I assume you are referring to C7, C11 and R12 as shown on the WE schematic on page 1 of this thread. I did not use any of those parts. I intended to try them but frankly never got around to it. I read somewhere that many WE 124 amps came from the factory without that network.
Building a Western Electric 124
- Thread starter Salectric
- Start date
Why build an amp with a poorly wound OPT? We know the 171-C, TO-330 and LS-63 work well in the 124 circuit despite the wide range of primary impedances. I suspect many other vintage OPTs would also be fine.
Let's start at the beginning. The WE 124 has no feedback around the OT. My posit is that the amp works because the 171C transformer is quite good and subbing another quite good OT in place of it (whether TO-330 or LS-63) should give similar result. paul_b states "None of this is as much of an issue if the OT is outside the feedback loop." I would think putting a poor OT in place of a good one and no feedback like the 124 gives less than optimal performance.
Many amps get built with middling OTs which gets corrected in part by feedback. Point being you could not do that with the WE topology without major redesign. And, I don't know an LS-63 works, it's speculative. But likely a good bet that it will, LS OTs are very good. Further, the wide range of primary impedances is introducing the Acro which has much lower Z than the original design. Both the 171C & LS-63 have the same primary Z, 10K. I don't know how the TO-330 behaves, have not checked one previously. But if it's like the TO-300 or TO-310 it's good too and why it works in your amps. Swap a Stancor A--38xx into it though...
No ref to UTC or LS-63 before mine, post #151. No ref I can find on web either using that OT in a WE 124 clone either. Weird as it seems such a natural as are most 1st generation Williamson OTs with primary Z of 10K - 12K. Includes ones like the Peerless S-265-Q & 16309 (conventional secs) and Partridge WWFB/CFB (multiple sec to series & parallel strap). Gets the mind racing, have all above except 16309 (2nd gen. Heathkit W-5M). Might be a future project there.
Here's the article I mentioned. I thought I had referred to it in this thread but apparently not.
Excellent, thank you! No wonder that no longer came up when I searched, basically gone from google indexing.
UTC LS-63 or 61 not hard to find. Company made them for many years. Then OPT bought the UTC rights from TRW early 90s and made them again. There are a lot out there and likely why the price remains consistent year to year.
Thanks,
I may start looking and put a pencil to a build cost.
If I go down this road it's a ways off... as I as resigned myself to 3 things in my que that have to be completed before adding too it.
Man self discipline sucks 😩
I understand the feeling @MrEd . It seems like there are always things to do in this hobby, and sometimes there are even other priorities in life that get in the way, like raising your family or doing your job.
From time to time I think of building another set of 124 amps. I have a nice pair of OPTs from a Sansui 1000a that might be very nice, and I even have a spare pair of Angela Universal power transformers, so I have the basics covered. But then I look around my room and see I already have 4 pairs of monoblocks lying around yet I use the 124 amps 99.9% of the time. Do I really need a 5th pair of amps?
From time to time I think of building another set of 124 amps. I have a nice pair of OPTs from a Sansui 1000a that might be very nice, and I even have a spare pair of Angela Universal power transformers, so I have the basics covered. But then I look around my room and see I already have 4 pairs of monoblocks lying around yet I use the 124 amps 99.9% of the time. Do I really need a 5th pair of amps?
Have a set of LS-63s now earmarked for this project. Somewhere in my piles of crap I have a 221G choke; correct for the 124 series amps. It's 5H on the schematics but DCR not shown. I'll add that info to the thread when I measure it. Hammond has a range of chokes at 5H and likely something close enough. Also looks like a generic 350-0-350V PT gets you within a few volts of the 124 B+. All of a sudden these look pretty doable.
Oh... now you're an enabler
Shame on you....
Guilty as charged: Build lust on 124 clones
You'd have to be more specific about what poorly wound is indicating. Is this really low primary inductance, excessive parasitic capacitance, poorly balanced capacitance, etc? The local feedback loops in the 124 make the circuit a lot less responsive to output transformer problems than you'd expect for seeing a pentode push-pull output stage.
Heyboer of Michigan make an excellent copy of the Peerless S-265-Q. The last time I ordered some they charged about $500 a pair including shipping. Dave Gillespie, over at Audiokarma, tested one in a standard Williamson circuit and compared it to the original Peerless. He said it achieved about "98%" of the original's performance. I've used them in a number of builds and actually prefer them to the originals, sonically. They exhibit less ringing in the high frequencies. I highly recommend them to anyone who wants to build this WE amp or an original, American-style Williamson. They're a terrific bargain. Plus, you get a 40 watt transformer as opposed to the UTC's 20 watts.
The only downside is Heyboer's fit-and-finish--they dip them in varnish and they can look a little rough, so a little light sanding and some paint might be in order, as in the pic below. And, they are *very* hefty, unlike the UTC. The lead time is usually about four weeks.
That's one in my avatar pic, also.
The only downside is Heyboer's fit-and-finish--they dip them in varnish and they can look a little rough, so a little light sanding and some paint might be in order, as in the pic below. And, they are *very* hefty, unlike the UTC. The lead time is usually about four weeks.
That's one in my avatar pic, also.
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Yes, if I ever built anything other than a Williamson. ;-) I like the sound of those 50% taps on the Peerless.
Hmmm... I pretty sure I have a pair of PHC-200s cluttering up the joint. Too much?
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