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Old 28th March 2013, 01:14 AM   #1
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Default Layout challange: Dual Maggie AMP148 based.

Having played with the small 9302 Magnavox 6BQ5 PP stereo amp for awhile, I've caught a second case of tube amp syndrome. I heard of another Magnavox tube amp used in Imperial and Concert Grand. Amp model is AMP-148. For those that don't know it's a bi-amp monoblock using six 6v6 PP for the lows (35w) and two 6v6 PP for the highs (15w), two 5u4 rectifiers, and two other 9-pin tubes probably 6EU7s.

I intend to find a pair of these (one already found) and make one large stereo (dual-mono) amplifier chassis out of it.

Any of you guys care to suggest some layouts based on the photo below?

Total chassis mounted parts count:
2 - large power transformers
2 - large output transformers
2 - small output transformers
16 - 6v6 output tubes
4 - 6eu7/12ax7 for pre. and phase inv.
4 - 5U4 rectifiers
6 - capacitors

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Old 28th March 2013, 01:35 AM   #2
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If I under stand you correctly you want to mount everything on one chassis and have 4 channels .
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Old 28th March 2013, 02:56 AM   #3
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Everything on one chassis. It's 2 channels in bi-amp configuration. There are 4 separate power amps and 4 outputs (2 left, 2 right) but only 2 inputs. I may eventually separate them and have the crossover in the preamp but I'm going to try it the way it is first.

Here's the first one I whipped up to start with.

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Last edited by lazzer408; 28th March 2013 at 03:26 AM.
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Old 28th March 2013, 03:28 AM   #4
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I don't know why I can't edit that post again but it's 20.25" x 16"
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Old 28th March 2013, 02:55 PM   #5
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The larger output transformers will work with a pair of 6L6GB which would save you a lot of space . Most likely not all the 6V6's are good and would have to buy tubes anyway .
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Old 28th March 2013, 09:16 PM   #6
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Originally Posted by battradio View Post
The larger output transformers will work with a pair of 6L6GB which would save you a lot of space . Most likely not all the 6V6's are good and would have to buy tubes anyway .
I have another 6L6 amp already. This one is partially for show. It has an awe factor of "look at all those tubes!". One thing I've considered is the location of the output transformers pairs (low and high). They should be next to each other. This way it's easier if I wanted to eliminate the bi-amp configuration and do eight 6V6s PP full-range on each channel. 2x6L6 or 8x6V6. Which has more potential?
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Old 28th March 2013, 09:56 PM   #7
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Originally Posted by lazzer408 View Post
I may eventually separate them and have the crossover in the preamp but I'm going to try it the way it is first.
Careful about eliminating the crossover at the speakers! In most cases doesn't work well. A better approach is a mild crossover at the preamp + its own proper crossover at the speakers.
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Old 28th March 2013, 10:00 PM   #8
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Originally Posted by lazzer408 View Post
2x6L6 or 8x6V6. Which has more potential?
Sound-wise 2x6L6, IMHO.
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Old 28th March 2013, 10:10 PM   #9
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2x6L6 or 8x6V6. Which has more potential?
It should be 4 X6L6 or 8 x6V6. Which has more potential? the 4 6L6 will sound better and more power out .
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Old 28th March 2013, 10:36 PM   #10
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Careful about eliminating the crossover at the speakers! In most cases doesn't work well. A better approach is a mild crossover at the preamp + its own proper crossover at the speakers.
What I mean about crossovers in the preamp is moving them out of the Magnavox and into a preamp. I assume there's a factory crossover of some sort in the Magnavox set to who knows what. If I relocate that into a preamp, I'll essentially have a 4ch full-range tube power amp having 2x35w (6x 6v6 each ch) and 2x15w (2x 6v6 each ch). I'll keep some caps on my tweets/mids for protection.

I'm interested in seeing (hearing?) how separate low/high output transformers will sound. There are good single op transformers out there but theoretically wouldn't separate opts be more efficient over a wider frequency range?

How does the 6v6 compare to the 6bq5?
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