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a riff on Drummer Wills 26 amp?

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Posted on August 31, 2015 at 04:16:42
vinnie2
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Location: North Carolina
Joined: September 28, 2013




After getting all the bugs out of my 26 preamp I began wondering if it could be morphed into a 26/26/45 amp ala Drummer Will.
In the schem above could I go from the bottom of the 470k resistor to the grid of the second 26 and from the bottom of the 470k resistor of the second 26 to the grid of the 45? The rest would be pretty much the same as Drummer Wills amp, with a 125 ese opt. Will's amp schem is above mine.
Oh, forgot to mention I am one power tranny short at the moment so I am running the 45 at 245vdc same as the 26's for the b+ just to see if I can get music out the other end. Is that enough to get it to operate?

 

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RE: a riff on Drummer Wills 26 amp?, posted on August 31, 2015 at 09:04:45
Caucasian Blackplate
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 You could run the 45's plate that low, but you'd want to use fixed bias to get any meaningful power.

 

RE: a riff on Drummer Wills 26 amp?, posted on August 31, 2015 at 09:25:54
vinnie2
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Location: North Carolina
Joined: September 28, 2013
 It would just be temporary to test the concept. Any thoughts on what cap and resistor to use?

 

RE: a riff on Drummer Wills 26 amp?, posted on August 31, 2015 at 09:27:46
Caucasian Blackplate
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Location: Seattle
Joined: June 18, 2004
 You're asking the least important question that you possibly could. More important questions might be:

Do I have 4 more filament windings for the 4 more tubes I'm adding?

With ~250V of B+, what operating point should I use for the 45? (and do I have a suitable output transformer)

 

RE: a riff on Drummer Wills 26 amp?, posted on August 31, 2015 at 09:37:22
vinnie2
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Location: North Carolina
Joined: September 28, 2013
 Actually I have already answered some of those. I am only doing one channel for now, and I have the filament trannies covered. I figure if I get sound coming out the other end I can take some measurements and see where I am on the load line. Just trying to get a working circuit for starters, so I need ball park for the cathode resistor and cap.

 

RE: a riff on Drummer Wills 26 amp?, posted on August 31, 2015 at 09:48:51
Caucasian Blackplate
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Posts: 8313
Location: Seattle
Joined: June 18, 2004
 What output transformer are you planning to use with this?

 

RE: a riff on Drummer Wills 26 amp?, posted on August 31, 2015 at 11:01:44
vinnie2
Audiophile

Posts: 4481
Location: North Carolina
Joined: September 28, 2013
 A 125ese for starters. I just got through tossing a 100uf cap and 820 ohm resistor in for the cathode on the 45 and to my surprise I got music out the other end. Not to bad sounding either . Now the real work starts.
Thanks

 

update ......., posted on August 31, 2015 at 11:09:00
vinnie2
Audiophile

Posts: 4481
Location: North Carolina
Joined: September 28, 2013
 Following caucasian blackplates suggestion, I stuck a 100uf cap and a 820 ohm resistor on the cathode of the 45 and it now is operational at least. The surprising thing is it doesn't sound half bad considering it is at about half the recommended plate voltage and I just took a wag at the cathode cap and resistor. Measured the grid voltage and current on the 45 and they are 35vdc and 4.3 mA respectively.
I guess I am going to have to give it one more try and drag out my design books and the tips I have saved from this forum and take another shot at doing a proper desigh for it.
So which end do I start at, the 45 and work back or the first 26 and move forward? I suppose Morgan will have something to say on that. Wish me luck.
I would still welcome any suggestions anyone might have on doing this thing up proper. I can see why Will was excited about his, the sound is really good.

 

RE: update .......Yo vinnie2 ..., posted on August 31, 2015 at 11:49:57
drummerwill
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Posts: 965
Location: St Louis Mo.
Joined: January 7, 2003

When I first tried the 26 DC 45 design using standard 26 and 45 O.P's ,
it didn't drive my GPA 604's to the levels of dynamic a 45 can drive in SET mode. It was only when I went from a 2 stage amp to a 3 stage amp could I get the levels I needed.

This is why I was advised by my friend Dennis Fraker just use a higher mu tube like the EML 30A in a 2 stage design...... Me looker for a cheaper solution just added a second 26....

My 3stage 26-26 DC 45 amp drives the 604 's to pretty loud levels
without another preamp stage..... which means a much "Purer" source
of music.

Keep pluggin away vinnie2 until it sounds best to you !

Willie

 

RE: a riff on Drummer Wills 26 amp?.......Not correct ..., posted on August 31, 2015 at 11:59:25
drummerwill
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Posts: 965
Location: St Louis Mo.
Joined: January 7, 2003

Vinnie that schematic is an older one that was later corrected by adding a 330K Grid bias resistor to the second 26..

Willie

 

RE: a riff on Drummer Wills 26 amp?.......Not correct ..., posted on August 31, 2015 at 13:39:48
vinnie2
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Posts: 4481
Location: North Carolina
Joined: September 28, 2013
 Thanks Willie. Is that the only change that needs to be made to yours?

 

RE: update .......Yo vinnie2 ..., posted on August 31, 2015 at 13:48:07
vinnie2
Audiophile

Posts: 4481
Location: North Carolina
Joined: September 28, 2013
 I tried a straight 26/45 first too, with the same results. Great little design you put together Willie.
Thanks!

 

RE: a riff on Drummer Wills 26 amp?.......Yep ....., posted on August 31, 2015 at 19:16:40
drummerwill
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Posts: 965
Location: St Louis Mo.
Joined: January 7, 2003

That's the only change !

Willie

 

Hey Willie......, posted on September 1, 2015 at 03:09:44
vinnie2
Audiophile

Posts: 4481
Location: North Carolina
Joined: September 28, 2013
 Would using the one 26 per channel preamp with the 26 amp in effect give me an amp that is 26/26/26/45? That ought to get the speakers movin!

 

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