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Old 8th July 2010, 03:33 AM   #1
tinitus is offline tinitus  Europe
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Default El Cheapo, builders thread

Hey, I thought it might be time to have a dedicated builders thread


Any builders around ?
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Old 8th July 2010, 04:16 AM   #2
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Change the 6AQ5 to 6P1P and the 12AT7 to a 6N2P and you are near a Chinese amp. They work fine by the way. Good cheap tubes.

6N1P is more prevalent as the input tube though. Either will work, along with 6N3P and 6N23P (more expensive). Tweaking the cathode and plate resistors is required as you switch from 1P to 2P to 3P to 23P.....

Nice idea to isolate the channels with diodes in the ps, but plain 1N4007s are fine at this point as they are always in conduction and see no rectification per-se.

An-tek AN-1T200 works fine for both filament (yea I know, heater) and B+ if you use the 6V tubes. It has two 6.3V windings,so they could be seriesed and used for 12V tubes.

Hammond and Edcor both make reasonable OPTs.

Lots of options to make sourcing easier.
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Old 8th July 2010, 04:29 AM   #3
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We built one. Based on a Scout LK48 donor the power supply is different, and we used EL84 strapped in triode, biased into Class A, no glable feedback.. CCS on the bottom of the LTP is a Morgan Jones style cascode. A real stunner.

Click the image to open in full size.

We've never taken it out of service long enuff to make it pretty.

Part of the magic of El Cheapo is how the distortion signature of the ECC81 cancels that of the output stage.

dave
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Old 8th July 2010, 04:26 PM   #4
dhieber is offline dhieber  United States
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It would be helpful to builders if voltages were indicated on the schematic.
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Old 8th July 2010, 06:53 PM   #5
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Quote:
Originally Posted by dhieber View Post
It would be helpful to builders if voltages were indicated on the schematic.
If someone indicates what they are, i'd be happy to do so.

dave
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Old 8th July 2010, 09:12 PM   #6
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Though its fore Simple SE and not PP, there might be some valuable info here, or ?
I hope George doesnt mind

Tubes & Transformers
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Old 8th July 2010, 10:16 PM   #7
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by dhieber View Post
It would be helpful to builders if voltages were indicated on the schematic.
Triad N-77U, says 115V, 100VA
I suppose that will be 2x 115V

Im also confused about choke T/E C354
Schematic says 1.5H/0.2A
Is that just smallest possible ?
Ehh, Triad C-24X have been suggested
And that is 15H/0.02A

Hmm, what to look fore as optimal ?
What kind of specs do we need ?
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Old 8th July 2010, 10:23 PM   #8
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Re: choke, Feel free to use more. We used 2 10H, 100mA and set the PS to supply a separately filtered supply for each channel.

dave
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Old 9th July 2010, 12:54 AM   #9
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The currently recommended choke is the Triad C-24X (1 H./240 mA.). The doubler's pair of LARGE 'lytics do a good job of crushing the ripple fundamental. However, the highly triangular ripple waveform contains overtones of the fundamental extending well up into the RF region. That trash, along with any SS diode switching noise, is the primary target of the choke. If you want to improve filter action, insert a LC section made from a RF choke and a 1000 pF. mica or NPO ceramic cap. between the doubler stack and the "standard" style inductor.

As for voltages, the needs of the 12AT7 based small signal circuitry rule the roost. The 'T7 triode sounds good with 200 to 220 V. on the plate and an IB of 3 mA. That makes a B+ rail slightly over 350 V. "perfect". By itself, the N-77U does not get there. Use 1 of the 2X "12" V. windings of a Triad VPS24-1800 to boost the B+ rail voltage up and the 2nd "12" V. winding to energize the heaters of the 12AL5 and the "finals".

Builders residing in "240" VAC zones can use the Triad power "iron" mentioned, as both the N-77U and the VPS24-1800 have dual primaries. Unfortunately, the Allied 6K27VF is strictly "120" VAC. Builders outside of North America need to find something else to power the B- rail. The requirements of the B- rail are modest. About 30 V., to power the CCS, and sufficient extra Volts to allow the 'T7 cathodes to follow the negative swings of the I/P signal. 40 V. should be plenty. Please observe that the schematic drops 90 V. of B- in resistors. The 6K27VF was chosen for its cost control virtues.

I recommend that potential builders read the Audiophile Talk thread that documents the project's history. Yes it's very lengthy, but (IMO) worth your while.
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Old 10th July 2010, 05:16 AM   #10
tinitus is offline tinitus  Europe
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Hey, I found that Lundahl etc gets expencive, so I have looked at this EU supplier
Seems theres lots of affordable trafos etc

Frag Jan zuerst- Ask Jan first: Roehren und mehr

When using 6V6(GT?), I thought why not make all filament/heater 6V
And maybe an adjustable pure SS regulated supply for the CCS curcuit
And maybe also on ECC81
And I would build mono amps

I suppose thats possible ?
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