Maco Super 75

[238]

Trying to find out the value of the 2 resisters that hook to pin 3/11. One on each tube. They look to be 100 ohm/ 2 or 3 watt, not sure. They are hooked to the orange wire. The blue wire, the one for negative VDC, goes too pin 5/9 has a resistor on the end of it. It looks to be 22 ohm, but not sure of the watt. It is blue, so wonder if it a special resistor? Thanks for any help. 238

[Deleted User 30222]

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[238]

None of the schs give the values of resisters or caps. That sch is for a 75. Most is the same except how the wires hook to the tubes. Thanks. 238

[238]

Found out what i thought was a resister is a choke. It is the one that goes to pin 5&9. The 2 that goes too pin 3&11 i believe are 100 ohm. Not sure yet. 238

[MDYoungblood]

None of the schs give the values of resisters or caps. That sch is for a 75. Most is the same except how the wires hook to the tubes. Thanks. 238

The reason those schematics don't have values was because when building those amps, Maco used a variety of tubes, I'm not sure which you have. Look at the schematics for the larger amplifiers, the drive section (tube('s)) might resemble the Super 75.

3's

Greg

[238]

The early macos came with 6lb6 tubes. I think all the orange face & the 75s came M2057. Most of the others had 8950 tubes. I have a 200 that has 6lb6s in it. They have all been change to all finals. I wish i had a 300 with 6lb6 tubes. 238

[MDYoungblood]

What tube is in your amp? Most of the chokes were 22uH but the resistors varied from 220 to 470ohm if my memory serves me. The M2057 or the 8981 was a Chinese clone of the 8950, they said it was a direct replacement but be careful about these claims.

3's

Greg

[238]

The choke is 22uh i found out. My amps have M2057s in them. But you can use 8950s. The M2057 tube was, as the story goes, was made for Maco in the GE plant in Owensboro, KY. You have to change a resistor to use the 8950, or you will wear out your 8950 fast. When my M2057s die i will change. 238

[238]

I have question about the input resistor? One of my 2 tubers has a 22 ohm resistor the other a 48 ohm. My Super is keying to high, about 100 watts swings 150/180. Will the size of the resistor effect the amount of drive? 238