So a friend brings over his neighbors amp over. Recently 1 of the tubes blew and he replaced only the one. I have replaced all the diodes on doubler circuit. Has a new cap bank. Replaced the resistor for metering, B- floats. Installed a 50k resistor for bias shutoff. It only goes to ground when keyed. Anyways after doing all this and checking. Tube on right side starts to glow pretty quick. Switch to plate current, I meter is in the far right corner. Its pegged actually. I need to check a few caps yet. The 3 pins on the tube sockets are directly grounded as they are measuring grid and plate current thru CT of transformer. Anyone run into this problem before? This has a built in driver. Needs a small radio with very little drive. To be honest I don't like this amp. Very cheaply put together.
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black Cat JB2000
- Thread starter Crusher
- Start date
The best part of the amp is the fixed Tune. LOL. Talk about cheap. No way to compensate for changes in tube. Guy didn't even know how to run amp. At one point he used the input tune to set his carrier. He had set it so his input was around 4.0, but had a high carrier.
Figured it out. All 5 pins on bottom of tubes are shorted together. I had removed HV and metering all together and started doing continuity test thru circuit. Disconnected bypass caps and everything and that is when I discovered tubes shorted internally.
Guess that will teach guy to only replace single tube when he had one blow inside amp. But it cost me a 30-50% tube of my own as well to discover this
LOL. Well I learned something new. I have never seen a tube shorted like this before. Oh well. Part of the learning curve.
That is the correct way to set the amp's carrier with the tuner on the back when using the stock driver tube. It's basically a JB 150 driving a pair of 3-500Zs.
Alan
If you're gonna be cheap retubing a multi tube box and just replace one tube.....be real cheap and buy a used tube. It's almost always easier to get two old tubes to play nice together than it is to get one old one and one new one to run even.
Lots of new tubes have received shorted grids and holes burnt through their plates due to this mistake. Unless you're going to run the amp well below rated specs, matching tubes are essential. Otherwise the strongest one will hog most of the drive power and self destruct under full load.
Lots of new tubes have received shorted grids and holes burnt through their plates due to this mistake. Unless you're going to run the amp well below rated specs, matching tubes are essential. Otherwise the strongest one will hog most of the drive power and self destruct under full load.
Myself & Triple-OOO are looking for the schematic diagram and user Manuel/operating Manuel. For the black Cat JB2000 Amplifier.
Thank You.
Thank You.
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