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Palomar 300a low receive on operate.
- Thread starter Jimbo165
- Start date
When this amplifier is on standby, you should still hear a "click" when the radio is keyed. Yeah, this sounds wrong, but it's the way this model is built. That "click" on standby serves to let you use the preamp while the transmit side is still on standby. This is a feature most other amplifiers don't have. And the reason that those amplifiers have only two relays. The third relay lets you use the preamp while the transmit amplifier is still on standby.
To do this, that third relay has to go "CLICK" when you key the radio even if the switch is set to standby.
I'll guess that you don't hear that "click" on standby when you key the radio.
The other job this relay does is to activate the transmit relay when the switch is moved from standby to operate. A 300A that's working right will have TWO relays operating when the amplifier is set to operate and the radio is keyed. (AND the preamp is off).
The transistor at the lower left of your picture is the same one that's at the lower-left corner of the schematic you included. This one senses the radio's RF power.
Remove this transistor from the board. Put the board back in place, fasten the ground screw and see if the radio now has receive with the switch set to operate.
If the radio receives now, the problem lies with that transistor. Maybe you turned it around the wrong way. The 2N2905 transistor the factory used was round and made of metal. Your transistor is plastic. Should work, if it's the right type. ***AND*** it's turned around the right way.
Small detail: If it got turned around wrong, this can damage that type transistor.
For that matter, what type did you use to replace the original metal transistors?
But that's the quick test. Pull it out and see if you can receive with the switch set to Operate now.
73
To do this, that third relay has to go "CLICK" when you key the radio even if the switch is set to standby.
I'll guess that you don't hear that "click" on standby when you key the radio.
The other job this relay does is to activate the transmit relay when the switch is moved from standby to operate. A 300A that's working right will have TWO relays operating when the amplifier is set to operate and the radio is keyed. (AND the preamp is off).
The transistor at the lower left of your picture is the same one that's at the lower-left corner of the schematic you included. This one senses the radio's RF power.
Remove this transistor from the board. Put the board back in place, fasten the ground screw and see if the radio now has receive with the switch set to operate.
If the radio receives now, the problem lies with that transistor. Maybe you turned it around the wrong way. The 2N2905 transistor the factory used was round and made of metal. Your transistor is plastic. Should work, if it's the right type. ***AND*** it's turned around the right way.
Small detail: If it got turned around wrong, this can damage that type transistor.
For that matter, what type did you use to replace the original metal transistors?
But that's the quick test. Pull it out and see if you can receive with the switch set to Operate now.
73
Last edited:
Thank you nomadradio it is fixed now. I made a mistake on that transistor when I replaced it . I had mismarked board as for orientation and had that transistor wrong. When I took it out to test like you told me I found out what I had done. I am thankful for your help and the older gentleman LOL cause I am 68 myself is grateful . I just enjoy learning about these old amps. Thank You again.
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