Scott 222C

[nre]

This unit came in a couple weeks ago, a 222C. 

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The owner has had problems with having it service by others.  It was very dirty with years of dust accumulation.  The unit is, based on my initial look, all original.  The underside does not appear to show any rework by others.

Pulling all tubes, replacing the rectifier with a solid state plug-in and bringing the B+ to 420VDC reveals problems.  So first thing will be to replace the multi-caps, the germanium bridge rectifier with silicon.

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And before you begin working on the amplifier attach a grounding strap that ties back to the Earth lead at the box and check the fuse.  All Scott amps use 2.5A slo-blows.  The one in this unit was 12A(!!!).

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[nre]

The multicaps, all, must be replaced.

C201, 202 and 203.

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[nre]

Selenium rectifier must be removed and replaced with Silicon, 4A.

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[nre]

There are sources for multi-cap cans, CE Manufacturing fabricates them in a manner similar to Mallory, they claim they're identical.  Hayseed Hamfest stuffs new cans using discretes and they sell a set specifically for the 222C/D. 

When prepping for a replacement can, twist the locks back and wiggle the can free.  If the insulator cracks you'll need to replace it and that means drilling out the rivets.  The rivets can then be replaced using fasteners.

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[jwarren_NRE]

Multi-caps replaced, power supply for -55VDC filament string replaced.  All resistor are ceramic composition, non-inductive consistent with carbon composition.

C201

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C203

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C202

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Filament string:

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Things are now looking much better!

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[jwarren_NRE]

The American Radionics 0.1uF are to be replaced with polypropylene films.  The CDE orange drops are fine for this application.

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[jwarren_NRE]

Last issue of VTV discussed the 299C/D and 233 amplifiers.

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[nre]

Caps installed. 

There are two types of Orange Drop capacitors made by CDE (the originals were made by Sprague).  Use the 715P type which are Polypropylene.

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[nre_admin]

Going to give these a go in the 222C.   From Russia, no supply chain issues.

EL84M

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[nre_admin]

%THD v. power dissipated into 8Ohm NI resistor, 1000Hz, CHA&B.  Tubes are EL84M SOVTEK.

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[duder1982]

I love seeing these rebuilds. I too used the Sovtek EL84M in my 222c. Nicely done.