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Palomar 300a

RickeyKay

New Member
Dec 25, 2021
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0
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62
Hello, I’m having a couple problems with the amp, the caps have been replaced!!! My problem is when it’s on, operate, low, ssb, all tubes were warm and lit, when I tuned up the amp, the transformer started to hum real hard. So I shut the unit down!!! The transformer I did a visual is the one that’s 2.5 inches wide, with 3ohms out on pins 5 and 6 of the plug from transformer. It is the lower voltage transformer!!! When I plugged it back in for another test, the two driver tubes were dead, took the tubes had them tested, 91 percent for both!!! I’m stumped, there are some relays that are on the unit but can’t find in the schematic!!! Is there a service manual for this unit so I can test voltages, etc!!! Any help would be appreciated!!! I see nomadradio commenting on these units, seems to have a lot of knowledge!!! Thank you!!!
 

Dmans

Sr. Member
Jan 22, 2017
1,273
1,550
173
Georgia
I would check rectifier diodes in the bottom of the RF unit. Are you sure the capacitors were installed with the correct polarity?

There is no Service Manual for this unit that I know of.

The link below maybe of some help.
https://www.worldwidedx.com/threads/a-palomar-300a-in-distress.238839/

Operators manual and Schematic attached below.

73
David
 

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RickeyKay

New Member
Dec 25, 2021
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0
1
62

Jay Mojave

Sr. Member
Nov 17, 2015
319
597
103
69
Be advised there are two types of power supplies in the 300A, the shown diagram shows a voltage doubler circuit, and there are other 300A amps that use a full wave bridge circuit in the power supply. Good call to check the diodes, Nomadradio has said that the 4 diodes in the fullwave bridge power supply circuit often fail, so removing the 4 1000 V PIV diodes, and installing 2 diodes per leg, 8ea 1000V will fix this.

Why the driver tubes now don't light up I don't know. Hard to give good advice from your trouble discription. Maybe disconnected in the process?

I removed the filament and HV wiring from the transformer plug to see if my transformer would just sit there and not get hot just without any load. It worked ok. Found shorted diodes and shorted filter power supply capacitors, and opened fuses. Suggest hiring a Tech who has experience with HV High Voltage power supplies. Safety first.

Jay in the Great Mojave Desert
 

Dmans

Sr. Member
Jan 22, 2017
1,273
1,550
173
Georgia
When I plugged it back in for another test, the two driver tubes were dead, took the tubes had them tested, 91 percent for both!!!

Trace Pins 1 & 12 from your driver tube sockets and look for the bad connection. Don't overlook bad solder connections from the circuit board to the tube sockets.

If the finals are lit, there is 12VAc available from the transformer.

73
David
 

Jay Mojave

Sr. Member
Nov 17, 2015
319
597
103
69
One other little thing I would like to say here. Some how I have been sucked into fixing the worlds most screwed up Palomar 300A Amp, u name it, its burned up! Oh good!

I contacted the chief Engineer at Palomar, someone named Bob. I asked for copy of files and any documents on the 300A Amp. As the published stuff on the 300A does not cover all the different configurations found. And even to pay for any costs. Crickets heard in the background, as not even a reply email, or you CB'ers are all criminals ect.... I was expecting that.

I have done a lot of business with Palomar buying ferrite cores and such to reduce RFI ( Radio Interference) and build Baluns for antennas. I still get their advertisement emails.

So I will try again and see what happens.... Maybe there's a office rat some were that knows the filling system and can put his hands on all the 300A stuff.

Jay in the Great Mojave Desert
 

nomadradio

Analog Retentive
Apr 3, 2005
5,323
7,645
573
Louisville, KY
www.nomadradio.com
Ummm, would that be "Palomar Engineers", the company who is still around these many decades later? They're still very much in business. And they have nothing to do with the famous Palomar linears of the 70s

Not the same organization as "Palomar Electronics". They were located in Escondido when the 300A was made. Not the same people as Palomar Engineers.

At all.

The 1979 FCC ham reg revisions put the last nail in the coffin for the 300A. The 350Z model was intended to be a more-believable "ham" amplifier, but the new regs outlawed selling it as well. And that was the end of Palomar's amplifiers.

The published schematic is correct for only one of several production versions of the 300A. There were changes to the relay lineup, placement and relay type. The small board where negative bias is rectified and filtered was made in two versions. The input-matching circuit for the 300A's Low side is missing from the published schemo.

Sure woulda been nice if there were a 'shop' manual like a motor vehicle used to have. Engineering changes made during production would be described in detail, along with the range of serial numbers for that version.

Biggest hint is the serial number. Doesn't have one.

And I haven't even gotten to the power-supply differences.

It's an orphan.

73
 

Jay Mojave

Sr. Member
Nov 17, 2015
319
597
103
69
Thanks Nimadradio for the different Palomar companies explained. I might try another call for kicks and to prove iam wrong again.

Jay in the Great Mojave Desert.... Incerdiable rain lately
 
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AudioShockwav

Extraterrestrial
Staff member
Apr 6, 2005
7,368
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Sierras Near Yosemite National Park
As a creepy 9 year old kid, my uncle Marion took me out to the desert to dig for gold. We filled up the back of a pickup truck with dirt and went into Mojave to have it processed. It had $60.00 worth of gold that cost $100.00 to process.

Jay in the Great Mojave Desert

About 2 weeks ago I was exploring a little creek back up on a hill and found this.
It is flooded and can't get into it, I think I will go back up there this summer.

73
Jeff
 

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Jay Mojave

Sr. Member
Nov 17, 2015
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597
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This appears to be a hole in the ground, get a powerful light and look it over. Maybe pan some of the dirt. In Red Mountain Ca there going thru old tailings, and a armored truck shows every once and a while. I was never invited there.

Jay in the Great Mojave Desert
 

AudioShockwav

Extraterrestrial
Staff member
Apr 6, 2005
7,368
4,970
343
Sierras Near Yosemite National Park
It is quietly picking back up here, some small private mines have popped up in this area, price of gold makes those tailing piles look good.
I look for areas like this, after that snow, then warm rain it caused a lot of rapid runoff.
Here you can see were water has washed some debris down the hill and is exposing part of a quartz vein.
If you follow that down the hill to the little creek below.......

73
Jeff



20220103_140306_HDR.jpg
 
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