Bush DAC90A dial lamps

[Skywave]

I have a Bush DAC90A on the bench which needs replacement dial bulbs: 3.5 v, 0.15 amp., MES. Unfortunately, these seem very difficult to find, and even if I could find some, I do recall that the illumination of the tuning dial is poor with these anyway. So, does anyone know of a modification whereby a more common type of bulb could be used and hopefully give better illumination of the tuning dial at the same time?

Thanks.

Al.

[Joe]

3.5V 200mA lamps are available and work fine.

If they are too dim for your liking you can up the shunt to 250Ω as this was the original value. Bush lowered it as it was found that if the set was switched off and on again quickly the current surge would blow the lamps.

- Joe

[Yorkie]

Ray at the 'Radio Workshops' in Worthing specialises in restoring and selling DAC90A radios for a living, and when restoring them, converts the dial lights to 6.3V by fitting a small transformer. That of course requires that the value of the shunt resistor needs to be changed or there is a risk that the valve heaters are over-driven. This mod ensures that not only are bulbs more widely available, the lights do what they're supposed to do - light up the dial.

The thing about the DAC90A dial lights (in the context of the DAC90A the term 'light' is something of an oxymoron), is that even if you can find the right bulbs, the dial is dimly lit. Some say that this is simply a characteristic quirk of the set, but really, what's the point of dial lights that aren't fit for purpose?

This link might be of interest:

http://www.radio-workshop.co.uk/bulbs.shtml

David.

[Joe]

The one on the right has lamps, the one on the left LEDs.

   

- Joe

[Tedzed1]

Quite cheap on here:

http://www.technologysupplies.co.uk/Bulb...mA-Pack-10

[Skywave]

The thing about the DAC90A dial lights (in the context of the DAC90A the term 'light' is something of an oxymoron), is that even if you can find the right bulbs, the dial is dimly lit. Some say that this is simply a characteristic quirk of the set, but really, what's the point of dial lights that aren't fit for purpose?

David.

Exactly, David: that was one of the significant points I raised in my initial post.

Just out of interest and fascination, etc., I did do some sums to see if a simple mod. could be done to fit 'standard' 6.3v 0.3 A bulbs. Of course, that doesn't work for two main reasons: (a) there is only 100 mA in the heater chain as it is and, alternatively, (b) fitting a shunt resistor to feed an extra 200 mA to the bulbs requires a dropper resistor that then dissipates a great deal of heat . . . and as we all know, it's the heat from the dropper (as fitted - and that heat being a lot less that that from the proposed dropper) that tends to cause discoloured cracks in the cabinet.

Interesting idea, though, about fitting a small mains transformer to power two 6.3 v. 0.3 A bulbs separately from the rest of the set: I assume that there is space on the chassis to fit it. I'll have to have a look in my transformer box to see if I have a suitable item: either a 6.3 v. or a 12 v. secondary winding one should do (assuming the current capacity is adequate - which, of course, is not a lot).

Anyway, I'm glad you brought this to my attention: thanks . . . but I wonder why I didn't think of that solution . . . perhaps because it is too damn obvious!

Al.

[Skywave]

Transformer mod. for dial lamps now fitted.

The donor transformer came from a plug-in 'wall wart': its label stated 14v. @ 400 mA. I wired it to two 6.3v 0.3 amp. bulbs connected in series and obtained 12v. across the pair. The transformer needed a clamping bracket so that the transformer could be secured to the chassis: that was easily accomplished by using a scrap piece of aluminium and simply cutting and bending it to the required size and shape. I managed to squeeze the transformer + clamp behind the IF valve and the two IFTs - as you can see in the photo. The resulting dial illumination is excellent - as can also be seen from the photo.

[attachment=8088] [attachment=8089]

With the removal of the old 3.15v. bulbs (which were O/C anyway), the dial bulbs shunt resistor of 75Ω was replaced by 27Ω to maintain the correct current of 100 mA through the heater chain.

Thank you, David, for bringing this mod. to my attention.

Al. / May 31st, 2013 //

[pwdrive]

Nice fix Al.

Lawrence.

[Yorkie]

Looks great Al.

A DAC90A with a lit-up dial - novel eh!

I've never quite grasped the mindset of those who say 'you'll devalue the set - it's not original any more' etc. The DAC90A isn't a Ming Dynasty vase - it must be about the most ubiquitous set there is, which is why so many people cut their teeth on them, and in any event, such mods can be removed, albeit it would be a retrograde step in my view. Ray at Worthing fits this mod and also removes the 2-pin plug on the rear apron and hard wires a new mains lead. It doesn't devalue his sets - last time I checked they were £90.00 each.

[Geaney]

Great fix. If I ever get one of these sets that is one mod I will definitely include.

I'm starting to think that restoring a DAC90A is a sort of rite of passage in this community so I'll keep my eyes out for one

Cheers,

John