HT for a car radio
 

I need to build a power pack for a car radio , I was wondering has anyone had success in using a mains tx and transistors I would be interested regarding the cct , thanks ,Mick.

Re: HT for a car radio
 

Once you use transistors as the switching elements, you aren't tied to 50Hz transformers. You're free to go higher in frequency, which will make things a lot smaller, lighter and easier to package. The numbers of turns in your windings scale down significantly, too.

One thing is to avoid the Royer self-oscillating type and have a separate driver and oscillator operating the power transistors. ~this avoids a few pitfalls.

No designs in my head at the moment, but there are lots around. some done for the vslve era amateur radio projects in RSGB publications. Also an inverter for any DC voltage can be changed by just redoing the turns for the secondary to make whatever voltage you want.

Have a look for applications notes by Silicon General, Linear Technology inc, Texas instruments, International rectifier.

David

Re: HT for a car radio
 

There are circuits around which use mains transformers in what are called "Solid State Vibrators". These are evolutions of the sort of thing used in WWII, but the electromechanical switcher is replaced by a transistor, driven by a pulsing circuit. So, switching the 12-0-12 winding, you can take HT off the 240 winding.

There certainly have been a number of threads on SSV on the forum in the past.

As David points out, an inverter will be more efficient, but finding the transformer may be more difficult. If you find the carcass of an old RT like Pye Cambridge, there'd be an inverter consisting of 2 x OC35's and a small transformer there which would do.

B

Re: HT for a car radio
 

Try one of these!!
$6.50 Australian ~ 3 quid for you. Post free.
Adjustable from 60 volts to 400 volts at a max of 200 mA.
Gotta be a BIG radio to asik for more than that.
I bought 8 of em for new valve tester, and ALL test excellent if a bit noisy, BUT a simple choke and cap filter just about removes all the noise. It switches at around 75 kHz, so out of "most" radio tuning or IF range.

measures 60mm X 50mm X 20 mm overall.
From eBay

Joe

Re: HT for a car radio
 

Those look useful, what are they listed as?

Re: HT for a car radio
 

In the late '60's, I had a car radio with vibrator pack. My vibrator was duff, so i borrowed a circuit from some US book from the library. Basically, a couple of OC28 with a couple of 300R emitter resistors and it ran as intended with the vibrator. I found the right resistor values by feeling the OC28 surface temperatures.Obviously, avoid TOO HOT.
I have the circuit somewhere, but you should find it somewhere in a late '60s electronics comic.
Les.

Re: HT for a car radio
 

They are listed thus:
DC-DC 8-32V to 45V-390V ZVS High Voltage Step-up Module Capacitor Charge Board
DC-DC 8-32V to 45V-390V ZVS High Voltage Step-up Module Capacitor Charge Board

They are also regulated which, I didn't mention previously, using a simple feedback loop.
If you take 200 mA at 400 volts ( they do get to 400, then foldback ) primary current is pretty high.

Hope that helps,

Joe

Re: HT for a car radio
 

Les- takes me back to my first car, with a valve radio. the vibrator was U/S, so I mentioned it to my mentor- an old school GPO TO, mate of my dad. Walk this way, he said, and minutes later I had a new vibrator in my hand. Some electronics firms in London had a circuit based on a pair of OC28, and a tuned circuit based on a pair of transformer coupled circuits. I did build it ,but had problems with the generated noise.

Re: HT for a car radio
 

Probably similar to the one pictured in post #1 of this thread:-

https://www.vintage-radio.net/forum/...ad.php?t=41944

It wouldn't work in my application. I still have it somewhere if anyone wants it, but it has no base.

Re: HT for a car radio
 

Thanks Joe I have ordered one ,cheers Mick.

Re: HT for a car radio
 

Station X, similar, but from memory, I had no base resistors.
I see then you were replacing a 7 pin version. They were a clever design whereby as well as the primary switching, the HT was also switched (commutated) to give DC without a separate rectifier. rectifier.
I seem to recall Dr. Hugo Holden, occasionally of this forum, overhauled a number of these with serious quality work involved.
The switching frequency depends more on the transformer than any other single factor I think.
Les.

Re: HT for a car radio
 

Hi!

I've certainly seen a two transformer arrangement in RSGB using two identical 12–0–12V 3A mains transformers – the first (power step–up) transformer is switched by 2 × 2N3055 power transistors, then the primary of the second feedback transformer connects to the ends of the stepup transformer secondary via a 1k5 11W resistor in each lead, with the 12–0–12V winding of the f/b transformer connects to the two bases, the centre–tap going to 12V positive via a 1k 5W resistor and 220 ohm to chassis for d.c. bias. The 2N3055 emitters were common and went to 12V negative via a current feedback resistor of about 0.47 ohm 5W

The article I found it in says the 1k5 11W resistors may have to be adjusted in value to get sustained oscillation without a very large primary current – my drawing software is playing up so I'll have to post it tomorrow!

Chris Williams

Re: HT for a car radio
 

( given the spirit of VR) a case for something like the old TL494 SMPSU regulator, or it's modern day equivalent ( something for the up-to-date blokes to work on). Works well enough at 12v in ( or possibly higher, as I used it as an HT source for a Xenon strobe).
Problem with mine was finding a transformer working at the frequency . I made one from a circuit I "developed " from an old GEC telecoms design. Circuit must have been reasonably noise free, as we noise tested the power rails for harmonics. I never tried the capacity of the output, but I did have this circuit running an old light box of one 8w tube ( albeit through dropper resistors to drop the HT after strike). I did mention this in some past posts, looking for an equivalent for a ferrite core, and someone suggested a transformer out of an old laptop PSU.
sTATION X - ( as said in a vintage TV program), if you can find TL494 then there's an idea to work on.8-)

Re: HT for a car radio
 

The RAF had wee static inverter modules for larger aircraft, giving 240V AC from 24V DC. Used OC35's, if I remember, back in the early 70's.
Late 60's/early 70's - spRadio(Sailor) used KTG1200's in their 500V HT modules for their marine HF Tx's . Later upgraded with KTG2400's.

Regards, David

Re: HT for a car radio
 

Joebog1's Australian DC to DC PSU Modules - $A6.50 each - from where ? eBay, Hong Kong, Wuhan, - where ?
Hey Joe - any chance of your DC Valve Tester design block diagram, or general info, please ? As well as normal 240V 50Hz Mains for my workshop, its fully kitted out for 24V DC from a Sailor 1000 series marine SSB R/T Rig's 40A 24V Charging Unit( keeps two big tractor batteries fully charged up), & HT PSU.

Regards, David

Re: HT for a car radio
 

OOPS!! My apologies, it came from Amazon not eBay.

They now cost $13.06 plus $3.99 shipping, but that could be due to our dollar.

Original specs:

DC-DC 8-32V to 45V-390V Step Up Boost Converter Module ZVS High Voltage Capacitor Charge Board
Descriptions:

High Voltage Boost Module
Module Properties: Non-isolated step-up module
Input Voltage: 8~32V input(the default is 10~32V input.)
Input Current: 5A (Max)
Quiescent current: 15mA (12V liter 50V, the output voltage, the higher the current will increase too quiet)
Output Voltage: +45~390V continuously adjustable (default output ±50V)
Output Current: 0.2A Max(with input, output pressure related, the higher the output voltage, output current is smaller)
Output Power: 40W (Peak 70W)
Working Temperature: -40 ~ + 85 degrees (ambient temperature is too high, please enhance heat dissipation)
Operating frequency: 75 kHz
Conversion efficiency: up to 88% (efficiency and input and output voltage, current, pressure-related)
Short circuit protection: Yes.
Over current protection: Yes. (Input current exceeds 4.5A, reducing the output voltage)
Over voltage protection: Yes. (Output voltage exceeds 410V, lowering the output voltage)
Input reverse polarity protection: Yes (non-self-healing, reverse burning fuse, try not reversed.)
Installation: Four 3 mm screws
Wiring: free welding output terminals
Size(L*W*H):60 x 50 x 20 mm

Applications:

1.Pressure test power.
2.Hunting,eradication of mice.
3.Capacitor charging, electromagnetic guns, power supply.
4.The power supply for your electronic device, according to your system can set the output voltage value.


Yes I read a little Chinglish.

There is no city/state/country of origin supplied. They came fairly promptly though.

Joe

Re: HT for a car radio
 

I've just today received two of the modules Joe has been talking about, which I ordered from AliExpress about 10 days ago (cheaper than those selling on eBay).

Got one connected up and it seems to be fine and dandy (just trying it out at 200V), but have not yet tried to verify the limits. Only thing that I do note is that the pair of blue twin terminal blocks are extremely cheap and nasty (but easily replaced if required) apart that, everything seems fine and the multiturn pot controls the voltage very nicely; :clap:.

If we get a mouse plague like down Aus, I'm ready for them!

B

Re: HT for a car radio
 

I've had one of those modules supplying HT for my cutlery box amp for over the best part of a year. They were about a fiver when I bought mine. As you say, they regulate well enough but if you are thinking of pushing them toward their limits then it'll need a bigger heatsink and/or fan. Mine put s out 250VDC at 60-90mA. Best of luck chap!

Re: HT for a car radio
 

I've currently got one running at 225V in to a 5k load so ~45mA (~11W) and it's happy with that; hardly warm.

I think the info that comes with them talks about enhanced cooling being required at some point. It's a RU7088R fet doing the work.

Given that these units run at 75kHz, I suppose a "proper job" is required to enclose them such that noise is kept low?

B

Re: HT for a car radio
 

In my amp I had to put an earthed aluminum plate (all I had at the time!) just to cover the top side or the pre-amp would pick up noise.

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

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?

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.

B

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

Re: HT for a car radio
 

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

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

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.

Re: HT for a car radio
 

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