HT power supply for battery receivers.

[Geordie McBoyne]

Found an article in the GFGF magazine No. 128 about the construction of a transistor power unit designed to replace the HT battery.
The oscillator operates between 100 to 200Hz.
Not a lot of information about making the transformer. "A transformer wound on a M-42 core (0.5 -10V)  at 100V at 4W. There is an anode spannung of 100V at 10mA with a inner resistance of about 1Kohm."

A circuit of an HT power supply appeared in a 1958 Radio constructor magazine.

Geordie McBoyne.

[Cleggy]

There are various designs out there - quite a few under the heading of "solid state vibrator". The newest designs I've seen make use of Li-ion cells. Finding a transformer of just the right physical size and just the right characteristics often seems to be a pain.

[Geordie McBoyne]

This is the circuit of the HT power supply in the January 1958 Radio Constructor magazine and titled "A Transistor D.C. Converter"
The transformer is hand wound and based on a miniature 3S4 output transformers with modified windings. The "T" and "U" laminations have the dimensions shown in the attachment and are stacked 1/4in deep. A feedback winding is added and consists of 60 turns of 36 s.w.g. enamelled wire.

Geordie McBoyne.

[Ed_Dinning]

Hi David , T & U lams are difficult to get these days, but the modern EI 30 , an E&I lamination should work nicely and is available.
Stalloy material will do but a more modern grain oriented material such as Unisil will also be OK

Ed

[BusyBee]

The first circuit shown is very similar to the idea which I have used a number of times over the years. Maybe not of the most efficient designs but I have usually used old computer power units for supply (generally 12V at several amps capability) so don't have to think about battery life. I have generally used a multivibrator, regulating the supply to 5V for the multivibrator. I use logic level mosfets for transformer switching, and supply, either the 12V to the transformer or, regulate the 12V downward for a more precise output voltage. It appears feasible for feedback to the regulator (12V side) for better regulaion but I have not had a need for it with my applications. I have mostly used more complex output filtering to reduce spikes etc. I use normally available mains transformers. I have done a little on measurement of efficiency but would have to lookup to check my figures. Just to say that the efficiency seems to be very much dependent on load and can vary quite a bit.

I have spent a little time looking into things and have planned to use an Arduino with carefully controlled switching times for comparison (to minimise cross over reduced efficiency and spike effects) but have not got round to it yet. Obviously this would directly replace the multivibrator, the output switching logic level fets being driven directly. Another thought thas had ocurred to me that needs a look is that a failure in the drive could cause problems. I have had an occasional blown transistor on tests but some of the supplies I have experimented with have been reasonable high power - In one case a twin parallel transformer design which drew an initial surge switching off the old Xbox psu I was using (rated at 14A I think). In the end, before I pretty much finished with >100V supplies, I changed to using fairly efficient voltage multipliers instead as the switch on surge from low voltage is a tricky problem whereas multipliers are more straighforward, in my experience. Obviously for most puposes, and especially for battery circuits. a simple invertor is a good move.

Tracy

[Radio Fixer]

Why would you want to build a SMP power supply?  Interference and complication.
For portables a string of PP3 batteries is easy to do neatly.  Buy the proper connectors not solder to the batteries.  Batteries last for ages but use re-chargeables if playing for hours, who does ?

In the pic the batteries are held together with double sided sticky pads.
   

If its not a portable then just build a small mains non switched supply and hide it in the set or behind.

Gary

[Murphyv310]

Hi.
I use a string of PP3's usually alkaline, in fact a KB Rhapsody I have hasn't had replacements since 2004 and the HT is 70v.
Rechargeable Ni-Mh are a bit hit and miss as they are lower voltage so an extra one is required, charging is awkward they either all need to be disconnected or you make a suitable charger for them wired in series. All this to my mind is pretty pointless as alkaline batteries last a long time in a battery portable.
I've tried electronic inverters for HT with little success due to RFI. Batteries all the way for me.

[Geordie McBoyne]

Many years ago I modified a Mallory vibrator unit so that the switching contacts were replaced by a 555 timer to provide the drive for a pair of FETs. The 555 was set to give a square wave with a 50:50 mark space ratio at 200Hz.
I was put wise to the fact the power FETs have a high source to gate capacitance, typ. 1000pF. The modified unit did work but it wasn't a truly plug-in device so another modified vibrator was made which dispensed with the 555 and the switching contacts controlled the FETs direct.

Geordie McBoyne.

[Nick]

Don't need anything fancy.

I do a bit with Nixies and did this design about 10 or 15 years ago:

https://nick.desmith.net/Electronics/NixiePSU.html

It's proved very popular with several 100 being made and used for all sorts of things, including for electrophoresis, guitar effects, small valve amps etc.

[Murphyv310]

How is it though for RFI Nick?