DIY ST-35 questions

[RuralUrban]

I'm sure this has been answered before, so please forgive me...
On the rev D PCB, what is the purpose of C14,15;R47,R48 ? What would their values be if they were installed ? I know they are not needed, just curious ? more RF suppression ?

The rev D PCB has locations for three terminal regulators in the cathode bias circuit, can they be used ? If so, what would the other changes be to utilize them ? Would they be standard LM317's or LM340's (the adjustable types) ??

Has anyone wired up Edcor CXPP25 OT's ? Will the primaries (Blue, Brown and their assoiciated UL taps) phase the same as the Z565-48 clones and hammond 1650's, or has it already been determined and experienced that they will be out of phase with these examples, and should be reversed so that I have an amplifier and not an oscillator ? I know there's always a 50/50 shot at getting it right, (or wrong if you're a pessimist) but I'd just like to know if the answer is already known ?

Why did my Triode ST-35 board and parts kit ship with 1N4007's, are'nt they supposed to be UF4007's ?? I'm aware of the difference, I just wonder if some testing was done and perhaps it was determined that there is no gain in using the UF's in this power supply ?

I know that the power supply is massively filtered as is, but, if using a C354, is there a limit on the amount of uF's that can be added, or will the CL90 protect the diodes in even a ridiculous case of insane overkill.(?) I am thinking of adding an SDS type add-on filter board, (My own breadboarded design, however) which is why I ask. Plenty of room since I am using a 10x17x3 chassis, which is really comfortable. I also realize that the law of diminishing returns apply, and more cap really wont make much if any difference. Why not, (?) is what I am looking for, I guess.

Thanks in advance to anyone that can help with any of these questions. This is my 2nd DIY ST-35, and it should be up and running in days.

R.U.

[Ty_Bower]

C14/C15 and R47/R48 are part of a low pass filter. Shannon says it's for a "triode design".

The three pin regulator would be a LM317. Do a search on the ST35 forum for LM317, and you'll find further details.

I hook up my amps with an 8 ohm dummy load (cemented resistor) and an oscilloscope. It's hard not to spot the oscillator, and the leads are reversed easily enough, thanks to the terminal block design.

[Shannon Parks]

The extra step filter locations were put in for further modding, but honestly I've never used them. :)

I did build a LM317 ST35, as did Ed Brown, I believe. Search for that info.

With the low ESR filtering in the design, 1N4007s are probably fine.

How much extra capacitance are you thinking of? In the first section and/or second?

[RuralUrban]

Thanks Shannon and Ty for the responses.

I did already stuff the board with the stock variable resistance bias scheme, but I love this amp so much, there will certainly be a wish for a third one in the future. The regulators seem like they would really be a no fuss solution, automatically biased correctly no matter how many times you "roll" tubes.

I also stuffed the board with UF4007's I had on hand, but thanks again for the info, the 1N's maybe can get used for an instrument amp in the future. Neither cost a fortune so no big deal.

I have four UCC 470uF@450V that I plan to parallel with each 120uF (C9-12), so the additional capacitance will (would) be applied to all three stages of the supply. (Unless someone strongly suggests this would be a bad idea). These electro's are one model better ESR than UCC's standard gen purpose caps. I am using one of the Antek toroidal PT's, which spec wise appear to be able to supply enough current for three DIY ST-35 amps simultaneously. Cant wait to hear how the Edcors compare to my first build, which used the Z565 clones.

Like my first go at the DIY ST-35, this amp is coming together just beautifully. However the final product turns out, I want to thank Shannon and anyone else who was involved in making this kit a reality for all of us. There is really little if any room for improvement, You took a great design and made it pretty much perfect. I have gotten so much enjoyment out of my first one, I spent all last winter trying to build speakers that would be worthy. Not sure I accomplished that, but its all part of the DIY bug that I have had for over thirty years.
Thanks,thanks, thanks -
R.U.

[Shannon Parks]

I'd probably advise to just add the large cap to only the B+ stage at C10. First stage would probably blow diodes from inrush and the last stage will be filtered enough.

Thanks for the kudos!