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Old 30th April 2002, 03:44 PM   #11
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The Lundahl LL7902 is a fine line input. It can be used 1:1, 1:2 and 1:4 as well. It would fit for this application.

Thomas
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Old 1st May 2002, 01:42 AM   #12
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Default How to run 26?

Thomas,
Is LL1667 / 15mA 270H anode choke good load for 26 driver?
How do you recommend to run the 26 as 45 driver?
Are batterys for 26 filaments must be?
Did found from net RCA 26 only. What manufacturers
26 did you recommend?

Sorry for so many questions.

Tõnu
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Old 1st May 2002, 12:29 PM   #13
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Default Re: How to run 26?

Quote:
Originally posted by tõnu
Thomas,
Is LL1667 / 15mA 270H anode choke good load for 26 driver?
I'm not going to do your homework for you
I guess you can figure that out yourself...

Quote:
How do you recommend to run the 26 as 45 driver?
What exactly is your question ?

Quote:
Are batterys for 26 filaments must be?
Either battery or very very well filtered DC from
current source or passively filtered supply

Quote:
Did found from net RCA 26 only. What manufacturers
26 did you recommend?
I'm not a tube roller and I don't compare tube brands

Regards

Thomas
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Old 1st May 2002, 04:28 PM   #14
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OK, I spotted this thread and I want to add my 2 pfennigs:

The transformer coupled line stage I am using I built almost as a joke, to see what the effect of microscopic source impedance would be on my system. It has remained in my system for over a year now with the only modification being an upgrade to the output transformers.

The line stage uses 6C45Pi, with a grid choke, loaded by a 5K:8 step-down (25:1 step-down) transformer such as would be used at the output of a 45 power amp. In fact the line stage can drive speakers directly - it's a "spud" amp. Bias is 2 AA batteries in the cathode for about 2.3V. I agree with Vinylsavor that this is just barely enough bias but with the grid choke it seems to work OK in practice.

The line stage feeds a transformer volume control of the type sold for controlling speakers in multi-room setups, and this feeds the power amplifier input.

The line stage source impedance is something like 5 ohms, and this allows you to use an 8 ohm nominal volume transformer which is very cheap to buy. I like the sound of this combination and it seems to perform well enough that I can reliably hear any and all changes in the equipment downstream from it, which is always being tweaked and changed.

One advantage of the low impedance is that cables seem to be less of an issue and you can run a simple twisted pair to and from the transformer volume control and not worry about hum.

I can't say I have really done "shoot outs" against other preamps but this is one way to go that I have used and enjoyed. Vinyl savor, you might remember we tried this ugly little spud preamp for a while in Arhus.

I have recently thought about regulating the power supply with gas regulators since it is so easy to try. Currently it is a simple CLCLC passively filtered supply.
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Old 1st May 2002, 04:44 PM   #15
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Hey Epsteinerin!

Good to have you in this thread.

2.3V bias on the tube ? What output level do your
sources have ? I assume your digital source has the
usual 2V RMS ? If so, the linestage clips at 0dB output!

I have done some measurements of grid current on various
high gm tubes, including this Ruskie firecracker.
Postive grid current starts anywhere between -0.5 to -1V bias.

One can argue about the sonic significance of grid current
effects, but for sure it adds non linearities.

For a linestage I would prefer to operate the tube at a minimum
of 4V bias to avoid grid current effects even at full output.
However with this tube then there is not enough headroom
on the negative side, which means it runs into cut off at
peaks.

That's why I wouldn't really recommend this tube for line level
applications.

Thomas
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Old 1st May 2002, 04:46 PM   #16
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By the way: No more Pfennigs over here, J! euro cents!
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Old 1st May 2002, 06:08 PM   #17
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Default Many thanks

Thomas, thanks for all.

Tõnu
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Old 1st May 2002, 07:03 PM   #18
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Quote:
I assume your digital source has the
usual 2V RMS ? If so, the linestage clips at 0dB output!
Well, that makes sense but in practice it doesn't sound like it. Hmm. Are you gonna make me go and measure now?

I'll report back.
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Old 1st May 2002, 09:22 PM   #19
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Hi J.

I guess the grid choke helps the grid current issue, but
if you have regular 2V RMS sources (quite sure) then the
pk voltage is +/- 2.8V. So in transients the Rooskie's grid needs to be driven 0.5V positive. This requires power, which your CDplayer or DAC most likely can't deliver. So the peaks will be rounded off. probably not to badly clipped, but still rounded.

Thomas
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Old 1st May 2002, 09:47 PM   #20
dice45 is offline dice45  Germany
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Thomas,

vinylsavor but peace-of-mind-destroyer!
Poor Jeremy now has to find out the truth.
Querulant !

However, have to agree with yor points.
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Greets,
Bernhard
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