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Old 17th Sep 2017, 7:36 pm   #1
cernem1alt
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Default Bush DAC90A problems.

It's that old chestnut again a bust waveband switch on a DAC90A

Sadly mine is to far gone and I was wondering would a modern 2 pole 2 throw rotary switch surfice? has anyone fitted a modern replacement if so what?

I see there are a few posts on repairing the old one and a bit about modifying a 2 pole 4 throw so any ideas

sorry if this is a repeat topic

Many thanks Mike
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Old 18th Sep 2017, 9:41 am   #2
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Default Re: Bush DAC90A waveband switch again

Hello Mike

I am pretty sure that you would be able to fit a modern two pole two way switch, have a look at either ESR electronics or Rapid electronics, these switches can be set to up to 12 positions as the stop on them is adjustable. Failing that try electrojumbe and if push comes to shove I might even have one that will suite.

Best wishes

Ken
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Old 18th Sep 2017, 11:27 am   #3
David G4EBT
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Default Re: Bush DAC90A waveband switch again

I'm sure there's been a thread - maybe in 'Success Stories' showing a neat way to replace the DAC90A bandswitch.
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Old 18th Sep 2017, 7:48 pm   #4
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Default Re: Bush DAC90A waveband switch again

Thank you Ken and David for your replies I am going to go with the adjustable rotary switch I found one today online now I have never come across one of these yet believe it or not so I shall have to pay attention to wiring it up and fixing the stops etc another radio learning curve just what its all about
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Old 18th Sep 2017, 7:52 pm   #5
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Default Re: Bush DAC90A waveband switch again

Hi Gents, this switch is a pretty slimline type, not all modern ones will fit in, although electrically they will do the job.

Ed
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Old 18th Sep 2017, 8:11 pm   #6
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Default Re: Bush DAC90A waveband switch again

They're a fairly common radio and occasionally do get broken for spares. You could try a request in the parts wanted section.
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Old 18th Sep 2017, 8:49 pm   #7
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Default Re: Bush DAC90A waveband switch again

I'm about to break one for spares (cabinet in many pieces and a bent chassis!) so I'll see if the wavechange switch is serviceable.
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Last edited by Dickie; 18th Sep 2017 at 8:52 pm. Reason: typo.
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Old 18th Sep 2017, 10:55 pm   #8
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Default Re: Bush DAC90A waveband switch again

I did rather think size might be an issue it was a right performance getting the old one out, I think many years ago someone snapped the waveband on my set then tried to wrench off the front knobs to get inside the box and chipped those however they have been repaired using some stuff I have called JB Weld then smoothed to shape with my dremel small lick of paint and only I know. The waveband switch lost the copper ballbearing piece the set from the smell of it (lavender water old ladies face powder) I reckon got put in a wardrobe and forgot about. Richard if you have an intact one I may get back to you if I cant work it with this modern rotary switch

Regards All
Mike M1ALT
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Old 21st Sep 2017, 5:50 pm   #9
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Default Re: Bush DAC90A waveband switch again

Update I tried fitting a modern rotary switch that is a no no not enough room so I am going to have to find an original Bush DAC90A waveband switch

Mike M1ALT
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Old 21st Sep 2017, 10:27 pm   #10
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Default Re: Bush DAC90A waveband switch again

There's a neat diagram somewhere - either on or off the forum, which shows how to use a Lorlin wave-change switch as a replacement, but I'm blowed if I can find it. I didn't bother bookmarking it as the DAC90A is my least favourite radio and holds no attraction to me.

However, this youtube video might be of interest, by a guy called Yannis Karalis, who supplies new DAC90A dials of any type, has designed and can supply a PCB to replace the tag-strip, has done various improvements (dial lights, hum reduction OPT rewind etc). He's also drawn up what looks to be a neat and comprehensive '90A repair manual.

'Bush DAC90A Switch repair':

https://www.bing.com/videos/search?q...B8AC&FORM=VIRE

Here's his website on 'Bush DAC90A Easy Restoration':

https://www.yanniskaralis.com/bush-d...sy-restoration

A low resolution section of the manual can be found here, which you can judge for yourself:

https://docs.wixstatic.com/ugd/ac5ed...fae80f794f.pdf

Hope that's of interest to DAC90A fans.

Good luck with the switch repair Mike.
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Old 23rd Sep 2017, 2:08 am   #11
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Default Re: Bush DAC90A waveband switch again

A Lorlin switch (2 pole 6 way, or 3 pole 4 way or 4 pole 3 way, shorting) as sold by Maplin, etc., certainly will fit, unless the design has changed in the last 11 years.
I did it by setting the mechanical stop to 2-way, chopping off all the unused tags, bending the remaining ones almost flat, working out its orientation, and re-arranging the wiring (slightly longer on one and on the opposite sides to original) so the tag connected to chassis could be allowed to short to the bracket where it just about touched, if it wanted.
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Old 23rd Sep 2017, 11:41 am   #12
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Default Re: Bush DAC90A waveband switch again

Happily I have sourced an original
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Old 3rd Oct 2017, 1:01 am   #13
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Default Bush DAC90A C17 tone Cap question

Following on from a purchase of a DAC90A repair kit Having replaced various caps and bulbs I now turn to C17 tone corrector 1x .001 (1nf) to replace .003 for improved sound. My sets tone is quite pleasant to my ear the old C17 looks ok and going by the old saying "if it's not broke don't fix it" am I missing something here if I don't replace C17? curious to know the pros and cons of changing it.

Thanks Mike
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Old 3rd Oct 2017, 3:09 am   #14
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Default Re: Bush DAC90A C17 tone Cap question

I'd be interested to hear what's said, from what I gather it's meant to improve the treble response.
I own two DAC 90A's and not changed C17 as I don't have a problem with the sound.
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Old 3rd Oct 2017, 7:52 am   #15
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Default Re: Bush DAC90A C17 tone Cap question

If C17 is a waxy paper capacitor then it will already be leaking DC current and it will get worse. This will eventually effect the way that V3 works, and may lead to R10 overheating.
If you like the more mellow tone caused by the 0.003uF cap, then why not replace it with a new 0.0022 or .0033 uF 630v cap.
Worries will then be over.

Mike
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Old 3rd Oct 2017, 8:11 am   #16
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Default Re: Bush DAC90A C17 tone Cap question

I think if it is across the sound o/put transformer then most members advise a cap rated at 1500V.See previous posts of which there are many on these excellent little sets.

As stated high risk the wax one will be leaky after all these years.
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Old 3rd Oct 2017, 9:36 am   #17
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Default Re: Bush DAC90A C17 tone Cap question

C17 is connected between the anode of the audio triode and chassis. I would agree that the original wax capacitor here should always be changed for a modern type.

There are a number of mods for the DAC90A developed by P F Vaughan (Kalee20) that may be of interest to you - here.
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Old 3rd Oct 2017, 12:07 pm   #18
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Default Re: Bush DAC90A C17 tone Cap question

I've done several of these and only once lowered C17 to 390pF. I couldn't tell any difference.

I'd certainly change the original cap though; what you change it for is up to you. I've found that capacitors which are still OK quickly fail when you start using the set so change the lot while I'm at it. For all that it doesn't matter a mixture or old and new looks like a job half done.
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Old 3rd Oct 2017, 12:18 pm   #19
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Default Re: Bush DAC90A C17 tone Cap question

I would also change this cap.

The DAC90A does have a rather woolly sound to modern ears. People liked a lot of top cut in the 50s and most radios from that era sound similar.
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Old 3rd Oct 2017, 6:35 pm   #20
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Default Re: Bush DAC90A C17 tone Cap question

I always change C17 (Bush numbering) to about 500p. It really only needs to remove any residual IF. The original value has far too much treble cut for modern ears, and remember that the audio as transmitted now almost certainly has less treble than 60 years ago, so maybe it sounded ok then, but not now.

There's a mention on this forum somewhere that this particular cap may be a minor error that Bush never noticed. I think that's unlikely as it's the same value in the almost identical circuit of the Bush DAC10.

The treble cut capacitor across the output transformer (to reduce the shrillness of third-harmonic distortion?) is also a bit brutal and I reduce that too - but as stated above, ensure it's 1kV or thereabouts.

For those who don't notice a difference, maybe it depends how tightly set the IF bandwidth is. I align mine so it's relatively broad so local stations and my 'pantry' transmitters sound really nice after these two caps have reduced values.

Ian
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