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Old 29th October 2010, 10:22 PM   #1
thafred is offline thafred  Austria
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Default Power Supply Input Capacitor - JE simple 45 question

My knowledge of tube electronics is very thin so please be patient with me :-)

I want to use a 5r4wgbt rectifier instead of the 5y3 and wanted to know if the 10F cap at the first Filter stage can do any damage (specified first Filter Cap for 5R4 is 4F) The Rectifier is connected via a 340 Ohm resistor to the 10F Cap to tune the voltage followed by a 10H 150ma Choke and the second filter stage of 40F MKP (RCLC configuration)
The rectifier works at the moment and sounds fantastic (much better than the 5y3, same voltage) but Im concerned if I could suffer any defects in the long term.

I used five 2F PIO Caps for this first filter stage in my build. can I just disconnect three of those caps and use as an additional 6F capacitor between the first filter stage (then 4F) and the second 40F cap? (like RCRCLC?) how can this impact performance ?

Thanks for your Help!

Best,
Fred
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Old 30th October 2010, 03:57 AM   #2
20to20 is offline 20to20  United States
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Nothing to worry about. Your amp already has the 10H choke. If you look at the data sheet you'll see the 4uf is for a supply with no choke at all. The designers were very conservative back in the '40's because capacitors were huge with high voltage ratings. If you look at a 5U4 data sheet you will see the same 4uf specification. I have a Magnavox chassis on my bench right now that uses a stock 5U4 with 40uf input and only a 1Hy choke. Your 5R4 is rated at 250ma while the 5Y3 is rated for only 125ma. The 5R4 is a very hardy tube. Just a little higher voltage drop, normally undetectable power loss.
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Old 30th October 2010, 10:44 AM   #3
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I see for tube diode is important the trafo resistence like 100-200 ohm , some put 100ohm beetwen trafo and tube , can be this the case with new tubes?
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Old 30th October 2010, 01:08 PM   #4
20to20 is offline 20to20  United States
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Quote:
Originally Posted by nicoch46 View Post
I see for tube diode is important the trafo resistence like 100-200 ohm , some put 100ohm beetwen trafo and tube , can be this the case with new tubes?
Every transformer has its own limiting resistance that is part of the total required. A transformer may have more than is required, by itself. There is a formula for calculating the transformer resistance. The amount necessary will vary with the amount of input capacitance, plate voltage, current draw, added choke... crappy, cheap, tubes....
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Old 30th October 2010, 02:24 PM   #5
thafred is offline thafred  Austria
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Thanks for your Help 20to20, exactly what I needed to hear!!!

Now.. where is that WE 274B again ;-)
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