Palomar Skipper 300 Question(s)

[jtrouter]

Hello all
My newest project was to bring a Palomar Skipper back from the dead, I found the problems fixed it and even found a set 0f good 8950 tubes for
it. However most tube amps that i have worked on they have had large resistors with wire wrapped around going to each plate cap and or little ferrite beads. The Skipper
does not have either? Is it not a safety item to not have the resistors feeding the tube caps? If so what size do i need to use? And should i also
do i need the little ferrite beads and if so what type do i use? I did check the schematic and from the factory it does not use any of either. But if it makes them safer i would rather use them i just eed to know what to use. Thank you and look forward to hear back.

 

[nomadradio]

We use four turns of wire on a 47-ohm resistor on each plate cap. Nothing magic about that combination, just seems to work reliably.

The tiny ferrite beads that Palomar used saved them the labor of wrapping wire around resistors. Just one problem. Somebody overdrives or mistunes the amplifier sooner or later. The ferrite beads overheat, crack and fall off. Now there is no suppression of unwanted feedback at all. Policy here is to replace that bare wire on the plate clip with a wire/resistor suppressor choke. You can overheat this kind of suppressor same as you can a ferrite bead. The difference is the wire/resistor choke won't fall off.

That's my experience with the ferrite-bead parasitic-suppressor choke. They break and go away.

73

 

[jtrouter]

We use four turns of wire on a 47-ohm resistor on each plate cap. Nothing magic about that combination, just seems to work reliably.

The tiny ferrite beads that Palomar used saved them the labor of wrapping wire around resistors. Just one problem. Somebody overdrives or mistunes the amplifier sooner or later. The ferrite beads overheat, crack and fall off. Now there is no suppression of unwanted feedback at all. Policy here is to replace that bare wire on the plate clip with a wire/resistor suppressor choke. You can overheat this kind of suppressor same as you can a ferrite bead. The difference is the wire/resistor choke won't fall off.

That's my experience with the ferrite-bead parasitic-suppressor choke. They break and go away.

73

Thank you, one last question what wattage should the 47 ohm resistor be? I am sure it will be more than the 1/4 and 1/2 watt ones i have in stock so i want to order the correct size. And as always thank you for the fantastic guidance. And i forgot to ask why are they used?

 

[nomadradio]

Typical parasitic choke is wound on a 2-Watt resistor for tubes this size.

73

 

[jtrouter]

Typical parasitic choke is wound on a 2-Watt resistor for tubes this size.

73

that was my guess, again as always thank you!

 

[jtrouter]

Typical parasitic choke is wound on a 2-Watt resistor for tubes this size.

73

I just ordered a box of 2 watt assorted resistors, I have 22ga solid wire is that large enough? If not is it safe to use two strands twisted together? The wire diameter on a similar size amp used 1mm diameter solid wire which is about 18ga.

 

[jtrouter]

I just ordered a box of 2 watt assorted resistors, I have 22ga solid wire is that large enough? If not is it safe to use two strands twisted together? The wire diameter on a similar size amp used 1mm diameter solid wire which is about 18ga. Now i was doing some more reading and it said to use carbon resistors not metal film like i ordered? should i reorder and get carbon resistors. Its hard when you do not understand?

 

[nomadradio]

The 1mm size is probably a better bet. Wouldn't recommend smaller. What we have always used is larger. Just the same we have seen that size wire in factory-built linears that worked just fine, so you should be good to go. Never tried to find out how much smaller size I could get away with.

73