NAD ( modded JCM800 content )

griff10672 said:
according to everything I've read ...... the 6550's when in a " 50 watt " amp like in a 2204 ..... should be treated as 25 watts each when biasing ... because that's what the transformer is designed for ....
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Do you have any references for that you can toss my way? I haven't been able to find much in the way of a technical explanation of this beyond "my tech told me so." I would think biasing the 6550's like 6550's isn't going to cause the amp to put out more than 50W, because other things will limit the output. And the little extra current draw at idle seems so tiny as to not matter to the power transformer. But, I haven't looked too closely into this and might be missing something.
(Edit: one possible thing, from some more digging around after posting, is that the so-called strain comes from asking the amp to provide enough power for the tubes to dissipate 49W amongst themselves, if biasing to 70% of 35W, or 58.8W if 70% of 42W. But, I haven't worked out all the details on if/how that'll actually affect the amp.)
griff10672 said:
I also have a Ceriatone 2204 running EL34's ...... they both sound great ..... but the 6550's just add some friggin push and girth the EL34's don't ....
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Yeah, there's just something there with the 6550's. Nice big open chord/power chords sound like they're going rrRAWWKkk! At least from what I can tell from @Bxlxaxkxe's demos.
 
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Mike Oxhuge said:
Awesome build! How does it compare to the stock 2204?
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It's got more gain ..... it's a lot tighter due to some of the mods to the circuit .... no flub ....

with a Superdrive or a Chiron in front of it you can get pretty close to some modern tones with it

but as a old school metal amp this thing just friggin slays
 
7704A said:
Do you have any references for that you can toss my way? I haven't been able to find much in the way of a technical explanation of this beyond "my tech told me so." I would think biasing the 6550's like 6550's isn't going to cause the amp to put out more than 50W, because other things will limit the output. And the little extra current draw at idle seems so tiny as to not matter to the power transformer. But, I haven't looked too closely into this and might be missing something.
(Edit: one possible thing, from some more digging around after posting, is that the so-called strain comes from asking the amp to provide enough power for the tubes to dissipate 49W amongst themselves, if biasing to 70% of 35W, or 58.8W if 70% of 42W. But, I haven't worked out all the details on if/how that'll actually affect the amp.)

Yeah, there's just something there with the 6550's. Nice big open chord/power chords sound like they're going rrRAWWKkk! At least from what I can tell from @Bxlxaxkxe's demos.
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yes exactly what I read ...... so you're not " taxing " the power transformer ..... there's also strong opinions out there to treat them as 30 watts each ...

there isn't a lot of difference in settings between the two ... so I just aimed in the middle ...
 
Even if you were basing it on 35 watts, you're still at 54% which is still great. I would have done the same.

What were you seeing on the screens?

I watched the video Lyle Caldwell did on a '69 Park 150 he worked on 4 years ago. That would be my desert island amp! It was a hybrid cathode and fixed bias design. They used a cathodyne PI, but it had a 12au7 follower behind it to drive the KT88s. It had a huge Partridge OT and the PT might as well been a cannon ball. That amp sounded MASSIVE!
 
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