Full PS after choke

[skyboltone]

I have a 9H choke rated at 225MA. What are the disadvantages of putting plates and all the other taps on the smooth side of the choke? Is this a tone issue?

Sure is nice and smooth over there.

thanks in advance
Dan

[MarkB]

That's called a choke input filter. The voltage you get out of it will be much lower - something like 90% of HV instead of 140%. In that sense, it's a waste of PT secondary winding. I have seen it in one stereo console I pulled apart, but never in a guitar amp. A Google search of "choke input filter" will get you lots of info - there are advantages, but I forget the details other than just more smoothing as you mention. You can also use a choke for the plate, and one for the screen.

[David Root]

Only downside I can see is lower plate/screen voltage compared with capacitor feed. Smoooth is good! Where did you get that thing? It must be a monster at 225 mA unless it's very high DCR.

[rhinson]

hello, sunn amps (dynaco power section) used used a choke(s) pre plates in many of their amps. you have to have a very large current rating to get the full benefit of the smoothing because as it is met and exceeded the inductance drops sharply to maybe a third of it's rated value and the filter cap you pair it with has to take over. some of the big sunn amps used 2 chokes in parallel. rh

[skyboltone]

Let me restate here. RH is right. It will still be a capacitor input filter but the first cap will be followed by the choke, then the plates, then an RC filter, then the screens, then an RC filter than the PI, etc. etc. Modeling it with Duncan's PS software shows it really looking nice with everything over there.

I'm still looking at 1.3 to 1.4 times the AC input to the rectifier for the B+1. Just moving the choke to the left in the scheme. This is a very nice 9H 250MA choke. I mispoke earlier it's not 225MA but the full 250MA, it will handle the load, it's not a swinging choke.

I just wonder, since HAD and just about everybody else taps the plates after the first cap, do we want that ragged 10 volt or so ripple on the plates as a part of the tone.

Dan

[skyboltone]

Only downside I can see is lower plate/screen voltage compared with capacitor feed. Smoooth is good! Where did you get that thing? It must be a monster at 225 mA unless it's very high DCR.

120 ohm

Out of a transmitter. It's a Stancor from about 1960. I'd say it's roughly three times the size of the fender 5H.

Dan

[dehughes]

IIRC, older AC15s had a choke input filter, as does the new Top Hat Supreme 16 head. Supposed to be killer....and a very different vibe than a cap input filter. Might want to try it just for kicks...