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nuvistordave 13th March 2012 08:21 PM

Maggie 8802 6V6
Just bought one from an Auction site. Came with toobz. Nice and clean. Has 4X 6V6 2 6EU7 and a 6CA4 rectifier. I paralleled a 47u 350V cap with the input, swapped out the finals coupling caps with same value Mylar films, rewired to get unit powered up and applying global NFB, added volume controls and the unit was up:o

Measured those ultra-fi output trannies with my LCR; they are 8K pri and 4 Ohm (only) secondary. Less than 2H P-CT provides the power BW all the way down to 150 Hz or so. Leakage inductance on the order of 25mH.

Firing up she puts out about 8WPC into 4 ohms. About 280V on the plates and 270 on the screens. Front end has about 250V. Outputs run about 100 mA into a common 180 ohm cathode resistor, biasing at 18V.

Will keep you posted as I get the thing upgraded. Edcor and a chassis builder in Oregon also on the auction site havind hardwood sided chassis for $70 have already been contacted.

mckaymckaymckay 15th March 2012 12:08 PM

Ive just got one of them last week and upgraded quite abit so far.

Ive found the amp is probably one of the fastest reacting amp ive heard... voices are so clear and you can make out each word with ease.

Ive already replaced all resistors/capacitors on it, but the biggest change i noticed was the coupling caps changed from 0.047 and 0.47, to 0.01 and 0.1 Jupiter vintage tone yellow.

nuvistordave 16th March 2012 09:18 PM

Actually the coupling caps in mine are .047 and .0047, which kind of goes with the output transformer response. The phase splitter is a funky open-loop paraphase; one would be much better going with a direct-coupled Cathodyne type.

Haven't changed any values yet; except for adding 10K global FB resistors and hooking then to the input tube cathode resistors. The output iron has surprisingly good transient response even without any compensation; just one cycle of ringing that quicly damped on the 3 kHz square waves.

mckaymckaymckay 17th March 2012 10:26 AM

The output trannys suprisingly go very low when the coupling caps are changed.

My sub hardly did anything when the original 0.047 and 0.47 caps were in place, but now it gives a nice low response.

As well as the 2k2 resistors, you have added in some 10k from the output tranny to pins 9 on the 6eu7?

nuvistordave 31st March 2012 12:54 AM

Nevertheless those el cheapo output transformers had to go. My junk box donated a pair of Eico Stereo 40 OPT's. These are 5.5 H CT to plate, and the leakage inductance is well under 25 mH (blows away the Maggies by over 3X on BOTH spex). I also swapped in a 6U8 to the front end, wired as a direct-coupled split load inverter. Coupling caps are 0.1uF polyprop MLF types; feeding 249K grid return resistors. Finally I removed the common cathode resistor and for each channel used a 10V Zener and 2-220-Ohm resistors; each bypassed with an audio grade 47 uF cap to ground. I removed the rectifier tube and went with 4007F diodes feeding a 50-Ohm resistor into 330 uF. Now the power BW extends from 30 Hz to 30 kHz, and power is 10W. Some steel wool working up the lustre of the chassis, and a couple of 3/4 by 2" oak side pieces bolt in the steel bottom plate; donated from an old solid-state receiver.

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