Plate supply after Pi filter/choke?

[LeftyStrat]

I'm unable to find it now, but I vaguely remember a thread on here about taking the plate supply from after the pi filter (clc), rather than before actually improves the feel of the amp.

I think it may have been in a discussion about Brian May's amp.

Anyone experimented with this? Anyone ever try it on a Rocket?

[ToneMerc]

If memory serves me correctly, hit Matt H up.

TM

[sluckey]

taking the plate supply from after the pi filter

Vox AC-15 does this. All the old Sunn amps did too.

[matt h]

(deleted)

[Pierre]

Funny you should bring this up! Attached is a schematic for the amp that I just finished with a choke input and loosely based on the rocket. I used the rocket topology but with a Liverpool tonestack and a 5879 pentode for the second stage. The amp sounds great!

[Pierre]

double post

[LeftyStrat]

However, I'm a fan of chokes in power supplies, whether choke input or in a pre-plate pi filter. It really depends on the amp's "big picture," though.

I've noticed a trend, all the amps I love have chokes.

[LeftyStrat]

Funny you should bring this up! Attached is a schematic for the amp that I just finished with a choke input and loosely based on the rocket. I used the rocket topology but with a Liverpool tonestack and a 5879 pentode for the second stage. The amp sounds great!

Thanks for sharing. Your power supply looks exactly like what I had in mind.

[Roe]

this really is the way to go with ac30 type amps and tweed champs.

[bruce egnater]

Different input circuits require different transformer specs.

[matt h]

(deleted)

[LOUDthud]

I've used a Pi filter on a couple of bass amps. The choke doesn't need to be that big. You only need inductance in the Henrys if you limit your caps to 20uF. Run a sim with PSUD2. Those old Sunn amps used 1.5H/50ohm with 20 or 30uF on either side for 60W. The 2000S (Noel Redding) amp used two chokes in parallel and same caps as did the Model T, a favorite of Doom players.

For a 150W 4x6550 amp I used 100uF, 0.3H, 235uF. Ripple was about 1V pk-pk at full power. Ripple looks like a sine wave. Enormous clean low end. A smaller 2xEL34 amp used 100uF 0.6H/11ohm 220uF with similar results. I never tried it on a guitar amp, might be too bassy.

[pdf64]

Attached is a schematic for the amp that I just finished with a choke input

Pierre, just to clarify, your schematic shows a reservoir capacitor input smoothing arrangement (pi filter as it's cap - choke - cap).
Choke input arrangements have a choke then a cap and have a lower Vdc output, hence Bruce's comment.
Hope that helps - Pete

[bruce egnater]

See this attachment.

[gingertube]

Anyone tried a Gyrator (Electronic Choke)? They are starting to appear quite regularly in supplies for DIY HiFI Tube Amps.
Cheers,
Ian

EDIT: For those who are wondering what I mean I have added the following example.
With the link at the bottom out, it works like an electronic choke. That is it opposes current change and presents a high impedance to residual ripple. The series resistor after the choke will develop a current dependent voltage across it, and that is fedback, via the cap to the MOSFET gate. OR you can think about it as an inverting amplifier with a capacitor in the feedback, making it behave like an inductor.

With the link in, the electronic choke action is reduced (by capacitor divider action) but capacitance multiplier function is added.

Cheers,
Ian