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Tubelab Discussion and support of Tubelab products, prototypes and experiments

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Old 9th November 2018, 02:45 AM   #301
Tubelab_com is offline Tubelab_com  United States
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Location: West Virginia panhandle
do you still have boards left?
At this moment there are 6 boards left. I will get some more when funds permit (soon).

Hope everything is going okay with you.
I'm fine. Tubelab has barely paid its bills for the last couple of years, so I took on the paid contract job mentioned above to pay the bills and fund some new stuff that could happen next year. This means that tubes will stay cold for a while, and I may not be here as often as usual. There are two or three amps that are partially completed using these boards, and something new that will develop into some new SE and P-P amp designs.......

Meanwhile this prototype sits dark on the bench. It makes 50 WPC on that Antek Toroid, and 80 WPC on a regulated power supply. It will likely be a new Tubalab board next year. There is an SE flavor that is in the early perf board proto stage. So far it only exists in simulation.
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Tubelab, it's 5 year mission. To explore strange new tubes, to seek out new circuits and topologies, to boldly go where no tube has gone before......
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Old 16th November 2018, 03:51 PM   #302
Mr_Zenith is offline Mr_Zenith  United States
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Tubelab Universal Driver Board, 2015 version
I'm speaking as a longtime lurker here, but it's good to hear you're okay. Not as many sparks - or as much smoke - rolling out of your shop as in your Florida days, regrettably, but it's gratifying to hear of more good things to come. Hey, we can't be exploding things all the time now right? I'll definitely stay tuned regardless...

Paperweight: I used to live in Asheboro until about six years ago. Before the move I was working on a pair of KT88 monoblocks based on an old Acrosound circuit (itself another incarnation of the Williamson amp), but then my work made me an offer I couldn't refuse. In a way I'm glad it did, as this driver board appears to be a much better front end for this circuit. But it'd have been great to have someone to have a fellow conspirator just a few miles down the road.

And so as not to stray too far off-topic, I'm off to the basement to look for those parts...

Last edited by Mr_Zenith; 16th November 2018 at 03:57 PM. Reason: I forgot the magic smoke...
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Old 16th November 2018, 08:20 PM   #303
Paperweight is offline Paperweight  United States
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Location: Lexington, NC
I don't get out of the house very often except to go to work. My brother stopped by today and we swung by a model train hobby shop in Spencer. Then we went to Sauers Veneers. If you're into building speakers, guitars, furniture, etc those guys have some amazing stuff. I want to eventually build a set of Jim Holtz and Curt Campbell's Bordeaux speakers. I'm waiting for the cabinet kit to show up on Speaker Hardware.

I ended up buying a set of 60 watt output transformers from Dynakitparts.com and a pair of Classic Tone 40-18069 power transformers. The power transformers can be wired for a good number of B+ configurations and has plenty of current available.
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Old 18th November 2018, 03:19 AM   #304
TheGimp is offline TheGimp  United States
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I finally got a chance to play with the driver board again as I'm home taking care of my ex while she goes through Chemo.

I have a 6N23P in the first position and a 6CG7 in the driver position.

I'm not running any feedback

Output is a pair of 6S3P with an Edcor CXPP30-MS-5K opt with a B+ of 350V.

The 6P3S are biased around 25mA for class AB1 because I can't get more out of one position. I think I need to diagnose the bias supply in that channel before I go on.

Best I can do so far is 10Vrms out before clipping with the lowest bias set of tubes I have.

I swapped to a hotter set of tubes (32mA at -37V bias) and got 21W out which is probably getting close to expected.

I can't get Audio Tester to run any more, so I've switched to ARTA.
If there are no dogs in Heaven, I don't want to go there.
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Old Today, 12:53 AM   #305
TheGimp is offline TheGimp  United States
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Changed R26 and R36 from 150K to 60K and got the bias range I think will work for most of the tubes I want to experiment with.

Bias is set at 44mA with 360V B+.

One of my 6N23P has a bad section which was causing distortion problems.

I now get glitches at about a 6.28ms interval that I have to trace down. It is not line rectification related, so I guess it's shotgun time.
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