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Western Electric 124 amplifier
Western Electric 124 amplifier
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Old 17th October 2014, 12:54 PM   #21
Salectric is offline Salectric  United States
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Can anyone tell me the function of the RC network across the OPT primary (C7 and C11---.004uf and R12---30K pot)? See Post #6 for schematic. There is no mention of this adjustment in the manual so presumably the pot was set at the factory.
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Old 17th October 2014, 04:04 PM   #22
kevinkr is offline kevinkr  United States
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Western Electric 124 amplifier
Presumably to damp the primary windings. (Stability and to improve square wave response?)
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Old 18th October 2014, 06:36 AM   #23
Paul Joppa is offline Paul Joppa  United States
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Quote:
Originally Posted by kevinkr View Post
Presumably to damp the primary windings. (Stability and to improve square wave response?)
I agree. The leakage inductance of the OPT windings will raise the impedance seen by the tubes, increasing their gain and thus reducing the stability margin of the feedback loop. The RC functions as a sort of Zobel to cancel the OPT reflected load resistance plus leakage inductance. Since the transformer is not perfectly symmetrical, the pot allows optimization of high frequency performance.

My story would sound better if I had any idea what performance was being optimized! Probably a service manual would give a clue, if one still exists.

The dual feedback loops to the cathode and screen grid(!) of the input tube are very unusual.
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Old 18th October 2014, 08:19 AM   #24
Zero D is offline Zero D  United Kingdom
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Default Re Post 6 screenie

I'm not an valve expert, or any other but shouldn't R1 go to the V1 input & the input ground connection go to the circuit ground ?

Valves do look great, & can sound good, no doubt
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Old 18th October 2014, 09:49 AM   #25
Salectric is offline Salectric  United States
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I also have a question about the OPT impedance. Several places have said the 171-C is 10K. Doesn't this seem high for PP 6L6? They typically are in the 4K to 6K range. I realize the 124 is not trying to maximize output. It only outputs 12W at the lower B+ setting. Thoughts?
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Old 18th October 2014, 12:59 PM   #26
lukerandall is offline lukerandall  United States
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Originally Posted by Salectric View Post
Luke, I too am interested in building an amp based on the WE 124 design. Someone in this thread mentioned an article somewhere from a guy who built one on a Heath chassis and tried different OPTs (including the WE 171C). He concluded that the magic in the 124 amp is actually in its circuit design and not the iron used. He compared his amp to an actual WE 124 and found that he was able to surpass the original in sound quality using a different vintage OPT and some other updated parts. Unfortunately, the site where that article appeared has been closed but I have a copy of it in my files. If you want to read it, I can look for it and send it to you.

All I know from firsthand experience is that a pair of true 124 amps can sound absolutely wonderful. There is a store not too far from me that specializes in vintage gear and I have heard the owner's pair several times on various speakers. Not quite the same as hearing them in my own home, I admit, but what I heard in his store was very nice indeed. Also, his 124s have WE 350B outputs which are supposed to be pretty special as well.

Hi Thanks for this info. I would love to read the article if you could find it. My email is: Pompeipaints@gmail.com
I thought that OPT meant output transformer> Is the 171c an input transformer or output? I thought it was an input type. I was thing about getting a vintage NON- W.E. input trans. that matched the specs of the 171. I understand that you do not need an input transformer to run these. I do not understand how the amp could run with or without the transformer input. I know the transformer input changes the impedance but that is the little i know. I plan on using a hammond transformer for the power supply and for the output. I have some beautiful old MUllard EL37 (Similar to 6L6) tubes that I want to use for this project. How far along are you on your 124 project? Do you know anything about the difference between the 124 and the 142 amplifiers? I am excited about beginning soon. I need to keep researching to figure out exactly how to do this project. Thanks for your reply.
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Old 18th October 2014, 02:18 PM   #27
Salectric is offline Salectric  United States
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The article I recalled is the one at the link in Post #9 above.

The output transformer used in the 124 amps (as well as some other WE amps) is the 171-C.

My plan for the 124 is to wire it into a pair of DIY monoblocks I built a few years ago. I will probably use Hammond 1650R output transformers since that's what are in the amps already. The 1650R is 5K which has worked fine with 6L6GC, Kt77, KT 88 and KT120 all in fixed bias.
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Old 18th October 2014, 02:53 PM   #28
lukerandall is offline lukerandall  United States
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OK I have just read the article about 124 amps that is linked above. It is giving me some hope for a decent outcome. I have two questions after reading this link .

1. "Very Important" - Buck the line voltage with a 6.3v filament transformer


What does this "buck the line voltage" mean?

2. Can anyone tell me of a couple different vintage output transformers that might be comparable to the W.E. 171 C? I am interested in trying a vintage Transformer but don't want to spend the huge money for Western Electric.

3. I am still unclear about the input transformers. Are these an important part of the sound? Should I not even worry about that arrangement?


THANKS FOR ALL OF YOUR HELP. LUKE
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Old 18th October 2014, 04:37 PM   #29
GaryB is offline GaryB  United States
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Western Electric 124 amplifier
Quote:
Originally Posted by lukerandall View Post
. . . Do you know anything about the difference between the 124 and the 142 amplifiers?
Here's a copy of the WE142 schematic. It's also a 6L6 push-pull amplifier but the circuit design is more conventional.
---Gary
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Old 18th October 2014, 09:42 PM   #30
kevinkr is offline kevinkr  United States
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Western Electric 124 amplifier
You might want to talk to Jack Elliano at Electra-Print, he can make a set of output transformers with 10K PP primary impedance and a single or multiple secondaries as you prefer. I have used his output transformers in a couple of my projects and am very pleased with their performance.

He is not too expensive, and you could spend much more and end up with something not appreciably better.

Other possible options on the vintage front would be UTC, Chicago, Acrosound, etc..

FWIW, IMHO the 124 is a much more interesting circuit than the apparently later 142...
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