6v & 90v DC Power supply

============================ Those 'inexpensive inverters' might need some attention in respect of the 'hash' they create , possibly causing interference in the receiver.

Frank

I need to generate 6v DC and 90v DC from a 12v DC automotive electrical system to power an RT-70A/GRC surplus military radio. I need about 250 mA at +6 volts and about 75 mA at +90 volts. I was thinking about using the guts from an old battery back up but it would be a bit of a kluge. Are there any 90 volt regulators in the 78xx series? How do I get the voltage up to where I can get something that I can get the 90 volts from. Getting the 6 volts doesn't seem to be a problem. A 7806 off the battery should work for that unless any of you can see a problem doing that. Maybe the common common would be a problem. Right now I'm running it off of an HP6299A and an HP6236B with commons jumpered. I'd like to be able to go portable with it.

Hello James,

You can build a step-up or flyback with the LM3478. Tough to solder though, it's a TSSOP package. Don't know what current you need but just pick a suitable FET.

For 6V I'd use a buck regulator instead of wasting 50% of the energy in a series regulator.

Regards, Joerg

90V @70ma is only 6.3W and a step-up of no more than 90/12=7.5. This would be something like a 24VAC center-tapped transformer turned backwards with a multivibrator drive of the secondary at 50-60Hz and the usual primary is rectified and capacitor filtered to produce the 90V. Since the reflected current is only about 1/2A, you can then feedback the rectified HV to drive an error amp that regulates the center tap down to 9V or so.

Hello James, Speaking as a cheapskate ham/hobbyist, how about salvaging parts from a computer power supply. Find a dud power supply for free at computer shops/dumpsters/rubbish tips/roadside etc. Salvage the TL494 integrated circuit that can be found in many computer power supplies.

You could build a 90 Volt power supply as Ray Robinson has down here

Here is a link to the TL494 Data sheet

This link tells you how to use the TL494 IC

Use another TL494 in a buck converter for your

12 Volts to 6Volts power supply module. Look at the bottom of this page for more info. Your 7806 is probably a better idea, saves a lot of messing about. Or you could use the guts of a mobile phone car charger. The charger that fits into the cigarette lighter in a motor car. You can find them in pawn shops for a dollar or two. Dud ones even cheaper. Usually just a broken connection from rough handling. Look at page 7 Figure 10 Step down converter.

In the few car phone chargers that I opened, the IC was a MC34063 and the schematic was very similar to that shown in figure 10 Just change R1 or R2 slightly so that you get 6 Volts out. You may have to check/change the value of resistor Rsc to be closer to that shown in figure 10 You might even get away with not changing the inductor. Try it and see if the original inductor works well enough for you.

A ton of reading, bits and pieces for free or dirt cheap. What a great hobby, this is James, eh!

Regards, John Crighton Sydney

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True for any kind of inverter.

73, Bill W6WRT

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Excellent info, John. Thanks!!

73, Bill W6WRT

Do it the way the original radio did it -- dynamotor. You can still find them in the back room at a lot of military surplus electronics junk stores.

Jim

Hello again James, I just came across this site while looking for something else.

Look at the the 6V AC from 12 V DC. Nifty!

Here is another

You want DC out so you will have to fit a bridge rectifier and filter capacitors to the output of the transformer just like Harry Lythall's circuit above.

Regards, John Crighton Sydney

So, put the cam thingie on some sort of spindle, with some kind of depth gauge thingie, (maybe a slide pot and a stick), and map the disks, and just make the same waveform from ROM?

Good Luck! Rich

Well, tastes vary, but really! Who wants a music box that makes it sound like you're at a skating rink? ;-P

cheers! Rich

Hello Jim,

But then be prepared for some major restoration. The bearings of a lot of these are nearly shot, mostly from sitting in an attic for decades. It's like old pond pumps. They run fine for a few weeks and then the racket increases, some weird noises appear, things get hot and they seize up.

I restored an old Hammond organ. These generate the tones in a similar manner. A motor (plus a start motor) and over a hundred pickup coils on the long secondary shaft. 20 hours of hard work got it going again but we have accepted the fact that some of the bearings are pretty much over the hill. So it needs 2-3 starts to coax it to run without that mild screeching in the background. Getting spare parts from a company that went out of business 30 years ago just isn't going to happen.

Regards, Joerg

On Tue, 27 Dec 2005 05:58:18 GMT in sci.electronics.design, john snipped-for-privacy@tpg.com.au (John Crighton) wrote,

So why is the guy from TI showing NTE transistors for the power switching? Nothing in the TIP line good enough?

Well, being the insufferabley pedantic researcher that I am, I came up with a page:

that about a third of the way down, says: "... Accurate imitation of the Hammond sound with simple electronic circuitry was difficult, because the subtly-changing phase relationships between tonewheels could not be easily replicated...."

OK, fair enough. :-)

I guess a piano is even harder - they don't even reproduce well from a live recording! :-)

Cheers! Rich

Hello Rich,

That has been tried many times. Several rather expensive electronic organs have come out claiming to emulate a Hammond. So far the real enthusiasts do anything to get their hands on the real thing, knowing that there will come a day when the last one croaks. IIRC it was Paul Shaffer (the guy who makes the music at david Letterman's show) who spent the equivalent of a luxury car to have one restored.

Regards, Joerg

Probably good enough for his measly 32 volts. I need to modify that circuit to work on outputs of 90 volts and 6 volts.

Hello Rich,

Ok, I am not much of an expert on instruments or music in general. But a Hammond organ can fill a living room with a sound that, with the eyes closed, you'd think you are sitting in a cathedral. And lots of rock bands wouldn't use anything else. That is why a lot of Hammonds have been "sawed in halves" so they can be transported to the next gig. You could even buy split versions built into professional transport cases.

Regards, Joerg

They have a Hammond B3 at my church, with the Leslie speaker. There is another model Hammond in storage that needs a lot of work. Someone had it on their screened in porch and the finish is ruined, but it still plays.

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

People like the old Hammond organs like the B3 because the can't go out of tune. The mechanical tone generator makes sure of that. They only sound like a skating rink in, get this, A SKATING RINK!

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida