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TO-3 SYMASYM

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#507
Carl, what is up? I did not hear from you for quite a lot time.
Did you receive the PCBs?

I have finished the "1st floor" (small resistors, diodes and capacitors) this morning.

Best regards - Rudi_Ratlos
 

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#516
Carl, please check the polarity of C4 / 470µF / 16V.

I will have a closer look at it later on.

The MICA capacitors that your ordered, are very good!

I ordered the wrong ones, 😡 ,with a much too wide grid and too thick legs, and I spoiled the nail-file of my spouse. O dear!

Best regards - Rudi_Ratlos

Carl: you do not have to do a new DIGIKEY-order for the 22K resistors!
They are just to delimit the current flowing through the LEDs!
Take a 10K, 6K8, 4K7, ..., use Ohm's law: 35V rail-voltage - 2V forward drop across the LED - divided by some mA - giving the value of the resistor.
 
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#519
Rudi_Ratlos said:
Ryan,
a transformer with 2 x 28VAC secondaries will give you about +/- 39VDC (roughly) after rectification.
Please take in account deviations in mains voltage, ..., as well.

This voltage may be critical for "sensitve" input transistors, like the 2SK170.

I therefore recommend you to solder the cap-multiplier and use a Z036 Zener-diode so that the frontend's voltage will be delimited to 35.3V (roughly).

Best regards - Rudi
Click to expand...

Rudi,
Do I understand you correctly: I only need to replace the 33V zener with a 36V zener in the cap multiplier for safe operation at 39V rails?

Thanks,
Ryan
 
#520
Ryan, I advise you to buy 2 pairs of 36V and 39V - Zener Diodes and measure them before use.
Zener diodes usually have an allowance (tolerance) of 10%!

If you want to use your 2 x 28VAC transformer and want your input transistors (f.e. 2SK170) being protected from damage
due to over-voltage (Vgds = 40V !), then use a 39V Zener (resp. 36V).
This will delimit the frontend-voltages to 38.4V (35.4V respectively).

The one, who has the best knowledge, how to operate a SYMASYM from higher voltages than 25VAC, is EVETTE.

As far as I remember, EVETTE operates one of his SYMASYMs from +/-50 VDC.

Joseph: is there anything you changed (exept rail-capacitors) to operate the SYMASYM from such high voltages?
Which type of input transistors did you use?

Best regards - Rudi_Ratlos
 
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