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Old 9th September 2011, 11:39 PM   #1
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Default Suggestions on driver stages for big tube MI amps.

I was hoping to get design suggestions for driver stages for my pet project, a big 200W tube bass head. It's more a thought exercise at this point, as I'm sure the price of a 200W OPT with good bass response will shock me back into reality.

As to what's already out there with 200W driver stages, there's of course Dogzilla:
Click the image to open in full size.
with its DC coupled followers, which is basically what an Ampeg SVT uses:
Click the image to open in full size.

There's the Weber AB200:

Link removed by moderation

which uses an interstage transformer, which is a little unique for MI.

Thoughts? Of course using SS followers is always an option but I wonder if that might not be a goode solution for MI.
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Old 12th September 2011, 04:16 PM   #2
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Nobody cares? Just thought of another candidate, how about a DC coupled pentode LTP like in the Tim Mellow OTL? I don't think I've come across that yet topology in commercial MI amps, but I bet that is because using small tubes as drivers is much more cost effective.
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Old 12th September 2011, 04:57 PM   #3
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The MI guys have all moved to the instrument & amps thread which is where this thread belongs. I'll move it there..
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Old 12th September 2011, 07:00 PM   #4
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Quote:
Thoughts? Of course using SS followers is always an option but I wonder if that might not be a goode solution for MI.
My thoughts.....Mosfets are your friend. I use them in HiFi and MI. The bigger the amp the more they help.
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Old 12th September 2011, 07:37 PM   #5
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Quote:
Originally Posted by leadbelly View Post
<snip>
There's the Weber AB200:

Link removed by moderation

which uses an interstage transformer, which is a little unique for MI.

Thoughts? Of course using SS followers is always an option but I wonder if that might not be a goode solution for MI.
Please repost link to schematic, but please note in the post that it is a link to the schematic.
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Old 12th September 2011, 07:58 PM   #6
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Click the image to open in full size.

This is a link to that schematic.
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Old 12th September 2011, 09:15 PM   #7
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I like ampeg and would start there. What's the deal with Weber going the mile with a transformer coupled EL34 as driver (which would be able to truely drive the output tube) but wasting the potential with series capacitors and 15kohm gridstoppers? Might as well use a wimpy 12ax7 then!
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Old 12th September 2011, 11:48 PM   #8
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Originally Posted by SemperFi View Post
I like ampeg and would start there. What's the deal with Weber going the mile with a transformer coupled EL34 as driver (which would be able to truely drive the output tube) but wasting the potential with series capacitors and 15kohm gridstoppers? Might as well use a wimpy 12ax7 then!
The more I look at the Weber design the less I like it. I think you're right about the grid stoppers: they are that size to primarily limit grid current when overdriven and not just to prevent RF oscillation. I looked at pictures and the interstage transformer is just a wimpy little thing. I think it's probably a mediocre design wherein reusing as many existing catalog parts as possible was a primary design objective.
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Old 13th September 2011, 11:04 AM   #9
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Hi
DC connection with tube or FET driver will kick *** on any cap connection! the bedst cap is the one that have just been replaced by a DC connection.
*
best regards
Karsten
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Old 14th September 2011, 07:27 PM   #10
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Originally Posted by 211hojbjerg View Post
Hi
DC connection with tube or FET driver will kick *** on any cap connection! the bedst cap is the one that have just been replaced by a DC connection.
*
best regards
Karsten
...so your suggestion is?
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