[Drake] [DrakeRadio] TR4C filter cap

[William Houghton]

Hi Dick,

1) I haven't measured the length of the cable on my AC-4 but I would guess its about 2 to 2.5 ft. Without the multi-cap can, the 260V supply terminal would see twice the AC-4 cable length between the 260V terminal and the chassis ground (i.e a wire from the 260V source in the supply to the terminal in the radio and another wire between the supply's ground and the radio's ground). Ideally you want the voltage source terminals in the chassis to present a good AC ground between the terminal at the radio's chassis. At RF going through 4 or 5 feet of cable might not make for a good ground. Adding the caps on the chassis I suspect is a solution for this. There is a series resistor from the 260V supply that drops it down to 250V if I remember the schematic. Adding a cap here does the same - making a good RF ground. 

The amount of capacitance you need depends on the expected load and the amount of ripple you can accept. As a general rule, increasing the capacitance decreases the ripple but will increase the peak diode current during the time that the supply diodes are forwarded biased. I think the values you have will be fine. 

Just my guesses as to why it was done this way.

Bill


________________________________
From: Dick KF4NS <kf4nsradio at verizon.net>
To: DrakeRadio list <DrakeRadio at yahoogroups.com>; drake at mailman.qth.net; Drake list at zerobeat <drakelist at zerobeat.net>
Sent: Tue, July 6, 2010 12:34:57 PM
Subject: [DrakeRadio] TR4C filter cap

  
I plan on replacing the multi cap can with individual caps as part of 
the restoration, but first I have a couple questions.

1. Why is it there to begin with since the AC-4 has already filtered 
the 250V and why are there 3 different cap values? ( I already 
replaced the 10mfd at 25V right at the pin8 connection of V19A with a 
10 @ 50V)

2. The three values I have in mine are 60-20-10mfd at 250V so I 
planned on using a 100-33-22 @ 350V but would appreciate your input on 
these values I chose.

73, Dick KF4NS
St Petersburg, FL 33714 USA
Keep The Glow! 


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