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previous: Robert Hi Kevin,I am glad ... -- 3/20/2000 4:32 AM

Re: 73 Marshall rebuild...I did it!!!!!!!

3/20/2000 12:35 PM
kevin Hamilton	Re: 73 Marshall rebuild...I did it!!!!!!! I was told that changing to 100k resistors made the high voltage easier on the power tubes and also make the tone "browner". I don't know exactly how, but since I had the amp apart, I figured what the hell. As for negative feedback, I have a choice. Let me explain what "extra things" I did to the amp to give me more tonal options. My 73 Superlead has 4 speaker output jacks in the back and also a polarity switch up front. When I redid the amp I rewired the AC power for a 3 prong plug and completely bypassed the polarity switch. What I use it for now is to select which size bias resistor and speaker tap I want to use. One position is 27k/16 ohm tap like the JTM45 and early plexis. The other position is 47k/8 ohm tap like later 68-70 Marshalls. I also replaced 2 of the 4 speaker outputs with two way switches. The first switch lets me either jumper or split the V1 cathodes. The second switch lets me either use the .68 cap on V2 cathode pin 3 or bypass it. All of these "mods" are completely reversable and there really is a difference in tone for each position. As far as tone differences with the NFB you definately hear it. In the 27k/16 ohm position the amp is cleaner, darker, and smoother. It's a very bluesy tone. The 47k/8 ohm tap is louder, rawer sounding, and has more gain. Now, if you were to try one, then unsolder it, and put in the other to try, you might not notice that much of a difference. With a switch you just turn the amps standby switch off, select the new position, turn the standby switch on, and play. The difference just jumps out at you. Same thing goes for the spilt/jumpered switch and the .68 in/out switch. Kevin

3/20/2000 12:35 PM

kevin Hamilton

Re: 73 Marshall rebuild...I did it!!!!!!!

I was told that changing to 100k resistors made the high voltage easier on the power tubes and also make the tone "browner". I don't know exactly how, but since I had the amp apart, I figured what the hell.

As for negative feedback, I have a choice. Let me explain what "extra things" I did to the amp to give me more tonal options.

My 73 Superlead has 4 speaker output jacks in the back and also a polarity switch up front. When I redid the amp I rewired the AC power for a 3 prong plug and completely bypassed the polarity switch. What I use it for now is to select which size bias resistor and speaker tap I want to use. One position is 27k/16 ohm tap like the JTM45 and early plexis. The other position is 47k/8 ohm tap like later 68-70 Marshalls.

I also replaced 2 of the 4 speaker outputs with two way switches. The first switch lets me either jumper or split the V1 cathodes. The second switch lets me either use the .68 cap on V2 cathode pin 3 or bypass it.

All of these "mods" are completely reversable and there really is a difference in tone for each position. As far as tone differences with the NFB you definately hear it. In the 27k/16 ohm position the amp is cleaner, darker, and smoother. It's a very bluesy tone. The 47k/8 ohm tap is louder, rawer sounding, and has more gain. Now, if you were to try one, then unsolder it, and put in the other to try, you might not notice that much of a difference. With a switch you just turn the amps standby switch off, select the new position, turn the standby switch on, and play. The difference just jumps out at you. Same thing goes for the spilt/jumpered switch and the .68 in/out switch.

Kevin