[Milsurplus] [MRCA] Easy DC to DC inverter

[Ray Fantini]

Modern transistors have Ic rating that those old designers could never dream of, the Ic on a 3055 is 15 amps or 120 watts or so, going to also look and see what happens with modern power FET devices being that I have been playing with them a lot.

Ray F/KA3EKH


From: scottjohnson1 at cox.net <scottjohnson1 at cox.net>
Sent: Tuesday, June 25, 2024 12:15 PM
To: Ray Fantini <RAFANTINI at salisbury.edu>; MMRCG at groups.io; mrca at mailman.qth.net
Cc: milsurplus at mailman.qth.net
Subject: RE: [MRCA] Easy DC to DC inverter


This looks like the old Tripp-Lite circuit.  They just kept adding more transistors in parallel and a bigger xfmr to increase output, I think they sold units from 30W up to at least 1200W, if you want to stabilize the frequency , you simply add an astable 555 circuit in one leg of the feedback circuit.
Simple, and easy to fix without much head scratching!

Scott W7SVJ

From: mrca-bounces at mailman.qth.net<mailto:mrca-bounces at mailman.qth.net> <mrca-bounces at mailman.qth.net<mailto:mrca-bounces at mailman.qth.net>> On Behalf Of Ray Fantini via MRCA
Sent: Tuesday, June 25, 2024 08:12
To: MMRCG at groups.io<mailto:MMRCG at groups.io>; mrca at mailman.qth.net<mailto:mrca at mailman.qth.net>
Cc: milsurplus at mailman.qth.net<mailto:milsurplus at mailman.qth.net>
Subject: [MRCA] Easy DC to DC inverter

Some ideas work so well and are so simple is hard to wrap your head around them. Last couple years have been playing around with solid state inverters for powering tube equipment in the field. Recently Craig, N3TPM turned me on to this simple circuit, have also seen this several places on the internet so decided it was time to try it for myself. Near as I can figure it's a multivibrator or at least that's how I drew it. I have put together a couple of these on the bench and have to say that due to its low parts count and simplicity find it hard to beat. Uses a regular transformer and, in this case, using a center taped twenty-five-volt two-amp transformer and it develops 120 volts on the secondary all day long. The transistors are nothing special, just 2N3055 or the like from the junk box. Unloaded current drain is only around six hundred mills and with Rx being 680 ohms the running frequency is around sixty cycles, increasing Rx raises the frequency and lowering Rx decreases the frequency. When Rx is 250 ohms was running around fifty cycles and at 1.2 K was just above seventy cycles.
Have not tried it yet but would like to see what this will do to substitute a mechanical vibrator, going to assume that it will work but have not gotten that far yet myself.

Additional comments are commentary: Do not read if easily offended!
Ok, so I know that there is a plethora of cheap Chinees crap out there that you can buy for nothing all day long but screw that stuff. Why buy when you can build? The advantage of this circuit is its low frequency so there are no big noise issues, it uses cheap junk parts and can be understood and repaired by anyone with minimal understanding of electronics, just try repairing or replacing something on one of those small micro inverters.
Basic assumption: We do this because this is what we want to do, not because it's easy, or cheap. If we were only interested in getting on the air and racking up contacts there are way better things then playing around with this stuff. Don't know, maybe some feel they may not be up to the task of understanding or building their own but what better way to learn? Big advantage to working with a lot of this old military stuff or any vintage hardware is its bigger, easy to work on and easy to understand where as modern equipment that's microprocessor driven or using LSI devices and surface mount technology are way more difficult to deal with.
Least that's how I see it, or perhaps I am just a victim of my own prejudices along with my own personal history and preferences, maybe in twenty years people will look back and regard these as the "Golden Days" when cheap Chinee's junk freed us from having to use soldering guns?
As you can tell it's a slow day at work, and I have time to sit around and write up such dribble.

Ray F/KA3EKH
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