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Last Edited:
12-Sep-2004


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.

 

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