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Old 1st January 2009, 04:05 PM   #31
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Quote:
Originally posted by coresta
I use mine with G3 tied to cathode , should i try a real full pseudo triode Pete ?
Pierre
I measured slightly better characteristics with G3 connected to the plate. Also seems safer having it tied there - it is fairly closely spaced to G2...

Pete
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Old 1st January 2009, 07:03 PM   #32
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Quote:
I use mine with G3 tied to cathode , should i try a real full pseudo triode Pete ?
I still have my Tubelab SE running with the VT225's in it. I just wired the VT225's in place of the Chinese 300B's and the amp sounds better than it ever has (never tried high dollar 300B's though). I wired G3 to ground just because it seemed like the right thing to do. I will try connecting it to the plate the next time I have the amp down on the workbench.

A few years ago I plotted curves (manually) on an EL34 connected both ways. The G2 = G3 = Plate connection definitely showed some signs of "tetrode kink" that was not present with G3 tied to the cathode.

I plan to try a pair of the VT225's in push pull in the near future. My old favorite P-P amp the 300Beast has blown another power supply cap, so it is currently dead. It is the only amp that I made in the "pre Tubelab" days that I still have. I think that it is overdue for a rebuild.

While I was up north I designed a "universal P-P driver board". It is similar to the 300Beast driver but far more flexible. I plan to "test" a bunch of the sweep tubes that I collected during the tube sales that several vendors ran last summer. I will also experiment on some VT225's and a few other WWII surplus tubes that I have.
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Old 1st January 2009, 07:11 PM   #33
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Pete, those measurement screenshots in your link, how were they produced?
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Old 1st January 2009, 07:43 PM   #34
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Quote:
Originally posted by astouffer
Pete, those measurement screenshots in your link, how were they produced?
I have an HP 8903A audio analyzer. They are reasonably priced in the used market (unlike an Audio Precision box). I think I paid $900 for one freshly calibrated from an instrument rental company.

By itself the 8903 doesn't have any good way to make graphs, but it is fully programmable and controllable through GPIB.

A while ago I bought a copy of HP VEE, which allows you to make test programs using a visual interface. The plots you see were generated by test software I've written for VEE.

A runtime-only version of VEE is available for free... so I was thinking of posting my programs so that somebody with an HP 8903 could use these. So I was about to post a topic to see if there are any 8903 owners who want to be the beta site...

Pete
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Old 1st January 2009, 09:14 PM   #35
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Quote:
Originally posted by pmillett


I have an HP 8903A audio analyzer. They are reasonably priced in the used market (unlike an Audio Precision box). I think I paid $900 for one freshly calibrated from an instrument rental company.

By itself the 8903 doesn't have any good way to make graphs, but it is fully programmable and controllable through GPIB.

A while ago I bought a copy of HP VEE, which allows you to make test programs using a visual interface. The plots you see were generated by test software I've written for VEE.

A runtime-only version of VEE is available for free... so I was thinking of posting my programs so that somebody with an HP 8903 could use these. So I was about to post a topic to see if there are any 8903 owners who want to be the beta site...

Pete
Pete,

I have an 8903 and a GPIB card - will be glad to be a Beta tester. You can PM me offline if you wish.

-- josť k.
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Old 1st January 2009, 10:12 PM   #36
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Quote:
So I was about to post a topic to see if there are any 8903 owners who want to be the beta site
Yep, I've got one too. I got it for $75 in non working condition. I fixed it. It has died, and I have fixed it again something like 3 times in the 10 years that I have had it. No GPIB card yet but they shouldn't be too hard to find. The trick is finding one with suitable drivers for VEE. I will be willing to experiment with your programs.

Quote:
By itself the 8903 doesn't have any good way to make graphs, but it is fully programmable and controllable through GPIB.
It will control an analog XY plotter. Unfortunately mine died several years ago and those have become hard to find.
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Old 1st January 2009, 10:31 PM   #37
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If you a copy of LabView someone has written a driver for the 8903A. Its available from www.ni.com
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Old 2nd January 2009, 03:32 PM   #38
wicked1 is offline wicked1  United States
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Does anyone know where to get these tubes?
I've been searching for years now! When I first started looking EVERYONE had them, and I got a couple. But, I wanted some spares a couple of months later and no one had any. I'm on the waiting list (or was) at several different tube brokers.

So, anyway, I haven't been using these tubes in my amp anymore because they do sound very good, and i'm sort of saving them for special occasions. I'd love to have a spare set so I can listen to them w/out fear of it being my last time.
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Old 2nd January 2009, 04:01 PM   #39
coresta is offline coresta  France
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ipay had one pair last week ... Pierre
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Old 8th January 2009, 02:14 AM   #40
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I'm not sure of this is a violation of the forum rules (if so, moderators plese delete my post!)... but since people have been having a hard time finding 307A's I thought I would mention that I just listed a few 307A's (singles and matched pairs) on ebay at what I hope is a reasonable price...

Terrible, having more tubes than money

Pete
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