Another DAC 90 - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Mike. Watterson · 13th Apr 2019, 11:59 am

https://www.vintage-radio.net/forum/...ad.php?t=97053
Ed writes "Some sets have the holes to mount the auto TX under the dropper"

tim.norris · 13th Apr 2019, 1:57 pm

I fitted a capacitive dropper to a Dac 90 in the same place as the original dropper after removing the asbestos . Suppose i could have painted it green to match ! works well and runs cool . Regards. Tim.

60 oldjohn · 13th Apr 2019, 3:05 pm

The two TX mounting holes are visible when the Dropper is removed. The TX is fitted on top of the chassis in place of the Dropper. You also use a 6.3v MES bulb instead of the original hard to find ones. The TX is only around 50mm square, it is an auto TX so the set is still has a Live chassis. This is an original Bush circuit.

John.

DangerMan · 13th Apr 2019, 4:16 pm

I found an original Bush auto transformer at a Radiophile do many years ago. Here it is fitted into a DAC90 whose dropper was completely missing when bought.
Not the best photo in the world I'm afraid, but shows how straightforward the modification is. All holes were already present in the chassis.

Pete

Glowing Bits! · 13th Apr 2019, 10:40 pm

Here's some pics of Ed's tranny, one of the mounts had to have a piece hacked off it to clear the valve holder, it works very well.
Rick.

Davewantsone · 14th Apr 2019, 10:34 am

An auto Tx if the winding goes O/C it puts the full mains across the set.
If a capacitor goes O/C it puts no voltage across the set.
If a capacitor goes S/C it blows the mains fuse.
If a auto Tx goes S/C it may blow the fuse but would tend to blow the winding and put full mains across the set.
So you pay your money and take your choice. I prefer the radio to look original.
I know someone who says he has a Bush Dac set. If you look inside its a transistor radio! The variable tuning capacitor plus the loud speaker are the only original parts still being used!

Paul JD · 14th Apr 2019, 10:59 am

Quote:

Originally Posted by Sideband

Even X capacitors can be used as they are designed to fail O/C.

Not correct. Y class capacitors are designed to fail open circuit, X class are not.

kalee20 · 14th Apr 2019, 12:09 pm

Quote:

Originally Posted by Davewantsone

An auto Tx if the winding goes O/C it puts the full mains across the set.

Unlikely in my opinion - if the "top" bit of winding went O/C, there would be no power to the heaters. If the "bottom" bit of winding went O/C then the "top" bit would still be in circuit and act as a high-inductance choke, so the heaters would see very little current. As an iron-cored thing it may saturate with the higher-than-normal voltage across this portion of the winding, but the heaters would still be under-run rather than over.

coopzone · 16th Apr 2019, 2:10 pm

Hello again,

In the end i ordered a 3uf motor run capacitor from RS. Picture attached of it fitted. It works a treat the current through the heaters is 197ma.

I ended up using a 200ohm 25watt resistor (as shown) and a 3uf 440v AC capacitor with a 100k 1watt resistor in parallel with it.

The resister acts as a surge limiter and drops the voltage to around 210vac for the rectifier and eventually the HT supply rail.

Derek

13th Apr 2019, 11:59 am	#21
Mike. Watterson Heptode Join Date: Dec 2014 Location: Limerick, Ireland. Posts: 901	Re: Another DAC 90 https://www.vintage-radio.net/forum/...ad.php?t=97053 Ed writes "Some sets have the holes to mount the auto TX under the dropper"

13th Apr 2019, 1:57 pm	#22
tim.norris Hexode Join Date: Feb 2012 Location: Blackburn, Lancashire, UK. Posts: 282	Re: Another DAC 90 I fitted a capacitive dropper to a Dac 90 in the same place as the original dropper after removing the asbestos . Suppose i could have painted it green to match ! works well and runs cool . Regards. Tim. Attached Thumbnails

13th Apr 2019, 3:05 pm	#23
60 oldjohn Dekatron Join Date: Dec 2004 Location: East Yorkshire, UK. Posts: 3,988	Re: Another DAC 90 The two TX mounting holes are visible when the Dropper is removed. The TX is fitted on top of the chassis in place of the Dropper. You also use a 6.3v MES bulb instead of the original hard to find ones. The TX is only around 50mm square, it is an auto TX so the set is still has a Live chassis. This is an original Bush circuit. John. Last edited by 60 oldjohn; 13th Apr 2019 at 3:11 pm.

13th Apr 2019, 4:16 pm	#24
DangerMan Heptode Join Date: Jul 2009 Location: Stoke-on-Trent, Staffordshire, UK. Posts: 719	Re: Another DAC 90 I found an original Bush auto transformer at a Radiophile do many years ago. Here it is fitted into a DAC90 whose dropper was completely missing when bought. Not the best photo in the world I'm afraid, but shows how straightforward the modification is. All holes were already present in the chassis. Pete Attached Thumbnails

13th Apr 2019, 10:40 pm	#25
Glowing Bits! Octode Join Date: Oct 2011 Location: Wrexham, North Wales, UK. Posts: 1,457	Re: Another DAC 90 Here's some pics of Ed's tranny, one of the mounts had to have a piece hacked off it to clear the valve holder, it works very well. Rick. Attached Thumbnails __________________ Rick, the annoying object roaming the forum.

14th Apr 2019, 10:34 am	#26
Davewantsone Hexode Join Date: Dec 2011 Location: Wigan, Greater Manchester, UK. Posts: 291	Re: Another DAC 90 An auto Tx if the winding goes O/C it puts the full mains across the set. If a capacitor goes O/C it puts no voltage across the set. If a capacitor goes S/C it blows the mains fuse. If a auto Tx goes S/C it may blow the fuse but would tend to blow the winding and put full mains across the set. So you pay your money and take your choice. I prefer the radio to look original. I know someone who says he has a Bush Dac set. If you look inside its a transistor radio! The variable tuning capacitor plus the loud speaker are the only original parts still being used!

16th Apr 2019, 2:10 pm	#29
coopzone Hexode Join Date: Jan 2018 Location: Cannock, Staffordshire, UK. Posts: 268	Re: Another DAC 90 Hello again, In the end i ordered a 3uf motor run capacitor from RS. Picture attached of it fitted. It works a treat the current through the heaters is 197ma. I ended up using a 200ohm 25watt resistor (as shown) and a 3uf 440v AC capacitor with a 100k 1watt resistor in parallel with it. The resister acts as a surge limiter and drops the voltage to around 210vac for the rectifier and eventually the HT supply rail. Derek Attached Thumbnails