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A Palomar 300A in distress
- Thread starter Dmans
- Start date
All i can say is WOW. Good job Dmans.
Keeping track of where all those wires go has got to be a headache. I'm currently doing the same except for the wires. Getting a headache here trying to figure out what i all need for this. I ordered cap's, diodes, and resistor's off the schematic and some of the cap's in mine don't jive with what's in the schematic. and there's more 0.01 uF caps in it than what the schematic show's.I orderd 25, .01 uF 1kv caps ant it took 27 in total.
They could of done a better job.
I used a 5 inch long piece of multi- colored telephone cable and pulled out a piece of wire, split it in half and soldered one piece to where i removed a wire and one piece to the wire.
I also put numbered part's tag's on each part in numerical order as i took them out and just reverse the order to put it all back together. Wish me luck. My tag wire came off the white wire that soldered to one of the cement resistor's.
C-ya Trapp
Keeping track of where all those wires go has got to be a headache. I'm currently doing the same except for the wires. Getting a headache here trying to figure out what i all need for this. I ordered cap's, diodes, and resistor's off the schematic and some of the cap's in mine don't jive with what's in the schematic. and there's more 0.01 uF caps in it than what the schematic show's.I orderd 25, .01 uF 1kv caps ant it took 27 in total.
They could of done a better job.
I used a 5 inch long piece of multi- colored telephone cable and pulled out a piece of wire, split it in half and soldered one piece to where i removed a wire and one piece to the wire.
I also put numbered part's tag's on each part in numerical order as i took them out and just reverse the order to put it all back together. Wish me luck. My tag wire came off the white wire that soldered to one of the cement resistor's.
C-ya Trapp
I got a 300a too and measured the caps from 1976 and unbelievable they test ok, their values test actually higher than their ratings, how is this possible a 45 year old electrolyte capacitor not deteriorating? Plus sadly it did not come with it's transformer box, please help me out and advise where to get this 300 volt 1.5A / 12 volt 3A transformer or replacement?
Just because those capacitors test good with the tester's low voltage doesn't mean they will last very long. The most common way for them to fail is to break down and short inside when full voltage has been applied for a while.
Feel free to prove this to yourself, but untold thousands of other folks have already found this out the hard way. When that kind of part gets old the internal chemistry breaks down and they fail. No real mystery. The manufacturer's specifications generally claim a service life of no more than a few thousand hours total. Feel free to check that out for yourself, too.
Good luck on the transformer. Lotsa 300A amplifiers out there with no transformers. Not so many transformers with no linear.
And 3 Amps won't cut the mustard for the amplifier's 12-Volt AC requirement. The 300A wires pairs of 6.3-Volt heaters in series. Each pair draws just over 2 Amps. That makes the total 6 Amps, not 3.
73
Feel free to prove this to yourself, but untold thousands of other folks have already found this out the hard way. When that kind of part gets old the internal chemistry breaks down and they fail. No real mystery. The manufacturer's specifications generally claim a service life of no more than a few thousand hours total. Feel free to check that out for yourself, too.
Good luck on the transformer. Lotsa 300A amplifiers out there with no transformers. Not so many transformers with no linear.
And 3 Amps won't cut the mustard for the amplifier's 12-Volt AC requirement. The 300A wires pairs of 6.3-Volt heaters in series. Each pair draws just over 2 Amps. That makes the total 6 Amps, not 3.
73
Got the wiring all figured out on my 300A (I Think)
Fired it up and it popped the 1000uF 50 V Cap i installed on the high voltage board.
Sounded like a 12 gauge shot gun going off, Smoke and pieces of the blown up cap all over the place. Installed another cap and ran it a while and noticed the cap getting hot so i shut it down.
The original cap was a 1000uF 25V and i bumped the voltage to 50V and left the 1000uF the same. Here's the cap i bought for it.
https://www.jameco.com/webapp/wcs/s...toreId=10001&catalogId=10001&productId=147256
I wonder if i got a bad set of cap's, wrong brand or speck?
C-ya Trapp.
Fired it up and it popped the 1000uF 50 V Cap i installed on the high voltage board.
Sounded like a 12 gauge shot gun going off, Smoke and pieces of the blown up cap all over the place. Installed another cap and ran it a while and noticed the cap getting hot so i shut it down.
The original cap was a 1000uF 25V and i bumped the voltage to 50V and left the 1000uF the same. Here's the cap i bought for it.
https://www.jameco.com/webapp/wcs/s...toreId=10001&catalogId=10001&productId=147256
I wonder if i got a bad set of cap's, wrong brand or speck?
C-ya Trapp.
When the 1000uf cap shorts, it usually overloads the rectifier diode that feeds it. Fails as a short, now it puts AC voltage onto the DC-only electrolytic capacitor. Not good for it.
We got in the habit of replacing the rectifier diode whenever that cap is replaced. The time it takes to test the old one is more expensive than the rectifier diode. A new one won't be shorted and blow out a new cap.
The peak voltage that cap will see is no more than 18 Volts, so a 25-Volt rating is plenty high enough. Sounds as if the voltage rating has nothing to do with the premature failure you saw.
73
We got in the habit of replacing the rectifier diode whenever that cap is replaced. The time it takes to test the old one is more expensive than the rectifier diode. A new one won't be shorted and blow out a new cap.
The peak voltage that cap will see is no more than 18 Volts, so a 25-Volt rating is plenty high enough. Sounds as if the voltage rating has nothing to do with the premature failure you saw.
73
Thank's for the quick get back Mr. Nomad.
I'm hoping the 1000uF cap is the one i circled in this picture is the one i popped, and the 1N4005 diode i circled is the one your referring to.
It may be possible this 1N4005 diode i got from Jameco may be fubar. I never checked them, But i'll pull the 1N4005 diode and test it.
So as i read your comment, The 1000uF cap i replaced new shorted out, Overloaded the new 1N4005 diode i replaced new and now with the diode that's now fubar, it will overload the new 1000uF cap i just replaced?
C-ya Trapp
I'm hoping the 1000uF cap is the one i circled in this picture is the one i popped, and the 1N4005 diode i circled is the one your referring to.
It may be possible this 1N4005 diode i got from Jameco may be fubar. I never checked them, But i'll pull the 1N4005 diode and test it.
So as i read your comment, The 1000uF cap i replaced new shorted out, Overloaded the new 1N4005 diode i replaced new and now with the diode that's now fubar, it will overload the new 1000uF cap i just replaced?
C-ya Trapp
Yeah, that's the picture. Shorted cap will blow the rectifier diode. Shorted rectifier diode will blow out a new cap. Only works when both are okay at the same time.
73
73
Hey Nomad, I picked up another 300A and the driver tubes have pin 3 and 11 isolated in a weird way.
Ever see that before?
Not seeing the HV relay on this one either