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SET 300B project


henry4841

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This is a project I have been working on for a few weeks. It takes me that long making and prepping a chassis. A lot of work goes into making a presentable case to house a special amplifier. I built a SET 300B probably close to a decade ago on a Bud chassis and it is one of my favorites. I would like to think my case work and electronic skills have improved since building that amplifier so I decided to take it apart and start a new build but using most of the old parts. I did order a new PS transformer with some more secondary voltage but I already have some excellent  One Electron output transformers so their is no need in replacing them. Below is the progress I have made with more reports and pictures forth coming. 

 

 

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More pictures of the parts removed from old build waiting to find their new home. The sockets that hold the 300B tubes are not made where you can just drill a hole and be done. I drilled as big a hole as possible with what I have then nibbled out with my jig saw and new blade where the pins go through the chassis. Should look professionally installed when finished with no gaps. Just need to start putting everything together in the next few days, weeks. Old and slow. 

 

 

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Henry, this is looking really nice, the dovetails came out terrific. Makes me want to finish up a couple tube projects I've not finished. I have to finish a couple other things first, though.  Miss my 2a3 amps.

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  • 3 weeks later...

Up and running but not finished. Also picture of my man cave. Not polished ***** and span as some of our members listening room but suites me just fine. Details and problems encountered with this build forthcoming in a few days. Still waiting on some parts I ordered last Monday from Mouser. Mouser's service leaves a lot to be desired of late. 

 

 

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Just thought I would mention that big screen TV decided to go dark yesterday afternoon. Took the back off to see if it had any bad caps in the power supply, looked good, and then tightened the screws that hold the two boards that also make ground and the picture came back. I now hope a bad ground of the boards was the problem. Something I learned from watching youtube video's of tech's repairing TV's. Bad ground of boards a common problem. 

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To many too count but I am old and slow now working only a couple of hours a day. I just finished this amp yesterday after destroying one of my One Electron OPT's. One of the 300B tube socket connections was too close to the chassis and arced over shorting out the transformer. As it happens at times this One Electron OPT is no longer available making the problem worse. I had to install two Hammond 125Ese's on top to finish the amplifier. Not as pretty as when first shown but not too bad looking considering. I possible could have installed both OPT's underneath the chassis but then I would have big holes left where the old transformers were mounted. The other option is to start over with a new top plate which I have the material to do but not the desire at this time. This was after all a rebuild of an old 10 year old build. Luckily the big 300B tubes hide the OPT's some. Sounds and test excellent never the less. Not as much 2nd harmonic on distortion analyzer as some of my other SET builds which was very surprising. I need to do some tidying up underneath before showing my work. I had it looking real neat and proper but then I had to get the dang thing to work. During finding the short problem and fixing it, removing and reinstalling wires it takes a toll on neatness. 

 

 

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This is where the problem lay. It is the way the tube socket is made for the 300B tubes. I first had to drill out the largest hole I could then nibble out where the pin connections are when first building the top plated for all the components. The picture shows after removing the socket and filing away more material where there is no longer electrons jumping from the socket to chassis. This was not an easy find being that during first testing the amp work perfectly and tested good but when I hooked it up to my main system it started blowing fuses. It was a coming and going problem, the hardest to find and fix. The arcing destroyed my precious OPT for this amplifier. The best OPT's I ever have bought. It happens. 

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  • 3 weeks later...

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