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Old 6th Nov 2019, 12:46 pm   #50
ms660
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Join Date: Apr 2011
Location: Cornwall, UK.
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Default Re: Vintage Radio and Phonograph cutter schematic

Quote:
Originally Posted by Levente View Post
Hey Lawrence, another quick question and thank you for your advise in advance as always...

I thinking to change the value for the second filter capacitor. Would a 100uF ,275 WKG 350 Surge be an acceptable choice? I know the voltage calls for a 450V rated cap but there I will not get more than 250V and these can capacitors I have are really a god quality.

I kept the first filter connected to the 5Y3 the same 16uF/450V

Would this reduce the hum?

!
It should be rated the same as the reservoir capacitor which is 450 volts, here's why...

1) The rectifier is a directly heated rectifier, the rest of the valves aren't, that means that the voltage on the rectifiers cathode and the rest of the HT line can be much higher than it otherwise would be after the other valves have warmed up and drawing their full current.

2) A fault condition could exist such as the heater supply for all the valves other than the rectifier goes missing for whatever reason, ie: poor connection, open circuit heater winding on the transformer etc, if that were to happen the HT voltage would rise to the peak value of the AC voltage that's presented to the rectifiers anode(s) The manual gives a figure of 320 volts AC at the anode(s) that is the RMS value, however, as said, the reservoir capacitor would charge up to the peak voltage of the AC therefore putting the HT line at a DC voltage that's equal to the peak of the AC voltage, the peak value of a sinusoidal AC voltage is its RMS value multiplied by 1.414, ie: 320*1.414 which equals approx. 450 volts....

Would increasing that capacitors value reduce the hum to a noticeable extent....It depends where the hum is coming from, soon find out if a suitable one is fitted.

Lawrence.

Last edited by ms660; 6th Nov 2019 at 12:59 pm. Reason: clarity
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