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Old 21st June 2006, 08:35 PM   #1
Ryssen is offline Ryssen  Sweden
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Default Crosstalk in twintriodes?

If I use twin triod like 12BH7 or 6SN7 for stereo will there be crosstalk?
I mean 1 half for left and one for right.
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Old 21st June 2006, 09:42 PM   #2
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There could in theory be some coupling from cathode to cathode through the heater.

Just tie one side of your heater supply to ground. If you have to float the heater at a high voltage (in a cathode follower) put a cap from the resistor divider to ground.

It's really nothing to worry about. Even in the worst case scenario of inter-element parasitic capacitance you'll probably get more crosstalk from other sources.
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Old 21st June 2006, 09:43 PM   #3
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I wouldn't worry about it. It's going to be pretty much insignificant.
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Old 21st June 2006, 09:48 PM   #4
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I'll guess that there's 3 pF capacitance between the plates. That's 2 megs impedance at 20 kilohertz. Combined with the plate resistance of about 10K, this is a 2000:1 voltage divider, giving 66 dB isolation at 20 KHz, 86 dB at 2 KHz. I think that's more than good enough. 30 dB MIGHT be noticeable...
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Old 21st June 2006, 10:06 PM   #5
wa2ise is offline wa2ise  United States
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When you consider that the potential crosstalk is between related signals (left channel and right channel of the same program material), 30dB would not be noticed at all. Now, if the two channels had unrelated program material, then you'd object to that crosstalk.

Don't worry about it (I assume that the signals are related).
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Old 21st June 2006, 10:24 PM   #6
Ryssen is offline Ryssen  Sweden
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Quote:
Don't worry about it (I assume that the signals are related).
Ok,then I don´t worry then.
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Old 21st June 2006, 11:05 PM   #7
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Default Crosstalk between triodes

Crosstalk can occur not only by capacitive coupling but by stray electrons from one section getting attracted to the plate of the other section. Most modern dual triodes are designed to close-off any openings in the plates, but some older types, especially 1940s-vintage 6SN7GT and 6SL7GT tubes had pretty large openings that let this thing happen. I once built a two-stage amplifier using a single 6SL7GT and it had a very strange distortion that I tracked down to this type of coupling.

Putting a shield between the sections is the best. The old 6CG7 did this, but it later got replaced by the 6FQ7 which eliminated the shield. Other tubes with built-in shields between the sections include the 6BQ7, 6DJ8, and 6N1P.

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Old 22nd June 2006, 05:55 AM   #8
Jeb-D. is offline Jeb-D.  United States
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I'm using a vintage Tung-Sol 6SU7GTY, wich is a dual triode, in my amp. At first I had your concern but decided to do it anyways. One triode on L channel the other on the R. They are constant current loaded and at full volume swing 260Vp-p. There is absolutely zero crosstalk. First I disconnected the L input and the R speaker. Turned it all the way up, couldn't hear a thing even with my ear to the speaker(Ok, there was a very small hum from the power supply, but it's a SE amp, give me a break!). Then I tried it vice versa, same thing. Then I hooked it to the scope, there were no traces of the other channels signal.

Perhaps it was just this type of tube or the constant current loading. But that's my experience with this matter.
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