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Old 9th Jul 2019, 6:58 pm   #101
DonaldStott
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Default Re: Yet another Bush DAC90A

Here's a photo of the diffuser with the annoying glue I would like to remove: -
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Old 9th Jul 2019, 11:28 pm   #102
Ian - G4JQT
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Default Re: Yet another Bush DAC90A

I've made a replacement diffuser cut from an ice cream box. Still stable after 20 years!
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Old 10th Jul 2019, 7:46 am   #103
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Default Re: Yet another Bush DAC90A

The original diffuser is made from cellulose nitrate. If you are replacing it, don't throw it away, you might as well have some fun burning it (it is highly inflammable, burns fast, cleanly and completely).

Use of ice-cream box is interesting, I used a piece of 0.5mm translucent polyester sheet for mine.
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Old 10th Jul 2019, 12:05 pm   #104
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Default Re: Yet another Bush DAC90A

Interesting idea to make a "...replacement diffuser cut from an ice cream box" - how translucent is that?

And using " ...a piece of 0.5mm translucent polyester sheet" seems like the way forward if only I had some lying about in the spares department.

Any concerns about heat from the bulbs with these two options??
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Old 10th Jul 2019, 12:26 pm   #105
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Default Re: Yet another Bush DAC90A

The bulbs don't get very hot as they're so dim. You'll have to dig around for translucent boxes and find something appropriate, but it shouldn't be difficult.

Or maybe a piece of clear plastic rubbed with Vim or something, or maybe just a piece of paper glued to one side.
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Old 10th Jul 2019, 2:04 pm   #106
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Default Re: Yet another Bush DAC90A

Quote:
Originally Posted by Mike. Watterson View Post
What happens with a pulse input?
No ringing on a square wave?
If you have a series CR circuit, in parallel with a series LR circuit, with the two R's equal and the C and L related by L/C = R² then the thing looks purely resistive and constant with frequency. No ringing anywhere!

See here where the modified tone corrector circuit is described (as well as other things).
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Old 10th Jul 2019, 2:30 pm   #107
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Default Re: Yet another Bush DAC90A

Quote:
Originally Posted by Ian - G4JQT View Post
Or maybe a piece of clear plastic rubbed with Vim or something, or maybe just a piece of paper glued to one side.
Some transparent plastics develop a 'milky' white opacity on the surface if they're wiped-over with the right solvent. This might be an option.

(Confession: I discovered this by accident when I tried to clean the nicotine-staining off the front plastic of a typical 1970s cheap panel-meter. I don't know if the solvent shifted the nicotine stains - because the entire front went opaque-white, rendering the meter scrap!)
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Old 11th Jul 2019, 8:16 am   #108
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Default Re: Yet another Bush DAC90A

If you can lay your hands on a scrap LCD TV or LCD PC monitor, they quite often have a sheet or two of diffusion material. They also have a polariser(?), this gives kaleidoscopic effects when removed from the screen and viewing the world through them

They'd be plenty of material for a DAC90A too, plus if the lamps and reflector are in excellent condition, putting silver tape (circa 2mm wide) all the way around the clean edges of the dial glass, can give a nice even glow, I did this on my recent Cossor 501AC resto.

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Old 11th Jul 2019, 8:53 am   #109
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Default Re: Yet another Bush DAC90A

I would leave the back diffuser exactly as it is. Why risk spoiling the originality of the receiver in an attempt to erase a mark that is impossible to see when switched on? Celluloid has strange properties and could easily be damaged by any cleaning agent.

These models are now 70 years old and it would be a shame to reconstruct one from a modern plastic carton.

Don't get me wrong, if the diffuser is cracked, broken, missing or defaced then the substitute opaque ice cream container sounds ideal.

Just a thought. John.
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Old 11th Jul 2019, 12:01 pm   #110
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Default Re: Yet another Bush DAC90A

I really appreciate the responses from everyone on the diffuser issue and a special thanks to those who sent a PM offering replacements - as usual I've learned a lot from this discussion.

For now I think I will just take the advice from John (Heatercathodeshort) and leave the back diffuser exactly as it is - it's not cracked, broken, missing or defaced and I have cleaned it up with spray foam.
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Old 11th Jul 2019, 12:14 pm   #111
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Default Re: Yet another Bush DAC90A

I intend to replace the diffuser on the DAC90 I'm repairing for the simple reason that the original is highly flammable, as has been pointed out in this thread. O.K. The original has survived the best part of 70 years with no mishaps, but 'better safe than sorry' to coin a phrase.
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Old 27th Jul 2019, 2:02 pm   #112
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Default Re: Yet another Bush DAC90A

We're definitely on the Home Straight now with this DAC90A - can't believe how long it's taken but there have been some lengthy interruptions due to other, mainly family, priorities!

Thanks to Forum member Northyorks1 (Ian) I now have a nice new piece of plexiglass to replace the original and highly flammable cellulose nitrate diffuser.

I've also sprayed the bulb and diffuser holder with gloss white paint which should improve the amount of light getting through.

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The set is sounding good although it does seem rather sensitive to external interference.

The Dropper is still running very hot (in my opinion?) and there is that typical smell you get when things are too hot?

And now for the funny part?

I was hoping for final assembly this weekend but have some bolts and brackets that I really can't remember where they came from?

It's been so long since the set was disassembled - any ideas what these are and where they should go: -

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Old 27th Jul 2019, 2:13 pm   #113
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Default Re: Yet another Bush DAC90A

Loudspeaker fixing brackets ?

Lawrence.
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Old 27th Jul 2019, 2:51 pm   #114
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Default Re: Yet another Bush DAC90A

The two at the left side of picture one hold the chassis to the cabinet I believe (one at either end, into brass threads set into the bakelite).

The other two in that picture may fix the back cover on?

The second pic, as Lawrence say look as if they hold the speaker in place.

Cheers,
Colin
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Old 27th Jul 2019, 9:32 pm   #115
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Default Re: Yet another Bush DAC90A

Thanks Lawrence - of course the second picture shows the Loudspeaker fixing brackets !

Thanks Colin - of course the two at the left side of the first picture hold the chassis to the cabinet while the other two in that picture fix the back cover on !

So I have two missing bolts for fixing the back cover on - they are 3/8 inches long but does anyone know what thread size?

And finally (!) I need to touch up some paint on the back cover - does anyone know which colour of brown was used??
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Old 28th Jul 2019, 10:51 am   #116
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Default Re: Yet another Bush DAC90A

Just to add to my frustrations that are curtailing final assembly (see my Post #115 above) I'd forgotten that at some point "The Phantom Twiddler" had replaced the dust cap on the loudspeaker with a Velcro sticky pad: -

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I'm of the view that I should to do the job properly and source a replacement dust cap but to what extent will the Velcro pad be impacting on sound quality - if at all?
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Old 28th Jul 2019, 11:00 am   #117
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Default Re: Yet another Bush DAC90A

Looks like standard original stuff to me.

Lawrence.
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Old 28th Jul 2019, 12:08 pm   #118
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Default Re: Yet another Bush DAC90A

That dust cap is larger in diameter to the one on a DAC90A speaker I have, which measures approx. 3/4" and leaves approx. 1/8" all around between it and the circular 'rib' in the centre of the cone. The speaker in my case is a Celestion K6QO 1734, but maybe Bush used other makes during the production Run. As to the Back Fixing Screws, if the surviving one I have is original, it's approx. 7/16" long, including the head, and appears to be 4BA to me.
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Old 28th Jul 2019, 1:02 pm   #119
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Default Re: Yet another Bush DAC90A

Looks original to me, Personally, I think I would leave it anyway with the chance of damaging the cone getting it off.
Steve.
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Old 28th Jul 2019, 2:00 pm   #120
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Default Re: Yet another Bush DAC90A

Quote:
Originally Posted by ms660 View Post
Looks like standard original stuff to me.

Lawrence.
Me too. I've seen lots of speakers with a dust cover like that, though admittedly the dust cover on the Celestion speaker of a DAC90A that one day I might finish restoring is as shown in the second pic below. As to the mounting screws for the back panel, yes, they're 4BA. The two that secure the chassis to the cabinet are 2 BA as shown in pic 1 below. (The speaker securing brackets and screws can also be seen in the that pic).

As to what colour paint to use to touch up the back panel, see what tester pots are currently available from the DIY stores. Some time ago I designed a router slot-cutting jig to make backs for several of my radios that had missing ones as shown in pic. At the time, the closest colour I could find to match most radio backs was 'Double Espresso' matt emulsion paint from Homebase, but I guess colours get renamed over the years - 'Mocha' or whatever. I just looked at what 'tester pots' were available from Homebase, B&Q et al. Tester pots are cheap and go a long way! Enough for two coats each side of four WCR backs at least.

If the colour turns out a shade too light, you can always darken it down with a smidgen of black.

Hope that helps.
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