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Old 28th July 2006, 05:34 AM   #1
jarthel is offline jarthel  Australia
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Default feedback on Thorsten's legacy "universal dht" amp

I've search here and in AA and can't seen to find much discussion on this amp.

thanks for the replies.

ps. maybe I was using the wrong search criteria so I wasn't getting good search results.
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Old 28th July 2006, 11:09 AM   #2
JimW is offline JimW  United States
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Default legacy

I am guessing you have read Thorsten's article at Thunderstone audio. I have a pair of these, at least a variation. I used the el84 driver. I departed from the Legacy as descibed by TL in a couple of places. I used a cathode resistor (1760 mills 12w) and bypass cap (22u polypro) on each leg of the 300b filament circuit, which is how I think the original Verdier design was implemented, although I added a pair of WE (ultra path) caps (6u GE motor run caps) from each side of the filament to b+ tap of OT. You might note that this implementaion results in different bias on each side of the output tube due to the dc filament supply. I am not sure if it will affect tube longevity, western electric allowed for use of dc on the filaments per their data sheets. I have the filaments polarized oppsite each other on the amps, and rotate the tubes amp to amp periodically. In addition, my psu is nothing special, a clc (small tuning cap, choke, and large cap for main b+, with additional rc for the driver stage. The driver stage needs a pretty smooth dc to avoid hum, so the extra rc stage. This was actually based on advise from TL, since I wasn't going to do the regulated supply thing. The hum level at the speaker terminal is low, about .6-.8mv. I will say these amps sound very good - easy to listen for hours without fatigue!
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Old 28th July 2006, 02:01 PM   #3
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I made the amp using an SV83 driver and changed the bias on the 300B a bit too. I also used Electron One output transformers.

For the power supply, I used an outboard 200mA/500V HP Regulator. The filament supply was onboard and I used a pair of 5VAC Hammond transformers with a hum-pot. I ended up with a small bit of hum - sound was really nice - lots of snap - with plenty of detail and good treble extension. 8ws of power just wasn't enough when listening to AC/DC though!
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