50Hz-60Hz Reel to Reel question

elnaldo

Lunatic Member
Hello. I'm fixing an AKAI GX-600DB, that is labeled "220V", but I see the circuit match the 110V version, with addition of a 220 to 110 step down autotransformer inside the cabinet.

In the service manual, there is a 50-60 Hz switch, which changes some circuits, specially adds capacitance to the AC motors. My unit doesn't have that, and the capacitors match the 60Hz version.

I'm running the machine now at 50 Hz, not 60, and I measure a 83-84% of the rated speed, what match the difference between 50 and 60 Hz. My guess is that is normal , and I'll leave it alone since converting the unit seems too complicated.

My question: Should I add capacitance to the AC motors? The capstan motor is labeled 50/60Hz - 3uF/2uF. And the manual also shows, when switched to 50Hz, the motor connects another capacitor in parallel. I've tried with alligator clips, and the speed stays the same with 2, 3 uF even with 4uF.
 
Check the capstan motor pulley and see if it has two diameters to choose from. In some cases, a capstan sleeve or even a different capstan has to be installed.
 
Check the capstan motor pulley and see if it has two diameters to choose from. In some cases, a capstan sleeve or even a different capstan has to be installed.
Checked the capstan and motor pulley, it doesn't have that option (I've seen that in other Akai machines).

It seems in this model it's managed electrically, but only in the "Universal" version, not in this unit.
Perhaps I can install a larger capstan, even one to run at 15 IPS (It's 7.5 now)

What about the capacitors? Do tey need to be upsized to run at 50 Hz?
 
The higher specified capacitance value is for 50Hz operation. It's a synchronous motor, which requires quadrature phase offset (90 degrees) between the two windings, and greater capacitance is necessary to achieve that when operating frequency is reduced. Speed isn't governed by the cap, but torque will be low if the cap is wrong. I guess you could consider making or purchasing an AC line frequency changer.
 
Thanks!

I can study the schematic and change the circuit according to the 50Hz switch shown if needed...

I'll ask the owner the use he will give to the machine and replace all 3 the motor capacitors (I have some spare motor run capacitors rated 400V). If needed, I'll check how to change the circuit, or buy a freq changer

It seems the 50-60Hz switch changes the AC voltage feeding the motor. At 60Hz, it's fed by a higher voltage from the primary. Does this makes sense to you?

I've highlighted both positions of the switch, yellow at 50Hz, green at 60Hz. As you can see, the primary is used as an "autotransformer" using higher voltages at 60Hz.

output-50hz.jpg


output-60hz.jpg
 
The higher operating voltage at 60 Hz makes sense because the motor is an inductive load and higher voltage is needed to maintain winding current at higher frequency. In my younger days, I made a 120 Hz capstan motor power source in order to convert a 7.5 IPS machine to 15 IPS. It worked perfectly at first, but it had to deliver a lot of voltage to get adequate torque and it destroyed the motor after a while. I think that wretched contrivance is still sitting around here somewhere, waiting to be cannibalized.
 
if the motor involves a pulley or gear reducer somewhere, usually that will also be different from 50 to 60 hz since the motor will run at a different speed.
 
I see the pulleys and the flywheel don't have 2 positions, but I don't know if it's the same part for 50 or 60 Hz units. In the "universal" model there is a 50-60Hz switch what is not present in my unit, and the manual doesn't mention to change some pulley when changing the freq. I don't know how the speed is controlled in that model.

I'll do the capacitors change, and see if it's easy to rewire the supply from the transformer to match the schematic.

If not, I'll forget about the speed issue.
 
Guys you were right all the time, there is a pulley to change, not easily visible. The service manual doesn't mention it, but the user manual does.

capture8305.png

Now I need to figure how to change the voltages according to the 50 Hz schematic.
 
Lucky you, its just a matter of moving the belt rather than finding the proper one or having one made.
 
Should I worry about the higher voltages connected now? Perhaps it's just some small % of overheating that won't affect the motors (actually the machine was working like this since the '70s or early '80s)
 
I suggest you configure it exactly as designed. Over the years, a lot of grief has resulted from discarding the judgement of engineers.
 
What is your mains power there?

Agreed with configuring it to the factory setup that best matches what you actually get.
 
I have 220 V 50 Hz, but even if the unit has a label (added) that says "220V 50Hz", the setup inside matches the 110V 60Hz version, with addition of a step down 220 to 110V transformer inside the cabinet.

I'll do what you suggest, to trace the schematic, and re wire for 50 Hz. It seems (apart the added capacitance to the AC the motors) there are 3 wires that I need to change: transformer to capstan motor, and 2 wires from transformer to the tape size switch, All the rest seems the same in both models.
 
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