VM (Voice of Music) Model 730 "Tape-O-Matic" Repair Journal and Photos
by Chad Hauris, Retro Electronics and Audio Lab, Midland, TX. 6/30/07
Please click the photos for larger views.
This VM unit dates
from around 1962. It features a compact design which is common in the
early 60's for tube equipment...it also leads to a hotter-operating
unit. Some of the tubes are positioned sideways for compactness.
The machine had no functionality except for rewinding and the tubes lighting up.
First, we disassembled the machine and found two belts needed replacing (take-up reel and capstan).
The mechanism chassis separates from the electronics chassis by
removing screws around its edge, and unplugging the electrical cables.
The bearing plate must be removed to put the capstan belt around the
flywheel, and the belts for the take-up reel and capstan must be
threaded down through a hole in the mechanism chassis.
After replacing the belts, we decided to test the electronics. We found
that the main electrolytic filter capacitor was leaky, causing the
voltage to the preamp stages to drop due to excessive current draw
through a power supply resistor and distorted sound. We always like to
replace old electrolytic capacitors as they are frequently bad (as in
this case). All electrolytics were replaced plus one paper caps. Other
capacitors were ceramic which do not tend to degrade nearly as much.
Here are the new capacitors in the chassis. The compact chassis did not give much room to mount the new caps!
A fuse holder was also installed in the AC line.
Here is the VM model 730 recording. A bar-type tuning eye indicator indicates record level.
Another view of the model 730 Tape-O-Matic.
V-M 730 schematic.
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