That's a 35vdc difference in B+ after full-wave rectification. There are things you could do to equalize that difference (different rectifiers, dropping resistors, etc.), but none of them would be ideal in my opinion. If I were putting a lot of time, money and effort into quality monoblocks, I'd want the power supplies to match so that both amps are running optimally.
If nothing else, I would definitely use solid state rectification with a Williamson build. You will need a low impedance power supply to ensure stability with the Williamson circuit. With a solid state PS, you will not need to use a choke, just use a lot of capacitance, which is cheap nowadays.
I built a pair of Willaimson mono amps 26 years ago and still love them.
Looking at your first post again, you wrote that your transformer is 300-0-300. I guess that's AC effective voltage, so your DC would end up at 1.4 x 300 V = 420 V. Add an RC smoothing filter or two and you'll hit the 400 VDC value. However, as I wrote before, please don't worry if your DC is off by a few percent. When I designed this amp I made sure there is some flexibility. The amp will work perfectly if the B+ voltage is off by 10%.
You get 420V with no load. The moment you load it the voltage goes down. That transformer gives ~400V DC with a ss full wave rectifier, 220uF cap and around 200mA load. Adding chokes, filters etc will reduce that value.
After considering all this I think I will maybe slow this project down and do it right. I'm going to buy a used 278x and 2 w-5 chokes locally. I will likley build one and the other at a later date. Maybe Santa Claus will bring me the other 278x! I build guitar amp too and the 272jx was going to be used for guitar amp originally.
If the voltage drops substantially under load, there is either not enough capacitance or the transformer is too lossy.
Only at no load, root 2 x AC volts is the peak. In a practical FW CT cct under load the voltage is more like 1.25 X wdg rms.
FW Bridge makes better use of the secondary copper, something called utility factor.
For large loads we would never see a properly designed rectifier use FW CT, whether C or L input to filter. 🙂
Duncan's Power Supply software is extremely accurate. If you put in the primary and secondary resistance figures of the power transformer, and know the current draw it will accurately predict voltages at the various stages of the amp. I also like being able to see the ripple of each section. This allows you to efficiently design a power supply with just the right amount of capacitance, resistance and inductance instead of just using the brute force method, which I find sloppy. It won't show you the impedance, but hey it's free.
It is fast and simple to use once you figure it out. Help from someone speeds up the learning curve exponentially.
It is fast and simple to use once you figure it out. Help from someone speeds up the learning curve exponentially.
If you can squeeze 400VDC out of the 272JX you'll be fine. The original "American" Williamson, the "Musician's Amplifier" put forth by Sarser and Sprinkle in 1950, called for a B+ of 400vdc, and tubes ran at about 390Vp and 36 volts bias. This was done to keep screens of the triode-wired 807s well under 400vdc, since KT66's were difficult to obtain in the US at the time. It works perfectly well and still gets you 22wpc in UL mode.
It is in there. Plot output for two different loads, perhaps 5K and 10X higher 50K. Do stuff with Ohmslaw, Thévenin, and Kirchhoff.
That's DC impedance. AC impedance is more difficult but we are usually more interested in transient response. Many essays on the web go into this. (Bring pinches of salt.)
You are using 55 years old speakers, but you're worried about a few percent offset of the B+ voltage? I think that's funny 😀
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The outputs are nice and i have been saving them for awhile. Just want to try and hit the value vs quality target. However, If I amuse you that's fine! I was the class clown many years ago and it might be the reason the math surrounding making changes to proven circuits is intimidating to me 🙂
The speakers are Yamaha NS-30 and sound very good to me BTW. 😉
The fact is I was not too worried about voltage difference using the the 278x and 274bx initially. I'd purchase them both used and they area much better price than new. The seller also has a couple of chokes. too. My first choice would be to use the transformer i have being the 272jx. I'm more of a builder and less of an engineer 🙂. The design side of things is not my greatest strength.
The outputs are nice and i have been saving them for awhile. Just want to try and hit the value vs quality target. However, If I amuse you that's fine! I was the class clown many years ago and it might be the reason the math surrounding making changes to proven circuits is intimidating to me 🙂
The speakers are Yamaha NS-30 and sound very good to me BTW. 😉
I have built the Altec 345a circuit several years ago and liked it. I think, as a few posters have mentioned, it makes more sense to copy the design the UL transformers came from. being the PA-600.
A very exceptional and rare pair of speakers, if you're not familiar with them. Also, with that level of sensitivity, all the more important that the monoblocks should be well-matched in sound and performance. It's not just about voltages.
