Another Maggy Thread

Hey jay, Yes the inputs will be up front. Star ground (of a sort) for sure. I have attached a layout(kinda primitive) that i made up that I am going by. Thanks
 

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Been working on this a little more... most of the wiring is done except for input jacks, outputs, Iec connector, etc. Some of the wiring left will wait till I have made a base(enclosure). Couple more pics of progress.....
Stan
 

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Well I finished up on the Maggie today and I am very pleased. No hum!!! and beautiful sound. (at least there was after i corrected the heater connections on one 6gk6--I had pins 5 and 6 wired instead of 4 and 5--oops!) So far I have only listened to it in the shop on some crappy Sony bookshelf speakers but i can tell it is gonna sing when i take it into the house. Took some voltage readings:
channel 1 6gk6: channel 2 6gk6:
pin 9----11.94/11.94 11.36/11.36
pin 8---- 304.5/305.2 306/304
pin 7----303/303 305/300
pin 3----11.92/11.92 11.45/11.45
channel 1 12ax7 channel 2 12ax7
pin 1----155 156
pin 3----1.53 1.53
pin 6----295 295
pin 8----5.3 5.2

Kegger or Jay or anyone, do these voltages look about right? Thanks for all the help. Stan
 

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Stan your outputs look fine,
Based on a 150ohm shared cathode resistor your dissipating about 11-11.5 watts, good

But your readings on pin 8 and 6 of the 12AX7 are quite off, like your plate load resistor
is not 330k but like 330 ohm, or your cathode resistor is bigger then you think you have. (bad tubes?)
(the voltages should be simular to 1 and 3,..(8 more like 3, and 6 more like 1)
 
Thanks Kegger, I'll check those resistors out( won't be the first time i screwed up between xxxK and xxxOhms). Tubes are brand new so they should be ok. I will report back later.
 
Hey Kegger, How 'bout this---- I forgot to put in the cathode resistor on both 12ax7s!!!! :D That would definitely explain it. Guess I got in a hurry. What an arse!!!! Thanks for pointing out the problem :yes: I will add them in tommorrow. As a side question, what would changing the value of the 1k screen resistors do? Thanks again for your help. Stan
 
Alright well at least it was easy to track down, changing the value on the 1k grid
resistors won't do much, there just a stopper for tubes that "might" need it, I use
between 1-3k on output tubes.

I did some more testing on this circuit a while back, really need to put a scope on
it to truly dial it in, but you can use a single 13k resistor where the 2 paralell 27k's
are being used in the circuit...(I may update the schem for the sheer ease of it)...

Keep us updated..:)
 
Thanks Keg. Just to clarify, I left out the 3.6k resistor to pin 8 . I'll add it in this evening and se how she looks.
 
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Added in the 3.6k resistor and the voltages came in line. Amp sounds great! Still a small amount of hum but nothing i can't live with. Overall I am very pleased. Don't know if it is the 6gk6's or the circuit improvements but it sounds "beefier" , more umph and clarity than anything with el84's i have heard. Thanks for the help guys. Stan
 
The thread that won't DIE!

How did that amp finally turn out Stan?

Anyone else build anything from this thread?
 
It was a very good sounding amp. I think the 6gk6's are great tubes....alittle better than el84's. Punchier, tighter bass. A friend has this amp now and is enjoying it. stan
 
The thread that won't DIE!

How did that amp finally turn out Stan?

Anyone else build anything from this thread?

Well I followed the thread off and on and eventually got of my duff and recapped an AMP175-67 chassis that had been setting on a shelf for a while. Used some of the mods discussed. Some still to be implemented. Its singin' in the basement system now driving a pair of NLAs. I wouldn't have thought NLAs be a great match but in the small area sounds better than I expected. I still need to really go through it and check voltages, etc. as I'm sure there's been some resistor drift etc that when corrected would bring it along even more.

Thanks to all the contributors to this thread :thmbsp:
 
Hey Cool, yes I find MOST of the carbon comp resistors in these things have drifted A LOT..

Unfortunately in this type circuit too pretty much all of the driver circuit resistors are critical
to the operation of the phase splitter, the cathode and plate resistors on the triodes, an the
grid resistors of the output tubes all play a part of setting it up properly.
 
When/if you decide to do any mods or other circuits if you want to post what your
thinking and have some check it over I would be happy to take a look, and yes I've
made a few changes to some of the recent circuits.

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

Also if anyone is interested I took one of the lower voltage push pull 6v6 maggies and
redid the circuit for low feedback an a 12au7 as the driver/splitter, worked pretty nice.
(I could post the schem, including the supply for this one)
 
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