My buddy John Piro has a knack for finding obscure vintage hifi pieces and has built up quite a collection. A couple of summers ago, he offered his spare blonde plinth'ed HF400. I had just acquired my first and only genuine Gray Research 108C viscous damped tonearm and couldn't pass up the opportunity to pair them up.
 |
| Capstan Drive |
The Gray Research HF400 turntable employs a unique drive system. Strictly speaking, it is not an idler drive. A round section rubber belt is partially embedded around the outer rim of the platter, which is driven directly by the motor shaft. Capstan drive is probably a more appropriate technical term.
 |
| 45 + 78 rpm capstans |
To change speeds, the corresponding 45 or 78 rpm capstan (or bushing as termed in the manual) is placed over the native 33 rpm motor shaft.
 |
| D&R turntable drive system Courtesy of jamesvanarsdale.com |
AFAIK, the only turntable from this era which also drove the outer periphery of the platter is the equally rare D&R turntable, but as depicted above, it uses a rubber idler wheel.
 |
| Seiko-Epson drive system Courtesy of audio-heritage.jp |
The Gray Research capstan drive may have been the inspiration for Mr. Takeshi Teragaki's three turntable designs for Seiko-Epson - ∑2000, ∑5000 and ∑5000II.
Servicing Tips
Download a pdf file of the Gray Research HF400 Manual for more detailed information.
This iron platter/bearing combination weighs close to 20 lbs. The 1" spindle tapers to 13/16" which turns on a 1/2" thrust sphere at the bottom of the sintered bearing well.
After experimenting with a couple of belt sizes, a 3/16" (cross section diameter) x 36" polyurethane round belt x from McMaster Carr, catalog #3044K705 gave the steadiest stroboscope readings at all speeds.
Disassembly
Remove the four screws as indicated by the red arrows.
The plinth lifts from the bottom frame.
The top plate is a massive 1/4" thick metal resting on rubber pads at each corner. Prior to installation of new rubber pads, motor vibration could be felt at the tonearm finger lift.
With new rubber pads installed (+ new motor mounts, see below), vibration was practically nil. The material I used looks very similar to replacement rubber soles used by shoemakers.
Removing the motor
To release the motor from the mounting bracket, straighten and pull out the cotter pins.
 |
| Left = worn out motor mounts Right = fresh motor mounts |
Another source of vibration were perished motor mounts. Brand new replacements are available from Surplus Sales of Nebraska - Rubber Shock Mount, Part No. RPS - 426-0001.
New rubber mounts installed
Before reassembly, I cleaned the motor and re-lubricated the bearings with engine oil.
The sound is very energetic!
I've been enjoying my entire mono LP collection with the HF502!
View it in action! 😊
