Tube newbie, anyone familar with s-5 k-502? Help needed please - diyAudio
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Old 14th August 2014, 01:46 AM   #1
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Join Date: Aug 2014
Location: Ft. Myers, FL
Default Tube newbie, anyone familar with s-5 k-502? Help needed please

First off I would like to say hello to everyone here, I have lurked around the site a bit and decided this looks like the place for me. I have been into audio equipment for quite sometime and consider myself experienced (a little at least) in trouble shooting, repair, and restoration of solid state equipment. After reading the many reviews and posts on the s-5 tube kits I decided to order the K-502. Being the "hobbyist" that I am I couldn't just build the kit as intended and decided to do some mods. I built a chassis, upgraded coupling caps, installed snubbers across filaments and HV, removed input dc blocking caps from signal path, used a uf4007 from bridge rectifier to filter cap, upgraded binding posts and rca jacks and upgraded volume pot. After finishing the project I get absolutely no output . The tubes glow fine and there is no sign of the obvious such as bad soldier joints, reversed polarity on components ect.. Nothing is shorting out or too hot. I know there is several threads on this amp and I have spent hrs researching and thought it would be best to post here and ask the experts for help. I came across the on thread recently where a member was having a similar problem with a K-12 kit and it ended up being a grounding issue with the binding posts, I don't think that is the issue here though. Also I see the Voltsecond mods mentioned on almost all the threads, his webpage seems to be out of commission does anyone know where I could access this info? All info and help would be greatly appreciated. BTW I haven't took any measurement's yet and hope to get a chance to work on it a little more tonight.
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Old 14th August 2014, 03:16 PM   #2
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Join Date: Jul 2008
Location: Belfast
Hi jhow5757, welcome to the forum.

Nice build

A few years back I built a K502 and did all your mods plus changed the output transformers to Hammond 1609s.

Using a valve amp without speakers attached could damage your output transformers, so a quick check there might be prudent.

As you have no sound from either channel the fault is likely to be in a part of the circuit that is common to both channels. I would first check that you're getting a B+ exiting that UF4007 mod. IIRC it should be around 210 Vdc

On the signal input side make sure you that you have extended the volume pot out of the pcb correctly.

When white moths were on the wing,
And moth-like stars were flickering out,

Last edited by Soonerorlater; 14th August 2014 at 03:33 PM.
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Old 15th August 2014, 01:35 PM   #3
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Join Date: Aug 2014
Location: Ft. Myers, FL
Thanks for the info, I would think the opts should be fine as they are brand new and never ran without a load. I will check the B+ voltage exiting uf4007 and report back as soon as I get a chance. Hopefully I will find time to get back at it this weekend.
Thanks again,
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