working on a Palomar 300 mobile amp w four MRF455s,
I need the schematic, the keyer board is damaged.
RX amp and TX not switching.
Roger
I need the schematic, the keyer board is damaged.
RX amp and TX not switching.
Roger
-
You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
Palomar 300 mobile amp w four MRF455s need schematic
- Thread starter Rogerbird1
- Start date
This separates the front panel from the main board. They are all the same on these amps.
http://www.cbtricks.com/Amp/palomar_other/400/palomar_400_sch.pdf
http://www.cbtricks.com/Amp/palomar_other/400/palomar_400_sch.pdf
Yeah...holy cow. I haven't seen one in that configuration before.
Q1 is the keying transistor, type 2N3904. It's the one between the right-hand relay and the fuse holder. If it checks bad, the two 1N4148 diodes D1 and D2 are also probably bad as well. This often happens when someone decides to try a driver amplifier. This one is meant to use with a radio only.
73
73
The key circuit is a bit different. in this one, it uses a TN2095 for the Key and the same for the Preamp. Both 1n4148 measure good. I will check the transistors next. They appear ok with an OHM meter. And one of the small coils on the left hand relay, has a hole burnt in it.. the other coil on the right hand side was replaced with a 220k resistor, and cut... I see from a restoration video I watched, that all 4 coils should be 22uh ...
('old school 300 BI Linear Rebuil/Repair Retro-Fitted with HG 2290's' Same amp inside..)
Turns out, one of the two 22uh coils was swapped with a 220k resistor and the other had a hole burned through it. Replacing both and cleaning up the soldering, got it up and running. Screen shots of the video I found help me verify the components. Also comparing to the schematics you all posted, helped as well. Thanks!
The Pi network on the output is kinda cool for keeping the signal somewhat clean. What I totally dislike is the RF input wiring. All the way from the relay, to the front panel power level switch, it runs down an unshielded trace. Then, it goes half way back down the board on an unshielded orange wire, to the input splitter. If your goal was to couple as much RF output, back to the input side as possible, this is what you do. It would take a lot of effort to give the input, a bigger antenna to "catch" RF from the output side, than this.
LOL, how much do you want to bet the original chokes on that board, were the small green, plastic molded ones with the standard color code on them? Whoever worked on it last knew their color code (other than the multiplier) but, not the difference between it being on a resistor or an inductor.
Last edited:
Totally sure that is what happened.. but when I opened it the 220K resistor was cut... May have been cut and soldered and the solder gave out.. which is why the amp originally worked then quit on its new owner. I replaced the inductors with proper wire wound 22uH coils.
Thanks again for all the help and suggestions.
Rogerbird