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Old 21st December 2010, 06:50 PM   #21
rknize is offline rknize  United States
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You'll also need to tweak the source load resistor as well. George mentioned that this was one of the changes he would like to make to this PCB: allow for separate supply rails for the FETs so that they don't have to stretch all the way from B+ to B-. You wouldn't even need a B- on the PCB anymore if you supplied your own +/- 100V rails.

Obviously you can do with with a bit of trace cutting.
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Old 23rd December 2010, 01:14 AM   #22
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Default an update......

The amp is up and running. I'm running it on my main system with a variac at about 90% of full throttle until the Edcor XPW131 shows up.

I've been chasing a problem of one channel not working since yesterday....long story short, the vintage 4 pin ceramic socket wasn't making good contact with the tube pins, so I unsoldered the socket, extracted the contacts, re-tensioned them, and re-installed. Problem solved, at least until the contact tension Peters out again.

I ended up removing R5, R6, C6, C7 from the board and putting them on a perf board daughter board mounted to the side of the chassis. This solved two problems; the caps on the board were too tall for my chassis (they touched the bottom cover), and this change allowed me to use big honkin' Panasonic TS-ED and TS-HB snap ins. I also changed R5 to 3K 6 watt and C7 to a 180uf Panasonic TS-HB snap in. With the Hammond 273BX (350-0-350) the B- is around 230V.

I'm still trying to get the hang of this MOSFET thing; I'm assuming that the total voltage across the MOSFET (B+ to B-) needs to be at least as much as the driver tube voltage swing plus some margin, is this correct?

A few tweaks remain. The square waves are quite square, with a little wiggle/underdamped response at the top of the wave. I'm going to swap the metal films in the amp for CC, and/or use a higher value R.
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Old 19th June 2011, 12:02 AM   #23
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Which volume pot have you all used? Is there one that can directly be soldered on the board?

Doug
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Old 19th June 2011, 02:32 AM   #24
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Quote:
Originally Posted by Doug Kim View Post
Which volume pot have you all used? Is there one that can directly be soldered on the board?

Doug
I use Alps 100K Ohm.
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Old 24th June 2011, 09:19 PM   #25
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Quote:
Originally Posted by Evenharmonics View Post
I use Alps 100K Ohm.
Click the image to open in full size.
I purchased an Alps 100k Ohm which looks just like the one in the pic (blue velvet), but it does not fit to the Tubelab SE board. I must have checked the spacing between the pins before ordering, and I can use the pot for my Aikido project anyway so nothing hurts.

Anyways, which pot fits to the board without modification?

Doug
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Old 24th June 2011, 10:33 PM   #26
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Sorry, I didn't realize the pin spacing is different. I have it mounted on chassis and wired it to the board. Is it possible to bend the pins little to fit the board?
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