Express Documents

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Ron Worley
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Re: Express Documents

Post by Ron Worley »

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 »

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 »

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

Ron
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novosibir
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Re: Express Documents

Post by novosibir »

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 diminishing the 1K resistor!

The 'Express Sound' partially benefits from the extreme mismatch of the OT's primary impedance, when EL34s are used (6.6K instead of ~3.5K).

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

Larry
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soma_hero
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Re: Express Documents

Post by soma_hero »

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 »

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 »

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 »

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 »

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 »

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 »

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 »

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

Post by robtone »

Ron,

What program did you use to draw this layout? It looks better than any thing I have seen.
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Ron Worley
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Re: Express Documents

Post by Ron Worley »

Microsoft Visio, it's really easy to use .....
Ron
TheGimp
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Output tubes in TrainWreck

Post by TheGimp »

Greetings.

Great site and wonderful documentation on the TW Express.

One question please?

With regards to t he schematic, shouldn't V4 and V5 be "EL34 or 6L6" instead of "EL34 or 6V6"? The 6L6 is a closer match to the4 EL34, and the 6V6 is not rated for the plate voltage present.

Well, that was two questions but the first shouldn't count.

Cheers.

Sven
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