
Beardyman
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Default Re: HT for a car radio

Ah, yes, I see. Perhaps getting a portable radio near it whilst the PSU is operating with a nominal load may give you a ball park idea?
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Old 22nd Jul 2021, 2:11 pm   #23
Bazz4CQJ
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Default Re: HT for a car radio

I've just tried that; as we might have expected, LW and MW are really badly affected. Holding the set about 10" from the module, few stations make it through. So, a good RF enclosure, seems like it would be needed to power a radio, and if it's in a box, a fan may be needed.

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Old 22nd Jul 2021, 7:54 pm   #24
David Simpson
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Default Re: HT for a car radio

Just ordered one of Joe's modules from Amazon(made by "Jackskings") - 5.39 inc. P&P. Probably will experience the same RFI as others have. However, I have a decent selection of cast ally Eddystone boxes, & a couple of ex computer 12V fans.

Regards, David
PS. Just a thought - after my recent banging-on about old two-pin plugs & AC/DC sets. If small enough & reliable enough, such modules could enable doing away with using the house/workshop's 240V AC Mains(and all the safety issues involved), & a safe LV bench supply of a couple of 12V car batteries be used. DS

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Old 22nd Jul 2021, 9:20 pm   #25
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Default Re: HT for a car radio

Quote:
Originally Posted by David Simpson View Post
Probably will experience the same RFI as others have.
The HF generation and harmonics is implicit in how switch mode things work. The difference between the good guys and the bad is in whether it gets let out or not.

You never get all the isolation you'd like in one move, so you have to think like an onion and use several layers, impeding the muck a fair bit as it tries to pass each layer.

Good layout keeps down the size of loops of circulating AC currents, and shepherds currents where you want them to go while nulling the amount going where you don't want it to.

Then comes a box with feed through capacitors etc.... add ferrite rings to season to taste.

David
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Old 22nd Jul 2021, 9:52 pm   #26
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Default Re: HT for a car radio

To David Simpson,
I have it all in my head at present and have a load of other projects going on at present. I will CAD it out and publish it but really its not complex. Essentially three variable supplies plate, screen and grid with meters on all legs so I can see current and voltage. Its not for newbies though !! as miss setting can destroy even a large valve in very short time. The whole idea behind it is for matching my 5B/254 valves for my amplifier build. BUT I have thought about adding a few rotary switches to obtain switched voltages and ten turn pots to control voltages. Power transformer is a custom one of mine but it will be easy enough to use one or two extra ones, perhaps back to back to acheive the same purpose. It IS "in the mill" and will appear soon ( no exact promises. ) I will be using my old MKII AVO chassis and superb cast chassis rails with new front panel.
The Avo still actually works but has the traditional sticky meter and I had to repair one of the pots where there was a join between two different thickness nichrome wires, and the weld had broken. THAT was a %$##$@% job!!!!!.


Joe
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Old 22nd Jul 2021, 10:22 pm   #27
Oldcodger
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Default Re: HT for a car radio

That is why I mentioned(#13) the TL494 from my history. We used this (circa 20+ years ago) to generate on shelf supplies for Channel and Group translation equipment; and noise was a consideration. The circuit was, from memory a TL494 as per data sheet with a Zener diode to limit. As I remember, the noise levels generated were well within the limits for fdm. I made mine to supply a Zenon tube for car timing, and I don't remember any problems with noise on the radio.
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Old Yesterday, 11:12 am   #28
David Simpson
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Default Re: HT for a car radio

Quote:
Originally Posted by joebog1 View Post
To David Simpson,
I have it all in my head at present and have a load of other projects going on at present. I will CAD it out and publish it but really its not complex. Essentially three variable supplies plate, screen and grid with meters on all legs so I can see current and voltage. Its not for newbies though !! as miss setting can destroy even a large valve in very short time. The whole idea behind it is for matching my 5B/254 valves for my amplifier build. BUT I have thought about adding a few rotary switches to obtain switched voltages and ten turn pots to control voltages. Power transformer is a custom one of mine but it will be easy enough to use one or two extra ones, perhaps back to back to acheive the same purpose. It IS "in the mill" and will appear soon ( no exact promises. ) I will be using my old MKII AVO chassis and superb cast chassis rails with new front panel.
The Avo still actually works but has the traditional sticky meter and I had to repair one of the pots where there was a join between two different thickness nichrome wires, and the weld had broken. THAT was a %$##$@% job!!!!!.


Joe
Bang-on Joe, I too used an old AVO VCM Mk2 as the basis for my DC Valve Tester which I built several years ago. Thought that the MK2's cabinet was too small, so used an empty Marconi TF995A/2 Sig Gen's cabinet which is much larger. However, my effort, although it works great, is built along vintage 1950's/60's analogue circuitry methods. So 21st century circuitry, along your proposed design is definitely the way forward. In fact several Forum chaps are now following similar paths as yourself.

Regards, David
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