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Old 13th Mar 2018, 12:57 am   #1
bill knox
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Default Bush DAC 90 and DAC 90A

Hi all

Can somebody please tell me what the difference is between a DAC 90 and a DAC90A electrically and physically just so I can tell them apart

Regards

Bill
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Old 13th Mar 2018, 1:03 am   #2
paulsherwin
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Default Re: Bush DAC 90 and DAC 90A

The DAC90 uses octal valves and the 90A uses rimlocks. That's the most obvious difference if you can see inside through the back panel.

I think all the 90s have speaker cloths and the 90As have metal mesh grilles.
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Old 13th Mar 2018, 1:19 am   #3
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Default Re: Bush DAC 90 and DAC 90A

And 90s will likely have a well fried upper right back panel from the dropper heat!
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Old 13th Mar 2018, 1:37 am   #4
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Default Re: Bush DAC 90 and DAC 90A

A third difference that's easy to spot is the position of the wave-change knob on the side of the cabinet. In the DAC90 the knob is about mid way between the top and bottom of the cabinet side, in the DAC90A it is mounted lower near the bottom of the cabinet.

Sorry about the quality of the pictures but you get the idea.
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Old 13th Mar 2018, 1:57 am   #5
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Default Re: Bush DAC 90 and DAC 90A

Well, in the DAC90, the knob on the side is quite big, it's mounted midway down like you say, but it's the tuning knob! The wave change knob is on the FRONT.

The DAC90a has a small pointer knob on the side, this IS the wave change knob, the one on the front is the TUNING.

The DAC90 underneath has several small holes and two big holes, to adjust the trimmers while in the cabinet and to unscrew the knobs. The DAC90a just has the two big holes.

The DAC90a is an improvement, and just looks nicer as a chassis. And it does not get so stinking hot. However, the DAC90 does perform slightly better!
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Old 13th Mar 2018, 2:08 am   #6
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Default Re: Bush DAC 90 and DAC 90A

Sorry that was sloppy of me, the side knob on the 90 is tuning. The remarks about the position of the side knobs remains valid.
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Old 13th Mar 2018, 7:34 pm   #7
mark pirate
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Default Re: Bush DAC 90 and DAC 90A

Quote:
The DAC90a is an improvement, and just looks nicer as a chassis. And it does not get so stinking hot. However, the DAC90 does perform slightly better!
The DAC 90A is a much improved design, the tuning knob on the DAC 90 was on the side of the set, this caused problems when tuning, due to being next to the aerial. As you moved your hand away the set went slightly off tune
In the newer set the tuning knob was changed to the front, while the wavechange was fitted to the side.

Internally the newer model is much better to work on, the nasty asbestos lined dropper box was no longer required with the new rimlock valves, less power to lose via the much smaller dropper. At last the back panel was no longer likely to catch fire!

Mark
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Old 13th Mar 2018, 8:00 pm   #8
60 oldjohn
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Default Re: Bush DAC 90 and DAC 90A

Also if it's black in colour it's a DAC90, also in brown and cream. The DAC90A was only made in brown and cream and possibly a few after market colours out there.


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Old 13th Mar 2018, 8:40 pm   #9
60 oldjohn
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Default Re: Bush DAC 90 and DAC 90A

I thought I would include a few photos, not that you need them after all that explaining. The last photo is my everyday set which in that position a DAC90 would not last very long but this is essentially an AC90, the dropper was binned and replaced with an autotransformer. After a couple of hours the top of the set is warm, not hot. Also the tuning knob was changed for the later style because they were too slippery as were the front knobs.


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Old 14th Mar 2018, 12:36 am   #10
kalee20
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Default Re: Bush DAC 90 and DAC 90A

Quote:
Originally Posted by 60 oldjohn View Post
Also the tuning knob was changed for the later style because they were too slippery as were the front knobs.
I can vouch for that - the plain, smooth, tapered knob of the DAC90 is not user-friendly at all!

The DAC90a look almost the same, but they are slightly deeper and are ridged. Much better. Later DAC90a's had a different style again...
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Old 14th Mar 2018, 12:54 am   #11
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Default Re: Bush DAC 90 and DAC 90A

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Originally Posted by kalee20 View Post
I can vouch for that - the plain, smooth, tapered knob of the DAC90 is not user-friendly at all!

The DAC90a look almost the same, but they are slightly deeper and are ridged.
Smooth knobs were abandoned fairly quickly - I think most of the DAC90s I've seen have the ridged knobs familiar from early 90As.

Quote:
Originally Posted by kalee20 View Post
Later DAC90a's had a different style again...
Two, in fact. Mid period DAC90As have very chunky, deep, solid knobs: late ones a much shallower knob but with a perspex disc at the back of it.

The 90A does get hot enough that by now the majority of cream sets have at least the beginnings of a crack on top caused by heat stress: standard walnut bakelite isn't so vulnerable to heat, and I've yet to meet a walnut set with a crack unless from impact. Whether because of the fragility of cream cases or just for economy, a very few late cream 90As were factory painted cream over ordinary bakelite. I took pity on one at the local flea market that was peeling badly, stripped off the remaining paint and decided to leave it as it then was, in a milk chocolate colour much paler than the usual brown.

Paul

Last edited by Paul_RK; 14th Mar 2018 at 1:02 am.
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Old 14th Mar 2018, 3:04 pm   #12
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Default Re: Bush DAC 90 and DAC 90A

My black DAC90 must be quite an early one, date inside reads August 1947.

Cream dial, says 'Aircraft' on the far left of the dial, smooth knobs, yep, not great for slippery fingers, oh & you have to tune just past the station you would like to listen to, so when you move your hand away, you receive the station you're really interested in

All good fun, except the hole, you know, at the rear, top right

I prefer the sound of a standard DAC90 to the sound of a standard DAC90A.

Unless you follow Kalee20's modification, in which case, the latter sounds fuller.

Once you spot the differences, you can't help but spot the inaccuracies of various TV dramas when they use a DAC90A when really, it should be a DAC90 ... still amazingly popular sets ...

Mark
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Old 14th Mar 2018, 6:24 pm   #13
60 oldjohn
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Default Re: Bush DAC 90 and DAC 90A

I briefly mentioned that my DAC90 has been converted to an AC90. I took out the asbestos lined mains dropper and replaced it with an auto tx as shown at the bottom of the manufacturers DAC90 sheet. This enabled me to use a 6v bulb from its own tapping, greatly reduced heat, and no chance of it giving you asbestosis. I cut out the burnt area of the back and made a "patch" from a back with the same type of back. The TX was made by Ed Dinning same TX has tappings for use in the DAC90A gets around the hard to find bulbs plus other benefits.


John.
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Old 18th Mar 2018, 5:27 pm   #14
bill knox
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Default Re: Bush DAC 90 and DAC 90A

Hi

Thanks everyone for the "familiarisation" between the 2 versions, I now know what to look for.

Many thanks

Bill
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