I drew it with some schematic symbols by Joel Tunnah, just copied and pasted into a drawing program (I used an old one called Picture Publisher, Paint or Photoshop should work) and connected them with lines. I used the program's text tool to add labels and did a little editing to get some symbols that weren't in Joel's library (the power trans., filaments).
Not the easiest way to do it, but I like the results. You can download the symbols here: http://www.joeltunnah.com/
I used the tektronix style set.
The .0015 value is correct, in this article, http://members.tripod.com/~gabevee/maggie.html
they use an even smaller one, .0012, apparently it works.
Another odd thing, the .0015 and 100pF caps in each channel appear to be factory original, but are not identical in both channels, some are tan and some are reddish, they must have just had bins of the same value by different manufacturers and just grabbed a few for each amp without regard for using matching brands in each channel.
Not the easiest way to do it, but I like the results. You can download the symbols here: http://www.joeltunnah.com/
I used the tektronix style set.
The .0015 value is correct, in this article, http://members.tripod.com/~gabevee/maggie.html
they use an even smaller one, .0012, apparently it works.
Another odd thing, the .0015 and 100pF caps in each channel appear to be factory original, but are not identical in both channels, some are tan and some are reddish, they must have just had bins of the same value by different manufacturers and just grabbed a few for each amp without regard for using matching brands in each channel.
hi radtech
i am no expert, but i had refurbished two of those Magnavox amps
they had purposly different caps in each channel
each channel had different feedback resistors as well
only one chanel had brilance control
Magnavox never cared about flat frequency response of the amp
rather they tried to have balanced presentation all across
from turntable to speakers
i have many amps, but SE Magnavox from old console i have is the most musical amp i ever heard (not pp)
i am no expert, but i had refurbished two of those Magnavox amps
they had purposly different caps in each channel
each channel had different feedback resistors as well
only one chanel had brilance control
Magnavox never cared about flat frequency response of the amp
rather they tried to have balanced presentation all across
from turntable to speakers
i have many amps, but SE Magnavox from old console i have is the most musical amp i ever heard (not pp)
Here's a pic of what I'm starting with, still have a few decisions to make, such as should I convert it from 6EU7 pinout to 12AX7 pinout.
Also have a few options for the cathode resistor, it has one 4W 100ohm for all 4 6BQ5s, got hot enough to burn up a wire running under it.. I bought some 200 and 400 ohm 4W resistors, figure on either a 400 in each cathode, a 200 in each output pair, or two 200s parallel for all 4 tubes. Open to any suggestions.
Also have a few options for the cathode resistor, it has one 4W 100ohm for all 4 6BQ5s, got hot enough to burn up a wire running under it.. I bought some 200 and 400 ohm 4W resistors, figure on either a 400 in each cathode, a 200 in each output pair, or two 200s parallel for all 4 tubes. Open to any suggestions.
Attachments
I had one of those old stereo Magnavox SE amplifiers in high school. Had a pair of 6BQ5 and IIRC a single 12AX7 (not 6EU7) It sounded way better than it ought to have. These days I have 3 dht based SE amps and a pair of PP 300B monoblocks, that little amp was probably the start of it all, although I did not realize it at the time.. 
I would replace the 6EU7 with 12AX7, they are electrically identical except for filament configuration and pin out which of course is totally different.. LOL The 12AX7 option will give you a lot more choices in terms of tube rolling potential. Good 6EU7 might tend to be a little more costly as well.
I rebuilt a magnavox stereo pp amp with a quartet of 6V6 some years ago, it actually sounded pretty good once completed.
I would replace the 6EU7 with 12AX7, they are electrically identical except for filament configuration and pin out which of course is totally different.. LOL The 12AX7 option will give you a lot more choices in terms of tube rolling potential. Good 6EU7 might tend to be a little more costly as well.
I rebuilt a magnavox stereo pp amp with a quartet of 6V6 some years ago, it actually sounded pretty good once completed.
Yeah, I figured the 12ax7 pinout will give me more options and be easier to get.
You can see in the pic that there's also a hole cutout for another socket, could put a preamp in there maybe, although I'm thinking of using it as an amp for my Rockman X-100 guitar amp so I'll probably just need line level.
You can see in the pic that there's also a hole cutout for another socket, could put a preamp in there maybe, although I'm thinking of using it as an amp for my Rockman X-100 guitar amp so I'll probably just need line level.
Hi Radtech,
Thanks for the advice in the other thread. I have been listening to the amp for a few days and it sounds nice. I did notice some low frequency distortion when I cranked it up playing music with a lot of bass. Do you think this is tube related or leaky capacitors? I ordered replacement capacitors and will not use the amp until I install them. Could you provide more detail or suggestions on the following?
Connection details on how you will replace the single 4 watt resistor multiple resistors.
Tube replacement. Should I replace all tubes or just the EL84s? Any suggestions on reasonably priced tubes (Ebay vintage or Partsexpress new)?
I would also like to replace the power cord. Any thoughts on adding a fuse and the fuse value? Should I use 2 or 3 prong power cord?
Thanks
bcrescen
Thanks for the advice in the other thread. I have been listening to the amp for a few days and it sounds nice. I did notice some low frequency distortion when I cranked it up playing music with a lot of bass. Do you think this is tube related or leaky capacitors? I ordered replacement capacitors and will not use the amp until I install them. Could you provide more detail or suggestions on the following?
Connection details on how you will replace the single 4 watt resistor multiple resistors.
Tube replacement. Should I replace all tubes or just the EL84s? Any suggestions on reasonably priced tubes (Ebay vintage or Partsexpress new)?
I would also like to replace the power cord. Any thoughts on adding a fuse and the fuse value? Should I use 2 or 3 prong power cord?
Thanks
bcrescen
I'm not really at the point where I can give you good answers on most of those questions.
Replacing the other tubes... if you don't want to rewire it for 12AX7s, and the tubes in there check/sound ok, I don't see any reason to change them.
About the cathode resistors, currently all of the 6BQ5 cathodes are tied together and go through one 100/4W to ground, there's a couple of options I'm thinking of..
1) Replace the 100/4W with 2 x 200/4W in parallel. This would just divide the power between the two, letting them run a bit cooler.
2) Replace it with 2 x 200/4W, disconnect the cathodes of the right channel tubes from the left channel ones, and connect one resistor from each channel's cathodes to ground. This should help isolate the two channels, but you'd have to add another capacitor and probably hook the hum balance pot center lug to ground, maybe through a resistor?
3) Replace it with 4 x 400/4W, one for each tube. Again you'd have to add capacitors and change the hum balance, not sure if there's any good reason to try this way though.
Replacing the other tubes... if you don't want to rewire it for 12AX7s, and the tubes in there check/sound ok, I don't see any reason to change them.
About the cathode resistors, currently all of the 6BQ5 cathodes are tied together and go through one 100/4W to ground, there's a couple of options I'm thinking of..
1) Replace the 100/4W with 2 x 200/4W in parallel. This would just divide the power between the two, letting them run a bit cooler.
2) Replace it with 2 x 200/4W, disconnect the cathodes of the right channel tubes from the left channel ones, and connect one resistor from each channel's cathodes to ground. This should help isolate the two channels, but you'd have to add another capacitor and probably hook the hum balance pot center lug to ground, maybe through a resistor?
3) Replace it with 4 x 400/4W, one for each tube. Again you'd have to add capacitors and change the hum balance, not sure if there's any good reason to try this way though.
" I�m also thinking of adding wood to my amp. Hope your amps sound as good as they look. Did you disassemble and paint the chassis?"
Yep, cheap and easy to make. A simple picture frame, glued, stained, and poly'd. That is a Foreplay II, older kit. Super easy to assemble with great support from Doc.
Yep, cheap and easy to make. A simple picture frame, glued, stained, and poly'd. That is a Foreplay II, older kit. Super easy to assemble with great support from Doc.
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