May need to reinforce the chassis

[Jamier]

Derek,

     I have no experience with the Kaiju, but I can tell you adding a PS choke in resistor position 2 of the SII PS was not beneficial. It did not reduce the noise much and seemed to kill the top end of the amps response. I have no explanation for this, only my experience with the change. The choke That I used was a Hammond with the appropriate specs ( I forget the model number, but I have them around here somewhere if you want to know the model). I think that in a parafeed amp the plate choke shields the OTs from PS noise so any mods to the PS will have less influence on the noise and might even hurt your performance in the long run. You should probably change your PS in a step-wise fashion so that you will know when you have gone too far, if going too far is possible. Maybe PB or Doc can give you more input on this.

Jamie

[Deke609]

adding a PS choke in resistor position 2 of the SII PS was not beneficial. It did not reduce the noise much and seemed to kill the top end of the amps response.

Thanks Jamie - that's an interesting result. Regarding lack of noise reduction - I wonder whether the stock filter circuit is already so low ripple that the choke adds nothing (does the voltage doubler help with smoothing?) -- in which case the noise is coming from elsewhere? Perhaps the heater voltage or just the operation of the output tube?  Or the choke itself? Dunno. As to how a choke in the power supply might attenuate high frequency response, I'm stumped and baffled. 


But to your point about taking it slow and doing one bit at a time: absolutely. The only tweaks I'm married to are the film cap replacements. My experiences with film caps in my SIIs have convinced me that I like what copper foil caps do to the sound.


Despite my willingness to play around with shielding and layout, and to swap in different caps, I am loathe to change any elements of the circuit design set out in the schematic for simple, obvious reasons: (1) I have no idea what I'm doing in that regard; and (2) the guy that designed the circuit (PJ - in the case of the SII, Kaiju and Beepre) very much does.


So the choke-for-resistor swap, if I were to do it, would be an experiment. And as I think more about it, I'm inclined to do some of these power supply experiments on a little scratch build "Nickel Wonder" preamp that PB turned me onto - something I've been meaning to experiment with, but just haven't gotten around to.


So, time to dial it back a bit. I still like the idea of a larger copper chassis - so I will focus on whether it is doable and something I'd enjoy doing.


cheers,


Derek

[Paul Birkeland]

I wonder whether the stock filter circuit is already so low ripple that the choke adds nothing

Yes.

in which case the noise is coming from elsewhere?

Yes.

Perhaps the heater voltage

Until you add the DC filament supply, yes.

or just the operation of the output tube?

Once the DC filament supply is added, then yes.

[2wo]

If you do consider a film power supply, the caps after the voltage doubler are 2 caps in sieres to handle the higher voltage. Each pair could be replaced with a single ~100u >450V film or motor run...John

[Deke609]

Ah, yes, I see that. Thanks John. That would make things simpler and  smaller. I am definitely considering it for down the road and hope in the next month to settle on an enlarged Kaiju chassis/layout that will permit me to try it without much hassle.


And then I plan to rebuild one of the SII's on the stock Kaiju chassis. Lots of room for parafeed caps and other stuff then.  And just for PB: imagine all the copper tubing I could pack into that!   


cheers,


Derek