Palomar 300a amplifier

[Tweetybird]

This guy will sell you a hundred for fifteen bucks. Three-eighths diameter cap.

https://www.ebay.com/itm/LOT-100-MA...241141?hash=item36281d4635:g:dSIAAOSw3v5Yp2RB

Had a look at RF Parts. They show only the quarter-inch size.

73

Bought them

Just make sure to put a parasitic-suppressor choke on each of the four final tube's clips.

Good chance all you see between the clip and the plate choke where the four of them come together is plain bare wire.

The factory originally slid a small hollow bead of ferrite over each of the four plate-cap wires. It served as a choke for VHF frequencies. Serves to prevent the tubes from oscillating.

Just one problem. The ferrite bead would get hot, crack and fall off the wire.

Usually happened the first year it was used in any regular way.

That was a long time ago. What we do is to wind a four-turn coil around a 47 or 56 ohm 2 Watt resistor. The resistor's leads are usually long enough to reach from the top of the plate choke to the tube's cap.

Some amplifiers appear to work okay without these chokes. And some amplifiers will oscillate and cause headaches. The extra frequencies this produces are called parasitic signals.

The chokes serve to suppress this. Hence the name.

Or you can roll the dice and see how it behaves without them.

73

Where is a a good source for the wire for the coil and the resistor between the three palomar I need 14

 

[Tweetybird]

Bought them

Where is a a good source for the wire for the coil and the resistor between the three palomar I need 14

I will have 94 extra spring clips if you need some 3/8 inch

 

[Tweetybird]

I will have 94 extra spring clips if you need some 3/8 inch

I have all kinds of stranded wire 12,14,16 18,guage all are different thicknesses

 

[Tweetybird]

I have all kinds of stranded wire 12,14,16 18,guage all are different thicknesses

When separated the individual strands I'm talking about

 

[nomadradio]

Ahh, solid copper wire 18, 20 or 22 gauge is fine. Just stripping the plastic sleeve from a hunk of discarded doorbell wire will do the job.

Hardware store has that.

73

 

[Tweetybird]

Ahh, solid copper wire 18, 20 or 22 gauge is fine. Just stripping the plastic sleeve from a hunk of discarded doorbell wire will do the job.

Hardware store has that.

73

I have solid 12 but can get whatever size I ha twire comunacation wire its solid like phone wire I got wire and there broken amps

 

[Tweetybird]

I have solid 12 but can get whatever size I ha twire comunacation wire its solid like phone wire I got wire and there broken amps

Three broken amps

 

[Tweetybird]

Three broken amps

I change circuit boards at work like 1200.00 wholesale an I can post picks some one might have a use or there has be gold

 

[Tweetybird]

I put the tubes in, at dead key the watts went through amp(4 watts) when I placed the switch in operate 0 watts I could hear the relay key click. The tubes light up. Going to recap next,then the keying relay. If that does not work the pn2905 transistor will be attempted, its tiny an looks harder to do than the recap.

 

[Tweetybird]

Just make sure to put a parasitic-suppressor choke on each of the four final tube's clips.

Good chance all you see between the clip and the plate choke where the four of them come together is plain bare wire.

The factory originally slid a small hollow bead of ferrite over each of the four plate-cap wires. It served as a choke for VHF frequencies. Serves to prevent the tubes from oscillating.

Just one problem. The ferrite bead would get hot, crack and fall off the wire.

Usually happened the first year it was used in any regular way.

That was a long time ago. What we do is to wind a four-turn coil around a 47 or 56 ohm 2 Watt resistor. The resistor's leads are usually long enough to reach from the top of the plate choke to the tube's cap.

Some amplifiers appear to work okay without these chokes. And some amplifiers will oscillate and cause headaches. The extra frequencies this produces are called parasitic signals.

The chokes serve to suppress this. Hence the name.

Or you can roll the dice and see how it behaves without them.

73

I put in one for each tub. The were only two ferrite beads left on the 300a none on the skippers

 

[Tweetybird]

I put tubes In, it powers up. Barefoot watts pass through amp, i put it in operate no watts at all come out?

 

[nomadradio]

Does it do this on High and Low side, both?

More than once we have seen heat damage to a section of coax that leads from the High/Low switch to the underside of the final-section circuit board. It runs just alongside the final tubes. If they got hot enough at some time in the past, the insulation inside the coax could soften, so that the center wire shorts to the shield braid inside the coax.

Drive power to the four final tubes, in both High and Low side now gets shorted to ground before it can reach the tubes.

We use a teflon coax to replace it when this happens. Just don't use foam-insulated coax. It melts at an even lower temperature than the solid-plastic dielectric coax the factory used inside that amplifier.

If Low side works, but High side won't, then you have a different problem.

73

 

[Tweetybird]

Does it do this on High and Low side, both?

More than once we have seen heat damage to a section of coax that leads from the High/Low switch to the underside of the final-section circuit board. It runs just alongside the final tubes. If they got hot enough at some time in the past, the insulation inside the coax could soften, so that the center wire shorts to the shield braid inside the coax.

Drive power to the four final tubes, in both High and Low side now gets shorted to ground before it can reach the tubes.

We use a teflon coax to replace it when this happens. Just don't use foam-insulated coax. It melts at an even lower temperature than the solid-plastic dielectric coax the factory used inside that amplifier.

If Low side works, but High side won't, then you have a different problem.

73

I read that thread and changed the coax. It did not help still nothing. It was r58u coax. The plastic relay clicks,the caps look new,I ordered new anyway.new pn2905 transistors too I checked the operate and hi lo switch they seem to be ok.?

 

[Tweetybird]

I read that thread and changed the coax. It did not help still nothing. It was r58u coax. The plastic relay clicks,the caps look new,I ordered new anyway.new pn2905 transistors too I checked the operate and hi lo switch they seem to be ok.?

Source for teflon coax I put regular in.

 

[Tweetybird]

No power low or high not even the four watts from the radio. Nothing.