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Palomar Skipper 300 Red Plating

EchoKilo

Member
Nov 16, 2018
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Palomar Skipper 300 I converted to 6KD6. So to preface this for better understanding i bought this amp a month ago and it was DOA. I knew the tubes where probably trashed but I was replacing them nevertheless. Came with the 8950s so I knew it was probably over driven. Two of the four rectifier diodes were cracked in half and it had two Mallory 100mfd 450v capacitors in it. Replaced the diodes with 1n5406 and the recap kit I bought had two 450v 120uf caps. When the 8950s were still in it it worked for about an hour. It keyed 75 and swing 200 got some radio checks it sounded good. I took a standby on the air about 20 minutes after the whole amp began to vibrate and one of the 8950 tubes began to internally arc and blew one of the new caps I just put in. Thus why I coverted to the 6KD6s. After getting my box of glory the new tubes heated up I was glad I rewired the filaments correctly. I flipped it off standby into operate and the tubes began to red plate after 30 seconds. So I killed everything and began combing the schematic. To find someone stacked two 470k ohm resistors in parallel where only one was supposed to be. I tested the resistors and lo and behold both were open like a soda can. So back to waiting for the mail I put a new 470k resistor in and flipped it back on and it was normal for about 30 seconds and then red plated again. This is where I am at a loss. Is it the 2 capacitors throwing off the plate voltage because the schematic shows two 350v 60uf caps at 700v to the plate and the new ones are 450v volt 120uf is putting 900v on the plate. ( two 350v caps in series equals 700v while the two 450v shows 900v) could the voltage difference be contributing to the higher amp draw causing the red plating? Also from my understanding pin 2 of the tubes is the cathode going to a 17uf inductor to ground. Now correct me if I'm wrong inductors dont usually fail. None of them are burnt. I see in the schematic there are 4 of them but in my amp I can only find 3. Could those inductors be the fault? At this point I am about to change out the decouping ceramic caps along with all the chokes. Two peices that usually dont go bad but I am at a loss. I included the schematic maybe someone whom sees this can see something I missed. Other than replacing the diodes and changing out the caps twice rewiring the filaments and the resistor feeding the B+ what could I be missing? Thank you all for your time 73s
 

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Looking at that section that feeds into those filter caps it looks like the previous owner tied the transformer directly to one of the caps and the standby and operate switch are breaking the plate voltage. I see three relays on the back panel. Which one feeds the b+? This wire coming off the transformer tying directly into the cap doesn't look right to me. I included pictures of the relays and a reference to where that wire is tying to this is what it looked like before I changed the caps. In the schematic it looks like the transformer runs through a relay into those caps not directly.
 

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Many times when the contacts on a HV relay fail, they fail stuck closed. He might have been too lazy to troubleshoot/replace the relay so the next best solution was to be able to at least cut off the plate voltage "some" way... lol
 
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