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-   -   HT for a car radio (https://www.vintage-radio.net/forum/showthread.php?t=181854)

vinrads 11th Jul 2021 5:11 pm

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.

Radio Wrangler 11th Jul 2021 5:19 pm

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

Bazz4CQJ 11th Jul 2021 11:38 pm

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

joebog1 12th Jul 2021 8:54 am

Re: HT for a car radio
 
1 Attachment(s)
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

wave solder 12th Jul 2021 9:28 am

Re: HT for a car radio
 
Those look useful, what are they listed as?

MotorBikeLes 12th Jul 2021 6:49 pm

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.

joebog1 12th Jul 2021 9:51 pm

Re: HT for a car radio
 
Quote:

Originally Posted by wave solder (Post 1389465)
Those look useful, what are they listed as?

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

Oldcodger 12th Jul 2021 11:10 pm

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.

Station X 13th Jul 2021 8:54 am

Re: HT for a car radio
 
Quote:

Originally Posted by MotorBikeLes (Post 1389683)
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.

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.

vinrads 13th Jul 2021 4:07 pm

Re: HT for a car radio
 
Thanks Joe I have ordered one ,cheers Mick.

MotorBikeLes 13th Jul 2021 7:30 pm

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.

Chris55000 13th Jul 2021 8:41 pm

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

Oldcodger 13th Jul 2021 9:40 pm

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-)

David Simpson 21st Jul 2021 9:28 am

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

David Simpson 21st Jul 2021 5:07 pm

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

joebog1 22nd Jul 2021 4:56 am

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

Bazz4CQJ 22nd Jul 2021 11:35 am

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

Beardyman 22nd Jul 2021 12:57 pm

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!

Bazz4CQJ 22nd Jul 2021 1:08 pm

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

Beardyman 22nd Jul 2021 1:36 pm

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.


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