I bought this amp without tubes I think there is a couple of different ones used doe any know how to tell which ones I have yellow face black plastic switches any help would be appreciated I know there is a wealth of knowledge on here thanks for listening
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Palomar 300a amplifier
- Thread starter Tweetybird
- Start date
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
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
You save:
$700.00 (7% off)
Price:
US $9,300.00
$447 for 24 months
https://www.ebay.com/itm/Vintage-Pa...887466?hash=item4d90076caa:g:XesAAOSwT2dZ58HS
Somehow this just never gets old
I think I saw that one.
I sold one just like it , wasn't as good of condition as that one but still in nice shape. Tubes were in good condition and clean inside. Came from the home of a silent key. Think it sold for less then 2 bills. Average was 3-400.
I sold one just like it , wasn't as good of condition as that one but still in nice shape. Tubes were in good condition and clean inside. Came from the home of a silent key. Think it sold for less then 2 bills. Average was 3-400.
The last one I had was bought for $185 bucks.
And traded for a Yaesu 101 B.
It is crazy what people want for these things now.
Years ago, before Flea bay we found them at yard sales on the weekends.
73
Jeff
And traded for a Yaesu 101 B.
It is crazy what people want for these things now.
Years ago, before Flea bay we found them at yard sales on the weekends.
73
Jeff
Tube came 6lf6 matched for plate voltage we will see if it works was real dirty cleaned it looks like caps are new they are small 100uf only putting four watts in I will start on low dont have a variac
A friend of mine bought a 300a at a yard sale. He bought the amp with no power supply for a few bucks and found the power supply at another table. I think the grand total was 14 bucks for a working amp.
I ordered wrong tube need 3/8 clip where can I get them are plumbing spring clips the wrong metal?
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
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
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
Gotta key down on Friday night. There was a time when I would have soldered the leads to the toobs to get on the air.