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Old 7th November 2005, 04:16 PM   #1
HugoR is offline HugoR  Canada
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Default Need help with tube test data - fast

Hi,

Would like advice before buying tubes. I am about to buy 4 6AN8A pairs (2 pairs/brand) and asked triode matching datas from the dealer.

Circuit uses a pair of 6AN8s for gain/phase splitting and has bias adjustment for each channel as well as test points and trimmer pots for DC and AC balance of each channel.

Is triode matching important in these conditions?

Here's the test data from the Zenith, Rogers valves.
Data is Triode / Pentode, in uMhos, measured/tested on Stark 9-66 Mutual Transconductance test set.

Rogers
4900/4100
4900/4700
4650/4200
4850/4250
4250/3800
3400/4100

Zenith (USA)
3400/3600
4500/3800
5000/4100
3900/3700

Zenith (UK)
5100/4100
5000/4050
3900/3650
4550/3850
3400/3950

As you can see, "matching" sets of triode-pentode tubes in brands is difficult.

Thanks for any and all help.
HugoR
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Old 7th November 2005, 04:18 PM   #2
SY is offline SY  United States
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If the triodes are used as a split load (like the Dyna circuit), matching them is not terribly important.
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Old 7th November 2005, 04:31 PM   #3
HugoR is offline HugoR  Canada
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The circuit is a three-stage feedback amp employing a common 6AN8 triodepentode as the voltage amp and phase inverter. The input signal is applied to the 6AN8 penthode grid, after being coupled through a 15000 ohm isolating resistor. The penthode acts as a voltage amp and DC-couples the signal to the grid of the triode phase inverter.

HugoR
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Old 7th November 2005, 04:34 PM   #4
SY is offline SY  United States
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That sounds like the Dyna circuit. Are the plate and cathode resistors of the triode equal? If so, it's a split load, it's operating under nearly 100% feedback, and the matching is not critical.
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And while they may not be as strong as apes, don't lock eyes with 'em, don't do it. Puts 'em on edge. They might go into berzerker mode; come at you like a whirling dervish, all fists and elbows.
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Old 7th November 2005, 04:46 PM   #5
HugoR is offline HugoR  Canada
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IIRC, plate and cathode resistors are equal to 27000 ohm, 1W.
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Old 7th November 2005, 05:27 PM   #6
HugoR is offline HugoR  Canada
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I am wrong.
Plate resistor are different. See the circuit bellow.
R7 = 27000 ohm
R9 = 39000 ohm

Thanks
Attached Images
File Type: jpg frac-sch.jpg (62.8 KB, 102 views)
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Old 7th November 2005, 06:43 PM   #7
SY is offline SY  United States
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Without commenting that the guy who drew this schematic should be taken behind the barn and spanked with an axe, you left off the important bit- the triode phase splitter in question.
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Old 7th November 2005, 07:26 PM   #8
HugoR is offline HugoR  Canada
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SY,
I am sorry. Image was too big!
The link of the complete schema is bellow... Hope it will work.
I appreciate your help.
Hugor

Click the image to open in full size.
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Old 7th November 2005, 07:41 PM   #9
HugoR is offline HugoR  Canada
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Retrying with the link Click the image to open in full size. .

Don't know how to handle IMG If link doesn't work. Sorry.

Thanks alot.
H
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Old 7th November 2005, 07:43 PM   #10
HugoR is offline HugoR  Canada
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Wow! Works this way.
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