All,
My friend, the owner of the Kris 600 SSB I recently repaired, brought me a Palomar Skipper 300 to see if I could repair it for him. Since I take plenty of pictures of before and after (mostly so I can get to the AFTER) I figured I would post a thread here in the hopes it could help someone in the future.
Pre-Emptive Disclaimer:
If sweep tube amps are not your "cup of tea" my feelings are not hurt if you bypass this thread completely.
So my friend tells me that the Palomar quit keying all at once but was working well up to that point. In fact he had someone replace the filter capacitors in it recently.
Upon inspection, I could see why filter capacitors were necessary. Below is what I found below deck.
It appears that a filter capacitor explosion had previously happened. But doesn't explain why it quit keying suddenly.
A closer look showed me where the keying problem started.
The yellow circled area above shows the input to the 12 volt transformer lead disconnected. Whoops, no 12vdc, no keying circuit!
So my plan was to clean up the filter cap tar, add some equalizer/bleeder resistors across the filter capacitors, re-solder the input lead to the 12 volt transformer and send this guy home! At least that was the plan...............
A closer look at the high voltage circuit revealed a crack in a glitch resistor (.5 ohm/5w)
Removal of the resistor from the circuit and testing showed it completely open. This got me to thinking about the rectifiers (exploded filter cap, glitch resistor cracked???)
Since I have a handful of 1N5408's, I proceeded to replace them all. (My earlier mention of my plan..........
)
So above is after replacement of the rectifiers, addition of equalizer/bleeder resistors, replacement of the glitch resistors and replacement of several other 2 watt resistors.
During the replacement of these components, I found a repaired another unexpected problem.
A closer look at the fuse holder will show a crack about half way around the housing right at the chassis mount flange.
So with all of these things repaired/upgraded, I fired it up and tested it. It had good high voltage and a strong 12vdc supply to the keying circuit. So after inputting a 3 watt AM dead key, the relay keyed but no output.
Subsequent tries and I noticed some arcing in the 4 pole relay. This 4 pole relay only uses 2 poles. One set for "turning on" the high voltage (grounds one side of the secondary) and one set of poles sends 12vdc to the operate/standy-by switch. (Note-This amp has the strangest set up as far as relays are concerned!! This 4 pole relay actually sends power to activate another relay that switches the input cable either straight thru (when in Stand-by position) or through the tubes (when in the Operate position)
So after determining that the Potter-Brumfield relay is no longer available, I decided to use a 4 pole relay previously removed (but working when removed) from my Hygain Afterburner. Since this relay is not a "plug and Play" replacement, some "engineering" was required.
Below is the result of my "engineering".
I strapped 2 poles together to share the load for each circuit. So what previously used one set of contacts for each function now uses 2 sets of contacts for each function. The relay is mounted with 3M double sided tape.
So on with the testing. The amp worked well and keyed correctly about..........................5 times!!
Further testing revealed the new relay set up was working flawlessly. High voltage was turning on correctly and the 12vdc was switching correctly sending power to the Stand-by/Operate switch. That is where all action stopped. Remember I said that in the operate position 12vdc goes to the "coax switcher" relay (it is more complex than that since the Pre-Amp relay works in conjunction with this action. Remember I said it has the strangest set up as far as relays are concerned) The 12vdc was going to the common pole of the Stand-by /Operate switch but not going any farther.
Removal of the switch and testing with an ohm meter confirmed the switch was not connecting the 2 poles. But it looks like I finally caught a break with this one. The switch is assembled with screws. I took the switch apart and cleaned all of the contacts. There is also 3 terminals on this switch. So upon re-installing the switch, I flipped it over so that it is now using 1 terminal that has never been used. I didn't take a picture of the switch when it was apart but below is the switch when I re- installed it.
Further testing of the amplifier was at last successful!! 600 watts output on SSB with 20 watts PEP in from a Bearcat 980 SSB.
Of course I can't leave well enough alone so I changed the power cord to a 3 prong cord, added a ground screw to the rear panel (that was a bit bigger than the stock4-40 screw), added a tuned input circuit and converted the stock meter bulb to an LED bulb in the original socket. The LED was just for my own entertainment and to see if I could make it work. Pictures below. The input tuning adjustment is just above and slightly to the right of the fuse holder. Input SWR is 1.6:1. Good enough.
Below is the tuned input circuit.
This was a fun project for me. A bit aggravating at times but an educating experience for me. I hope this may help someone in the future.
Do not be fooled-
HIGH VOLTAGE IS PRESENT IN THIS UNIT AND CAN KILL YOU!!! ALWAYS BE SAFE AND IF YOU ARE UNSURE OF YOUR ABILITIES-DO NOT TOUCH IT!!!
73's
David
My friend, the owner of the Kris 600 SSB I recently repaired, brought me a Palomar Skipper 300 to see if I could repair it for him. Since I take plenty of pictures of before and after (mostly so I can get to the AFTER) I figured I would post a thread here in the hopes it could help someone in the future.
Pre-Emptive Disclaimer:
If sweep tube amps are not your "cup of tea" my feelings are not hurt if you bypass this thread completely.
So my friend tells me that the Palomar quit keying all at once but was working well up to that point. In fact he had someone replace the filter capacitors in it recently.
Upon inspection, I could see why filter capacitors were necessary. Below is what I found below deck.
It appears that a filter capacitor explosion had previously happened. But doesn't explain why it quit keying suddenly.
A closer look showed me where the keying problem started.
The yellow circled area above shows the input to the 12 volt transformer lead disconnected. Whoops, no 12vdc, no keying circuit!
So my plan was to clean up the filter cap tar, add some equalizer/bleeder resistors across the filter capacitors, re-solder the input lead to the 12 volt transformer and send this guy home! At least that was the plan...............
A closer look at the high voltage circuit revealed a crack in a glitch resistor (.5 ohm/5w)
Removal of the resistor from the circuit and testing showed it completely open. This got me to thinking about the rectifiers (exploded filter cap, glitch resistor cracked???)
Since I have a handful of 1N5408's, I proceeded to replace them all. (My earlier mention of my plan..........
)So above is after replacement of the rectifiers, addition of equalizer/bleeder resistors, replacement of the glitch resistors and replacement of several other 2 watt resistors.
During the replacement of these components, I found a repaired another unexpected problem.
A closer look at the fuse holder will show a crack about half way around the housing right at the chassis mount flange.
So with all of these things repaired/upgraded, I fired it up and tested it. It had good high voltage and a strong 12vdc supply to the keying circuit. So after inputting a 3 watt AM dead key, the relay keyed but no output.
Subsequent tries and I noticed some arcing in the 4 pole relay. This 4 pole relay only uses 2 poles. One set for "turning on" the high voltage (grounds one side of the secondary) and one set of poles sends 12vdc to the operate/standy-by switch. (Note-This amp has the strangest set up as far as relays are concerned!! This 4 pole relay actually sends power to activate another relay that switches the input cable either straight thru (when in Stand-by position) or through the tubes (when in the Operate position)
So after determining that the Potter-Brumfield relay is no longer available, I decided to use a 4 pole relay previously removed (but working when removed) from my Hygain Afterburner. Since this relay is not a "plug and Play" replacement, some "engineering" was required.
Below is the result of my "engineering".
I strapped 2 poles together to share the load for each circuit. So what previously used one set of contacts for each function now uses 2 sets of contacts for each function. The relay is mounted with 3M double sided tape.
So on with the testing. The amp worked well and keyed correctly about..........................5 times!!
Further testing revealed the new relay set up was working flawlessly. High voltage was turning on correctly and the 12vdc was switching correctly sending power to the Stand-by/Operate switch. That is where all action stopped. Remember I said that in the operate position 12vdc goes to the "coax switcher" relay (it is more complex than that since the Pre-Amp relay works in conjunction with this action. Remember I said it has the strangest set up as far as relays are concerned) The 12vdc was going to the common pole of the Stand-by /Operate switch but not going any farther.
Removal of the switch and testing with an ohm meter confirmed the switch was not connecting the 2 poles. But it looks like I finally caught a break with this one. The switch is assembled with screws. I took the switch apart and cleaned all of the contacts. There is also 3 terminals on this switch. So upon re-installing the switch, I flipped it over so that it is now using 1 terminal that has never been used. I didn't take a picture of the switch when it was apart but below is the switch when I re- installed it.
Further testing of the amplifier was at last successful!! 600 watts output on SSB with 20 watts PEP in from a Bearcat 980 SSB.
Of course I can't leave well enough alone so I changed the power cord to a 3 prong cord, added a ground screw to the rear panel (that was a bit bigger than the stock4-40 screw), added a tuned input circuit and converted the stock meter bulb to an LED bulb in the original socket. The LED was just for my own entertainment and to see if I could make it work. Pictures below. The input tuning adjustment is just above and slightly to the right of the fuse holder. Input SWR is 1.6:1. Good enough.
Below is the tuned input circuit.
This was a fun project for me. A bit aggravating at times but an educating experience for me. I hope this may help someone in the future.
Do not be fooled-
HIGH VOLTAGE IS PRESENT IN THIS UNIT AND CAN KILL YOU!!! ALWAYS BE SAFE AND IF YOU ARE UNSURE OF YOUR ABILITIES-DO NOT TOUCH IT!!!
73's
David
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