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Old 24th May 2012, 2:34 pm   #1
mark2collection
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Default Modified Bush DAC90A.

Hi folks,

This brief writeup is about my second DAC90A repair. My first DAC90A thankfully, was simply new caps and a dust out (Circa 2005, still going strong :O)

However, my second set was so poor, it was a case of ornament or spares. Then, looking deeper and folllowing the modifications from Kalee20 (Put on here some years ago it would seem), she lives again! This set really was ripe for the mod.

https://www.vintage-radio.net/forum/...ad.php?t=35784

Rather than repair pictures, attached are pictures of my original DAC90A (Non modified circuit - Before) and of my latest repair (Modified Circuit - After) which show the output frequency response. I've not attached pictures of the second set as found or how she looks now, though I will upon request! (She really was very poorly, a colleague thought I'd dug the set out of a 1st Class Cabin from The Titanic!)

New caps were needed, new dial chord, new lamps, replacement output transformer, some resistors, dial reflector re-paint, replacement dial glass, replacement power switch/volume control, replacement speaker, most of the internal wiring replaced, rust treatment, plus a good clean and a polish. Still, it was complete, original and authentic!

Mark
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Last edited by Station X; 5th Jun 2012 at 10:09 am. Reason: Link to modification added.
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Old 24th May 2012, 5:42 pm   #2
kalee20
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Default Re: Modified Bush DAC90A.

Did you do all the mods - including the hum neutralisation to the UL41 cathode? (Which I regard as necessary but really not nice!)

The frequency spectrum content 'after mod' looks fuller than 'before mod' but that could be down to programme content. (I'm assuming that you didn't have the luxury of a noise generator and a broadcast-quality modulated RF source!)

Thanks for comments, whatever! Incidentally, my DAC90A gets several hours a week use - no problems whatever!
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Old 5th Jun 2012, 9:30 am   #3
mark2collection
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Default Re: Modified Bush DAC90A.

... I did indeed carry out all mods, including the hum neutralisation.

The Spectrum Analyser (Klark Teknik DN60 with RT60) I used, thankfully, has a White Noise generator built in, which was promptly fed to my Sstran AMT3000 A.M. Transmitter. Not a definitive test by any stretch, but proved my ears were not deceiving ... the set does sound fuller ... excellent work Kalee20 ...

Aside from the capacitors, resistors & wire, all other parts are Genuine Bush items, although for the solid core wire, I retained the original sleeving, which responded well to foam cleaner

Am enjoying both DAC90a's during these Diamond Jubilee Celebrations ...
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