Hi,
Hope somebody can help me here.
I have a Bloodhound, which was generating far too much heat. It got so hot that the glass of the output tubes kind of melted.
Anyway, I changed the tubes, and the plates are still getting red after a few minutes the amp is on. And more, I took it to a tech and the guy says the amp is oscillating at a very high frequency.
Anybody ever had this happening to their amps?
EVER HAD YOUR WHOLE CIRCUIT OSCILATING?
Moderators: pompeiisneaks, Colossal
-
LeftyStrat
- Posts: 3117
- Joined: Fri Jan 14, 2005 6:58 pm
- Location: Marietta, SC, but my heart and two of my kids are in Seattle, WA
Re: EVER HAD YOUR WHOLE CIRCUIT OSCILATING?
My guess is a failed part in the power amp. Discharge the caps, pull the tubes, and measure things like screen resistors. Not familiar with the amp topology, but cathode resistors and caps if it is cathode biased. Bias circuit if it is fixed bias.
It is likely not in the preamp, so you want to concentrate on the power amp stage. Work from the output tubes outward, checking for component failure.
I'm assuming of course you haven't changed anything in the amp recently.
Your tech should have a scope, he should be able to find the problem, otherwise you need a new tech.
I would not fire up the amp with tubes until the problem has been identified. You don't want to burn up any iron.
It is likely not in the preamp, so you want to concentrate on the power amp stage. Work from the output tubes outward, checking for component failure.
I'm assuming of course you haven't changed anything in the amp recently.
Your tech should have a scope, he should be able to find the problem, otherwise you need a new tech.
I would not fire up the amp with tubes until the problem has been identified. You don't want to burn up any iron.
-
skyboltone
- Posts: 2287
- Joined: Wed May 10, 2006 7:02 pm
- Location: Sparks, NV, where nowhere looks like home.
Re: EVER HAD YOUR WHOLE CIRCUIT OSCILATING?
Classic HF and VHF birdies can often be located by taping a neon bulb to a chopstick. Isolate the wires on the bulb and just tape it on the end. The neon will glow brightest where the oscillation is strongest. Trace back from there. Lead dress usually, or a wrong/failed part. You've created a tank circuit inadvertently and it's taken off.
The Last of the World's Great Human Beings
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
Re: EVER HAD YOUR WHOLE CIRCUIT OSCILATING?
Hi,
Thankj you for the replies. Yes, I did change the PT - which was blown. I forgot to mention that before I had the problem mentioned here, the amp was blowing fuses, until it finally blew the PT. I THINK it was a faulty DC socket, which I already replaced - the wire was loose and the amp was switching on/off on its own and I guess that blew the PT or short circuited it.
Anyway, thank you.
Thankj you for the replies. Yes, I did change the PT - which was blown. I forgot to mention that before I had the problem mentioned here, the amp was blowing fuses, until it finally blew the PT. I THINK it was a faulty DC socket, which I already replaced - the wire was loose and the amp was switching on/off on its own and I guess that blew the PT or short circuited it.
Anyway, thank you.
Re: EVER HAD YOUR WHOLE CIRCUIT OSCILATING?
With the tubes going into thermal meltdown, it would seem that there is no bias at all to control plate current . There needs to be negative volts on the grids in relation to the cathodes of the power tubes.
PILA
PILA
love those tubes!