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Old 1st July 2006, 08:22 PM   #1
Ryssen is offline Ryssen  Sweden
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Default Morgan jones and cascodes

I was reading Morgan Jones book "Valve amplifiers" 1st edition,when i saw this:
"As mentioned before the only really satisfactory valve for use as the lower valve is the Ecc88;any other type will waste HT"

Is this true?
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Old 1st July 2006, 08:30 PM   #2
poobah is offline poobah  United States
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Of ourse it's true...
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Old 1st July 2006, 09:10 PM   #3
Ryssen is offline Ryssen  Sweden
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Hi hi..
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Old 1st July 2006, 09:20 PM   #4
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Default Re: Morgan jones and cascodes

Quote:
Originally posted by Ryssen
I was reading Morgan Jones book "Valve amplifiers" 1st edition,when i saw this:
"As mentioned before the only really satisfactory valve for use as the lower valve is the Ecc88;any other type will waste HT"

Is this true?

Not really. A triode with high gm is required at the bottom of a cascode. The ECC88 is an excellent, but not the only, choice. Rozenblit uses 2x 6s45p to form the cascode 1st gain block in his phono stage. My McIntosh MR71 FM tuner uses a 6DS4 nuvistor at the bottom and a 12AT7 at the top of its cascode TRF front end.

Jones is accurate in pointing out the ECC88's convenience, as 90 V. per section is quite satisfactory.
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Old 1st July 2006, 10:02 PM   #5
JoshK is offline JoshK  Canada
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Great timing, I read the same thing this morning.
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Old 2nd July 2006, 04:48 AM   #6
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Many others could work well.... 6AQ4 comes to mind
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Old 2nd July 2006, 12:56 PM   #7
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Quote:
6AQ4 comes to mind
Shhh! Let's keep that little tube a secret.
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Old 2nd July 2006, 01:08 PM   #8
SY is offline SY  United States
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(Perks up)

Oh, yes?
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Old 2nd July 2006, 11:16 PM   #9
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Quote:
Originally posted by Brian Beck


Shhh! Let's keep that little tube a secret.

D'OH! I did it again!
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Old 6th July 2006, 12:12 AM   #10
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Surely the type of tube will depend on the output amplitude required? E.g. as input stage in a power amplifier usually an output signal of a few volt only is required, so wasted voltage is of little consequence. I am not suggesting all tubes will do; I do not see the ECC83 in that role. But there are also disadvantages in using too high Gm triodes at low currents required for voltage amplifiers; they could operate on a steep slope in their transfer characteristics rendering work points critical. There are other factors beside a low operating Va for the input unit.

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