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Old 30th April 2007, 03:03 AM   #1
nodiak is offline nodiak  United States
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Default Scott 222c mods...?

Hello,

I have a 222c in fully restored condition, it sounds great. But I've come to crossroads of sorts, and am thinking about improving it. I've been considering the mods that remove the subsonic filter, tone controls, etc., getting the amp to only essentials.

I am getting a schematic from an amp builder who has done this, and would get experienced help as I am no tech.

Has anyone done this and can tell me something about the sonic improvements to expect?

Thanks, Don
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Old 30th April 2007, 04:41 AM   #2
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Don,

Getting rid of the signal shaping elements will be beneficial.

How far do you want to go? I can envisage a complete rework that uses the "El Cheapo" 12AT7 based splitter driver, SS B+ rectification, and combination bias for the 7189 "finals". The OEM power trafo will support all of the above.

Part of eliminating the signal processing circuitry affects the PSU. There is a 150+ mA./"50" V. negative rail that powers the series wired heaters of the phono section and signal shaping 12AX7s along with providing bias to the O/P tubes. I would divert that negative supply to powering constant current sinks, instead of heaters, while retaining the bias function. DC heater power for the phono section heaters would be obtained by voltage tripling the 5 VAC winding currently feeding the 5AR4 rectifier's heater. A 5AR4 draws 2.0 A. of heater current. A voltage tripler requires 6x the DC draw in AC RMS current. A pair of 'X7s running on "12" V. draw 300 mA. 6X 300 mA. = 1.8 A., which is less than the 2.0 A. a 5AR4's heater consumes. Combination bias "eats" the extra Volts of B+ SS rectification yields and it also allows for the use of a single bias adjustment pot. in each channel.
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Old 30th April 2007, 03:58 PM   #3
nodiak is offline nodiak  United States
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Eli, I've been very intrigued by the El Cheapo all along but unfortunately I don't have the experience to do the work. I'd like to try later when I have time, it would be extremely great to me to have those skills.
This 222c is in great condition and just restored a few months ago. The dilemma for me is whether to keep it pristine (in case I want to sell it later, if) or whether to take it to the next level. Just trying to get a feel for whether these mods do that.
When I learned this model has a subsonic filter of 12db @ 20hz built in I was disappointed as I like bottom octave bass. I use a powered sub from the center channel out. I'd really like to not have any filter on the bass.
Wondering what type of benefits the mods bring- will there be more transparency, or any other obvious changes?
Don
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Old 1st May 2007, 05:57 PM   #4
chrisb is offline chrisb  Canada
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Well, this is definitely a major "jump the shark" moment, because to a purist, even the upgrading to modern quality parts of components that have drifted off value in the 40+ yr life span of such units can seriously depreciate their "appeal" and collectible "value", regardless of the potential to significantly improve the speed, clarity and frequency response of the amp.

By today's standards, a very high percentage of the switching, EQ and tone control functions are completely redundant, and their wholesale excision, along with some circuit revisions, can certainly take the unit to another level - but of course, at this point, it's no longer a Scott anything.


I've built 2 versions of "El Cheapo" based circuit on this same Scott LK48 / 222 chassis (in my case with some revisions allowing use of existing tube rectified power supply) and with the very high quality of output iron, the performance is vastly superior to my Jolida 302 (EL34). In both cases my "donors" arrived with significant cosmetic challenges, or other unresolved "issues", didn't cost much, and the extreme makeover was planned from the start.

Even more conservative upgrades would require not only a decent plan of attack, but a fair degree of dexterity and expertise with the needle nose and soldering iron - while the chassis are not as compact as say a Decware Zen or Bottlehead Paramour, there's a lot more circuitry packed inside.
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Old 1st May 2007, 09:36 PM   #5
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If the Scott is in decent working order, leave it alone.... These are wonderful amps stock and will go up in value. Fine a junker for iron and put in it a nice new chassis and build to your hearts desire. Or sell the Scott and purchase some trannys......
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Old 1st May 2007, 10:35 PM   #6
nodiak is offline nodiak  United States
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Thanks for the replies. I hear what you folks are saying about messing with a functioning vintage piece.

The Scott is probably worth ~ $400-450 imo. I'm not sure if I'd get that much, maybe. I have seen some of the "I found this in the basement and it still works" types go for ~ $300.
If the mods would clean it up a bit more, and especially by removing the subsonic filter I'd get deeper, tighter bass, then they would be worth it I think.
Admittedly I'm just starting to think the tube preamp/digital amp thing as a change.
Anyone out there tried these mods on the Scott 222c? They are apparently what Mapleshade has done (for ($975!)
Don
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Old 2nd May 2007, 12:13 AM   #7
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Quote:
Admittedly I'm just starting to think the tube preamp/digital amp thing as a change.
No, no, a thousand times no!

A tube preamp and a tube/FET hybrid power amp mated to appropriate speakers can be a satisfying combination.

For crying out loud, buy a DVM and a soldering iron. Then, construct an "El Cheapo". Wade out into the DIY swimming pool.
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Old 2nd May 2007, 01:15 AM   #8
nodiak is offline nodiak  United States
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Eli, Might be time for me to do that. I'll go visit the local audio repair guy with the broken tube amps in the window. Might find a proper carcass with good trannies.
Don
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Old 2nd May 2007, 03:14 AM   #9
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How many watts do you want??... 222c is EL84's?? Subsonic filter keeps power from being wasted on very low inaudible rumble, etc. EL84s are not known to pound out deep bottom end anyway. Maybe some 6550s will be is needed for some kick and power.??
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Old 2nd May 2007, 05:27 AM   #10
nodiak is offline nodiak  United States
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crispycircuit, The 222c has plenty of power, my speakers are 95db. I like bottom octave bass for alot of the music i listen to- synthesizer,organ, strong percussion too. So I use a Rythmik sub from the center channel out. AFAIK this signal comes out the preamp and does not go through the amp/power tubes. So removing the subsonic filter should have an effect on the subs performance, hopefully allowing it to go deeper,stronger, and maybe cleaner. This idea was all that got me thinking about any mod to the circuit. Someone else recommended the other mods, which would I think improve the amp. But destroy it's credentials.
I better sleep on all this.
Thanks for help.
Don
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