No matter how anxious you are to "fire 'er up" and start enjoying your
newly acquired vintage H.H. Scott equipment, please DO
NOT PLUG IT DIRECTLY IN TO 120V AC without following these
Failure to follow these results could result in
and the unit could suffer catastrophic damage. If you want to gamble, visit Las
- Beg, borrow, buy or draw a schematic. If you don't have a schematic trace out the
point-to-point wiring (try that with modern printed circuit boards!).
Become familiar with the locations of major components and their basic functions. I
find it helpful to draw or obtain a component layout diagram with both top and
bottom chassis perspectives.
- Carefully remove the case (if present) and then remove the bottom cover. Look
for anything that looks to be missing or broken. Check for the mechanical
soundness and tightness of all fasteners. You don't want a heavy transformer falling
off! Look for any obvious signs of over-heated or badly burned resistors or leaking capacitors
- If you remove tubes at this stage, be sure and notate their respective
locations. On octal-base tubes, note the location of the key-pin on the tube. If
it is missing or broken off, be sure to carefully orient the tube
correctly in the socket. (Many tubes will use the same socket-type but you could damage the
tube, amplifier, or tuner by not returning tubes to their the proper location). Nothing
is more irritating then to realize that half the tubes have their numbers worn
off, or to find out that the tube placement sticker is missing and the receiver
doesn't have the tube numbers stamped in the chassis next to the socket. You'll also want to verify the tightness or tension of the tube
sockets with a dental pick.
- You'll probably want to do a light cleaning of the chassis and
transformers by brushing and vacuuming it. Use
caution not to rub off tube legends, faceplate or
tuning dial numbering!
- Removing heavy oxidation or pitting from the chassis is
probably not a good idea at this stage. Refer to the page on Controls for
details on cleaning contacts, switches, and potentiometers.
Still with us? Don't forget these additional important
preliminary power transformer safety tests:
- Power transformer primary-side continuity check. Connect an ohm-meter across the
UN-PLUGGED AC power cord plug or accessory
AC outlet. Turn the
unit's power switch on and read and note the resistance. A reading above 2 ohms,
(and below about 20 ohms) means the primary windings are probably OK and the power transformer's primary
windings are probably not shorted. An open or high resistance indicates a possible blown fuse or
open power transformer primary winding.
- Power transformer secondary-side continuity
check. With the unit UNPLUGGED; connect an ohm-meter across the
high-voltage secondary. One set leads to the rectifier tube and another
set goes to the bridge rectifier. (The low-voltage tube heater filaments are
likely to give readings of 1-ohm or less). Read and note the resistance. Typical
readings range from 40 to 200 ohms for the high-voltage secondary windings.
Remember: If your unit does
not pass these simple power transformer safety tests you should not
proceed to the next step.