Battery powered valve portable supply

[Aerodyne]

I've just uploaded this video:
http://www.youtube.com/watch?v=hANpXoJ5YWM

It shows basic details of a battery powered ('D' cells) and fully portable inverter generating 90V HT for use with valve battery portable radios of the 40s and 50s type. Using it makes the portable truly portable. For anyone interested enough to look further, I've uploaded a complete construction article on my website www.vintageradioworld.co.uk including PCB design, component layout, parts listing and case details together with a full description of how the thing functions. It is eminently simple, as I never go too complicated with my designs.
Also on the site are details of the second edition of my original book 'Vintage Radios: Collecting, Servicing, Restoring'. This is available for email download. I think it unlikely that anyone on Golborne would need this type of info but I thought I'd mention it.
Any feedback welcome (positive preferred!)
Tony

[Yorkie]

Excellent Tony - very well conceived and designed in every respect, with full constructional details including the PCB artwork and overlay. It's surely going to be a real hit with battery portable enthusiasts. Reassuring to know that the ripple is negligible and can be reduced still further. The results attained on the sound track towards the end of the video speak for themselves!

[Joe]

I like that, Tony. I've often thought about doing something similar but wondered if the multivibrator output would be too square to transform.

I'd have also ended up the same blind alley as you originally did, the difference being that I wouldn't have known how to extricate myself therefrom.

- Joe

[Refugee]

I have been looking at a 50Hz sine wave inverter from an old signal strength meter. It has 6 volt heaters and runs 6 volts up to 80 volts. The secondary is open circuit at the middle of the coil so it is no good without a rewind or a new transformer.
I am tempted to use a mains transformer backwards.

[Aerodyne]

Thanks to all for the positive replies.
David, the ripple was only one of the problems that beset me. Worse was the RF interference the thing generates but as I described in the text, I overcame this by fitting capacitors across two of the diodes in the bridge. This was sheer guesswork, poking and prodding without much aim or idea. Fortunately I got there.

Joe, I think you sell yourself short. I'm sure you would have got there in probably much the same way (or likely quicker) than I did. As for the multivibrator output being square, it sure ain't in this circuit because of the inductive effects of the transformer. No doubt lots of ringing going on, hence the RF interference I mentioned above. By the way the device doesn't cause interference to other radios or TVs, even when adjacent to them, so those caps across the diodes appear to be doing a good job.

Refugee, have you had a look at the circuit, and is your sine wave inverter somewhat similar? The idea of a 'backwards' transformer certainly works well in the power supply, so perhaps its worth a bit of experimenting.

Thanks again to everyone for the interest and I should add that the moral support I received from Col (Retired) was instrumental in keeping me focused during the development of the circuit, despite the numerous blind alleys.

Tony

[Refugee]

The inverter with a duff transformer has two germanium power transistors wired as a multi-vibrater and nothing else. The transformer itself sets the frequency.

[Aerodyne]

Refugee, you might find the current requirements for a four valve set to be beyond the basic multivibrator as it stands. I'm guessing of course as I know nothing of your inverter or its source of power, but I feel sure that there's little here that sufficient experimenting can't overcome.
Tony

[Refugee]

It looks like the time is coming for me to get it out and draw up the circuit.
It uses 6.3 volt valves and once had a lead acid battery driving the heaters directly. The inverter was also powered by the same battery.
There will be a delay though as my scope has packed up and either needs looking at or another duff one will have to have a PDA transformer rewind.

[Aerodyne]

If you plan to use a lead-acid battery again, you should be able to restore the working inverter. Because I use readily-available alkaline 'D' cells in my inverter, much greater efficiency is needed, one reason why I strongly suggest that anyone making the device should stick closely to the recommended parts list.
It would be interesting to see your circuit, Refugee, for comparison; I did mess about for some time with the component values in a standard multivibrator circuit but got nowhere. It is always possible that further experimentation might have yielded the requisite efficiency but at my age the brain gets tired and I ended up going in ever-decreasing circles!
Tony

[Yorkie]

I notice that Rapid sell the required Vigortronics VTX-4206-206 transformer for only £3.28 inc VAT, but as usual, orders under £30 attract a £3.99 delivery charge:

http://www.rapidonline.com/Electrical-Po...6v-88-3869

(Couldn't find it on Spiratronics website, but I'm probably not looking in the right place).

Another project that is definitely on the 'to-do' list!