[GreenKeys] Machine speed and VFDs

[Ralph Irish]

Going back a few decades, 


One of the earliest products from the DOVETRON company was a variable freq drive for Teletypes, aimed 
mostly at the Model 28. It was recommended that 100 speed gears be put into the machine, and then 'regulate 
down' in frequency, to achieve the proper shaft RPMs for the other speeds. 

I am certain that the product first showed up in RTTY Journal Classified Ads sometime AFTER Dusty Dunn, 
W8CQ, bought the Journal from Merrill Swan, W6AEE, back in the mid 1960s. 

I suspect that there are a few of these items that survived into this century, but who knows? Hank was a real 
innovator and when the additional speeds were authorized by the FCC there was a big scramble for locating 
gear shifts for various TTY models. As an alternative, the "VFD" idea was researched and finally introduced 
by DOVETRON. I am NOT crediting DOVETRON with anything more than likely being first in the 
marketplace. The overall idea was not new at that time. Just not common. 

I suspect that the motor wiring was interrupted and leads fed in and out of the cabinet, to go to the VFD for 
selection of optimal RPM settings for operation. 

This VFD from DOVETRON may have been the first, official product offered to the ham marketplace. 
However, with today's computerized world, the idea is probably done in an easier manner, with fewer items 
to get the multi-speed operations sought by many of today's RTTY gang. 

For now, 

Ralph - W8ROI 

- - - - - - - - 

----- Original Message -----

From: "Robert Goff" <robert.h.goff at gmail.com> 
To: GreenKeys at mailman.qth.net 
Sent: Sunday, September 2, 2018 9:48:54 PM 
Subject: [GreenKeys] Machine speed and VFDs 

This is probably a really stupid question, BUT: 

I was just looking at the gear chart in an old Atlantic Surplus 
catalog comparing the gear ratios from 100 speed to 60 speed on a 
model 28. It looks to me like for 60 wpm the 3600 rpm of the motor is 
being reduced to 525 rpm by the combination of the pinion and the main 
gear. For 100 wpm it is 857 rpm, approximately the ratio of 5:3. 

If you had a machine geared only for 100 wpm and you used a freq drive 
to reduce the motor speed to 2205 or so, so that the main gear was 
spinning at 525 rpm, would the machine then operate at 60 wpm? 

Has anyone tried this? Is there something I'm missing? Frequency 
drives for fractional horsepower motors have really gotten pretty 
cheap, and maybe easier to track down than 60/67/75/100 gear sets. 

Thanks, 
de Robert W7MKA 
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