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Modified Farm Radio

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Modified Farm Radio Empty Modified Farm Radio

Post by 35Z5 on Sun Apr 20, 2014 10:04 pm

This is something I've been threatening to do since I got this Mantola farm radio seven or eight years ago... I'd like to use it as a occasional player, but the puny 3Q5 audio always irritated me so I'd cut it off in a few minutes... Since it had it's fair share of crumbling rubber wiring, I'd already totally removed the AC/battery switch and associated wiring, so figured it's now or never(well about three weeks later)...

Modified Farm Radio Mantolar672_zps54f0e475

This Truetone D1123 is close to my radio, I've never found the exact schematic for the Mantola 672 version, used a rotary switch for AC/battery select instead of cord plug...

Modified Farm Radio D1123_zpsfb727cd6

After I finished the dirty work this is the circuitry, ARF member bikenswim suggested the filament circuit as used in a Emerson 505 portable... I'd been considering a 25Z6 to power 50L6(25L6) and filaments seperatly as a 35Z5 would be at the max current limit operating both... This method more or less gives a free 50ma to operate filaments... The 50L6, OPT & 8" speaker were mostly donated by the remains of a 1952 Zenith radio/phono(phono had been sawed off)... Original speaker was 6" mounted on a reducer board..Results are very noticeable, should have modified it sooner...

I had to get creative with marrying the schematics as my program isn't interested in coping from a outside source... .

Modified Farm Radio Mantola50L6_zps80ceddb0
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Post by harold wright on Wed May 14, 2014 9:26 pm

Nice work, 35Z5.

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Post by 75X11 on Thu May 15, 2014 6:58 am

You do nice work! Sorry For my late notice, my new job keeps me from noticing these things as soon as I should.
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Post by 35Z5 on Fri May 16, 2014 8:45 pm

'ppreciate it...

I did go back and added a fixed tone control circuit that's nothing more than a .002 & 150K resistor in series to ground off control grid(pin 5) of 50L6... Even with the increased output, was still a bit sharp sounding so I tried various resistances from the substitution box till I liked the tone... With a variable control, usually there is a 500K to maybe 1 meg control in series with the .002...

I've also added a pair of #159 wedge base dial lamps(same spec as 47) at either end of dial scale, it now glows in the dark... For those I used a small power transformer pirated from a junk solid state radio...

Modified Farm Radio Picture601_zps07309e3e

I secured the wiring after the shot...

Modified Farm Radio Picture596_zpsf99a0cd5
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Post by Marco-ni on Sat May 17, 2014 8:54 am

Nice, really nice 35Z5
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