Differences between 6SN7GTA and 6SN7GTB? - diyAudio
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Old 29th July 2007, 11:21 PM   #1
pftrvlr is offline pftrvlr  United States
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Default Differences between 6SN7GTA and 6SN7GTB?

I have two Sentinel 6SN7, one is GTA, the other is GTB. They look similar to me. Is there any difference between them?

I want to use them as a pair, but I know they might not match.
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Old 29th July 2007, 11:56 PM   #2
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Hi,

I don't know too much myself but this thread may help. Scroll down to '6SN7 variants':

Quote:
6SN7GTB* - Same as GTA, but with faster tube heat-up (11 seconds only).
[http://64.233.183.104/search?q=cache...lnk&cd=2&gl=uk


(Edit: Sorry for the editing. I tried to make a simple adjustment and I messed it up.)
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Old 29th July 2007, 11:57 PM   #3
anatech is offline anatech  Canada
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Hi pftrvlr,
I don't know off hand. The differences may be very minor, such as controlled heater warm up time.

Try them out. The worst that can happen is that they sound vastly different and you need to buy another pair. I doubt this will be the case.

-Chris
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Old 30th July 2007, 12:15 AM   #4
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The only difference between the 'A' version and the 'B' version is that the 'B' version includes what's called a "controlled heater warm-up characteristic". This helps to reduce the voltage imbalance on power up between cold filaments when stringing all the filaments in series, as was frequently done as a cost reduction measure for TV set design.

The main difference between the original 6SN7GT is that the peak positive plate pulse rating was increased from 1200Vdc to 1500Vdc in vertical deflection use, and that the control grid was beefed up for greater reliability in Class C, postive control grid, operation. The plate dissipation was also increased to 5000mW from 3500mW.

For use as a small signal audio amp, it shouldn't make any difference, and except for extending the plate characteristic into positive grid territory, the characteristics look pretty much the same.
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Old 30th July 2007, 01:41 AM   #5
pftrvlr is offline pftrvlr  United States
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Thanks for the replies.

I ran into a 6SN7 in positive bias before. I was puzzled that it actually worked. I did a search on this topic but did not get much info. Is it OK to run 6SN7 in positive bias?
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Old 30th July 2007, 02:38 AM   #6
anatech is offline anatech  Canada
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Hi pftrvlr,
Quote:
Is it OK to run 6SN7 in positive bias?
Not unless you can deal with very high distortion. This tube would require a driver tube. One would then ask, why do you need to do this?

Always consider the effect on your input signal as in positive bias, grid current flows and your nice high impedance drops way, way down. BTW, grid current can begin anywhere from a volt or less below ground, so try to keep your grid swing out of this area also.

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Old 30th July 2007, 02:53 AM   #7
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"Is it OK to run 6SN7 in positive bias?"

According to This Characteristic, it is.

This being for vertical deflection duty, or for Class C RF amps.
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Old 30th July 2007, 03:00 AM   #8
anatech is offline anatech  Canada
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Hi Miles,
What does the input characteristic look like at positive grid bias?

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Old 30th July 2007, 03:58 AM   #9
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What I have is the spec sheets from Frank's. It's probably not something to worry about for any reasonable audio use. For audio, I don't see any need for driving a 6SN7 into grid current, as that's for useage as a vertical deflection amp or amp/oscillator, or some low level RF stage (oscillator, frequency multiplier, driver).
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Old 30th July 2007, 03:51 PM   #10
anatech is offline anatech  Canada
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Hi Miles,
I was thinking along those lines myself. For RF or some kind of HF driver yes, but not for the average audio circuit.

I wouldn't be surprised if there was an audio circuit, somewhere in this world where a circuit using the 6SN7 was designed to draw grid current.

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