The following is from Bill
Bittle, an avid collector of vintage tube hi-fi and frequent
contributor to the Vintage H.H. Scott ListServer. Be sure and checkout Bill's
complete Vintage Tube
Audio web site. Here are Bill's recommendations for replacing amplifier components. (Thanks, B.B.!)
1. Replace the Selenium bias bridge rectifier with
a newer Silicon full-wave bridge which have higher current ratings. They'll last longer and
run cooler. This is cheap insurance, for without a stable bias supply you
could risk loss of your output transformers and/or tubes! Don't forget to reduce
the Bias (-) voltage with a suitable value dropping resistor, as silicon rectifiers are
typically more efficient.
2. Replace the bias-supply filter electrolytic capacitor.
3. Replace the multi-section electrolytic power supply (high voltage) filter capacitors (not always
necessary on tuners/receivers, but almost always necessary with vintage H.H. Scott
integrated tube amps like the 222, 299, LK-48 and LK-72 series.)
4. Replace all the signal-path coupling and bypass capacitors in the preamp,
phase-splitter and final output sections.
5. Replace the plate and cathode resistors in the in the amp's phase-splitter
circuits (take the time to carefully match the values of all four resistors).
6. Replace the plate resistors in the phono and tone-control sections of the
preamp. (Match the four resistors in the phono section and also match the four
resistors in the tone-control section).
7. Replace the cathode bypass capacitors in the preamp section. (Usually only
two caps which are two shared sections of one of the power supply filter multi-section,
'lytic caps).
8. Replace the capacitors that connect to the screen grid of the driver
section of the phase-splitter tubes. Note: 4 uF, 250v in the 299C/D (amps using 6U8
tubes) or .22 uF in amps using the 7199 tubes.
9. Replace the carbon resistors in the power supply section.
10. Use a "known-good" set of the correct tubes. (Don't let a tube checker be
the last word with respect to the quality of your tubes. Many times a tube will
check good, but work bad in an amp. Most tube checkers do not run at the
high voltages present in an amplifier. And most tube checkers have no way to test
a tube for microphonics or subjective sound quality). Always
finish by adjusting bias for lowest distortion and conducting a musical
listening test.
Vacuum Tube Valley
has recently assembled various components for your particular vintage H.H. Scott
gear, into what they call "Vintage
Hi-FI Rebuilding or Tune-Up Kits." They also offer custom-assembled
kits, upon consultation.
Charlie Kittleson has assembled these kits in an effort to save you time and
hassle in locating all the various bits and pieces Watch this web site
for a step-by-step 299-B rebuild, using the VTV Tune-Up Kit, in the near future.
VTV Tune-Up Kit prices and content vary by application, but include schematic
and instructions, 1-Watt, metal-oxide, low-noise, carbon film plate resistors,
high-quality 630V rating, Illinois Capacitor-MWR film caps, high-capacity
electrolytics for bias, cathode bypass and/or filament supply, and silicon
diodes for the negative bias and/or DC filament supply. Tubes and above-chassis,
can-type electrolytic capacitors are not included in the kits, but are available
from VTV, as well.
