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Old 10th February 2009, 08:50 PM   #11
diyAudio Member
Join Date: Jan 2006
Location: SAO PAULO - SP
Originally posted by JoshK
Where did you get this value for minimum impedance? I've never seen that before and it isn't in the aforementioned datasheet.

Originally posted by andyjevans

But there's no provision for inserting resistors before the rectifier in PSU Designer unless I'm missing something. Could you explain further?
Hi Andy , Hi Josh ,

No!! The use of protective resistor is a "good practice" when
you are using tube rectifiers , no matters if it is a damper diode
or double diode or even a general rectifier like 5U4 , GZ34 , etc .

The protective resistor aims to prevent , the cathode stripper ,
limiting the cold inrush current , thus increasing the tube life
and its reliability .

I ALWAYS do the calculation that I showed above , ALWAYS
using the data furnished by the manufacturer or the designer
of that individual tube ( no problem about that because I have
a lot of Tube Manuals and the Frank's Tube Page , to consult )

In the specific case of 6BY5GA , I could get this precious
information on my colection of Tube Manuals . It is a reliable
information , you can be shure about that , as follows :
6BY5GA - High perveance damper diode
Minimum effective plate impedance when used as
a general rectifier = 100 ohms ( per plate )
Ideal value for the filter input capacitor = 10 uf
Maximum output CC = 175 mA

You are correct , there is no provision on PSU Designer to calculate or insert these protective resistors .

IMHO , The PSU Designer is an excellent tool , to simulate the
conditions , the voltages , the currents and the general behavior
of any planned power supply , BUT in the real life , things happen
a " bit " different and then there is nothing more reliable than
the experience and the data acquired in the laboratory condition
from an old manufacturer or an old designer of tubes .

I think that these old engineers and old lab technicians , did know
exactly what they were doing . Or not ??
And they did their job very , very , very , well !!!!
Because all of us , even in the Very Large Scale Integration era ,
prefer the tube sound ( that was born in the 1900's ) instead
the modern and hyper-miniaturized " silicon " sound ,

Regards for all ,

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Old 12th February 2009, 06:04 PM   #12
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soulmerchant's Avatar
Join Date: Sep 2006
Location: Near Zurich
Hi Carlos

Thanks very much for your answer. This is crystal clear to me now.

Kind regards
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Old 12th February 2009, 06:11 PM   #13
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Tom Bavis's Avatar
Join Date: Jun 2002
Location: Macedon NY
You can increase the transformer winding resistance in PSU designer, or make the first filter section R-C to simulate an added resistor. In the former case, there would be two resistors used in the actual circuit, one per plate. Small transformers will probably be fine without adding resistors, large ones may give too much peak repetitive current.
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Old 12th February 2009, 09:40 PM   #14
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Join Date: Sep 2003
Location: London
You can increase the transformer winding resistance in PSU designer>>

Good thinking batman ...
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Old 13th February 2009, 01:52 AM   #15
diyAudio Member
Join Date: Jan 2006
Location: SAO PAULO - SP
Originally posted by Tom Bavis
You can increase the transformer winding resistance in PSU designer, ........
Yes . This is a valid way , to bring the PSU Designer simulation ,
closer to the real life .

As a starting point , you can use the formula that I wrote on
my post , above .

Regards ,

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