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Old 1st March 2013, 06:14 PM   #2551
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Hi!

none needed for DC coupling. But putting one on the grid wouldn't hurt either.

Thomas
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Old 2nd March 2013, 10:31 AM   #2552
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Maybe I've got something wrong, but at a certain point here there was a mention of a Tribute OPT for 26 with an option of attenuation. But I can't seem to find more any info (or my search abilities are limited).

Anyone knows about it?
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Old 2nd March 2013, 10:55 AM   #2553
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Hi!

Pieter developed these on my request. So far I got some made for the 10Y. They can be made for 26 as well. The ones for 10Y are shown here:

VinylSavor: Cool Links: www.tribute-audio.nl

Best regards

Thomas
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Old 2nd March 2013, 01:08 PM   #2554
Magz is offline Magz  United States
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Quote:
Originally Posted by anubisgrau View Post
Maybe I've got something wrong, but at a certain point here there was a mention of a Tribute OPT for 26 with an option of attenuation. But I can't seem to find more any info (or my search abilities are limited).

Anyone knows about it?
Or you could do what I did and use the Bent Audio autoformer volume controls in parafeed to function as both output transformers and volume controls. Works great, and you get 80% nickel laminations, remote control, left/right balance control and 61 1dB steps of volume control.
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Old 2nd March 2013, 02:56 PM   #2555
regal is offline regal  United States
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I don't think you can buy those any longer?
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Old 2nd March 2013, 06:56 PM   #2556
Magz is offline Magz  United States
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Originally Posted by regal View Post
I don't think you can buy those any longer?
John Chapman of Bent doesn't sell the assembled TAP-X units anymore, but he sells the parts for OEM (or DIY) use. Manufacturers such as Purity Audio use them (see the Purity Statement preamp as an example). I bought mine last year, and John was very helpful and always answered my questions promptly. Piece of cake to put together, too, just run the ribbon cable from subunit to subunit, in any order. The ribbon cable handles the power and control functions only; I made all signal connections with 23ga. silver in teflon. Not a cheap solution, but worth every penny for the features it provides.

Last edited by Magz; 2nd March 2013 at 07:01 PM.
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Old 3rd March 2013, 06:31 AM   #2557
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Hello guys!

I tested the Rod Coleman regulators I am going to use in the 26 preamp and I have some questions if you do not mind.

Click the image to open in full size.

I have the circuit for raw DC exactly the same as shown in the schematic above. I am using Hammond 166M18 (18 VCT vrms, 54 VA, 3A) and a Hammond 159ZC (60mH, 2A). On the 166M8, CT was not connected(not used).

Using a load of 1.5 ohms 20W, I can adjust the current on the regulator from 825 mA to 1.4 A no problem. My question is how come my raw DC voltage feeding the regulator was 28Vdc instead of the 18Vdc as per PSUD when my current is at 825mA up to 1.4A flowing to the load resistor?

What did I miss? Is that too large and I need to replaced the power transformer to a lower rms voltage output?

Thank you!

Abe

Last edited by amandarae; 3rd March 2013 at 06:35 AM.
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Old 3rd March 2013, 08:03 AM   #2558
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The 166M18 is certainly 18v rms, so it will yield near to 18V dc for a circuit that acts as a choke-input filter. The 159ZC should work well enough for the choke.

I'd try it with the first capacitor reduced from 440uF to a lower value - maybe even 5-10uF polypropylene.

The regulators will run hotter with 28V dc input - please make sure the heatsink keeps to a reasonable temperature (<65 deg C).
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Old 3rd March 2013, 08:05 AM   #2559
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That PSU looks fine to me. But to try it out you need to connect it to either the actual circuit or a bench construction of it. By that I mean connecting the + output of the regulator to one side of the 26 filament, the other side of the filament to the cathode resistor and the opposite end of the cathode resistor to the - output of the regulator. If you do this it should work. I suspect you are forgetting to insert the cathode resistor in the circuit.
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Old 3rd March 2013, 08:41 AM   #2560
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Hi Rod, Andy!

Rod, post #2513 shows the heatsink I am using (4.5 inches long, 2 inches tall, and 1.5 of depth).


Andy, you are right. I connected the regulator with just 1.5 ohm load and did not add the 10 ohm (cathode) resistor.

I am contemplating on changing the power transformer to say 10Vrms. I can only work on the preamp during weekends, so I am very slow on my progress. Will keep you updated.


Abe
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