Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: plexi50 on February 22, 2013, 08:49:00 am
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My god someone really butched this 1974 Marshall Super Lead. The entire preamp circuit for V1A & V1B was missing. I have the parts back on the board. Now i look at the bias and see that all the bias resistors & linkage to the bias feed have been cut off the board as well. The power tube sockets have been totally rewired with 150K grid resistors and 1Meg resistors off the tube plates pin#3 and over to pin 8 cathode. I dont want to know anymore already. Also it looks like someone added two power supply caps in the left corner to add to the PS capacitance. Possable because the original caps were or are going bad instead of just replacing them with new ones. There are two big capacitors next to the V1 side of the board. Why? To balance the weight of the amp? :laugh:
The work done by adding the terminal strip bias circuit was done very well. But why?
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I love to know what that person was thinking!
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It's starting to look normal again. Got the terminal boards off and replaced the bias resistors and 150K coupling to 220K / EL34. No 10uf/160VDC caps. I quess im out of them. Im done for the day
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This was my favorite hack job until I saw yours...
http://www.timeelect.com/hackmarshall.htm (http://www.timeelect.com/hackmarshall.htm)
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Steve,
Nice job on the restore.
What some folks will do to a show piece of history, is constantly
amazing to me. Thanks for putting that one back to where it should be.
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Not my work. See the copyright on all those pics?
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Thanks Steve I have now learned how to keep all my work a secret. Except I think I will populate the board add the wires and dip the whole thing in epoxy that way it is a total secret.
Thanks for sharing.
Keep up the good work P 50
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There's certainly no reason to modify/butcher an old amp today with all of the offerings out there and considering how the price of vintage gear has skyrocketed. Having said that, when I was a youngster I saw plenty of modded 1970s Marshall heads and silverface Fender amps. They weren't really considered classics at the time. When the JMP/JCM800 master volume Marshall amps hit the scene you could buy a 4 input Super Lead very reasonable. What were once commonplace mods to achieve tones that were not commercially available at the time is now considered sacrilege. Everything in it's own time, I guess.
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This was my favorite hack job until I saw yours...
http://www.timeelect.com/hackmarshall.htm (http://www.timeelect.com/hackmarshall.htm)
I had a 2204 come in last year with that black voodoo labs goop all over the board. I told him i was sorry but i couldnt work on it. I felt bad for him but mods like this are bad news period. I was starting to think that the cap block to the right of V1 was C4. :icon_biggrin:
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This was my favorite hack job until I saw yours...
http://www.timeelect.com/hackmarshall.htm (http://www.timeelect.com/hackmarshall.htm)
The amp is back to normal or should i say stock. Normal may be a 2x4 in the next one that comes in
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much nicer now. owner should be very happy now.
--pete
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nice work Plexi....you do a Super Lead proud. Hey, I just thought of something. If a guy wants a thunderous bass amp but is afraid of an old, cantankerous Ampeg SVT, simply stack 3 of these Super Leads on top of lots of speakers and wala, 300 watts of bad ass amp and no smoking tubes halfway thru the first set.....money is no object in this fantasy as you can tell!
:icon_biggrin:
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> The amp is back to normal
Thanks. That was really bugging me.
I'm sad/glad I don't have as-is pictures of my house fuse-box. While hardly a classic, it sure was wire butchery. Since not a classic, I bought a new box. There was no way to get a picture of how the wires ran through the house. I couldn't even draw it out. So much of that is being pulled-down and re-run-right into the new box. It's like a P2P wired amp only 30 feet long. And dusty.
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I remember an old bulidng built in the 20's. The wiring was so bad that the cloth was falling off of the wire. The wire itself wasnt even thick enough to handle modern day A/C or appliances. Just changing a wall light switch was brain surgery because if you so much as tried to move the wire more cloth isulation would fall off farther up in the wall behind the switch mounting. Ceiling fans were even worse. It is still standing today. The wiring has and never will be changed due to the slum lord management. It's a wonder that place hasnt burnt down
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Ok, I have a question. The red stuff on the solder joints. Rich K (Time Electronics - the link to the other hack restoration) uses that also. What is it and what is its purpose?
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It was used in the old days as a sealer to protect the solder joint from oxidation and stuff like that. It was green & red like nail polish. In this case someone knew just a little about that but used a red magic marker to simulate that. I have been seeing this a lot these days
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This was my favorite hack job until I saw yours...
http://www.timeelect.com/hackmarshall.htm (http://www.timeelect.com/hackmarshall.htm)
I have to disagree.. this STILL wins !
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> the cloth was falling off of the wire.
That's my parents' house.
Doesn't take a slum-lord. Replacing ALL the wiring in a plastered house is too-too-frightfully expensive.
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> The red stuff on the solder joints
The dab of red is not a sealer.
In Good Work, one person solders, another person inspects, and sometimes another inspector after. When the inspector eyeballs a joint and deems it "Acceptable", it gets a mark. The last inspector will at least check for a mark on every joint. There is often a tag on each chassis where each worker initials their work.
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Replacing ALL the wiring in a plastered house is too-too-frightfully expensive.
Don't I know it. It's why for many years the new wire I installed ran on the outside of the walls and into commercial metal boxes. As we gut each room down to the studs, then the wiring goes inside all nice and neat.
What prompted me to run new circuits on the outside (many years ago) was when I was replacing a breaker, and the wire that I had unhooked from the breaker, hanging in midair, lit me up because it was still live. Turns out that while there were a whole bunch of breakers in that box, just 1 had about 3/4 of the house on it.
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I just finished resoldering all the parts and rewiring most of the amp. Those posts that the wires were soldered to were so corroded they would not accept a good resoldering. The parts soldered on the board as well were pretty ratty looking. I pulled all the posts out earlier this week and just finished rewiring. There was an imntermitant crackle when i would chop stick the board and tap the posts. Crackle and future worries be Gone! Now it's done. Sounds great too!