The AM Forum

WAAYYYYY back in 2002 (no, not as far back as the days of vacuum tubes  ;)  [I had a college professor back in '73 who used to constantly say "Back in the days of vacuum tube, we did it like this ..... but of course ...... (etc.)]

Anyway, back in 2002, I built my "main" class E rig, and it's been flawless - until A FEW DAYS AGO !!!  I was taking to the Dirk-a-tron (WA2CYT), and had just signed out - and went back to make some quippy comment when - ALAS - the transmitter WOULDN'T TRANSMIT !!!!  ???

Not be be daunted, I looked at the overload indicators, and found one of the modules was indeed causing an overload and shutting the transmitter down.  Really.  I was indignant.  But, taking out my trusty Simpson 260 (analog meters RULE !), and measuring the DC resistance of the drain bus to ground, I found about 0 ohms.  Hmmmmmmmmmmmmmmmmmmmmm..... Looks like a blown FET - and after all these years, too..

So, I dutifully unsoldered the drains of the MOSFETs, one at a time and waited for the short to clear.... Got to the last one, unsoldered it, and the short was STILL THERE !!!  Well, it WASN'T a FET...  Maybe a TransZorb?  I unsoldered the drain protection transzorbs - the short was *still* there.   Hmmmmmm, now what?  There were only 2 components left - the output RF transformer and the RF bypass capacitor (a .15uF, 250 Volt unit).

Well, I unsoldered the bypass cap and VIOLLIA !  That was the problem.  A shorted RF bypass cap.  Replaced it with a nice orange drop and was back in business  8) 8)

Oh well, it was nice to get some of the dust off the RF output heatsink.  I haven't touched it in a LONG LONG time   ;)

Have a very happy and safe Thanksgiving (watch out for that high voltage !  :D

Regards,

Steve

11N90s Rock, not like the good old days trying to jam RF through a TO3

Tried to  get in this morning to comment on your cap failure... alas, didn't get through the masses.......


My orange drops only get very slightly warm to the touch..... (0.15uF  600V)
(The output transformers stay cool)

Someday, I was planning on taking Frank's advice, and putting in several smaller value caps...
But, it's been working FB, so why mess with it?

There's "no" RF on the DC lines outsid the transmitter... so I assume they are doing what they're supposed to..

orange drops have a lot of ESL above 1 MHz. That is why they run warm. I blew the foil caps in my 160 meter rig one by one. I had 5 in parallel. They really need low Z caps in parallel to do the complete job. 

I think there's a jinx involved, Steve. You were using that transmitter in March when we were talking and my mod tranny went west. Wouldn't surprise me if the Spirit of T.O.M. was involved somehow!  :o

At least you got it repaired a whole lot faster than I did!

Hi Todd,

I forgot about that :-)  Hey, what's T.O.M.  ?  I probably should know, but I'm not making a connection.

Happy Thanksgiving !

Steve

T.O.M.   =  The Old Man, the Father of American Amature Radio.

[/quote]

Hi Todd,

I forgot about that :-)  Hey, what's T.O.M.  ?  I probably should know, but I'm not making a connection.

Happy Thanksgiving !

Steve

[/quote]


You should be verry, verry carrfull...

Also inventor of the silencer for guns. And son of Hiram Stevens Maxim who invented the Maxim Machine gun.

He's haunting Steve's transmitter because it's Class E, instead of Class E-Z.  ;)

Happy Thanksgiving to you also Steve, Steve, and anyone else who dares to celebrate the holiday honoring pilgrims, injuns, and turkey sacrifice. I get hungry just thinking about it.

 

Machine guns and amateur radio......All from a guy in New England.

Where has all of our culture gone?

Are you believing this stuff?   Not me.  I figure an alligator clip fell off and shorted something.   Steve's just covering, blaming it on a defenseless capacitor.

Jon

Nah, I don't believe any of that malarky!!
Not for a second.

Obviously it happened because he was in QSO with Crappy Yellowy & Tinny the DIRK-A-TRON - PHASE POLICE!!

 ;D ;D ;D :o :o

              _-_-WBear2GCR

Yesterday we were chiding my son, home for Thanksgiving, about his school and football.   Well do you know what MIT is big in? Shooting.  They compete with the military academies and do well.   They beat the US Coast Guard last month and lost narrowly to West Point just this week.    So, I guess, hell yes,  Guns and Volts and New England.

http://mitathletics.cstv.com/sports/c-pistol/recaps/111907aaa.html

Jon

Hi Steve,

I had a cap crap out on my 1928 breadboard - main coupling cap off the feed choke. Turned it into a yodeler. One of those painted micamolds of yore. I guess it couldn't take the 350 VDC and awesome RF level that the 45 tube was dishing.

Mike WU2D