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Skipper 300
- Thread starter Tweetybird
- Start date
Nope.
470 means just that. 470 ohms. Yellow-Violet-Brown.
The suffix "k" means 1000. So, a 470K resistor is 470,000 ohms. Yellow, Violet, Yellow.
Big difference.
The bleeders in the picture are 240k. We usually use 220k, but Mouser was out of them when I needed to restock.
Any 2-Watt part with the resistance value in that range from 220k to 470k should work. Just use the same resistance for both bleeders.
73
470 means just that. 470 ohms. Yellow-Violet-Brown.
The suffix "k" means 1000. So, a 470K resistor is 470,000 ohms. Yellow, Violet, Yellow.
Big difference.
The bleeders in the picture are 240k. We usually use 220k, but Mouser was out of them when I needed to restock.
Any 2-Watt part with the resistance value in that range from 220k to 470k should work. Just use the same resistance for both bleeders.
73
I blew the 470.000k ones tooSo, here's how we install bleeder resistors in a 300A.
The original bleeders are still in place. No good reason to remove them.
But they don't do the job, wired across the series-pair of big filter caps. The two 470K resistors are simply wired in parallel. Together, they are still connected across the two series-connected filter caps. Series-connected capacitors won't bleed down effectively with this hookup.
The hookup in the picture puts one resistor across each filter, separately. That always works.
You can remove the old ones. Leaving them in place hurts nothing that I can see, so we didn't bother.
And yes, this is the nearly-oldest version of the 300A. They moved the big relay over to the chassis the next year. And then did completely away with the fourth relay later on.
You really need one bleeder across each capacitor in a series string.
73
Putting in new cap today new diodes too I only replaced the four three amp ones on the second recap. This time I replaced the one amp one too it was shorted and blew second cap job. First cap job was blown by putting 22ufcap on top of plate backwards I hope the third times a charm. Glad I only paid fifty dollars for it. It was making amps and just occiliationg. So I figured I'd recap it too just messed up it the first electronic repair I have tried if I can get it to work I will be happy. I hope it didn't blow the tubes too. I have an untouched skipper with the cracked tube to look at to make sure I put them in right and look for shorts in the fifty dollar one before I plug it in again
I feel like my idiot light just came on.
For those parts to immediately blow up the way they did makes me suspect that your 300A has a mismatched transformer on it.
The power transformer was made in two versions. One of them supplied about 560 Volts AC to a full-wave bridge rectifier. Took the form of a small rectangular block of black epoxy with four wire leads out the bottom, mounted alongside the two big filter caps.
Your RF deck was built to take the OTHER version of the transformer. It supplies about half that much AC voltage on the high-voltage winding, around 280 Volts AC. Your amplifier clearly has a full-wave voltage doubler circuit to rectify and filter the 800 Volts DC needed to power the tubes. The four individual 1N5408 diodes tell us that.
If you plug the higher-voltage transformer into the lower-voltage type power supply, it always goes "SLAM!" right away.
Haven't seen this happen in quite a while, but there are two possible ways to mismatch the amplifier and the power transformer.
If your RF deck had been built for the 560-Volt type, and you plug the lower-voltage transformer into it, the tubes will always be running at half the design voltage. You get an amplifier that is perpetually on "Low" side, no matter which way you flip the High/Low switch. No matter how good the tubes are.
And if you mismatch it the other way, the two big filter capacitors now will see nearly twice the voltage they are rated to tolerate. Causes them to break down almost instantly.
This is the only way I can see to burn up the two bleeder resistors, by putting twice the correct volage onto them. Those bleeders almost never overheat with the correct voltage on them.
Shoulda caught on to your remark about burning up the bleeders. Can't see any other way to make them overheat like that, except to use the wrong transformer.
No, the two versions of the transformer have *NO* markings to identify which one you have. And no markings inside that I have ever found.
They appear completely identical in every way, until you measure the voltage from the HV winding.
Safest way to tell is to find a 12-Volt transformer. Hook the transformer up to 120 Volts AC, and Gator-clip the 12-Volt side to the amplifier's power plug so that you are now feeding it 12 Volts into the amplifier's power cord and not 120 Volts. This makes it safer to put your AC voltmeter onto the HV winding's hookup on the power supply board and measure it.
Just measuring 560 Volts AC directly is above the safe limit for many inexpensive multimeters. If you get a reading of 56 Volts or more you have the "High" version.
And if the meter shows under 30 Volts, you have the right one.
And if I'm right that you have the High version transformer and the Low version RF deck, this is the only way to perform that measurement without blowing something up.
Darn! Wish I had caught on to this earlier.
73
For those parts to immediately blow up the way they did makes me suspect that your 300A has a mismatched transformer on it.
The power transformer was made in two versions. One of them supplied about 560 Volts AC to a full-wave bridge rectifier. Took the form of a small rectangular block of black epoxy with four wire leads out the bottom, mounted alongside the two big filter caps.
Your RF deck was built to take the OTHER version of the transformer. It supplies about half that much AC voltage on the high-voltage winding, around 280 Volts AC. Your amplifier clearly has a full-wave voltage doubler circuit to rectify and filter the 800 Volts DC needed to power the tubes. The four individual 1N5408 diodes tell us that.
If you plug the higher-voltage transformer into the lower-voltage type power supply, it always goes "SLAM!" right away.
Haven't seen this happen in quite a while, but there are two possible ways to mismatch the amplifier and the power transformer.
If your RF deck had been built for the 560-Volt type, and you plug the lower-voltage transformer into it, the tubes will always be running at half the design voltage. You get an amplifier that is perpetually on "Low" side, no matter which way you flip the High/Low switch. No matter how good the tubes are.
And if you mismatch it the other way, the two big filter capacitors now will see nearly twice the voltage they are rated to tolerate. Causes them to break down almost instantly.
This is the only way I can see to burn up the two bleeder resistors, by putting twice the correct volage onto them. Those bleeders almost never overheat with the correct voltage on them.
Shoulda caught on to your remark about burning up the bleeders. Can't see any other way to make them overheat like that, except to use the wrong transformer.
No, the two versions of the transformer have *NO* markings to identify which one you have. And no markings inside that I have ever found.
They appear completely identical in every way, until you measure the voltage from the HV winding.
Safest way to tell is to find a 12-Volt transformer. Hook the transformer up to 120 Volts AC, and Gator-clip the 12-Volt side to the amplifier's power plug so that you are now feeding it 12 Volts into the amplifier's power cord and not 120 Volts. This makes it safer to put your AC voltmeter onto the HV winding's hookup on the power supply board and measure it.
Just measuring 560 Volts AC directly is above the safe limit for many inexpensive multimeters. If you get a reading of 56 Volts or more you have the "High" version.
And if the meter shows under 30 Volts, you have the right one.
And if I'm right that you have the High version transformer and the Low version RF deck, this is the only way to perform that measurement without blowing something up.
Darn! Wish I had caught on to this earlier.
73
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Thanks I replaced the 4 diodes and the single 1 amp one and 2 120uf 450v and 1 25uf 1000v and 2 22uf and one 47 uf cap no rf goes thru amp on or off .the square 50 ohm 10watt thing has a black spot on it it's by the rf meter. I really messed this one up it was making watts just occiliationg now it dead.
Bad relays? Or blown foil traces on the relay board?
A power supply hiccup should not prevent barefoot power from passing through it with the power turned off.
73
A power supply hiccup should not prevent barefoot power from passing through it with the power turned off.
73
This is the skipper three hundred. I put the 22uf in backwards blew up. So I recapped today two 120uf 450v i25uf 1000v four 3 amp diodes one 1 amp diode two 22uf caps 1 47uf cap.no rf passes through amp the square 50 ohm 10 amp by rf meter looks blown has soot on outside
Whups. Had my mind fixated on a 300A. My mistake.
Okay, so is this the early Skipper that has the three relays mounted upside-down to the chassis deck with wires connecting them?
Or is it the later one with the relays on a circuit board bolted to the back of the cabinet?
73
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