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Heresy Woofer Output Down 6db?


DRBILL
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I hope I don’t get hooted off the forum for this, or that this isn’t drawing the saw through an old cut. Nevertheless. . .

Having finished the restoration of yet another vintage Zenith radio (10-S-153; 1937; Chassis 1004; ten tubes; 6L6s p-p in the final) but without output transformer or speaker, I decided to be innovative. I will mention that this radio has a wide bandwidth tuner perfectly capable of 30-10,000 Hz audio and the audio section is transformer coupled to the push-pull 6L6s. This is amazing quality for 1937!

So, I found a Type E network, a Heresy mid, and an E-V tweeter for a song from a guy who didn’t know what they were for and didn’t care.

I installed these together with a high quality Hammond output transformer and a 15” Jensen speaker that I had on hand. I replaced the 2.5 mH inductor with a 1955 Klipsch “spool” inductor, also 2.5 mH. The over-all results were amazing when listening to the several music stations here in the metromess that take pride in the quality of their audio. Except for being in mono, it was as good as most FM.

But there was a problem. The bass was altogether too light, not nearly as good as when I was using the 15” woofer by itself.

In the recesses of my corroded synapses, I believe I recall that the woofer output of the Heresy was down 6 db from the mid and tweet, and I believe this is what I am hearing. My instincts tell me to move the mid wire from terminal 2 to terminal 1 on the autoformer and cranking up the volume a bit. But since it is presently useable, I though I would wait until I took the pulse of the forum on this. Any suggestions will be appreciated.

What say ye?

Father Bill

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At another place on the forum I found a schematic that calls for a 16Ω resistor parallel to the mid when operating the mid from tap 1 to maintain the correct crossover point. This was offered as a correction for excessive brightness.

Nothing is ever a easy as first imagined! Time to get out the alligator clips and grope around.

Thanks, Gill, for the schematic. I should have pulled out my folio of "Dope from Hope."

Father Bill

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It is the floor model, and yes, it is one of the "desirable" models. They are getting awfully hard to find. It is beautiful to behold with its restored finish and replicated grille cloth. It was actually advertised as a "high fidelity" model! And that wasn't hype. How anything this old can perform so well is an inspiration to me.

Father Bill

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