Forums - Bias control switch on Zen Triode:

Mark

Seasoned Member

Posts: 259

Bias control switch on Zen Triode:
01/13/13 at 19:34:49

I was playing with the bias control switch on my Zen Triode [white one], and I do prefer the more aggressive position [rearward]; however, I'm noticing a certain 'scratchiness' in the volume control when the amp is warming up... That is, for about 20 mins. or so...

I first want to say that I have the Zen CD player with output control, and that I only have this issue with the CDP, and not when I have my tuner selected...

When I put the bias switch in the forward position, the problem largely goes away, sometimes disappearing altogether... Mind you, this situation shows itself with everything powered up, but no CD playing... So the amp is just idling at the time... But any fiddling with the volume control produces the aforementioned scratchiness, and also a point at the upper end of the volume where there is a 'flat spot' that produces a more hush tone for about 3 degress of rotation or so...

I'm thinking that there might be some kind of interraction between the tube output stage of the CDP and my Zen amp input stage, particularly the input tube... I tried a few different tube types, but still seem to have the symptom...

Any thoughts on this would be appreciated...(m.)

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If a rabbit defined intelligence the way man does, then the most intelligent animal would be a rabbit, followed by the animal most willing to obey the commands of a rabbit. -Robert Brault, writer (b. 1938)

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Steve Deckert Administrator If the 1st watt sucks why continue? Posts: 6246	Re: Bias control switch on Zen Triode: Reply #1 - 01/13/13 at 23:20:41 Have you tried a different 12AU7 in the CD player to see if the symptoms change any?
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Mark Seasoned Member Posts: 259	Re: Bias control switch on Zen Triode: Reply #2 - 01/14/13 at 00:12:49 Steve: I'm going to retry that... I don't think I gave it a good enough play... I'll try the one you shipped me, as I have a Telefunken 12 AU 7 in there now... It could just be a funky interraction between the CDP output tube, and the Zen input tube... (m.)
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Mark

Seasoned Member

Posts: 259

Re: Bias control switch on Zen Triode:
Reply #3 - 01/14/13 at 16:59:33

Follow-up #1: I tried rolling a few more output tubes into the CDP...

After a careful evaluation, I think the issue is getting enough total gain [from both the CDP and input tube of the Zen] to bring the amplifier to a suitable soud level without having to turn the CDP output pot up to a point where it is giving me the aforementioned symptoms...

That's the best I can describe it right now...

This morning, I have an Amperex BB 12 AT 7 [D foil getter] tube in the CDP output socket...

It's doing pretty well, as I think it has a higher output than the rest of the tubes I have on hand...

With the 12 AT 7, I'm reaching full amp output with no scratchiness or notch point on the upper part of the Zen volume knob...

Note: This may all be total BS... Need more evaluation time...

More later... (m.)

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If a rabbit defined intelligence the way man does, then the most intelligent animal would be a rabbit, followed by the animal most willing to obey the commands of a rabbit. -Robert Brault, writer (b. 1938)

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