Palomar 300a amplifier

[Tweetybird]

I ordered the 316 too

 

[Tweetybird]

A look at the diameter of the plate-cap clips will reveal the tube type it was built with.

If they are 3/8-in. in diameter, it came with 6LF6 tubes.

And if they're 1/4-in. it used 6KD6 tubes.

There are other numbers that will work, but the biggest concern will be how tall they are. The height of replacement tubes is nearly always taller than the ones it was built with. The tubes produce in the 70s were just shorter. Palomar stopped making the 300A in 1979 or so, and most any tubes you buy will be newer than the amplifier.

And too tall.

If one or more plate caps touches the metal cover while it's powered on, this is seriously bad juju for the power supply.

There is more than one way to skin this cat, but be mindful of the gap between those plate caps and the underside of the top cover.

And be safe!

73

One of the tubes is too tall thanks. Would have had another kapow

 

[Tweetybird]

Ok I checked all negative side of filter caps to ground. I got continuity on all but one. Rf passes through amp until it is placed in operate then no rf out?

 

[nomadradio]

The two large 450-Volt filter caps on the board underneath are wired in series. Only the 'bottom' one of the two has the negative side grounded. This is to give you the equivalent of one 900-Volt capacitor by stacking the two 450-Volt parts end to end.

73

 

[Tweetybird]

Ok thanks I'm trying to figure out where rf is going when placed in operate.

 

[Dmans]

It looks like the attached schematic may be an advantage to you in this endeavor.

73
David

 

[Tweetybird]

I have been trying to print this schematic . I just got a new printer I need to install

 

[nomadradio]

Sounds like it's time to ask which relay setup your 300A has.

We see plenty of problems from 40 year-old relays.

73

 

[Tweetybird]

The relay on top is the same as my skipper. it has one on filter cap board that is connected to the operating/standby switch i

 

[Tweetybird]

Should axial capicator be used ? Or can you use a radial capicator? For main filter caps

 

[Dmans]

Axial's are easier to use since the amp was designed and built that way originally. They are a bit harder to find now but can be done. Radials can be used with no difference in performance. You just have to be a bit "inventive" about making them fit physically.

The important thing is the value and voltage rating of the replacements.

Check the link below to a thread that is several months old. I rehabbed my own 300A that had some issues. There are some pictures attached to the thread as well. It may help you with yours.

https://www.worldwidedx.com/threads/a-palomar-300a-in-distress.238839/

73
David

 

[Tweetybird]

I have the radial ones I saved your thread

 

[Tweetybird]

I saw your thread and you found axial caps. I found 100uf 450v axial caps. Are those sufficient? They would fit better but I can make the others work. It would be nice to see a picture of how a pro used them. The caps I removed were 80% for the 450v but 110% for the 35v so the caps are not the problem. Changing the diodes too. How do you find the white relay you guys were talking about, the potter and brumsfeld one

 

[Tweetybird]

I found a place that sells the right caps. Pricey but ok it will make installing them easier. I need all the help I can get. I will do what you did in the rehab of the amp it's a new hobby for me patience I need to work on

 

[Tweetybird]

I'm going to make the light bulb tester first! This time I wanna quit smoking like the skipper did when a half done job was tried