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I like that build.  Nice tube you used too.  Are there hoards of these to be found in Japan anywhere?  :)

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Thank you guys,

To save cost for my future DIY projects, I am planning to make a universal power supply.

Toshiba 6RA6 is not easy to find in JPN but we can find imported 9RA6 in US.

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I'm always hoping I'll find some stash of tubes that are worthless to others but perfect for our use.  :)

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I powered up the first of my amp boards tonight.  I was able to get the balance to 0 but the offset lingers at 20VDC with the trimpot turned all the way.  This is using the power supplies that are slightly higher than 350VDC (366VDC).  

 

I forgot to put the tubes in when turning on the power for the first time.   :palm:  Would this have damaged anything?

 

Should I drop the value of the 1.5K resistor?  What would be a suitable replacement?  Should I look for other things to try?  

 

EDIT:

 

I just tried a second amp board with the same power supply but this time I remembered to put the tubes in first.  Same issue with the offset as the first board I tried.

Edited by chiguy

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Try 1.37K or even 1.2K for the offset resistor. 

 

Running without tubes is a very good way to burn up the CCS... 

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Hi Chiguy,

I had the same problem. You can solve it to lower the 1.5k resistor. See post 246,247, 248,381 and 382.

My amp is working fine now. I haven't tested with the servo on.

After an hour running all the offset voltages are within 1.5 volts, so I wonder if the servo is necessary.

I am now ready to build the amp in a case.

Good luck.

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There is very little drift in this design so the servo isn't as vital as with the KGSSHV but it helps as the tubes start to age. 

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Thanks!

 

Fortunately I realized I forgot tubes fairly quickly and immediately turned it off (within 30 seconds or so).  Everything seems to work (aside from the offset) when I powered it up again with tubes.  I guess I'll find out more when I'm actually listening to it.  

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If the CCS is toast then you couldn't adjust the offset and balance so it has to be working. 

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Took me a while to troubleshoot my latest problem.

I found the 24V 3W Zener on the output mosfet failed, shorting out the +350VDC supply. Symptoms were a slow ramp up of B+ voltage with the PS disconnected to the channels, and no B+ when one or two channels connected. B- was unaffected. The 3AT fuse did not blow, as the CCS regulated the current to the short.

Looking now to replace the Zener. Locally, I've found 1watt and the physically larger sized 5 watt. Will 1watt be adequate, or should I order a 3watt from Mouser and wait a week for delivery?

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Thinking this thru, the 24V Zener clamps the voltage across the grid and source of the FQPF 8N80C. The grid will only draw minor current if the zener's breakdown voltage is exceeded.

On second thought 1 watt should be fine.

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I am just doing the case work for the KGST. When planning to drill the holes in the bottom plate for the boards, do you guys use a printout of the boards as a model? If yes, how do you print it in the right size? I tried to print the KGST and PSU from the gerber files, but something is not right. The holes don't really fit. May be I don't have the right gerber files from the group buy?

 

Is there any other techique you would recommend to get it as exact as possible?

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if its the group buy here is the pdf of the board layout

 

http://gilmore.chem.northwestern.edu/kgst-miniv03.pdf

 

at least on my printer, it prints exactly the correct size.

 

 

if you want to measure instead, I can give you the hole distances

from any corner.

Edited by kevin gilmore

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Thanks Kevin

 

Amp board is production rev. 0.41

PSU ist version 1.0 (with the too big holes for m3 studs)

 

Hope you find the PDFs. Since these are the boards from the group buy, I think these files would come in handy for quite a few people. 

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I scan my boards @ 100% size before populating.

Gives me accurate dimensions for standoff hole distances.

 

I had a similar realization after I had populated the boards and was looking to drill holes.  My thought was to use the PCBs as a stencil and transfer it to a piece of paper or something.

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You can do this from the Gerber files if you have an image editor that can change the print resolution of an image without changing the actual size of the image (such as Photoshop).

 

1) Download gerbers from Kevin's usual place.

2) View gerbers on circuitpeople.com.

3) Download the generated images at a decent resolution - 2-300 dpi should be fine.

4) Open the silkscreen layer image in your photo editor.

5) Change the print resolution to whatever the original images were generated at by circuitpeople without changing the pixel size of the image (in Photoshop this is done by switching off "resampling" in the "Image size" dialogue).

6) Print from your image editor either directly to paper or to a file without scaling ("fit to page" or similar) applied.

7) Check you printout against the boards - they should match.

 

//UFN

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