In need of a Palomar 225 schematic.

[jhutch62]

Let me first start out by saying "Yes, I know it is illegal to use a linear amp on the 11 meter [CB] band," but I know that a lot of CBers use them anyway, so I thought I would ask here. With that said, I was wondering if anyone has a schematic for a 10 meter Palomar 225 linear amplifier with automatic side band that was manufactured Jan 1997? I did an exhaustive Google search and the schematics that I've found did not match the one that I have, they where slightly different and sometimes a lot different than my Palomar 225.

As the photo shows, the amp only has 4 transistors and just a handful resistors and diodes and is pretty basic. Hopefully someone will recognize this one and maybe point me in the right direction as to where to get a schematic.

Thanks.

 

[prcguy]

The thing is pretty basic, so the circuit board is your schematic. What doesn't it do?
prcguy

 

[jhutch62]

I bought it used a few years ago and I'm just getting around to seeing if it works. When I hooked it up, the receive pre-amp didn't work and it wasn't putting out any rf power. I checked the 2 pills [sd1446] and they seemed fine, so I just went ahead and replaced the two 2n222a transistors and the two electrolytic capacitors —and now, the pre-amp works, but there's still no rf power. It's most likely one of the small signal crystal diodes. I just thought that if I had a schematic, I could narrow down the area where to look, rather than pulling every component.

 

[prcguy]

Does the relay click when you put a few watts into it? You can check the base of the switching transistor with a voltmeter to see if there is a small voltage change when you key up. You could also pry the cover off the relay and manually switch it while transmitting to see if the rest of the amp works. If it does then you might just have a bad diode or coupling cap or resistor to the diodes feeding the keying transistor.

You can unsolder one side of the diodes or resistor to test them. You can't really check a PA transistor with an ohmmeter except for very basic problems like totally shorted or open, it really needs a proper transistor checker or you can make a little RF sniffer for your voltmeter and probe the base and collector for an increase in RF voltage and also see if its balanced between output devices when its putting out some power.
prcguy

I bought it used a few years ago and I'm just getting around to seeing if it works. When I hooked it up, the receive pre-amp didn't work and it wasn't putting out any rf power. I checked the 2 pills [sd1446] and they seemed fine, so I just went ahead and replaced the two 2n222a transistors and the two electrolytic capacitors —and now, the pre-amp works, but there's still no rf power. It's most likely one of the small signal crystal diodes. I just thought that if I had a schematic, I could narrow down the area where to look, rather than pulling every component.

 

[K5MPH]

I think this amp uses the 1N4004 Diodes for a protection circuit if one of them is blown it won't let current flow you need to check them out.....

 

[jhutch62]

Yeah, both relays work, the pre-amp and the RX/TX both click when actuated. I've only done some very basic troubleshooting, such as check for operating current at the collectors on both sd1446s, as well as check for symmetry between the two. When I checked the base current of the sd1446s, during RX it was 0 and when I keyed the mic, I got similar fluctuating readings on both.

 

[jhutch62]

Yeah, I've checked and replaced both 1n5404s which is the exact equivalent to the 1n4004.

 

[K5MPH]

Yeah, I've checked and replaced both 1n5404s which is the exact equivalent to the 1n4004.

sent PM......

 

[K5MPH]

Does it have the Blue or Black front face.....

 

[jhutch62]

It has a black face.

 

[K5MPH]

It has a black face.

I have a Schematic for a Palomar 225 with the blue face it looks the same as the black face .....

 

[Kb2Jpd]

Let me first start out by saying "Yes, I know it is illegal to use a linear amp on the 11 meter [CB] band," but I know that a lot of CBers use them anyway, so I thought I would ask here. With that said, I was wondering if anyone has a schematic for a 10 meter Palomar 225 linear amplifier with automatic side band that was manufactured Jan 1997? I did an exhaustive Google search and the schematics that I've found did not match the one that I have, they where slightly different and sometimes a lot different than my Palomar 225.



As the photo shows, the amp only has 4 transistors and just a handful resistors and diodes and is pretty basic. Hopefully someone will recognize this one and maybe point me in the right direction as to where to get a schematic.



Thanks.

A lot of those amplifier designs are based on the RF Motorola books. Most of the designs are run Class C for FM/AM and you change the bias to get Linear operating for SSB. Start with the MRF-455 examples.

It is good circuit for learning how to build and repair but most have awful rf filtering. Expect lots of harmonics. Use a big filter and a very clean radio or signal source.

Expect a ticket if you don't.

Adam Kb2Jpd


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