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my 2995dx
Guest
All Palomar 90As are not created equal. It was in production for a while, and had some revisions along the way.
Does yours have a trimmer capacitor on the solder side of the circuit board with the tube sockets on it?
If you do, start with that. Should be the input-tuning adjustment.
73
Does yours have a trimmer capacitor on the solder side of the circuit board with the tube sockets on it?
If you do, start with that. Should be the input-tuning adjustment.
73
That amplifier does have one annoying drawback.
The tubes pull anode current all the time, on standby and when it's keyed.
Yeah, sounds odd. Does tend to wear tubes out prematurely. In 1973 nobody cared.
We adopted the habit of cutting the ground foil around that end of R3. This cuts the ground circuit to the tubes.
A relay gets added with the coil wired in parallel with the coil of the factory relay. The new relay's normally-open contacts close across the cut in the ground foil when the amplifier is keyed, activating the tubes. And shutting them off in receive mode. The tubes breathe a lot easier when they're not pulling anode current.
Just need to choose a relay with a coil resistance of (roughly) 300 ohms or more. The new relay's coil current will add to the load on the keying transistor. The higher the new relay's coil-resistance rating, the less added stress gets put onto the keying circuit.
Cheaper than wearing out the tubes every minute the amplifier sits powered on standby.
73
The tubes pull anode current all the time, on standby and when it's keyed.
Yeah, sounds odd. Does tend to wear tubes out prematurely. In 1973 nobody cared.
We adopted the habit of cutting the ground foil around that end of R3. This cuts the ground circuit to the tubes.
A relay gets added with the coil wired in parallel with the coil of the factory relay. The new relay's normally-open contacts close across the cut in the ground foil when the amplifier is keyed, activating the tubes. And shutting them off in receive mode. The tubes breathe a lot easier when they're not pulling anode current.
Just need to choose a relay with a coil resistance of (roughly) 300 ohms or more. The new relay's coil current will add to the load on the keying transistor. The higher the new relay's coil-resistance rating, the less added stress gets put onto the keying circuit.
Cheaper than wearing out the tubes every minute the amplifier sits powered on standby.
73
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