Grandma's DAC90A - UK Vintage Radio Repair and Restoration Discussion Forum

idlesteve · 28th Nov 2014, 4:41 pm

I now have all the parts for the restoration of my late Grandmothers Dac90a.
All went very well and I enjoyed every minute.

It was found in my late Uncle's garage about 15 years ago in a bit of a state. I placed it in the airing cupboard for a week and cleaned up the chassis, plugged it in and stood back. Nothing at all other than a slight buzz.
I managed to get a service sheet from the local library (not much on the net then) and found 2 valves in the wrong slots! Swapped them round and it then worked fine (other than the speaker) which got thrown away not realizing that it could be fixed. Luckily a friend who never throws anything away had a similar unit which was OK.

I used it for a few months until the mains capacitor could take no more and exploded

(I now know they should all be replaced) it then went back into the loft until the other week. I was up there looking for something (I always forget what I went up for and end up coming down with something else) and come down with the Bush.

I had to restore it when my Mother saw it, she remembers Grandma buying it new and sitting with her Sister listening to it.

The wax capacitors were replaced first making sure all the remaining parts of the existing legs were removed from the tags, most were way out when checked with the meter.
The resistors were not that far out so I left them alone for the time being.

The shafts were lubricated, a drop of grease on the variable capacitor bearings and pointer slide.

The illumination bulbs are original but I like the characteristic of the dim display.

The dual 32-16uf capacitor reads 45-20uf but I decided to leave as it and see what happens.

Power was connected and turned on, after a few moments the set come on and sounded OK but with a lot of interference, however once the LED GU10's were turned off above my head all was well.

The sound is good with practically no hum (it has at some point had the pin 4 UL41 mod) and I spent a good few hours listening to Pulse 2 (or Pulse for old people as my Son says) all appears well but seems to lack a little bass, or is this normal?

I am very pleased with radio and now and is going to be Mum's Christmas present.

I did buy another one for spares but it is too good to break. I can see another restoration coming, looks like I have got the bug.

Nickthedentist · 28th Nov 2014, 4:56 pm

Well done! Make sure you put a low-current fuse in the mains plug (3A, or even 2A or 1A if you can find them) and ensure that the N connection (as opposed to the L) is connected to the chassis - do check with a meter set to its lowest ohms range with the set switched on but unplugged from the mains.

Lacking in bass? That's odd, normally the complaint is lacking in treble. Maybe the substitute speaker isn't quite right. Worth trying the one from your other set.

A lovely Christmas present, I hope it's appreciated.

And yes, they are addictive. They're my favourite non-VHF set, and I have at least 4.

Nick.

28th Nov 2014, 5:07 pm

Great, another one unbites the dust! In fact I am using mine now to listen to a Paul Temple drama from CD via a modulator (aka pantry transmitter). 1950's radio on a 1950's radio, perfect.

Quote:

I can see another restoration coming, looks like I have got the bug

Oh good, make them look nice and the "other half" won't mind that much.

idlesteve · 28th Nov 2014, 5:23 pm

Quote:

Originally Posted by Nickthedentist

Well done! Make sure you put a low-current fuse in the mains plug (3A, or even 2A or 1A if you can find them) and ensure that the N connection (as opposed to the L) is connected to the chassis - do check with a meter set to its lowest ohms range with the set switched on but unplugged from the mains.

The first thing I checked was the polarity just to be safe.
I think I will hard wire it as it is going to Mum and keep the Bush connector for my other radio.
I have actually got a 20mm 630ma fuse in the plug top at the moment (they fit snug if you close the contacts up) for testing purposes. I was going to fit one internally on a chassis mount fuse holder.
The speaker I have in now is an original one from the spare set. I will wait until the other one is up and running and compare the difference.

Hybrid tellies · 28th Nov 2014, 5:32 pm

Great write up. Great looking and iconic radio will probably now give you years of untroubled service

paulsherwin · 28th Nov 2014, 5:43 pm

You should use a proper BS1363 fuse in the plug top as these are designed to fail in a particular way (basically, not to explode when they blow). A bog standard 3A fuse will be fine, but as Nick says a 1A or 2A fuse will give a bit more protection if you have one available. The important thing is not to put a 13A fuse in there.

28th Nov 2014, 6:05 pm

Paraphrasing what Paul said, the plug top fuse is to protect the flex and has a very high rupturing current capability, i.e. it can blow safely in a very high current circuit (lesser fuses ionize inside and even when blown can pass a lot of current). Glass 20mm type fuses are fine inside equipment for circuit protection. It think the BS1363 fuse does this by being full of sand cooling down any ionizable gasses in short order.

Nickthedentist · 28th Nov 2014, 7:40 pm

Quote:

Originally Posted by paulsherwin

You should use a proper BS1363 fuse in the plug top as these are designed to fail in a particular way (basically, not to explode when they blow). A bog standard 3A fuse will be fine, but as Nick says a 1A or 2A fuse will give a bit more protection if you have one available. The important thing is not to put a 13A fuse in there.

Yes, the 20mm-fuse-in-the-plug trick is well known, but definitely not recommended.

1A fuses to BS1362 aren't impossible to find, e.g. http://www.ebay.co.uk/itm/10-x-1a-AM...item2c62697855

idlesteve · 28th Nov 2014, 7:59 pm

Quote:

Originally Posted by Nickthedentist

Yes, the 20mm-fuse-in-the-plug trick is well known, but definitely not recommended.

The fuse was put there just for testing purposes until I was happy with the set. It now has a BS 1A fitted.
I have a good stock of 1,2,3,5, and 13A BS fuses, I think I have some old 10A ones as well.

Nickthedentist · 28th Nov 2014, 8:43 pm

Good for you, you sound like you know what you're up to

emeritus · 28th Nov 2014, 9:52 pm

When I got one of these going for a friend some years ago (it turned out to be a duff valve that stopped working when it warmed up), the capacitor across the mains failed spectacularly as well. I wondered if this capacitor was provided to deal with brush ripple that I understand could be present on some DC mains? I did fit a suitably-rated replacement capacitor eventually, but it worked just as well with no capacitor present, with no noticeable hum even with the volume turned up to listen to medium wave continental stations in the daytime.

idlesteve · 29th Nov 2014, 10:54 am

Here are some photos of the radio.
(I attached some to the first post but for some reason didn't appear).

Nickthedentist · 29th Nov 2014, 11:03 am

That really does look very smart indeed - a very good job!

Note that the little cap mounted off the tagstrip to chassis (top left of your second photo) can be reduced in value considerably to give a less muffled sound.

BTW, is the red wire coming off the dropper suitably insulated to withstand the high temperatures? Normal PVC probably isn't up to the job, whereas heat-resistant stuff robbed from a scrapped electric cooker would be.

And is your new LS of the correct profile so that it doesn't contact the chassis? A lot of similar-looking Celestions have different basket profiles. It's all too easy for the grille to be connected to chassis if things aren't right here.

Nick.

idlesteve · 29th Nov 2014, 11:40 am

I replaced the cap with a 0.001uf as recommended in the posts that I read (strangely enough the original had gone to that very value).

The cable replaced is high temperature silicone, seemed OK with the match test!

The speaker is from the spare set and I think it is the original, the clearance is fine but I see how the wrong speaker can be lethal.

Here is a picture of the speaker (with a few repairs) that was fitted before, I have no Idea of the make.

Steve.

Tim · 3rd Jun 2015, 1:08 pm

Quote:

BTW, is the red wire coming off the dropper suitably insulated to withstand the high temperatures? Normal PVC probably isn't up to the job, whereas heat-resistant stuff robbed from a scrapped electric cooker would be.

Am I right in thinking one doesn't actually need that wire for the set to work? The voltage selector on this set simply shorts out relevant sections of the dropper. With the wire removed it is simply permanently set to 250 volts.

gary_crutchley · 3rd Jun 2015, 11:32 pm

Hi Steve,

I have a DAC90a, which I think is about the same age as yours. I love it, and use it almost daily. History, art and currently functionality in one box!

I think it's great that you have restored your Grandma's radio, I bet she would be very impressed indeed. It's amazing that these radios were made sixty odd years ago, and yet if you change a few components they just go on working. Something tells me that my iPhone won't match that longevity!

You've done a fabulous job with the set, I bet it is really special to your Mum. Well done.

Regards,

Gary

Skywave · 4th Jun 2015, 12:37 am

Quote:

Originally Posted by idlesteve

The speaker is from the spare set and I think it is the original. The clearance is fine - but I fail to see how the wrong speaker can be lethal.
Steve.

Just by chance, I've spent most of today overhauling a DAC90A myself. Radios like the DAC90A are not my usual line of interest, but when someone asks you to "have a look at it, please" - well, you kinda can't say no, can you? So having read this thread, I've written the following . . . .

I believe the reason for the lethality referred to above is that one 'side' of the incoming mains is connected (nearly) to chassis. If the metalwork for the 'speaker - and thus its expanded metal grille - can contact the chassis of the radio, then anyone touching that grille will receive a shock,

if the mains plug has been inserted the 'wrong way round'.

Al. / June 4, '15 //

ThePillenwerfer · 4th Jun 2015, 9:49 am

I've checked this before and the metal grill is isolated from the metalwork of the speaker.

- Joe

Billy T · 27th Jun 2015, 12:24 am

Quote:

I believe the reason for the lethality referred to above is that one 'side' of the incoming mains is connected (nearly) to chassis. If the metalwork for the 'speaker - and thus its expanded metal grille - can contact the chassis of the radio, then anyone touching that grille will receive a shock if the mains plug has been inserted the 'wrong way round'.

I am curious as to why 'originality' should be preferred and permitted to override safety, when a standard IEC 3-pin chassis socket could be installed and the old two-pin plug on the power lead replaced with the matching IEC plug, or the male pins disconnected and a hard-wired supply conductor installed.

It is all very well for the knowledgeable persons who frequent this Forum to maintain 'originality' but radios change hands over the years and the unwary could be caught out.

From my reading of many posts on this forum there seems to be a virtual paranoia over safety in the UK and EU, even for risks that are statistically miniscule. I am not opposed to safety legislation or testing requirements, but compared to the enormous number of domestic appliances (in various states of repair), and the likelihood of 'repairs' carried out by unauthorised persons, the vintage radio brigade would represent a minscule risk.

I have been involved in both Electrical and Electronic education, and held Office in Electrical Regulatory matters for some years, and found without exception that Education trumps Regulation hands down.

Cheers

Billy

paulsherwin · 27th Jun 2015, 1:13 am

If someone is restoring a radio for their own use, then they can do pretty much whatever they want with it. If they kill themselves as a result then that's their lookout.

It gets a lot more complex if the radio is passed on to others, even for free.

Firstly UK legislation introduced over 20 years ago strengthens consequential liability, so if you pass a radio on to someone else and they injure themselves then they may be able to sue you for damages. This was well intentioned legislation intended to prevent unscrupulous secondhand dealers selling dangerous appliances to unsuspecting customers, but it has had lots of unintended consequences.

Secondly, appliance safety testing rules apply at the time an appliance is manufactured or modified. If you add an IEC socket to a DAC90 to improve safety, then the rules current in 2015 apply, not those current in 1947.

This is off topic for the thread though.

28th Nov 2014, 4:41 pm	#1
idlesteve Diode Join Date: Nov 2014 Location: Bradford, West Yorkshire, UK. Posts: 8	Grandma's DAC90A I now have all the parts for the restoration of my late Grandmothers Dac90a. All went very well and I enjoyed every minute. It was found in my late Uncle's garage about 15 years ago in a bit of a state. I placed it in the airing cupboard for a week and cleaned up the chassis, plugged it in and stood back. Nothing at all other than a slight buzz. I managed to get a service sheet from the local library (not much on the net then) and found 2 valves in the wrong slots! Swapped them round and it then worked fine (other than the speaker) which got thrown away not realizing that it could be fixed. Luckily a friend who never throws anything away had a similar unit which was OK. I used it for a few months until the mains capacitor could take no more and exploded (I now know they should all be replaced) it then went back into the loft until the other week. I was up there looking for something (I always forget what I went up for and end up coming down with something else) and come down with the Bush. I had to restore it when my Mother saw it, she remembers Grandma buying it new and sitting with her Sister listening to it. The wax capacitors were replaced first making sure all the remaining parts of the existing legs were removed from the tags, most were way out when checked with the meter. The resistors were not that far out so I left them alone for the time being. The shafts were lubricated, a drop of grease on the variable capacitor bearings and pointer slide. The illumination bulbs are original but I like the characteristic of the dim display. The dual 32-16uf capacitor reads 45-20uf but I decided to leave as it and see what happens. Power was connected and turned on, after a few moments the set come on and sounded OK but with a lot of interference, however once the LED GU10's were turned off above my head all was well. The sound is good with practically no hum (it has at some point had the pin 4 UL41 mod) and I spent a good few hours listening to Pulse 2 (or Pulse for old people as my Son says) all appears well but seems to lack a little bass, or is this normal? I am very pleased with radio and now and is going to be Mum's Christmas present. I did buy another one for spares but it is too good to break. I can see another restoration coming, looks like I have got the bug.

28th Nov 2014, 4:56 pm	#2
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,843	Re: Grandma's DAC90a Well done! Make sure you put a low-current fuse in the mains plug (3A, or even 2A or 1A if you can find them) and ensure that the N connection (as opposed to the L) is connected to the chassis - do check with a meter set to its lowest ohms range with the set switched on but unplugged from the mains. Lacking in bass? That's odd, normally the complaint is lacking in treble. Maybe the substitute speaker isn't quite right. Worth trying the one from your other set. A lovely Christmas present, I hope it's appreciated. And yes, they are addictive. They're my favourite non-VHF set, and I have at least 4. Nick. Last edited by Nickthedentist; 28th Nov 2014 at 5:01 pm.

28th Nov 2014, 5:32 pm	#5
Hybrid tellies Nonode Join Date: Jan 2004 Location: 1966-1976 Coverack in Cornwall and Helston Cornwall. 1976-present Bristol/Bath area. Posts: 2,965	Re: Grandma's DAC90a Great write up. Great looking and iconic radio will probably now give you years of untroubled service __________________ Simon BVWS member

28th Nov 2014, 5:43 pm	#6
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,936	Re: Grandma's DAC90A You should use a proper BS1363 fuse in the plug top as these are designed to fail in a particular way (basically, not to explode when they blow). A bog standard 3A fuse will be fine, but as Nick says a 1A or 2A fuse will give a bit more protection if you have one available. The important thing is not to put a 13A fuse in there.

28th Nov 2014, 6:05 pm	#7
Guest Guest Posts: n/a	Re: Grandma's DAC90A Paraphrasing what Paul said, the plug top fuse is to protect the flex and has a very high rupturing current capability, i.e. it can blow safely in a very high current circuit (lesser fuses ionize inside and even when blown can pass a lot of current). Glass 20mm type fuses are fine inside equipment for circuit protection. It think the BS1363 fuse does this by being full of sand cooling down any ionizable gasses in short order.

28th Nov 2014, 8:43 pm	#10
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,843	Re: Grandma's DAC90A Good for you, you sound like you know what you're up to

28th Nov 2014, 9:52 pm	#11
emeritus Dekatron Join Date: Jan 2012 Location: Brentwood, Essex, UK. Posts: 5,337	Re: Grandma's DAC90A When I got one of these going for a friend some years ago (it turned out to be a duff valve that stopped working when it warmed up), the capacitor across the mains failed spectacularly as well. I wondered if this capacitor was provided to deal with brush ripple that I understand could be present on some DC mains? I did fit a suitably-rated replacement capacitor eventually, but it worked just as well with no capacitor present, with no noticeable hum even with the volume turned up to listen to medium wave continental stations in the daytime.

29th Nov 2014, 10:54 am	#12
idlesteve Diode Join Date: Nov 2014 Location: Bradford, West Yorkshire, UK. Posts: 8	Re: Grandma's DAC90A Here are some photos of the radio. (I attached some to the first post but for some reason didn't appear). Attached Thumbnails

29th Nov 2014, 11:03 am	#13
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,843	Re: Grandma's DAC90A That really does look very smart indeed - a very good job! Note that the little cap mounted off the tagstrip to chassis (top left of your second photo) can be reduced in value considerably to give a less muffled sound. BTW, is the red wire coming off the dropper suitably insulated to withstand the high temperatures? Normal PVC probably isn't up to the job, whereas heat-resistant stuff robbed from a scrapped electric cooker would be. And is your new LS of the correct profile so that it doesn't contact the chassis? A lot of similar-looking Celestions have different basket profiles. It's all too easy for the grille to be connected to chassis if things aren't right here. Nick.

29th Nov 2014, 11:40 am	#14
idlesteve Diode Join Date: Nov 2014 Location: Bradford, West Yorkshire, UK. Posts: 8	Re: Grandma's DAC90A I replaced the cap with a 0.001uf as recommended in the posts that I read (strangely enough the original had gone to that very value). The cable replaced is high temperature silicone, seemed OK with the match test! The speaker is from the spare set and I think it is the original, the clearance is fine but I see how the wrong speaker can be lethal. Here is a picture of the speaker (with a few repairs) that was fitted before, I have no Idea of the make. Steve. Attached Thumbnails

3rd Jun 2015, 11:32 pm	#16
gary_crutchley Heptode Join Date: Apr 2013 Location: Bloxwich, West Midlands, UK Posts: 554	Re: Grandma's DAC90A Hi Steve, I have a DAC90a, which I think is about the same age as yours. I love it, and use it almost daily. History, art and currently functionality in one box! I think it's great that you have restored your Grandma's radio, I bet she would be very impressed indeed. It's amazing that these radios were made sixty odd years ago, and yet if you change a few components they just go on working. Something tells me that my iPhone won't match that longevity! You've done a fabulous job with the set, I bet it is really special to your Mum. Well done. Regards, Gary

4th Jun 2015, 9:49 am	#18
ThePillenwerfer Octode Join Date: Mar 2011 Location: Sheffield, South Yorkshire, UK. Posts: 1,453	Re: Grandma's DAC90A I've checked this before and the metal grill is isolated from the metalwork of the speaker. - Joe __________________ "Experts are only good at one thing: explaining why something will not work!"

27th Jun 2015, 1:13 am	#20
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,936	Re: Grandma's DAC90A If someone is restoring a radio for their own use, then they can do pretty much whatever they want with it. If they kill themselves as a result then that's their lookout. It gets a lot more complex if the radio is passed on to others, even for free. Firstly UK legislation introduced over 20 years ago strengthens consequential liability, so if you pass a radio on to someone else and they injure themselves then they may be able to sue you for damages. This was well intentioned legislation intended to prevent unscrupulous secondhand dealers selling dangerous appliances to unsuspecting customers, but it has had lots of unintended consequences. Secondly, appliance safety testing rules apply at the time an appliance is manufactured or modified. If you add an IEC socket to a DAC90 to improve safety, then the rules current in 2015 apply, not those current in 1947. This is off topic for the thread though.