Express Documents

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jelle
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Re: Express Documents

Post by jelle » Mon Nov 24, 2008 9:34 pm

Nope, they did not forget the pot! :lol:

It's under the tab for 'resistors' in the XLS file.

jelle

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Ron Worley
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Re: Express Documents

Post by Ron Worley » Tue Nov 25, 2008 2:04 am

I didn't forget the Pot... or the Beer.. :roll:

No worries Larry!!

Ron
Last edited by Ron Worley on Tue Nov 25, 2008 11:02 pm, edited 1 time in total.

Zippy
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Re: Express Documents

Post by Zippy » Tue Nov 25, 2008 5:20 pm

So now we have "Express documents", "Rocket documents", "Liverpool documents", and "Schematics and Layouts".

Any chance of convergence rather than a tendency toward entropy???

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Ron Worley
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Re: Express Documents

Post by Ron Worley » Tue Nov 25, 2008 11:03 pm

That's Allyn's call, I have absolutely no moderator ability to do anything.....

Ron

PCollen
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Re: Express Documents

Post by PCollen » Tue Dec 16, 2008 8:18 pm

Although voltages are different, both the Express Schematic and Voltage Chart listed in this thread indicate a 15-18Vdc difference between the OT c/t voltage and the screen-grid voltage feeds. This would not be the case if a choke were to be used and I'm wondering if this voltage difference could be significant in the Express 'performance characteristics'. I wonder if the plate voltage would drop below the screen-grid voltage in this case , as it might in an amp with only 1 or 2 Vdc difference between the two.

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Ron Worley
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Re: Express Documents

Post by Ron Worley » Tue Dec 16, 2008 8:49 pm

I would put this into the TW discussion, it would be a good topic of discussion for all....

Ron
Ron

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novosibir
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Re: Express Documents

Post by novosibir » Tue Dec 16, 2008 8:57 pm

PCollen wrote:... 15-18Vdc difference between the OT c/t voltage and the screen-grid voltage feeds. This would not be the case if a choke were to be used and I'm wondering if this voltage difference could be significant in the Express 'performance characteristics'.
I really can't recommend to reduce the supply voltage difference between the plates and screens in an Express by using a choke or by diminishiong the 1K resistor!

The 'Express Sound' partial benefits from the extreme mismatch of the OT's primary impedance, when EL34's are used (6.6K instead of ~3.5K).

But this mismatch wouldt be an extreme stress for the screen grids, if the screen voltage wouldt be close to the plate voltage!

Larry
Larry's Website now with included Pix's Gallery

soma_hero
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Re: Express Documents

Post by soma_hero » Tue Dec 23, 2008 8:46 pm

Ron, on page 28 when you are discussing attaching the NFB wire to the presence pot, you mention the 100M resistor instead of 100k.

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Ron Worley
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Re: Express Documents

Post by Ron Worley » Wed Dec 24, 2008 4:38 pm

Hey, thanks for the catch, it's these little things that are hard to see...

A new version will be coming out fairly soon... I'm considering making one big build document for all 3 amps with break out sections where they differ (Output tubes, Rectifier, PS board, etc....
Ron

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martin manning
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Re: Express Documents

Post by martin manning » Sat Dec 27, 2008 2:30 pm

Ron,
Really great stuff here! I'll definitely have to take some time to read through this material.

My $0.02: Skimming through I noticed that on page 46 of the build guide you have:

4. Using a DMM, Place the black negative lead onto a good chassis ground. With the red positive lead, check and adjust the bias current to 40-45mA (Pin 5 on either power tube). Be sure that you take a periodic peek at the tubes to make sure that it’s not red-plating (glowing bright red). Turn the amp off immediately if it is.

Maybe this is not the place for a detailed description of how to set idle curent, but this statement is confused as written. It sounds like you are assuming a common 1R resistor from the cathodes to ground and looking for 40-45 mV on pin 5 (and so 40-45 mA)... but I don't see a resistor in the schematic, and that would be pin 8 anyway. The easy way out is just shorten that sentence to "Check and adjust the bias current to xx mA," but that likely wouldn't meet your high standard of thoroughness!

Cheers, MPM

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Ron Worley
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Re: Express Documents

Post by Ron Worley » Sun Dec 28, 2008 8:30 pm

Hey Martin-

I am using a 1R in an external box I built for biasing.... but you're right, it is ambiguous.... I need to do a thorough revision of the whole document.

The biasing section is certainly up for review, thanks for the input!!
Ron

arjepsen
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Re: Express Documents

Post by arjepsen » Mon Jan 19, 2009 4:43 pm

I think you're missing one 1M resistor for the phase inverter, in the latest BOM. (R10).
There's supposed to be used 3 of these in all, right?
(2 for PI, one for input jack)

Anyways, thanks for the docs. They're a great help!!

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Ron Worley
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Re: Express Documents

Post by Ron Worley » Tue Jan 20, 2009 12:45 am

You are totally correct, I omitted it ini this rev for some dumb reason- the LP and Rocket BOMs have it right.... WTF???

Anywho, V1.9 will be published asap to correct that!!

Thanks again.
Ron

fayser
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Unbelieveable

Post by fayser » Sat Jun 20, 2009 11:39 am

Ron.. it has to be said... this is an incredible piece of work... it's real pick your jaw up of the floor stuff.... well done to you and all the gang on this forum.. this has made it so easy for home enthusiasts like myself to entertain building one of the most revered amps of all time ... my hat is firmly off to you .

Tony

cbfurg
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Re: Express Documents

Post by cbfurg » Sun Jan 17, 2010 6:02 pm

Thanks for all the work put into this thing! it will be invaluable to me as a newer builder!

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