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Success Stories If you have successfully repaired or restored a piece of equipment, why not write up what you did and post details here. Particularly if it was interesting, unusual or challenging. PLEASE DO NOT POST REQUESTS FOR HELP HERE! |
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26th Jul 2008, 6:23 pm | #21 |
Heptode
Join Date: Apr 2003
Location: Newton Abbot, Devon, UK.
Posts: 761
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Re: Mid 1950s Bush DAC90A AC/DC 5 valve MW/LW radio
Hi Howard,
I've encountered a DAC90A do this, and never did get to the bottom of it. My current one doesn't have this happen, though it had to be extensively restored (all new caps, new set of valves, new speaker and output transformer, several new resistors, conversion to UL84) - it does sound good though, but I probably spent more on parts than on the set itself Another thought, have you cleaned the valve pins / holders? I've known this range to suffer with the pins becoming tarnished. Wire wool is useful to clean the pins, and a spray of contact cleaner and tightening any loose sockets with a fine screwdriver works well. I seem to recall someone else mentioning a crackling DAC90A being due to an bad contact in the mains dropper, causing a tiny arc? No definitive answer I'm afraid, but maybe some food for thought? Best regards, Colin |
27th Jul 2008, 10:57 am | #22 | |||
Nonode
Join Date: May 2005
Location: Godalming, Surrey, UK.
Posts: 2,593
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Re: Mid 1950s Bush DAC90A AC/DC 5 valve MW/LW radio
Quote:
That was done and the investigation was then concentrated around the audio stage. Quote:
One of the first things I do when I acquire a set is to take out all the valves and clean pins and bases. The bases in this set are in excellent condition. I replaced the wiring to the dropper but I rechecked the contacts and all is well. Quote:
A worn output transformer is the most likely cause of the crackling. I may well try and find a replacement and swap it to see if that sorts it out. It doesn't spoil the sound quality at normal volume but it's worrying that any day it might just expire. Howard |
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27th Jul 2008, 6:18 pm | #23 |
Dekatron
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
Posts: 7,580
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Re: Mid 1950s Bush DAC90A AC/DC 5 valve MW/LW radio
Howard. You may get some idea of the condition of the transformer by measuring the primary resistance. I found that mine varied from over 1K to 700 ohm. It should be about 600-700 ohms. Yesterday I stripped the transformer...not with the intention of rewinding it. I got down to the tenth layer before I found the break in the primary then found two. It didn't appear to be green-spot...wouldn't have expected it that deep into the transformer anyway so it was probably just wire failure due to excess current.
Rich.
__________________
There are lots of brilliant keyboard players and then there is Rick Wakeman..... |
2nd Aug 2008, 6:32 pm | #24 |
Nonode
Join Date: May 2005
Location: Godalming, Surrey, UK.
Posts: 2,593
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Re: Mid 1950s Bush DAC90A AC/DC 5 valve MW/LW radio
Hello Richard,
I've checked the output transformer. After the set had been idle for a couple of days the primary resistance was found to be 15k ohms (sic) and even higher the next day. I ran the set for a few minutes, switched off and retested it and it was then 1200 ohms. The Avo meter is still attached and the resistance is slowly climbing back up again. Methinks I need a new output transformer ! Howard |
2nd Aug 2008, 11:05 pm | #25 |
Dekatron
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
Posts: 7,580
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Re: Mid 1950s Bush DAC90A AC/DC 5 valve MW/LW radio
That's your problem then . I suggest you either contact Ed Dinning and see if he has any of his replacements available or see if Past Times Radio have any. I got my last one from there (I think the Bush AC11 uses the same transformer).
Ed supplies a complete new core and winding that fits the original clamp (although it's very tight and you will need a vice). Rich.
__________________
There are lots of brilliant keyboard players and then there is Rick Wakeman..... |
8th Aug 2008, 3:47 pm | #26 |
Nonode
Join Date: May 2005
Location: Godalming, Surrey, UK.
Posts: 2,593
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Re: Mid 1950s Bush DAC90A AC/DC 5 valve MW/LW radio
Hello again,
I managed to get another original DAC90A output transformer for under £5. The primary resistance on this one measured 602 ohms which is considerably better than the original one. It wasn't too difficult to swap it over in my DAC90A, the fiddliest bit was re-fitting the two bolts which hold the transformer in place, but fortunately I had a socket which fitted the nut. Crackling is all gone now, so I now declare this DAC90A restoration a success. Now to find a white DAC90A .......... Howard |
14th Aug 2008, 6:57 pm | #27 |
Retired Dormant Member
Join Date: May 2008
Location: Bath, Somerset, UK.
Posts: 37
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Re: Mid 1950s Bush DAC90A AC/DC 5 valve MW/LW radio
Hi Howard, brilliant restoration! The Bush DAC90A, as well as being a fantastic-looking radio, was what started my interest in old stuff! Before I saw one, I didn't think much of "retro" items. It was in 1998, when I was five years old, when I saw one in a shop by the sea, which sold mainly books. However there was one shelf which had old radios and record players on it, with a rather dusty DAC90A in one corner. I absolutely loved it, but as it was priced a £110, I couldn't afford it with my £2 pocket money.
That radio inspired me to buy a 1940s HMV set in a newspaper ad, thus starting my vintage radio collection. I went to the same shop the next year, and while all the other radios had gone, the DAC90A was still there, now £85. I still couldn't afford it. I somehow wound up at that shop at least once every year, each time it was still there, but at a slightly lower price. Every single time I didn't have enough money. Fast forward to today, about five hours ago. I went to the shop again. The Bush was still there, now looking rather tatty, priced at £45. I asked if it worked, and apparently it did when the owner first got it. I knocked him down to £35, and finally bought it! I've no idea if it works yet, there's no lead on it. Apparently it's from 1957 and the serial number is 73/182410. Here's a picture of it just after I bought it. |
14th Aug 2008, 7:01 pm | #28 | |
Dekatron
Join Date: Jan 2005
Location: Oxford, UK.
Posts: 17,866
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Re: Mid 1950s Bush DAC90A AC/DC 5 valve MW/LW radio
Quote:
I'm glad the vendor didn't insist on plugging it in. N. |
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14th Aug 2008, 9:00 pm | #29 |
Dekatron
Join Date: Feb 2005
Location: West Cumbria (CA13), UK
Posts: 6,130
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Re: Mid 1950s Bush DAC90A AC/DC 5 valve MW/LW radio
As Nick implies above, just plugging it in without a thorough check out first could have spelt disaster for it.
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Mending is better than Ending (cf Brave New World by Aldous Huxley) |
14th Aug 2008, 9:53 pm | #30 |
Retired Dormant Member
Join Date: May 2008
Location: Bath, Somerset, UK.
Posts: 37
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Re: Mid 1950s Bush DAC90A AC/DC 5 valve MW/LW radio
And that's precisely why I fished out the multimeter and the variac! It's been working fine for about an hour now. It has a great sound, I think the muffling is just part of its charm!
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