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Poor Man's Western Electric 124 Amp

With the prices paid for Western Electric 124 amps nowadays, I'm sure there are many people wondering what the big deal is. Oh sure, we have all heard the Western Electric 124's are the best sounding pentode amps made as well as the descriptions of fast, clean, quiet, stable and of course passes a great square wave ...blah blah blah.

But still, what's so great about an obsolete 6L6 phone company audio amp, must be the iron - That wonderful Western Electric 171C output transformer.


click image to enlarge

In my opinion - It's Not - Me not having the 4k to get into a pair of 124's or wanting to go through all the problems of matching amp models and rebuilding (devaluing) I decided to build mine from an old Heathkit W4 amp.
With several 10K output transformers on my shelves off I went to gutting that old tired Williamson Amp. If you look at the 124 circuit it is basically a floating para-phase but with balanced feedback independent of the output transformer.
This allows you to get an idea of just what the output transformer sounds like. After converting my first Heath amp (using 171C output transformers) and comparing to both prewar as well as postwar 124 Western Electric amps I found I had duplicated the magic of the 124.


The real fun started while swapping opts (lots of room on that W4 chassis). I settled with the UTC LS63 transformer - Not my first choice but one that fit and has a very nice balance form bottom to top. Clearly now they outperformed any stock 124. So much for that mythical Western Electric iron. Now get out and find you some old Heathkit amps. Save your nickels for a good pair of vintage opts and have fun  -- I sure did.

 -- Listed below are a few tips you might try that worked well for me --

 
  • Will work with any 6L6 family tubes but had best results with clear KT66

  • Add tube covers on front end tubes and you can use Western Electric 348, 6J7G or skip the covers and go with 1620 or 6J7 metal

  • Use balance jacks for W4 to permit output tube balance
    (one up on the 124)

  • Use protective network from prewar scheme
    (it rolls the top slightly but on my horns the balance is better)

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

 

This puts the voltages right for the 12 watt mode.  Also makes the stock W4 power transformer run cool.

- Michael -


Heath 124

124 Schematic

Heath 124

     

 

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