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    Building, troubleshooting and testing of these amplifiers should only be
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Chokes.. Importance of and function?


2001-04-07 10:03 pm

I'm new to tube DIY.

If somebody could please give me some information on chokes.

Specifically, how important is their value?

For instance, I have a design which calls for a 14H/75mA choke (rankin 2a3). Could I use a 15H/150mA choke? What affects would it have on the circuit?

Thanks for the help!

-- Aaron
If the choke is in the power supply, the current rating should be the same or greater than specified. The actual inductance is important only in that it will change where the resonances in the power supply occur. Sometimes this is a problem, but usually bigger is better than smaller.

Steve Bench has some useful info and and to aid in any PSU design, a copy of the free PSUD from Duncan Amps is worth it's weight in gold.


you'll find that tube circuits are easier to grasp than SS circuits. :cool:

Your 15H/150mA choke should be fine, it has a bigger core and has way more headroom towards saturation, hence way less strayfields. Which is good as far as you intend to build PS and amp circuit on the same chassis.

One thing to watch: the qualitiy of the choke, does it show any oscillations durning load change if you measure across it with an oscillosope. A PS choke should not sport any ringing. Because you do not want to shunt the choke with a small cap to cancel the ringing but :( act as a coupling cap for exactly the HF junk you do not want to couple thru.

PSUD II: strictly recommended! :)
Function of the choke: ideally (provided it its inductance is big enough and current is sufficient) it acts as a constant current device, having low DCR but very high ACR. It blocks the HF junk off from the evil world.

Ideally a constant DC current flows thru the choke. If you play around with PSUD, please try out an LC filter after the rectifier.
This will cause a considerable voltage drop, even more if you use a tube rectifier, but the desirable ideal of having DC current thu the choke can be achieved best. And, TME and to experience of all who tried it out, general consensus was it sounds best, too: tube rectifier and LC filter.