Magnavox 8802 visits Kegger

[Andyman]

I stopped by yesterday to pick up my Maggie 8802 PP 6V6 console amp that I gave to Kegger to "have a look at" a while ago because it seemed a bit lacking. I just expected it to have more substance than it did and be a bit ballsier than my 5 watt Almarro EL84 amp.

Well, this ain't your Daddy's Maggie anymore

Keg says there's 2 resistors in it that are the same and that's it, iron aside. The 6EU7s are now 6GH8As, the 6V6 outputs are 6K6s, and the power supply has been totally reworked.

I just plugged it in and began playing it and it's pretty amazing. First there seems to be much more gain overall and more midrange than the DIY ST35 clone I've been playing; I'm playing it lower off my preamp. It also seems a bit sharper, but that could be from the higher gain.

It's only been on about 20 minutes though and sounding really nice. I'll get Kegger over for a listen soon and see what he thinks and I'm pretty sure he'll be chiming in with the tech side of what happened here.

Thanks Buddy!! :thmbsp:

 

[WarrGo]

What is the Point in taking out the 6eu7 and replacing it with a 6GH8A?

Cost?

 

[gadget73]

The 6V6 to 6K6 swap is what has me scratching my head. I've got some 6K6 tubes, and I was wondering what they're really useful for. Most of the time people seem to go the other way, and use a 6V6 for its higher power.

 

[Sam Cogley]

I'm also curious about the 6V6 - 6K6 swap. I've got a pile of both types.

 

[Andyman]

IIRC, Keg says that the 6K6s draw less than the 6V6s so the power tranny doesn't get so darn hot. And the 6GH8A has some qualities that he likes better than the 6EU7s and the 12AU7s we talked about going to. It certainly has more gain than when I gave it to him, which is surprising because that was not what I expected after that driver swap.

FWIW, Keg knows his stuff really, really well. Plus he has some pretty darn good modeling programs that let him see what a lot of relatively obscure tubes can do. I can see his eyes light up when he finds tubes and starts thinking about what they can become and now I'm fortunate enough to have one of his one off creation/tweaks. :yes:

I'm pretty sure he'll chime in soon on this as he told me yesterday he was going to start a thread on it. So I'm sure there will be lots of interesting answers soon.

 

[golana]

What I like, is that I can undestand when he talks.

 

[Kegger]

Here is the schematic for both the supply an the audio circuit.

---------------

The whole story..

Andy brought me this thing a while back for a tune up, then it was well what about
the mod you did to Strawmans maggie, then he came an stole the 6EU7 tubes on me,
by all accounts Andy wanted cheap tubes an a different circuit, well I can do that.. :scratch2:

So per usual I check the stash for cheap driver tubes, I keep wanting to try something
with all these "junk" 6GH8's, then I find quite a few more I've collected in the container
with the same pinout, do some research an find triode curves for the pentode strapped
that I like quite a bit, basically they become tubes with an plate resistance of around 8k
and gain between 35-47, just about right for the voltage gain section, an if we run them
at 85-95 volts on the plate we can direct couple them to the actual triode in concertina
phase splitter, humm that looks pretty good considering the supply voltage available..
(the 6BL8 is a really good Drop In sub to this circuit, as are a few more).. :yes:

The output section:

If yu look at the schem you'll notice 6.6k at 4ohm, that's the original maggie output tranny
which if you convert to 8ohm gives you 13.2k, factor 8ohm speakers at like 6-7ohms gives
you say 12k, well heck that's exactly what 6K6's want, a bit more then a 6V6 "needs" but it
would work fine on an 6V6, now factor in the lower voltage of the maggie power tranny plus
the current you can draw it's like 7w dissipation on an 14w tube, the 6v6 is just loafing in it
and not really ran at it's best operating parameters, BUT the 6K6 is an 8w rated tube and is
perfectly happy at those same operating conditions, also for kicks the heater current draw
is less on the 6K6 then it is for the 6V6, (trying to help the little maggie pwr tranny to)..

I tested an whole bunch of 6K6 tubes and adjusted the cathode resistor for the pair to the
RCA silver label tubes, others drew more current and if using them I'd adjust the cathodes
resistors a bit higher to get same current, maybe 360 to 390ohms.

-------------------------------------------------

The knock on 6GH8 tubes is they test all over the map on the pentode section, I figured if
I triode strap them maybe there are less variances an they'll hold up better, it seems to do
what I was going for quite well, plus factor in those other swapping tubes being "strapped"
that the gain doesn't change as much as what it would if left them a pentode, an we'd not
need the gain a pentode would provide to drive either the 6K6 or the 6V6 for that matter.

So that's the story and I'm sticking to it..(anyone want to try building one?).. :thmbsp:
(The heater humm pot CT is still attached to cathode voltage of the output tubes)

 

[Andyman]

Keg:
C'mon over tonight and give it a listen. I'm surprised at how ballsy it is.

 

[BadassBob]

Ive always wanted to get a Maggie amp. Sounds like you have quite the winner there Andy. Id love to get together with you guys for a little jam fest one of these days :yes:.

 

[golana]

Sure looks like a lot going on, for not much goin' on. I like it, I also dig the use of
non-limelight tubes. :thmbsp:

I thought you try to not do double stage?

 

[Kegger]

It's not 2 gain stages, it's 1 gain and a non gain stage phase splitter.
Also it's not 2 stages using the same "tube", it's triode wired pentode
gain stage followed by a true triode concertina phase splitter second.
(not 2 consecutive stages using the same exact tube) just FYI..

Pretty much with just about any push pull amp you will have more then
1 stage, also while I do prefer circuits an certain way not all situations
lend themselves to what I would prefer to do on a DIY setup amp build.
(have to improvise now an then an utilize what's there to work with)..

-----------------

I got over to Andy's to hear it in his setup, it is a bit different then your
standard console amp, it's quite detailed an "hifi" sounding, not very tuby.
(pretty clean an clear, I liked it, some may prefer a more laid back sound)

 

[Kegger]

Ive always wanted to get a Maggie amp. Sounds like you have quite the winner there Andy. Id love to get together with you guys for a little jam fest one of these days :yes:.

Your always welcome by me, that goes for anyone in the area..:thmbsp:

 

[Andyman]

I gave it a longer listen last night when Kegger came over and it was pretty impressive. We agreed it's more of a "Hi fi" sound than traditional "tubey" as it is extremely clear and detailed and seems to have more highs and overall air than my other amps.

We played some Who ("Tommy"), some Allmans ("Stormy Monday" from "Fillmore") Brubeck, ("Take Five") and some Black Crowes ("Shake Your Moneymaker" and it all sounded great. Gregg and Roger's vocals were clear and warm, the guitars were right there and the drums were crisp. My daughter had a set in the living room for 2 years, so I know what a drum sounds like and that's what I heard last night. I'll have to do the old A/B thing with this amp and my other EL84 amps on an LP or CD, but this amp really seems to be the real deal. Kegger is interested in the relative gain setting too as the original circuit has a ton of feedback than this one very little. He also suggested that we could play with some values quite easily by swapping or even just clipping in caps, so that may happen too. Not that the amp is lacking, but maybe a small tweak could make a good thing better???

FWIW, this is a very cool project and one that really exemplifies the best of our hobby, much like many of the other DIY style projects out there; the Compactron amp and all the Econowave speakers, plus the Indignias all come to mind. Guys start tinkering with mundane, inexpensive items and parts and through a combination of curiosity sweat, and vision come up with results that far exceed expectations. I told Kegger last night it would be a hoot to use this amp in a blind test situation; I'll bet there'd be a lot of surprised looks when the curtain gets pulled on this mundane looking console amp. :yes:

Here's some pics. Keg has a bunch of 10uf caps, so he uses them in parallel to get the values he needs, in case you're wondering about the 4,3, and 3 bundles under the hood.

 

[stanbp64]

Looks great. Another design to add to my long list of future projects.:yes:

Stan

 

[Kegger]

There's a little bit larger version in the works as well, this one more voltage with 6V6G's..

 

[Stephen J]

There's a little bit larger version in the works as well, this one more voltage with 6V6G's..

Hmmmm.....:scratch2:...that chassis looks familiar. :yes:

 

[Kegger]

I wasn't sure where that one might have come from, there's I think 5 of those
quad mono 6V6 amp chassis here, that one had the nicest "looking" chassis.. :thmbsp:

 

[Andyman]

I'm really loving this amp, in fact, I'm trying to figure out the best way to move some connections so I can make it look as good as it sounds. BB King is sounding really sweet right now. Male vocals are sounding very much "in the room" :thmbsp:

I want to move the inputs, fuse, and power cord to the rear so I can dress it up with a nice hardwood case and either a polished or Hammerited chassis. I've even been thinking about braking a couple covers for the outputs to make them prettier, or maybe just some sort of filigreed cage to lay over them.

 

[golana]

WWKD
What-Would-Kegger-Do

Would he dress an amp? I don't think so.

 

[Andyman]

WWKD
What-Would-Kegger-Do

Would he dress an amp? I don't think so.

Ha!!

He'd rub it with his favorite Minwax Brazilian Rosewood Oil and Hammerite it.

But it's MINE now, so I'll dress it as I please, maybe with a bit of the left over Santos Rosewood veneer from my EWaves and match them up????