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It is currently April 13th, 2021, 6:02 am

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PostPosted: February 25th, 2021, 5:01 pm 
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Joined: January 14th, 2015, 11:15 pm
Posts: 448
Thanks for the update.

I am progressing on the build. I have more or less completed the power supply and am about to start wiring the circuit. Late February is the time of year here where the heat (90+) and humidity make conditions tough for enjoyable soldering so I can only work in the early mornings. Still, I progress slowly and once March arrives, things should be much more pleasant.

ray


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PostPosted: March 2nd, 2021, 2:41 pm 
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Joined: February 28th, 2013, 10:38 am
Posts: 1419
Some random thoughts after 5 days with these amps....

Most of you probably want to know how they sound.... Kinda hard to describe that, but let me tell you this: I plan on spending quite a bit of time going forward optimizing this design.

This design, as it sits now, is merely a proof of concept. No effort has been put into choosing the best tubes for the job (yet), so it's quite possible that there are better choices. The EL84 for a driver comes to mind, and there's a whole host of sweep tubes that might be better choices for output tubes. I haven't tried it yet, but the math suggests an EL34 will bias up correctly as an output tube if the cathode bias resistor is changed to 250ohms. Time will tell.

Being direct coupled, the amp can be twitchy to get the values right since any change to the driver stage affects the output stage. Those of you who primarily build existing designs, rather than doing your own design work, would probably be better off building known working variants of this design rather than wandering off on your own.

Roscoe

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PostPosted: March 2nd, 2021, 4:22 pm 
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Joined: July 24th, 2015, 4:17 pm
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Location: Parkville, Maryland
Roscoe Primrose wrote:
Some random thoughts after 5 days with these amps....

Most of you probably want to know how they sound.... Kinda hard to describe that, but let me tell you this: I plan on spending quite a bit of time going forward optimizing this design.

This design, as it sits now, is merely a proof of concept. No effort has been put into choosing the best tubes for the job (yet), so it's quite possible that there are better choices. The EL84 for a driver comes to mind, and there's a whole host of sweep tubes that might be better choices for output tubes. I haven't tried it yet, but the math suggests an EL34 will bias up correctly as an output tube if the cathode bias resistor is changed to 250ohms. Time will tell.

Being direct coupled, the amp can be twitchy to get the values right since any change to the driver stage affects the output stage. Those of you who primarily build existing designs, rather than doing your own design work, would probably be better off building known working variants of this design rather than wandering off on your own.

Roscoe

I found that when I was re-building a Dynaco ST-70 many moons ago and later when I had a Williamson-design stereo amp. that could take EL-34s, if I chose to do so, the EL-34s had a sweet spot at 38-ma cathode current. Any less and the amp would get kind of "dry" and edgy -- any more and the sound would get "dark" and smothered (relatively speaking - no pun intended). At 38-ma the mid-range got "creamy open" with great sound-stage presence.

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