#26 pre amp - Page 209

tcqanh · 01:16 PM

Quote:

Originally Posted by andyjevans

I don't use the 26 anymore, but when I did I used two Hammond 156C chokes in series, bolted top to bottom and wired out of phase - all the details are in the thread somewhere. That was a good sound and cheap to achieve. This gives you all the gain of the 26 with a Russian teflon cap in my case. The issue with this setup is hum - the Hammonds are prone to hum pickup so you need to place magnetic components carefully, and well away from the chokes.

Exactly, I did build an 71A preampli with anode choke of 150H. Hum is a bit quite although I isolate power transformer in separate chassis. The preampli lies next to the power ampli, so I don't have any problem on impedance matching. high and midrange of this are fantastic.

I have an idea. Take 27/56/76 or 6J5/ 6SN7 is role of CCS for 26, likes SRPP circuit. That means these tubes are top half, and 26 is bottom half. I will experiment that in near future. That time the schema will be simplest.....

tcqanh · 6th October 2012, 01:14 PM

Quote:

Originally Posted by tcqanh

I have an idea. Take 27/56/76 or 6J5/ 6SN7 is role of CCS for 26, likes SRPP circuit. That means these tubes are top half, and 26 is bottom half. I will experiment that in near future. That time the schema will be simple.....

Top half tube is maybe a DHT, I can take 2 windings of filament in out of phase. So no need to get DC filament because AC hum from filament will be a lot canceled together.

... promissing

Rod Coleman · 6th October 2012, 01:22 PM

The "cancelling" of ac in filaments is what a hum-pot tries to do.... it's not good enough for a line amp, firstly because the filament is not perfectly symmetrical, - and secondly because the cathode generates second-harmonics of the filament current.

The sound is much worse as well, because the ac-current generates cross-products with the music (intermodulation).

mogliaa · 6th October 2012, 03:11 PM

Quote:

Originally Posted by tcqanh

Exactly, I did build an 71A preampli with anode choke of 150H. Hum is a bit quite although I isolate power transformer in separate chassis.

I had a lovely 71a loaded with Mu follower gyrator. Filaments DC using Rod's regulator and was dead quiet
Go for dc filaments!
Ale

Wavebourn · 6th October 2012, 06:05 PM

What happened with 4P1L on epay? Only 2 sellers left...

One from Ukraine (selling matched pairs) and one from Czech Republc...

mogliaa · 6th October 2012, 06:07 PM

Quote:

Originally Posted by Wavebourn

What happened with 4P1L on epay? Only 2 sellers left...

One from Ukraine (selling matched pairs) and one from Czech Republc...

Hi Anatoliy,
Too late, all sold out thanks to us preaching all along the beauties of this valve. I bought about 15,000

Ale

Magz · 6th October 2012, 06:59 PM

OK, here are some pics of my completed 26 linestage. First the whole package of PS, linestage, umbilical and remote, then a closeup of the linestage, then the linestage in operation on my workbench.

Magz · 6th October 2012, 07:01 PM

Now for some nudies:

First is the Power Supply Internals, then two shots of the linestage internals.

mogliaa · 6th October 2012, 07:03 PM

Quote:

Originally Posted by Magz

OK, here are some pics of my completed 26 linestage. First the whole package of PS, linestage, umbilical and remote, then a closeup of the linestage, then the linestage in operation on my workbench.

Hi Magz,
Superb job, well done! Very neat! I wish mine could look like that.
Here is my current 26 preamp incarnation with LL2745 and HT using russian glow tubes and dn2540 CCS "a la Gary Pimm"....
Ale

mogliaa · 6th October 2012, 07:05 PM

And another one:
http://www.bartola.co.uk/valves/wp-c...908-171450.jpg

6th October 2012, 06:05 PM	#2085
Wavebourn diyAudio Member Join Date: Sep 2006 Location: Pleasant Hill, CA	What happened with 4P1L on epay? Only 2 sellers left... One from Ukraine (selling matched pairs) and one from Czech Republc... __________________ If I disappear suddenly, that means I finally created a time machine and pushed wrong button that brought me to Stalin's Russia. In any experiment any result is the result. Even if it is negative.

6th October 2012, 07:05 PM	#2090
mogliaa diyAudio Member Join Date: Dec 2009 Location: London	And another one: http://www.bartola.co.uk/valves/wp-c...908-171450.jpg __________________ "A mistake is always forgivable, rarely excusable and always unacceptable. " (Robert Fripp) http://www.bartola.co.uk/valves/

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6th October 2012, 01:22 PM	#2083
Rod Coleman работник diyAudio Member Join Date: Jul 2004 Location: Warwickshire UK	The "cancelling" of ac in filaments is what a hum-pot tries to do.... it's not good enough for a line amp, firstly because the filament is not perfectly symmetrical, - and secondly because the cathode generates second-harmonics of the filament current. The sound is much worse as well, because the ac-current generates cross-products with the music (intermodulation).