Vintage Synth Repair

At 18:09 Uhr +0000 08.06.2007, gil_we wrote:
> I've been readiung that running a 60hz device at a 50hz environment,
> can be destructive to the parts in the device - transformers can burn
> out or create fire, parts can get too hot etc.
>
> I'm planning to get an old 1942 made Hammond G ("Government" - like CV)
> which is US made, 110v/60hz, and run it at 220v/50hz using a step down
> voltage transformer. To convert the motor frequency I'm going to either
> change the motor to a 50hz one or to place one of the converter boxes
> available for that application in Hammonds.
>
> Should I care about the frequency issue ? can other parts get
> defected ? is that a dangerous step ? How many of you did that ?

Basically the previous replies already gave all the important stuff. But
there's more.

There are very few parts in a Hammond that actually "see" the AC and hence
may be suspectible to the frequency. Apart from the motors it comes down to
the mains transformer in the preamp (before everybody jumps please continue
reading). In fact the difference between a 120 and a 230 volts preamp (at
least for the later B-2 and C-2 models onward) is the different mains
transformer; all other parts in the preamp are the same.

But we're talking a model G. The "G" is different than the later "B-2" and
"B-3" because (if I'm not mistaken) it gets part of its power FROM THE
EXTERNAL CABINET.

The actual power supply in the "G" is extremely primitive: It's basically a
transformer for the tube heaters. That's all! It's the connected tone
cabinet that supplies the high-voltage DC(!) for the tubes (it's called the
"B+" voltage and is 200 volts if I'm not mistaken). Which of course means
that without the tone cabinet the organ preamp doesn't work at all. But it
also means  that there is essentially no "frequency issue" for the preamp:
It already runs on DC!
So, no cabinet - no working preamp (Leslies can supply that voltage as
well, btw).

If you want to use a "G" without a cabinet you need something similar to this:

http://www.tonewheelgeneral.com/build_page.php?item_no=BPLUS

Here's a schematic for the preamp used in the "G":

http://captain-foldback.com/Hammond_sub/schematics/a_preamp_later.gif


Now, about the motors. The motors are frequency dependent. There are some
frequency converters around. I'm running a C-2 on one and that works fine.
As far as I know there are some different models - some generate the
frequency as "pulses" and some generate a true sine (the latter probably
being better).

BUT: The "G" is basically a model BC internally. Which means that it
doesn't have a single tone generator but two (main generator and chorus
generator); including separate start and synchron motors.
Which means that a) exchanging the motors would cost a bit more or b)
making sure that the frequency converter can deal with two motors at once.


-- 
Malte Rogacki gacki@...
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"Don't forget to TURN ON THE SYNTHESIZER. Often this is the reason why you
 get no sound out of it." (ARP 2600 Owner's Manual)
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