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Old 31st January 2003, 02:17 AM   #11
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I'm open to other suggestions. If you have a preamp or poweramp schematic I would enjoy looking at it. I had heard so much about the sweet sound of the 26 I thought I would try it.

Joe
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Old 31st January 2003, 05:43 PM   #12
Joel is offline Joel  United States
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Quote:
Originally posted by burnedfingers
I had heard so much about the sweet sound of the 26 I thought I would try it.
Joe, just as a philosophical note - shouldn't you strive for transparency from your gear, not "sweetness" or any other kind of coloration?

Anyway, there's nothing wrong with building a project around a #26, but I wouldn't waste my time with preamps.

Why not pick your favorite directly-heated power tube and make an all DH power amp with two #26's as the first gain stage + driver?
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Old 1st February 2003, 11:23 AM   #13
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Joel

Do you have a design in mind that uses 26's in the front end?



Joe
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Old 1st February 2003, 11:49 AM   #14
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Default RCA 26

Hi,

here's an application note from the RCA Radiotron:

As an audio-frequency amplifier,the 26 should used wuth transformer coupling in order to secure the greatest amplification per stage.

Keep in mind this was published in 1933 though.(RC11)

This is a low mu tube with a factor of 8.3 at best so I feel it is best suited as a driver stage not as an input tube,unless you don't need the gain and don't intend to use global feedback.
Which is not recommended for transformer coupled stages anyway.

Typical operating point in this case:

Va 135 V
Vg -10
Rp 7K6
Ra 5.5 mA
Heater can be AC or DC at 1.5 V/1.05A.

Cheers,
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Frank
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Old 2nd February 2003, 03:35 PM   #15
Joel is offline Joel  United States
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Default Re: RCA 26

Quote:
Originally posted by fdegrove
This is a low mu tube with a factor of 8.3 at best so I feel it is best suited as a driver stage not as an input tube,unless you don't need the gain and don't intend to use global feedback.
Which is not recommended for transformer coupled stages anyway.
Frank, I just built an amp using two '01A's as gain and driver, and I can swing 40 volts with them on the grid of a 71A. With choke loading, the gain of each is 7.7 (at 1kHz) out a possible 8.

Joe, I don't think you'll find a commercial amp using that driver, and certainly an old amp design from the 1930's would need need to be reworked to be a hi-fi.
The key is finding an output tube that can be driven successfully by a 26. What would be nice is using just a single 26 to drive a more sensitive output tube. How about a 26 --> 6L6 ultralinear?

If you want to go more old-school, two 26's cascaded can swing a max of 60 or so volts, with transformer or choke loads. Probably 48V or less with RC coupling.
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