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Old 3rd August 2012, 12:55 AM   #1931
lexx21 is offline lexx21  United States
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Is there any way that someone could post a schematic of what would be considered a "best practices/results" design for this project?
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Old 3rd August 2012, 02:20 AM   #1932
Magz is offline Magz  United States
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There are almost as many designs as there are designers on this thread. Battery bias, filament bias, cap coupled, transformer coupled, autoformer coupled, parafeed coupled, choke loaded, CCS loaded, gyrator loaded, VC on input, VC on output, etc.

Take your pick, or mix and match.
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Old 3rd August 2012, 10:17 AM   #1933
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All depends budget & how complicated do you want to implement the #26.
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Old 3rd August 2012, 11:10 AM   #1934
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Is there any way that someone could post a schematic of what would be considered a "best practices/results" design for this project?
The two most important things IMO. Heater supply. (Rod Coleman's supplies are a no-brainer from what I've read) Still haven't implemented the ones I bought BUT I will.

And the PSU.

The rest is pretty much taste.
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Old 3rd August 2012, 12:15 PM   #1935
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Default DHT-26 LINE: Serving Suggestion.

Thanks Bas! You can use the Regulators when you're itching for an upgrade some time!

A lot of taste is involved in getting a 26 DHT line amp to sound the way you like, but how about a sketch that gets a newcomer to the thread started? This should not be too controversial, I hope.

Based on properly implemented HV and filament supply, using good quality transformers, and a high quality Lundahl LL1660 output transformer to drive cable well.

I have showed filament bias, so that degradation due to cathode coupling caps can be avoided. Fil Bias generates lots of heat in the Bias resistor, buts gives the least compromise to the sound. (I can post a battery bias version if anyone would like it).

The circuit assumes that Sources have dc offsets below 0.2V, or a series capacitor will be required.
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File Type: jpeg 26_Line_FilBias.jpeg (126.3 KB, 368 views)
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Old 3rd August 2012, 12:26 PM   #1936
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This should not be too controversial, I hope.
Indeed..not controversial at all from my point of view. For the frugal though...The LL1660 output tranformers are relatively expensive though. Same for good anode/plate chokes (And layout/humm issues). A good CCS adds complexity.

So I guess a plan B would be a simple RC version of your schematic above.
Say 22k plate load with 0,22uF coupling cap. A la 26 Menu

Last edited by Bas Horneman; 3rd August 2012 at 12:40 PM.
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Old 3rd August 2012, 02:01 PM   #1937
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Rod's schematic is excellent. The way I have it I'd have 4.5v on the filament negative and 6v on the positive. 95v on the plate of the 26. My cathode resistor is 5 ohms, which is two 10 ohms 20W in parallel. I have 12v going into Rod's filament supply. I use LL1660/5mA (3mA actual current) in 1:1 because it's effectively the first stage of my amplifier rather than a stand-alone preamp. I actually slightly prefer the sound of two Hammond 156C plate chokes in series as discussed and a 0.1 FT-2 teflon output cap, but this is very prone to low level hum and can only be cautiously recommended. If you can deal with the hum it's a much cheaper option.

But actually, I'm using a 4P1L in filament bias with a 20 ohm filament resistor and a LL1660/18mA. I've moved on. It's a close call but I like the treble and clarity of the 4P1L.

Andy

Last edited by andyjevans; 3rd August 2012 at 02:08 PM.
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Old 3rd August 2012, 02:10 PM   #1938
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Quote:
Originally Posted by Rod Coleman View Post
Thanks Bas! You can use the Regulators when you're itching for an upgrade some time!

A lot of taste is involved in getting a 26 DHT line amp to sound the way you like, but how about a sketch that gets a newcomer to the thread started? This should not be too controversial, I hope.

Based on properly implemented HV and filament supply, using good quality transformers, and a high quality Lundahl LL1660 output transformer to drive cable well.

I have showed filament bias, so that degradation due to cathode coupling caps can be avoided. Fil Bias generates lots of heat in the Bias resistor, buts gives the least compromise to the sound. (I can post a battery bias version if anyone would like it).

The circuit assumes that Sources have dc offsets below 0.2V, or a series capacitor will be required.
Sorry my ignorance, do you connect a 9V alkaline between cathode resistor & ground?
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Old 3rd August 2012, 02:17 PM   #1939
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Quote:
Originally Posted by merlin el mago View Post
Sorry my ignorance, do you connect a 9V alkaline between cathode resistor & ground?
Hi Felipe, Battery bias schematic is here!
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File Type: jpeg 26_Line_BattBias.jpeg (132.4 KB, 333 views)
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Old 3rd August 2012, 02:22 PM   #1940
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Hi Rod, what schematic do you use?
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