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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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25th Sep 2009, 9:04 am | #1 |
Triode
Join Date: May 2009
Location: Bradford, West Yorkshire, UK.
Posts: 35
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DAC90A Volume problem
Can somebody help?
When I turn the Volume knob to minimum, you can still hear the radio. Is this possible to repair? Thanks |
25th Sep 2009, 9:14 am | #2 |
Retired Dormant Member
Join Date: Sep 2009
Posts: 487
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Re: DAC90A Volume problem
it`s quite possible the carbon track on the "horse shoe" in the pot has work thin at the Earth end, are there any crackles to be heard when you use the volume control?
the Wiper could be dirty, OR... the resistor that takes that end to deck may have gone high value. |
25th Sep 2009, 9:26 am | #3 |
Triode
Join Date: May 2009
Location: Bradford, West Yorkshire, UK.
Posts: 35
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Re: DAC90A Volume problem
can't hear any crackles.
As a novice, how do i check out the components you mentioned? |
25th Sep 2009, 9:27 am | #4 |
Octode
Join Date: Aug 2003
Location: Welwyn Garden City, Herts. UK.
Posts: 1,906
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Re: DAC90A Volume problem
This can be quite normal.
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25th Sep 2009, 9:50 am | #5 |
Nonode
Join Date: Jun 2004
Location: Norwich, Norfolk, UK.
Posts: 2,543
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Re: DAC90A Volume problem
Yes, leaving on a bit of audio when the volume control is 'turned off' is a good way to let you now that the set's been left on. It's particularly important with battery sets, but also useful with mains operated ones... However, I'm not sure this feature applies to a DAC90a
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25th Sep 2009, 10:49 am | #6 |
Retired Dormant Member
Join Date: Jan 2007
Location: Westbury, Wiltshire, UK.
Posts: 2,451
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Re: DAC90A Volume problem
I have eleven DAC90As and they all have a bit of volume at minimum.
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25th Sep 2009, 10:56 am | #7 |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,787
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Re: DAC90A Volume problem
A very low volume at minimum is normal. A bad UBC41 can cause this symptom too though.
Paul |
25th Sep 2009, 11:55 am | #8 |
Dekatron
Join Date: Sep 2003
Location: Bolton, Greater Manchester, UK.
Posts: 6,644
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Re: DAC90A Volume problem
I had this over two years ago with a DAC90A on here. Paul's right - UBC41. Might be OK in another radio though.
Cheers, Steve P.
__________________
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25th Sep 2009, 1:14 pm | #9 |
Dekatron
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,061
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Re: DAC90A Volume problem
Disconnect from the mains. With the volume control at minimum, but the switch definitely 'on', measure the resistance between the control's wiper tag and the outer tag (the one that's connected to the metal braiding on the wires).
Ther resistance should be a few ohms at most. If it's higher, then the control is worn out as post #2. If it is OK, then the problam is almost certainly leakage within the UBC41. However, it's a fault that is almost certainly liveable with! |
25th Sep 2009, 1:22 pm | #10 |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,787
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Re: DAC90A Volume problem
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25th Sep 2009, 7:14 pm | #11 | |
Triode
Join Date: May 2009
Location: Bradford, West Yorkshire, UK.
Posts: 35
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Re: DAC90A Volume problem
Quote:
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25th Sep 2009, 9:28 pm | #12 |
Nonode
Join Date: May 2005
Location: Godalming, Surrey, UK.
Posts: 2,593
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Re: DAC90A Volume problem
Hello,
This problem can be caused by either a worn volume potentiometer or a slightly leaky UBC41. I have three DAC90As, two late examples and an earlier mid 1950s one and only the latter exhibited this problem and that definitely had a worn pot and I fixed it by fitting a new 500k ohm log potentiometer and DP switch. I gather that one can fit a 330pf capacitor between the grid and cathode tags of the UBC41 to correct the problem if caused by the UBC41. Howard |