EMRFD Message Archive 4411

Message Date From Subject
4411 2010-03-04 12:41:17 g0kla Explosion
I have been playing with power and learning some lessons.

I've got a successful working transceiver from the R2 and T2 with about 5W out from a 2N3866 followed by an IRF510. During the day on 40Ms I've managed a few SSB QSOs over about 100 to 200 miles. This is great progress from CW QSOs with the "first transmitter". (This is my complete station btw)

But 5W into a poor antenna is not easy, so I put together a push pull IRF510 amplifier. This draws too much current for my homebrew LM317 based PSU and needs a higher voltage than I can get from my battery, so first I needed to build a new Supply. In hindsight I could have just bought another battery and run then in series.

I blew up 6 TIP42s before understanding the safe operating zone on the datasheet. Now I understand why a pair of pass transistors could only handle 4 amps, when I thought the transistors should EACH be good for 6 amps. I was mistakenly running my tests at a low voltage to "keep the power down", but was putting over 20 volts from the Collector to the Emitter. With that voltage difference 2.5 amps will kill it and form a short circuit. Then the supply output shoots up to 35V and your test load is melted..

But the supply is now working and I have 7 amps available at 24 volts. This drives the Push Pull IRF510 amplifier nicely with 50 watts into the dummy load.

But back to that poor antenna, which is electrically shortened with two coils. The amplifier does not like it. In an effort to match it through the ATU I managed to blow a 2mm sized physical hole in one of the IRF510s. It sounded like a pistol was discharged in the shack. I was quite stunned. That's not supposed to happen.

On the bright side, the PSU is working really well and did not flinch.

4412 2010-03-04 13:44:39 Tim Re: Explosion
I had a friend who after graduating from engineering school get a job at the "Center for Non-Destructive Testing". I asked him, what's the fun in that?

Does a push-pull linear IRF510 amp really need regulated voltage? I mean, you don't want a bunch of ripple, but I'm not sure it has to be regulated, and from what I've done 25V-35V is a nice sweet spot for max power output with IRF510's.

I'm running from batteries 99% of the time when using my solid-state equipment so maybe I've forgotten how bad the ripple or lack of regulation can be.

Digikey and Mouser still have IRF510's but the stock status seems to indicate that they are not in current producti