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Skipper 300

This could be a real opportunity for you to ...
1) die
2) destroy some perfectly good parts in a spectacular manner
3) learn a little something about beam power pentodes in grounded grid amplifiers.
4) all of the above

I have a one tube RF deck with several replacement sockets that can test 9 pin small, 9 pin large, 12 pin, even 811's and 572's (at reduced voltage)
It started with a box
A transformer , 350-0-350 w/ 6.3 filament
Another transformer with multiple filament taps ( 10, 12, 36v etc)
A filament choke (for the 811 and 572)
Diodes for rectifying the HV
Caps for filtering the DC
Variable caps for the Pi output circuit
Bunch of stupid parts that aren't so stupid once you realize you need them

I can bake anything from a 6JU6 to a 572b for hours with drive from a Pierce oscillator and a buffer amp made from a CB driver (2SC2166 or similar) . The pierce oscillator used to be a Lou Franklin Expo board. The amp schema came from a ARRL qrp article. I suppose you could do just as well with an adjustable regulator on the B+ side of the collector of a CB chassis.
I even added some metering . https://www.w8ji.com/metering_ampli...ating_or_selecting_metering_resistance_values
And a dummy load .
After a spectacular cascade failure I added proper fuses and a three wire cord.
(see? I'm not that bright after all, or always..)

Tube testers for the most part will tell you if the tube inserted in the hole is shorted or not. The real test of a transmitting tube is , well , transmitting.

Sorry but I never did draw a schematic for my Franken-Amp and doubt I ever will.
This is an idea and exercise for the reader.
 
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kopcicle said:
This could be a real opportunity for you to ...
1) die
2) destroy some perfectly good parts in a spectacular manner
3) learn a little something about beam power pentodes in grounded grid amplifiers.
4) all of the above

I have a one tube RF deck with several replacement sockets that can test 9 pin small, 9 pin large, 12 pin, even 811's and 572's (at reduced voltage)
It started with a box
A transformer , 350-0-350 w/ 6.3 filament
Another transformer with multiple filament taps ( 10, 12, 36v etc)
A filament choke (for the 811 and 572)
Diodes for rectifying the HV
Caps for filtering the DC
Variable caps for the Pi output circuit
Bunch of stupid parts that aren't so stupid once you realize you need them

I can bake anything from a 6JU6 to a 572b for hours with drive from a Pierce oscillator and a buffer amp made from a CB driver (2SC2166 or similar) . The pierce oscillator used to be a Lou Franklin Expo board. The amp schema came from a ARRL qrp article. I suppose you could do just as well with an adjustable regulator on the B+ side of the collector of a CB chassis.
I even added some metering . https://www.w8ji.com/metering_ampli...ating_or_selecting_metering_resistance_values
And a dummy load .
After a spectacular cascade failure I added proper fuses and a three wire cord.
(see? I'm not that bright after all, or always..)

Tube testers for the most part will tell you if the tube inserted in the hole is shorted or not. The real test of a transmitting tube is , well , transmitting.

Sorry but I never did draw a schematic for my Franken-Amp and doubt I ever will.
This is an idea and exercise for the reader.
Click to expand...
I have a volt meter and can test for shorts ju
kopcicle said:
This could be a real opportunity for you to ...
1) die
2) destroy some perfectly good parts in a spectacular manner
3) learn a little something about beam power pentodes in grounded grid amplifiers.
4) all of the above

I have a one tube RF deck with several replacement sockets that can test 9 pin small, 9 pin large, 12 pin, even 811's and 572's (at reduced voltage)
It started with a box
A transformer , 350-0-350 w/ 6.3 filament
Another transformer with multiple filament taps ( 10, 12, 36v etc)
A filament choke (for the 811 and 572)
Diodes for rectifying the HV
Caps for filtering the DC
Variable caps for the Pi output circuit
Bunch of stupid parts that aren't so stupid once you realize you need them

I can bake anything from a 6JU6 to a 572b for hours with drive from a Pierce oscillator and a buffer amp made from a CB driver (2SC2166 or similar) . The pierce oscillator used to be a Lou Franklin Expo board. The amp schema came from a ARRL qrp article. I suppose you could do just as well with an adjustable regulator on the B+ side of the collector of a CB chassis.
I even added some metering . https://www.w8ji.com/metering_ampli...ating_or_selecting_metering_resistance_values
And a dummy load .
After a spectacular cascade failure I added proper fuses and a three wire cord.
(see? I'm not that bright after all, or always..)

Tube testers for the most part will tell you if the tube inserted in the hole is shorted or not. The real test of a transmitting tube is , well , transmitting.

Sorry but I never did draw a schematic for my Franken-Amp and doubt I ever will.
This is an idea and exercise for the reader.
Click to expand...
I understood the dummy load and the I could die part .
 
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Well recap did not go to well. I put the 22 if cap that goes to the plate cap. Kapow! I recapped it again and now it blew up the the 120uf 450v cap I just put in. Nothing is backwards this time. ?
 
Tweetybird said:
Well recap did not go to well. I put the 22 if cap that goes to the plate cap. Kapow! I recapped it again and now it blew up the the 120uf 450v cap I just put in. Nothing is backwards this time. ?
Click to expand...
I put 22uf that goes to plate cap backwards the first time.
 
Maybe the two resistors on plus side of 120uf 450v cap is shorted like it was on other end with the 22uf at other end on top of tubes?
 
The two little piggy back resistors are shorted. Should a total recap be needed again? Or just the one that blew kapow and the two resistors?
 
So, here's how we install bleeder resistors in a 300A.

BFwEJo.jpg


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
 
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nomadradio said:
So, here's how we install bleeder resistors in a 300A.

BFwEJo.jpg


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
Click to expand...
Mine are shorted out and need to be removed or replaced . it blew the new caps I put in the second time first time I messed up.putting 22uf on plate Cap backwards on other end
 
If it blew out new filter caps this suggests that the four rectifier diodes are damaged.

When the rectifier diodes fail and become shorted inside, they feed AC voltage into the DC-only filter caps.

Tends to blow up a DC-only capacitor pretty fast. Got in the habit of replacing the rectifiers any time we replace filter caps. Four rectifier diodes are cheap insurance, compared to blowing out new filter caps.

Checking them individually will reveal if they'e damaged. Just don't be tempted to replace just one or two. They're arranged as two pairs, each pair wired in series. The only way to make pairs of diodes match properly is to replace them all at the same time.

73
 
I am going to replace those too again. I do 2 22uf 25v I 47uf 25v four 3amp rectifier diodes 2 120uf 450v caps 1 25v 25uf cap and this time i will include replacing the shorted 470s and adding the two shown 470s. Are axial caps better i bought radial?
 
Tweetybird said:
I am going to replace those too again. I do 2 22uf 25v I 47uf 25v four 3amp rectifier diodes 2 120uf 450v caps 1 25v 25uf cap and this time i will include replacing the shorted 470s and adding the two shown 470s. Are axial caps better i bought radial?
Click to expand...
Are they two watt 470k resistors?
 

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