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LowRedMoon 20th June 2008 03:33 AM

Tube rectified LC PS for 6SN7 Aikido - choke DCR question
 
2 Attachment(s)
It's preamp madness time. I'm building a few of them this summer, including a 6SN7 dual mono Aikido (and also trying a few 12b4 designs).

I'd like to use a 5AR4 choke input supply, mainly because I have 5AR4's, a 330V PT and chokes on hand. The desired B+ is roughly 290-300V.
I'll be using a single PT and separate LC filters for each channel.

I used Hagerman's PSU calc at the bottom the page at: http://www.hagtech.com/theory.html to figure the desired part values.

The DCR of the Hammond 193C is only 181R, and the calculator indicates that I need a choke resistance of 420R in order to use a 220uF cap.

Is this simply a matter of adding a 250R resistor in series with each choke? If so, is it more apropriate to place it before or after the choke?

Thank you for your time.

Best,

Adam

Tweeker 20th June 2008 04:12 AM

This resistor is to reduce LC filter Q, or to lower B+?

If its the later case, use that resistance to add an RC section, in either case, dont forget to count the source resistance of your PT and diodes.

You can somewhat get away with not being critically damped given class A operation, there is no change in load to jar the psu and make for oscillations. You can check how well damped a psu is by using the stepped load function in PSUDII.

Eli Duttman 20th June 2008 04:40 AM

Adam,

You need to look at an old edition of the ARRL Handbook. THE proper way to execute a choke I/P filtered PSU is LCLC. The 1st filter cap. does not have to be huge. A low DCR in the 1st inductor is a good thing.

Full dual mono is not really necessary. Sharing the 1st inductor and 1st filter cap. usually works out OK. Individual 2nd inductors and reservoir caps. for each channel is good for separation.

Tweeker 20th June 2008 05:20 AM

Part of that is because in those days capacitance was orders of magnitude more expensive, whereas now a humongous 1,000uF+ cap (mind the charging surge) can cost less than a choke.

Splitting the supply with RC is probably fine, 250R 220uF gives a <3hz corner, most stereo information is much higher, and Aikido has good PSRR too boot. Im assuming 3 chokes arent to hand.

If you go way too low (say 193Q choke and 22uF) on DCR and/or capacitance on the input the supply will squeege badly.


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