Discussion in 'Amateur Radio Amplifiers' started by WD8BWW, May 22, 2017.
So you burnt it up ? lol
I just had to...
Please do forgive me. It is Sunday.
In my line of work, we call this, "MINT condition... that's Motors Intermittent, Noisy Transistors".
It is easy to blame it on the dead dude.
Some like it when work is dead.
I always expect gear to be completely screwed no matter what anyone says about it unless I can try it out first. It's not a problem really, just setting the expectations to the correct posture.
Well the owner is taking it well. He did buy it at a good price. So starting out he if it had worked it would have been a real find. But $430 for tubes and soft start, and other recommended mods are adding up. When he is done he will be invested at about what a good 922 is going for these days. I just hope there are no more surprises around the next corner.
Most of the stuff sold by H*rbach is OK to use. Some of the stuff isn't needed. It all costs more than it needs to. There's a lot of snake oil on the Internet. Tom W8JI trimmed the trash out of a TL922 here: http://www.w8ji.com/tl922_mods_parasitic.htm.
If that amp was sitting around not being used for quite some time, it should have been brought up slowly on a Variac and carefully observed for maladies before it was hit with full line voltage. If a tube develops a short or becomes terribly gassy a single burst of energy released in a momentary tube arc at initial turn on could cause major damage. A real professional knows this and treats every unknown amplifier condition as such. No amplifier gets turned on at my shop without being brought up on a Variac slowly initially. A really bad tube that can potentially cause the kind of damage you have encountered could have been caught beforehand. Although a bad tube can hold out for another time, it's still a routine worth going through if a tube is bad to begin with. A blown up 1 ohm 5 watt shunt resistor is a tell tale sign of a major tube failure. I believe the old saying that an ounce of prevention is worth a pound of cure. At this point you have to determine if the plate meter is open, a simple one second test with an ohm meter. Then a good set of tubes needs to be obtained. Remember, generally, amps do not blow up tubes, tubes blow up amps
yes sir !! I could not agree more. On this amp I did a full day of slowly bringing up the voltage with a Variac. I learned this refurbishing old test equipment. As I increased the voltage as soon as I saw the tube filament not lighting I pulled it. I think that was at about 50% voltage. Holding there I swapped the "good tube" between sockets and determined the other tube was bad. I then pulled both tubes and continued with the Variac to reform the electrolytics. Better part of the day of increasing the AC before the amp without tubes saw full voltage. I then installed the old good tube at the 50% voltage and slowly brought it up to full voltage. I let is run at full voltage about an hour. Then keyed it with no RF and that was when I saw the meter peg. That was when I started this whole posting chain on why the meter might be pegging. I got good and accurate advice leading to the bad resistor discovery.
Bottom line you are 100% correct on never just turning on high voltage equipment if it has been off for a while or you don't know how long it has not been powered. This has done in a lot of high voltage caps and tubes.
Well i pulled the amp apart, meter pulled out and measured the meter with 1k ohm resistor in series. There was no movement and I read right at 1020 ohms. Connecting the meter directly shows 15 ohm resistance between contacts and does move but just two needle widths.
It sounds like it may be good.
What happens when you test it using the Diode test setting ? (polarity observed.)