Look what the cat dragged in.
The filter caps looked perfect so I tried bringing them up slowly over 3 days to reform. I have never done that before, but these looked so good I thought I would try to save them. I think it worked.
I added the 1k screen resistors and 5.6k grid stop resistors. I noticed a funny cutting out on certain notes before I added the 5.6K's. It actually got a little brighter and better sounding after adding them.
I did a few other sacrilegious mods. like lift one leg of the bright cap on the volume pot. And bypassed the 1k v2 cathode with a 4.7uf cap. I tried .68 but liked the 4.7uf better. I also moved the bias voltage wire to before the standby and found that lifting the grid wires to V1 and V2a up away from the chassis, really quieted the amp up.
It sounds killer now. oh and I am really liking my new toy the Bearfoot Uber Bee ! Try one you'll like it.
Billy Z
here is a link to my photobucket with more pics.
http://s1039.photobucket.com/user/kings ... t=3&page=1
JMP 50w Lead 1971
Moderators: pompeiisneaks, Colossal
JMP 50w Lead 1971
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Last edited by billyz on Wed Jun 18, 2014 11:01 pm, edited 1 time in total.
Re: JMP 50w Lead 1971
Super, honey bee swwweeet. Wow.billyz wrote:Look what the cat dragged in.
Sounds good to me.billyz wrote:I did a few other sacrilegious mods.
Wait, what? Sure, removing the input will certainly quiet up an amp... I don't get it. Oh, do you mean moving them up, away from the heater wires?billyz wrote:found that lifting the grid wires to V1 and V2a really quieted the amp up.
I build and repair tube amps. http://amps.monkeymatic.com
Re: JMP 50w Lead 1971
lift the grid leads up away from the chassis into the air, not subtle reduction in hum. its old school marshall stuff.
I just edited the original post for clarity.
I just edited the original post for clarity.
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martin manning
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Re: JMP 50w Lead 1971
Very fine and well preserved specimen, and nice pictures too!
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Reeltarded
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Re: JMP 50w Lead 1971
MY AMP!!
Signatures have a 255 character limit that I could abuse, but I am not Cecil B. DeMille.
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Stevem
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Re: JMP 50w Lead 1971
Yup, lifting those grid wires up off the heater wires makes for a nice drop in 60 hz crap buzzin thru the amp!
It's hard to believe that they did not take the extra 20 seconds of manufacture time to do that!
It's hard to believe that they did not take the extra 20 seconds of manufacture time to do that!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: JMP 50w Lead 1971
Great looking amp Billy! inside of the chassis is still shiny. Bet it rocks.
Re: JMP 50w Lead 1971
Boy that is nice.
Re: JMP 50w Lead 1971
Very cool 
"- Yeah, can we have everything louder than everything else? Right!"- Ian Gillan
Re: JMP 50w Lead 1971
Nice catch, these pictures of the chassis are very informative
2203/2204-ish/Deluxe Reverb
Re: JMP 50w Lead 1971
I tried to take photos good enough to document the original wiring. This amp was as original as I have seen. Be sure to note the changes I made and don't confuse the pics. They are a bit mixed up.deeder wrote:Nice catch, these pictures of the chassis are very informative
I removed the short white vac bias lead from the bridge rectifier to the bias circuit. I added a yellow wire from the bottom of the standby switch to the bias circuit.
I don't know why anyone would want to use the original bias arrangement . But it easy to miss.
Btw, it still had a nice mullard 12ax7, also two later marshall labeled (red) 12ax7's, with the cross top glass, but I think they are yugo or ? After I play it awhile I'll install a set of rft el34's . The sovtek el34' big bottles don't sound bad though. And survived with the original circuitry.
Oh yeah, plate voltage is right at 440 on the 120 tap. When I got it was on the 110 tap. The plate voltage Was 465 there.
Yes, this amp just sounds great, hard to stop playing. Did I say the honey bee is sweet? I like this one better than the mad professor sweet honey ,hand wired. And I liked the hand wired better than the MP pcb version.
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Reeltarded
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Re: JMP 50w Lead 1971
Best amp, EVER.
Signatures have a 255 character limit that I could abuse, but I am not Cecil B. DeMille.
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groovtubin
- Posts: 1114
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71 Marshall
Man, thought the 71`s were HI voltage! Blown away with the 440 on 120 tap, i mean that`s like a bassman! I use the same voltage in my 100 watt Dumble HRM circuit! NO wonder it kiks butt!! Dang, i`d like ta hear that! Hmm...bassman/JTM power tranny n 71 super lead circuit with pihers n mullard caps,,yipeee!!Reeltarded wrote:Best amp, EVER.
Re: JMP 50w Lead 1971
I think alot of folk think old marshalls were 500+ because they tend to eat tubes and arc sockets etc. I think it more the lack of screen grids and the bias voltage being applied after the standby.
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groovtubin
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- Joined: Tue Feb 07, 2006 4:52 am
Re: JMP 50w Lead 1971
Sure i agree..like by the tube manuaul says 700B+ max for a EL-34 off top o my head??billyz wrote:I think alot of folk think old marshalls were 500+ because they tend to eat tubes and arc sockets etc. I think it more the lack of screen grids and the bias voltage being applied after the standby.