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Old 10th December 2008, 04:47 PM   #1
Madmen is offline Madmen  United States
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Default K-16LS Help Please

I just built my first tube amp a S5 Electronics K-16LS. I replaced the .22uf Poly Film caps with .22uf Orange Drop 716 series caps, the 33pf Ceramic disc with 33pf Silver Mica caps, electrolytic caps (22uf, 100uf, 220uf)with Ruby gold caps (100uf,220uf,220uf) , I added snubber caps 50volt 1uf Ceramic Capacitors, changed the rectifier to UF4007 diodes and I changed the 3w and 1w resistors to 5w. But when I turned the amp on for the first time it blow the 1.5amp fuse. I checked the board for shorts but cannot find any, I checked to make sure the electrolytic caps had the correct polarity ( the arrow points to the negative end ) and I checked the bridge which appears to be fine ( I unsoldered the diodes and checked them individually) . I also got the tone control and replaced the poly film caps and electrolytic caps.

I clipped a 270K 1/2watt resistor across C10 after I tried powering the amp up, which is how I think you are suppose to use a safety bleeder.

I have built other electronic projects before but I'm new to tubes and audio amps at this point I'm not sure what to do next. Do I need a bigger fuse because of the increase in the capacitor capacity?

I'm working on getting a book on tube amps but any resources you could recommend would be welcome.

Thanks for your time,
Bob
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Old 10th December 2008, 07:22 PM   #2
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Default Re: K-16LS Help Please

Quote:
Originally posted by Madmen
I just built my first tube amp a S5 Electronics K-16LS. I replaced the .22uf Poly Film caps with .22uf Orange Drop 716 series caps, the 33pf Ceramic disc with 33pf Silver Mica caps, electrolytic caps (22uf, 100uf, 220uf)with Ruby gold caps (100uf,220uf,220uf) , I added snubber caps 50volt 1uf Ceramic Capacitors, changed the rectifier to UF4007 diodes and I changed the 3w and 1w resistors to 5w. But when I turned the amp on for the first time it blow the 1.5amp fuse.
Hi Bob,

Quadrupling the size of the input capacitor in the power supply could very well cause the 1 amp fuse to blow. Especially if the capacitor is new and unused and/or unformed. I'd try a 2 amp slo-blow style first and see what happens.

You added snubber caps? Where, across the diodes? 50 volts is way too low. And 1 uF is too big. Should use .001/500V or higher.

How fast does the fuse go? Instantaneously, after one second or after several seconds? It makes a difference and helps to localize where the fault is. Instantly means a dead short somewhere near the PT. After a second is further down the line, and after several seconds could be as a tube heats up and begins drawing too much current.

Quote:
I also got the tone control and replaced the poly film caps and electrolytic caps.
Why? Electrolytic caps don't sound as good.

The Morgan Jones book "Valve Amplifiers" 3rd edition is the current book of choice. Available from Amazon and others.

Victor
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Old 10th December 2008, 08:19 PM   #3
Madmen is offline Madmen  United States
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On the tone control I replaced the 22uf 250v electrolytic cap with a 100uf 350v Ruby electrolytic cap, which appears to be in the B+ supply to the tone control.

The snubber caps I used where the ones Voltsecond has listed on his website from Mouser part number 80-C430C105M5U for use as snubber caps. As I understand it the heater filaments are only run on 6.3vac, do I need higher voltage higher capacity caps ?

I will look into the book you recommended, thank you.
( Just looked at the book, you recommend the "Valve Amplifers" book not the "Building Valve Amplifers" book both from Morgan Jones,correct? )


Bob

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Old 10th December 2008, 08:52 PM   #4
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Quote:
Originally posted by Madmen
On the tone control I replaced the 22uf 250v electrolytic cap with a 100uf 350v Ruby electrolytic cap, which appears to be in the B+ supply to the tone control.
Another quadruple size capacitor in the B+ line. Sometimes bigger is not better.

Quote:
As I understand it the heater filaments are only run on 6.3vac, do I need higher voltage higher capacity caps ?
You didn't say filaments so 50 volts is ok. My thoughts went to HV.

Yes, "Valve Amplifiers" is the primary one to have. "Building Valve Amplifiers" would be good if you plan to make more things from scratch.
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Old 10th December 2008, 09:23 PM   #5
Madmen is offline Madmen  United States
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I just disconnected the power transformer output side from the board (the mains side is still connected to the board , which is a black- brown-red-orange wires) and I still blow fuses, so there must be some thing wrong with the power transformer. Is there any way to check it ?

Bob
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Old 10th December 2008, 09:45 PM   #6
Madmen is offline Madmen  United States
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I'm a idiot, I misunderstood the directions and had the transformer set up for 240volt operation. I changed it for 120volt operation and know it doesn't blow the fuse. I still have to reconnect the power to the board before I call it all fixed.

I need to lengthen the transformer wires as they where short already, any specific wire I should use ?

Also how do I burn this amp in ?

Thanks for all the help,

Bob
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Old 10th December 2008, 10:26 PM   #7
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Quote:
Originally posted by Madmen
I need to lengthen the transformer wires as they where short already, any specific wire I should use ?
Use wire of at least the same size. Preferably stranded to keep them flexibleand and with at least a 300V rating. I like to slide a piece of insulating spaghetti over the solder joint and then cover that with heat-shrink tubing. Tape and heat-shrink would do just as well.

You can burn it in, or age it, simply by leaving it on all day. I'm not a big believer in esoteric audiophool burn-ins with white noise, etc.

Victor
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