50/50 Deep Mod

Triaxis, Quad Preamp, Stereo Power series, Recto Preamp

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Triaxstasy
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50/50 Deep Mod

Post by Triaxstasy » Sun Sep 11, 2011 3:45 am

Since I did it to mine and there´s not too much info floating around, here´s a detailed instruction to the 50/50 Deep Mod:

The blue text is copied from the original MB tech document for the modification:

before the mod:
Image
assembled and wired 6-20-1990 :D the board says "Mesa 50/50B , 1989"

MODIFICATION INSTRUCTIONS FOR FIFTY/FIFTY

When the Fifty/Fifty was first introduced, it was designated as the companion poweramp for our Studio Preamp. Now, with the advent of the TriAxis Programmable Preamplifier, we are offering a single mod which greatly improves the compatibility between the TriAxis and the Fifty/Fifty by adding warmth and fullness plus a little additional power.
Although the procedure is simple and requires less than one hour, you must REFER THIS SERVICE TO A QUALIFIED TECHNICIAN.

1. Bolt the filter choke to the side of the chassis near the input jacks. It is not necessary to drill holes. Just run the pair of 8-32 screws through the cooling slots and mount the filter choke horizontally. NOTE: To ensure proper grounding, “metal-to-metal” contact must be made. Scratch a little paint off the inside of the chassis where the hardware mounting the choke will make contact, and use the star lock washers between the chassis and choke.
The best location is in the third row of slots up from the bottom, farthest slot toward the rear. Thread the nuts on the bolts and – before tightening – slight the choke toward the front of the amp as far as it will go on that rear slot.

2. Solder the two orange choke leads across the 1000 ohm, 7 watts sand block resistor, R501, one lead to each end.
(I simply unsoldered R501 and put the choke leads in its place)
Image

3. Replace the cathode resistors and capacitors at V1, the 12AX7 tube nearest the input jacks. These four parts are lined up next to each other just to the right of V1, as seen looking from the front towards the inside rear of the chassis. R202 and R203 each become 2.7k and C5 and C6 become 15.6µF/35v. Be certain to align the “+” ends with the “+” sign on the circuit board.
original:
Image
modified:
Image

4. Look at the 8ohm speaker jacks and locate the red and orange wires. Unsolder these wires and add a .003µF disc capacitor between each wire and the jack where it was originally attached. Glue the capacitor bodies to the back of the jacks.
Image

EXTRA MOD INFORMATION

If you have one of the early Fifty/Fifty´s and it has a noticeable buzz in the background, here is a very simple cure:

1. On the V1 tube, remove pins 2 and 7 (counter-clockwise from the gap). These can be difficult to unsolder so it´s ok to clip off pins 2 & 7 just flush with the PC-board. Be sure to leave enough of the pin material so you can bend and solder to them. Then unsolder the grey and white wires which come from the Level Controls to the circuit board just below the cathode parts. Bend up the remaining pieces of the pins from the socket and solder the wires to them directly. The white lead goes to pin 7, the grey goes to pin 2. Lift C18 .1/400v cap for easier access.
Image
white=black
grey=red



Required parts:
- 1 Filter choke (I used a 125C1A from TAD @ 25€)
- 2 .003µF disc caps (I used Orange Drop 716P)
- 2 2.7k resistors
- 2 15.6µF/35V caps


edit: Since I had the complete board out of the chassis I went for "major overhaul" and replaced all filter caps ((4x 220µF/350V; 2x 50µF/100V; 1x 33µF/500V), all Orange Drop (there were 715Ps in which I replaced with 716Ps), a couple of resistors and all old ceramic tube sockets with new high-quality Belton-Micalex ones.
Mine was originally a 110V US Version so I got in contact with a small electronics workshop here in Germany who does custom power and output trannies and had them wire a customized 220V PT to the specs of the original (for 80€). It also has a higher quality WAGO connector.
I also unsoldered all original wiring and rewired the whole amp with new 18gauge high-quality silicon wire and shielded wires for input and Volume.
All 4 pots where replaced with new Bourns pots.
The small blue/white trimpot is a modification to the Boogie-typical fixed-bias....guess what?!? It´s now adjustable :-) (Thanks @ Crane !!!!)
The original fixed bias was set at about 21mA...ooooh, icy cold :nono: It sounds waaayyy better at about 35mA....

The final result is now the quietest tube power amp I have ever heard....and I simply love it!
After all modding:
Image

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mxr2000
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Re: 50/50 Deep Mod

Post by mxr2000 » Sun Sep 11, 2011 9:35 am

Great post but i can't see any Pictures :?:

ando
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Re: 50/50 Deep Mod

Post by ando » Sun Sep 11, 2011 9:52 am

mxr2000 wrote:Great post but i can't see any Pictures :?:
I can see them all. Some problem with your browser, perhaps.
Triaxis v2 (no fat mod)
Mesa Simul-Class 2:90
Marshall 9200
Marshall JMP-1
TC Electronics G - Major II
Digitech TSR-24
Boss GT-6
Ground Control
Fender Stratocaster
Gibson Les Paul
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Ibanez RG1620

mxr2000
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Re: 50/50 Deep Mod

Post by mxr2000 » Wed Oct 19, 2011 5:00 pm

I see it now

dbone
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Re: 50/50 Deep Mod

Post by dbone » Wed Nov 09, 2011 12:47 am

Nice job that's a big overhaul.
Triaxis V2.0 Recto nonfat
Mesa 290 Blue EL34/6L6
High gain Amp Switcher
88 Quad Preamp
89 Quad Preamp 
Simul 295 Stereo
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brion
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Re: 50/50 Deep Mod

Post by brion » Fri Aug 10, 2012 10:46 pm

I know this thread is old, but did you add a 6.3V lamp to your amp instead of the neon lamp? Can you show me how you connected this to the circuit? Thanks
Triaxis & 50/50
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Triaxstasy
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Re: 50/50 Deep Mod

Post by Triaxstasy » Sat Aug 11, 2012 12:33 am

Hi Brion,

I used a 125V,75W pilot light assembly (http://www.banzaimusic.com/Pilot-Light- ... round.html).
You can then use any 120V T3 1/4 (BA9s) light bulb in there.
The pilot light is wired according to the schematic.....so same way as the original one....
Image

brion
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Re: 50/50 Deep Mod

Post by brion » Sun Aug 12, 2012 11:42 am

Thank you.
Triaxis & 50/50
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1965 Fender Vibrolux Reverb
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illswando86
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Re: 50/50 Deep Mod

Post by illswando86 » Fri Sep 21, 2012 9:24 pm

Thanks for posting pictures of your work. This thread is about the only place I've found such detailed information on this mod. I'm considering having mine done. At the risk of asking a stupid question, are those 2.7k resistors .5W?
If I had $1,000,000,000 I be rich(for maybe 2 days. After that I'd just be Boogie-rich).

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Triaxstasy
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Re: 50/50 Deep Mod

Post by Triaxstasy » Sat Sep 22, 2012 12:46 am

Hi! The schematics say 0.5w but I used 1w metaloxide resistors. The two caps I used in there are High quality Panasonic caps...

illswando86
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Re: 50/50 Deep Mod

Post by illswando86 » Sun Sep 23, 2012 4:54 pm

Thanks again.
If I had $1,000,000,000 I be rich(for maybe 2 days. After that I'd just be Boogie-rich).

Evil13
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Re: 50/50 Deep Mod

Post by Evil13 » Wed Oct 31, 2012 7:48 am

Thanks a lot for posting this mod. Where were you able to get 15.6uF/35v caps? I have searched the internet and haven't been able to find them.

p.s. wonderful job on the the power amp!
Last edited by Evil13 on Wed Oct 31, 2012 9:29 am, edited 1 time in total.

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Triaxstasy
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Re: 50/50 Deep Mod

Post by Triaxstasy » Wed Oct 31, 2012 9:26 am

IIRC I used Panasonic 15µF/50V Gold Caps....

Evil13
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Re: 50/50 Deep Mod

Post by Evil13 » Wed Oct 31, 2012 9:29 am

Thanks!!!

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Triaxstasy
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Re: 50/50 Deep Mod

Post by Triaxstasy » Wed Oct 31, 2012 10:03 am

I just verified it with my old parts order list.... I used Panasonic FC 15µF/50V caps
http://www.banzaimusic.com/Panasonic-FC-15uF-50V.html

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