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Old 22nd November 2008, 02:51 AM   #71
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It seems odd that an EH tube would have no markings at all. Most of the EH I've seen have a relatively boring font in black print. Got a pic of your tube, by any chance?

Well, now I'm a liar. This one has yellow print.
http://www.newsensor.com/ProductHighLight.aspx?ProId=24

and this one:
http://thetubestore.com/12at7eh.html

and this one too:
http://www.tubedepot.com/eh-12at7.html
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Old 22nd November 2008, 02:55 AM   #72
N1ESE is offline N1ESE  United States
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Quote:
Originally posted by Ty_Bower
Got a pic of your tube, by any chance?
Click the image to open in full size.Click the image to open in full size.
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Old 22nd November 2008, 03:02 AM   #73
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Definitely Russian. I can see the flying saucer. The plates look about the right shape and size too, although that isn't conclusive. I'd wager it probably is a 12AT7, although it's still odd there is no printing on it. OK, maybe not so odd. My New Sensor KT88 have no printing on them either.

Have you triple checked the values of all the resistors installed on the board? There's only a couple dozen - it doesn't take long to go through them all with the ohmmeter. Keep the power off, obviously.

What's the primary impedance of your CXSE? Did you get the CXSE25-8-5K?
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Old 22nd November 2008, 03:06 AM   #74
N1ESE is offline N1ESE  United States
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Quote:
Originally posted by Ty_Bower
Have you triple checked the values of all the resistors installed on the board? What's the primary impedance of your CXSE? Did you get the CXSE25-8-5K?
Negative on the resistors. I could do that next I guess. Yes, the OPT is a CXSE25-8-5K. I'm currently running it in UL mode with no feedback. It sounds pretty much the same in Triode mode.

Will let the amp cool down and check resistors after this song finishes.
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Old 22nd November 2008, 03:10 AM   #75
chrish is offline chrish  Australia
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I cannot see any errors with the way the transformers are wired. Do you have access to a different 12AT7 input valve? You might find one at a music shop that sells guitar amps. Otherwise, I would pull the board out and check ALL of the component values on the board. You may have mixed up some of the resistors. Check with a meter. Not the first time I have made that mistake. My electronics knowledge is not that great, but what would the effect be of a burnt out current regulator?

Best of luck...
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Old 22nd November 2008, 03:13 AM   #76
chrish is offline chrish  Australia
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Was having lunch in between starting and finishing my reply... Looks like Ty has been thinking the same as me.

You should be getting good volume levels with that setup.

Good luck!
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Old 22nd November 2008, 03:27 AM   #77
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Quote:
Originally posted by chrish
Was having lunch...
Ha ha! It's half past eleven here... nearly midnight! But lunch does sound good. I wonder what's upstairs in the fridge?

As long as you keep at least 0.5 mA through the 12AT7, the gain doesn't change much and it should be reasonably linear. Overall amp gain should be from about 16.5 dB (0.5 mA) to 19.5 dB (10 mA) with a healthy 12AT7. Once the CCS falls under ~0.4 mA it turns to garbage. Frequency response goes in the toilet and amp gain is -50 dB. It just won't work at all.
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Old 22nd November 2008, 03:33 AM   #78
N1ESE is offline N1ESE  United States
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All resistors check out A-OK so that's not it.

Donut have another 12AT7 to try at the moment.
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Old 22nd November 2008, 03:51 AM   #79
n_maher is offline n_maher  United States
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Originally posted by N1ESE
All resistors check out A-OK so that's not it.

Donut have another 12AT7 to try at the moment.
I can test a few of the dozen or so that I have and drop a few in the mail to you Monday. Or if you're dying to get the thing running we might be able to hook up some time this weekend. Drop an email with your address at a minimum.
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Old 22nd November 2008, 03:55 AM   #80
N1ESE is offline N1ESE  United States
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Thanks Nate, email sent.
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