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Old 8th February 2003, 05:47 PM   #1
Jaap is offline Jaap  Netherlands
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Default anyone tried 12HG7 as a driver ?

I have those tubes and also a pair of LL1660/10mA interstage transformers. I wonder if I could use them together.
I already tried the el84 as a driver for the IT, but this sounded a bit 'stressed".

JH
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Old 8th February 2003, 06:19 PM   #2
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'HG is a neonoval (read: wide base with mini-9-pin arrangement) tube, and is either a video amp or a dissimilar dual triode...I forget.

Somehow I feel you want triode-mode specs, since triode's low Rp damps the IST. If you've been using pentode mode, that could be why it sounds weird.

Tim
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Old 8th February 2003, 11:53 PM   #3
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Default 12GH7

Hi,

Jaap,

This tube-sharp cut-off penthode- isn't really suited as a driver...however if you were to construct a Mu-Follower it could be put to good use as a CCS (sort off).

Your fellow countrymen use a penthode similar to that in their projects.

Let me know if you're intererested and I'll point you to some links.

Cheers,
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Frank
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Old 9th February 2003, 07:49 AM   #4
Jaap is offline Jaap  Netherlands
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Default thanks gentlemen

Yes, I have seen the mu-stage designs, didnot try it yet.
Must be a good solution because some people seem addicted to it.

At another forum one person said that the 12HG7 is a great tube for a driver. He uses it to drive a 813 tube with good result: screen 150V; B+ 400V, 4K plate resistor and 40 mA plate current. This person said it was a kind of 6H30.

any comments ?
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Old 9th February 2003, 10:21 AM   #5
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Default Re: anyone tried 12HG7 as a driver ?

Quote:
Originally posted by Jaap
I have those tubes and also a pair of LL1660/10mA interstage transformers. I wonder if I could use them together.
I already tried the el84 as a driver for the IT, but this sounded a bit 'stressed".
Assuming you're using the EL84 trioded, it's Rp will be around 2k6 to 3k4, depending on the B+ (assuming a flatish loadline). Thats no too bad and well within the 14k source impedance max set by Lundahl in the datasheet. So using it in this application, I can think of two possible issues.
1: the EL84 sounds a lot better with some current through it, 10mA being way too low IME. I tried some as a preamp stage, and it sounded a lot better between 30 and 40 mA than it did down low, even into a basically resistive load. It also measured quite a bit better with more current through it, distortion wise, over an order of magnitude from memory. At 10mA, any reactance will see the loadline elipse out into the non linear region of the curves, ie lots of THD/IMD.
2: Could there be a peak in the HF response with the setup you used?

Interesting comments from Pete Millett on AA wrt the 12HG7 being similar to a 6H30. Next time I come across some I'll have to give it a try.

Cheers
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Old 9th February 2003, 04:38 PM   #6
Jaap is offline Jaap  Netherlands
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Default I confess

that I used the el84 as pentodes. I have to go back to the breadboard.

Jaap
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