Wow! Very nice! I would love to hear a pair some time. It's hard to imagine what they really sound like... ;-)
After simulation, with the Hammond 272JX, your B+ voltage after the first choke will be 352VDC. A bit low for the amp you want to use it for.
I always use a 1.6X multiplier for my power amp power tranformers for B+ current. For example, if the amp design calls for 250mA at rated power, I will use at least 400mA transformer design.
An Edcor power transformer such as the XPWR117 would be perfect. You can use the 12VAC for the tubes... wire the output tubes in series and use 12SN7GT's instead of 6SN7GT's or wire the 6SN7GT in series to separate from the output tubes.
I just used the XPWR117 for an Eico HF-87 clone build and it worked out perfectly with SS rectification. With the XPWR117, you have to use a bridge rectifier topology.
I always use a 1.6X multiplier for my power amp power tranformers for B+ current. For example, if the amp design calls for 250mA at rated power, I will use at least 400mA transformer design.
An Edcor power transformer such as the XPWR117 would be perfect. You can use the 12VAC for the tubes... wire the output tubes in series and use 12SN7GT's instead of 6SN7GT's or wire the 6SN7GT in series to separate from the output tubes.
I just used the XPWR117 for an Eico HF-87 clone build and it worked out perfectly with SS rectification. With the XPWR117, you have to use a bridge rectifier topology.
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Thanks for that THD+N. The XPWR117 looks like a very reasonably priced transformer. I've never bought Edcor since I live in Canada and have always purchased Hammond transformers, if buying new. Digikey ships free for $100 and over. I see lots of folks buy them in the USA and they seem to have a great reputation. Thanks again Nick!
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Thanks grover, I really do like the sound of these. I must admit I have old ears and the Youtube frequency tests say I can only hear up to 13500hz LOL. I also run a Sunfire sub too. I really think the speakers sound wonderful will refrain from the verbose discriptors and say open sounding. The original design or marketing at the time was that the bass driver used the idea of a grand piano soundboard. The bass goes down to 45hz say the specs.
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You could use a Hammond 263CX, but you would need a separate filament transformer, but they are cheap.
If you do decide to build a Williamson type amp, and it is a close replica of the original circuit, be sure to apply Talbot Wrights modifications to the amp. They are worth while improvements.
Thanks for the info THD! I'll be sure to check out the 263cx and the Talbot Wrights mods. I have been finding that internet search engines have sure become crappy over the last several years. Do you have a link to a good resource for the Talbot Wrights modifications?
I did find a good discussion from and older discussion at audio karma.
Nice article on tweaking out a Williamson Circuit
https://audiokarma.org/forums/index...e-on-tweaking-out-a-williamson-circuit.20551/
So many dead links out there these days.
I did find a good discussion from and older discussion at audio karma.
Nice article on tweaking out a Williamson Circuit
https://audiokarma.org/forums/index...e-on-tweaking-out-a-williamson-circuit.20551/
So many dead links out there these days.
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The biggest issue with building these types of amps is stability (feedback). Each brand and type of output transformer will require a different capacitor in the feedback network. The Williamson has two main feedback networks, a lag network across the anode resistor in the first stage and a lead network from the 16 ohm tap back to the cathode of the first stage. You can't really guess what the cap values might be.
At the minimum, you will need a scope and signal generator (with square wave option) in able to get the square resonse as good as you can with whatever output transformers you have slected.
If you don't have or can't get this equipment, it is best to follow a circuit somebody else has already tweaked with the same output transformers.
At the minimum, you will need a scope and signal generator (with square wave option) in able to get the square resonse as good as you can with whatever output transformers you have slected.
If you don't have or can't get this equipment, it is best to follow a circuit somebody else has already tweaked with the same output transformers.
Thanks THD, I was going to follow the Electrohome pa-600 schematic. I have the outputs only from the pictured amp. I do have a scope but I have not really learned how to use it yet. I get on it sooner or later!
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I did buy a scope in the spring at an estate sale. I spent an afternoon looking at it and it's been sitting on my shelf since. I don't do much amp stuff in the summer. I do remember thinking a more basic one might have been easier to learn.
https://www.allaboutcircuits.com/test-measurement/oscilloscopes/v-1100a/
https://www.allaboutcircuits.com/test-measurement/oscilloscopes/v-1100a/
I tried the Talbot Wright mods some time ago and I wasn't very pleased with what they did to the sound of my Williamsons. It's quite a different amp, really. Personally I would stick with the Electrohome circuit, but you can always try them. In either case, you should build the original circuit before you try any mods, so you have a basis for comparison.
I think that is good advice grover.. I will likely build it on eyelet boards so changing values is easy.
I admit, my hearing may not be as acute as yours. I still have good high frequency extension in my hearing, but it seems phase and other anomalies get lost on my ears. People who swear they can hear a difference in something, I cannot hear.
I didn't notice anything (too) audible in the TW mods, but the specs did improve.
I concur, try the PA-600 as-is, then begin modifications if you see fit.
When I built my pair of Williamson mono amps, i did way with the DC current and DC balance and just used a 350 ohm power resistor. It biases up fine and has the correct voltage as indicated on the schematic.
Music is every bit as enjoyable to me. I think you brain fills in some info too. Or at least I know that to be true with bass frequencies. It's why 70's rock sounds much better when the ampeg svt tube amp was the bass amp.
I doubt my hearing is any better than yours. ;-) But I am very picky about "tone," for lack of a better word. Whatever else you want to say about the Williamson, the naturalness of voices and instruments are hard to beat, IMO. Does the original Williamson have higher distortion? Probably. Maybe that's what I like about it. ;-)
I also tried Kiebert's 1952 mods, wherein he subs a 12AY7 and 5687 for the 6SN7s::
https://dalmura.com.au/static/The Williamson Type amplifier brought up to date.pdf
I was especially interested in these because I'm fortunate to have the Peerless S-265-Qs. Not only was the input sensitivity increased to uncomfortable levels, but it had an "electronic" sound that was nothing like the original.
Which reminds me... Swingarm, I don't know what your preamp situation is, but the Williamson likes a hearty amount of voltage drive, relatively speaking. I used an Aikido-style pramp, which has plenty of gain to play with. Most preamps should be fine, and given your speakers' efficiency, you shouldn't have a problem, but I thought I'd mention it.
Kiebert must have gotten ahold of a "Wiiliamson" that someone just threw together with parts in their junk bin. The first part of the article does shine some light on an area that builders may overlook; using the correct resistors in the right area. A good low noise type resistor must or should be used in the anode of a main gain stage. The 2nd stage is more forgiving since it does not supply any gain, just phase splitting action. In the 3rd stage, the 50k's should be low noise as well.
I am using USA NOS 12SN7GT's in my UL Williamson's with AC filaments and I have zero hum.
Another issue highlighted is the need for a robust power supply which is essential for low frequency stability. I used a solid state power supply in my initial build so I never had any low frequency issues.
The cross-neutralization is interesting, I may have to try this and see what happens.
In my opinion, the biggest improvement to the Williamson amp is making it operate in ultralinear mode.