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In Reply to: RE: I feel like I should know this. posted by Corndog71 on August 15, 2013 at 06:21:11
You could use a SS rectifier without a delay circuit if you have caps that can handle the voltage increase or you can use a delay circuit or an inrush limiter but as the voltage comes up it will be higher with SS rectification than with tube by about 40-50 VDC so you still have to make sure the caps can handle the extra voltage.
I happen to like SS rectification in some amp circuits. Most PP amps like the Dynaco stuff is to my liking. I feel tube rectification was used to keep the voltage down but it having a cap right on the rectifier really defeated the purpose.
I also felt the amp sounded better with a 40UF cap on the rectifier then a 100R resistor right off the rectifier with a 40UF cap putting the output tranny B+ right there then the choke with a 40UF cap then leave the rest of the power supply circuit as it was. The amp sounded more lively with an extra stage of decoupling with the output tranny B+ wires before the choke. But that's only my opinion. I got the idea from a good friend and I figured it can't hurt to try it. The circuit then becomes C/R/C/L/C/R/C/R/C power supply. With a SS rectifier you could probably eliminate the choke and cap totally by adding more capacitance on the rectifier(80UF or a little more).
Follow Ups:
I probably should've elaborated. I plan to use Clarity TC caps which are 700V film caps. I was thinking C(45uF) L C(110uF) R C(110uF). This is what I did for my ST35 to good effect.
Obviously this will not be in a stock enclosure. I've just had too many issues with tube rectifiers that I would just rather go solid state. Copper Caps are another option but I would almost prefer to avoid the socket connection altogether and keep it internal.
The turn on delay circuit would allow the heaters to warm up before applying high voltage.
Rob C
The world was made for people not cursed with self-awareness
Too much UF on the stages after the choke. The TC's(time constants)are affected. Never go more than double the stock amount.
I would appreciate hearing more about the time constant issue. How does one know when the time constants have been adversely affected, and what exactly constitutes adversely affecting the time constants?
Hi Peter,
I really don't know if it is totally the TC's or just limiting bandwidths to get other bandwidths more pronounced.
The only thing I do know about it is that when you add loads of capacitance to the stages after the choke you create other issues to the sound. That is why when someone says after they do a power supply mod the bass is great and the highs are outstanding, usually it's because they compromised other areas of the bandwith. A good friend and a very qualified tech told me it was the TC's that was inadvertently affected. Maybe another audio hobbyist or tech would call it something different. I know I heard this myself whenever I did a mod using loads of capacitance after the choke. Depending on the type and amount of capacitance used would determine the type of sound I was hearing.
The rectifier, unless it was changed to SS(which lots of them were changed to) usually had 20UF but going to 40UF max was OK but that was the limit before the rectifier went into explosion. Better quality rectifiers could handle a bit more but that's all. SS there was no limit but the turn on was hard.
Here is some software from Duncan Amps for making calculations on a variety of power supply parameters:
http://www.duncanamps.com/psud2/index.html
Perhaps it could show what the limits are for the amount of capacitance before there is limiting of the frequency response, I don't know. I have downloaded the main software but haven't figured-out how it works yet. I think you might have to download some other files.
Regards,
Peter
Hi Peter,
If you ask Tre' on DIY Tubes he would tell you that the Duncan download for power supplies is only a tool to get you started. I have my friend Danlaudionut draw me a schematic whenever I am going to build something. He uses Duncan to get it going. The rest I do with my ear because at the end of the day what you listen to is all that matters. There are many parameters that go into designing anything, especially audio. Most of the stuff built was done long before Duncan had this download. The Duncan site just makes thing easier to get started.
I don't suppose you could elaborate on this a bit? Does it matter that the TC caps have very low ESR? 45uF-1.4 mili-ohms, 110uF-1.6 mili-ohms
I guess I could just use the 45uF caps. That'll save a few bucks.
Rob C
The world was made for people not cursed with self-awareness
You could also install a simple rail switch but you have to manually turn it on and off. The less you put in the less can break.
If you are having trouble with tube rectifiers it could be that you have too much capacitance right on the rectifier or you are using cheap rectifiers.
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