Scott 222A

[nre_admin]

Completed power supply and recap of a Scott 222A.  Some photos of the finished unit.


For this project I resorted to the Hayseed Hamfest 222A capacitor kit to replace the factory multi-caps.  The kits are a bit pricey and if I could find the cans they use would just make them myself.  That said, they do greatly facilitate the cap replacement.  The alternative is installing 16 cans in the already crowded underside.

[nre_admin]

%THD of each channel with new J&J 6BQ5 outputs, NOS Sylvania 6BL8 inverters.  The preamplifier has original Scott 12AX7s (Telefunken).  Amperex 5AR4, old.

<1%THD up to about 10VRMS across 8Ohm NI load.  Input is cross-correlated MLS at 196k sampling frequency.

[nre_admin]

Sine wave output at 1kHz and 30kHz.

[nre_admin]

I've found that the chassis can be stiffened significantly on these units if the OEM sheet metal screws are replaced with larger (#8) stainless sheet metal HEX head screws.  Each screw should be installed into the chassis flanges without the bottom cover in place.  Back out the screw and clean up the burrs with a file.  Vacuum the unit before attaching the bottom cover.

 

[nre_admin]

1khz square wave performance.

Typical for a good quality tube amplifier.  No evidence of ringing or oscillations.

[nre_admin]

Bandwidth at three different power levels/channel with the HF and LF pots, adjusted to obtain the 1kHz, squarewaves shown above.

[Capo72]

I'm looking forward to hearing this guy! I plan to build a walnut or mahogany case for it so it has WAF.

[nre_admin]

I'm looking forward to hearing this guy! I plan to build a walnut or mahogany case for it so it has WAF.

Excellent!