Choke specs for the Crack

[larcenasb]

I'd use the 470uF->choke->470uF in parallel with whatever film caps you have, then use 47uF or 68uF caps on the outputs.  The extra R-C power supply node shouldn't be necessary with the rest of the changes.

I'm sorry, please forgive my ignorance, but what do you mean "The extra R-C power supply node shouldn't be necessary with the rest of the changes."? What's an R-C power supply node? Is it the final PS cap?

[Paul Birkeland]

I'm sorry, please forgive my ignorance, but what do you mean "The extra R-C power supply node shouldn't be necessary with the rest of the changes."? What's an R-C power supply node? Is it the final PS cap?

The extra RC power supply node is the 270 Ohm resistor and whatever cap follows it.  With the choke and the increased capacitance, the extra filtering shouldn't be necessary.

[larcenasb]

The extra RC power supply node is the 270 Ohm resistor and whatever cap follows it.  With the choke and the increased capacitance, the extra filtering shouldn't be necessary.

Thank you, Paul for helping me understand. But what about the relationship between the last PS cap and the outputs for the "effective capacitance"?

If I don't use a last PS cap, just the two 470uF caps and the choke, how will that affect my effective capacitance? Will the 68uF outputs indeed effectively be 68uF or much less than that? Thanks!

[Paul Birkeland]

As PJ mentioned, they are effectively in series.  The larger the last PS cap is, the closer your coupling cap will be to giving its corner frequency as though it was the only cap that mattered.  With 470uF as the last cap in your power supply, your 68uF cap will perform better in this regard than if the last cap in the power supply was 220uF.

[trollchu]

Just to clarify before I order, I want two right?

I don't know, I could see situations where 1, 2, or 3 of these chokes could be used.  The specifics are up to you.

I'm aware I'm quoting a comment from 2014, but what kind of situation would call for a third choke and would there be any benefit to having that third or even the second choke in a Crack?

[Paul Birkeland]

More chokes will further reduce the presence of noise from the power supply.

[trollchu]

Thank you, Paul. If the first two chokes are replacing the two 270 ohm 5W resistors, where in the circuit could a third choke be acceptable and would it call for the same value of choke?

-Kalil

[Paul Birkeland]

You would need to redesign the power supply and use three chokes that are different than the two you already have.

[Tom-s]

Next thing we know someone makes a Crack using a pseudo dual mono powersupply with three chokes and loads the driver tubes with anode chokes like the LL1667 from Lundahl.
That’s five chokes in a Crack! 😇

[Paul Birkeland]

It would be tough to do choke loading of the 12AU7 in the Crack without abandoning the direct coupling or having a separate power supply for the driver stage with much lower voltage.

[trollchu]

I'd more love to see to see how someone'd plan to fit it all that in a Crack build, a dual mono power supply with three chokes sounds like a job for a master craftsman.

I have a couple more questions. I'm still in the midst of painting my Crack and the paint I'm using needs three weeks minimum drying time for best results, so I've got a lot of time to plan the mods I'd like to implement in my build. I'm planning to go with two Hammond 158M chokes on 1.5 inch spacers so that they still fit within the wood base and I'd like to mount them above power supply caps one and two. When it comes to mounting chokes, is there a way to insure that my placement of them won't cause inference with the PT-10, and can I test for that somehow?

These other questions are a bit off-topic for this thread, but for the third power supply cap, as well as both sides of the output caps, I'd like to run 100uf Wima's and I'm considering using four Wima's in parallel in place of the third power supply cap and two Wima's per side on the output. Would I run into any issues in running paralleled caps in any of these positions?

Lastly, what benefits are there to be found in bypassing power supply caps and what are some good options for a stepped attenuator in 2025?

[Paul Birkeland]

There isn't much concern about a power supply choke and a power transformer interfering with each other.  All those Wimas will take up a lot of space, that's the only issue I can think of.  Bypassing caps was pretty popular around 1995-2005, but power supply caps have improved, and the technical merits of adding bypass caps have become dubious at best.

[trollchu]

That's all quite reassuring to hear. If so, I think I've mapped out all my mods then, minus the pot.

The 100uf Wima's are cool cause they're still significantly smaller than a lot of other film caps, and for the third position, four of them side by side only take up 4.88 inches. They are the automotive grade Wima's, which are still polypropylene film and low ESR; they're also cheaper than 100uf Audyn caps right now. What I'm planning to do for those is to mount them to a sawed off piece of a clipboard and mount them on standoffs just like the chokes,  but I still need to check and confirm the height of the Wima's versus the height of the Crack, I want it all to fit under the wood chassis if possible.

It's a crimson red Crack build, with all the Wima's it'll be red inside, too. Thanks again, Paul.