|
Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
|
Thread Tools |
31st Jul 2019, 11:42 pm | #1 |
Hexode
Join Date: Aug 2014
Location: Dartford, Kent, UK.
Posts: 435
|
DAC90A with a faulty volume control – no surprise!
I have a DAC90A with a faulty volume control – no surprise!
Replacements are getting much harder to find and more expensive to replace but I have one in my stock which only has a ¾ inch shaft, that is too short, and a 1¼ inch shaft is needed, – see enclosed picture 20190731_192809 One way of fixing this is to use a shaft coupler but most of these are typically ¾ inch long and will be very tight and not quite work with the lengths needed. Do you know of another way to overcome this problem or do you have, say, a ½ inch long ¼ inch shaft coupler and would this work without wobbling? Cheers John |
31st Jul 2019, 11:52 pm | #2 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,535
|
Re: DAC90A with a faulty volume control – no surprise!
Drill and tap pot shaft and extender M3 or similar then join with some studding and threadlock? Might need some careful shimming to get flat lined up.
__________________
....__________ ....|____||__|__\_____ .=.| _---\__|__|_---_|. .........O..Chris....O |
1st Aug 2019, 8:36 am | #3 |
Rest in Peace
Join Date: Mar 2006
Location: N.W. Oxfordshire(Chipping Norton)
Posts: 7,306
|
Re: DAC90A with a faulty volume control – no surprise!
Blore Edwards stock a wide range of pots, including those with metal shafts for those wishing to use them. I have just ordered a 470k Log Pot. with D.P. switch for a DAC90A from them. Admittedly total cost including postage & VAT is about £13, but if other items are ordered at the same time, the postage per item works out less. They currently have a sale in progress, with many items reduced (Usual disclaimer - I have no connection with the firm other than as a customer)
|
2nd Aug 2019, 8:40 am | #4 |
Hexode
Join Date: Aug 2014
Location: Dartford, Kent, UK.
Posts: 435
|
Re: DAC90A with a faulty volume control – no surprise!
I didn't know that you could still get new ones!
So the Blore Edwards solution is going to be the answer - just a shame they have such high postage rates for such a small item. Thanks for your help. John |
2nd Aug 2019, 9:40 am | #5 |
Dekatron
Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 5,761
|
Re: DAC90A with a faulty volume control – no surprise!
You can get 470K switched log pots from Bowood Electronics, but they'll be the modern style with a plastic control shaft and won't have a circular metal body as did the original pot. They cost £2.45 each, and £2.85 P&P. (No VAT is payable).
https://www.bowood-electronics.co.uk...switched-p-652 Bowood is a well established 'man and his wife firm' and sell a useful range of other items of interest, including 1 Meg switched log pots which are also not so easy to find nowadays. Back in the 1980s, Wilf used to work for Bardwells in Sheffield, who some forum members will recall. Hope that helps.
__________________
David. BVWS Member. G-QRP Club member 1339. |
2nd Aug 2019, 7:42 pm | #6 |
Rest in Peace
Join Date: Mar 2011
Location: Basildon, Essex, UK.
Posts: 4,100
|
Re: DAC90A with a faulty volume control – no surprise!
You can buy small bore brass and aluminium tube on ebay, this can be used to join an extension 1/4 inch shaft. Probably 8mm would be about right, but best to ask the internal diameter. Drill through the tube and shaft and pin.
Mike |
2nd Aug 2019, 9:26 pm | #7 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,998
|
Re: DAC90A with a faulty volume control – no surprise!
What about:
https://www.cricklewoodelectronics.com/MLG470K.html "Rotary Pot with DPST Mains Switch 470K Log" £3.50 +VAT. |
3rd Aug 2019, 8:36 am | #8 |
Hexode
Join Date: Mar 2012
Location: East Yorkshire, UK.
Posts: 354
|
Re: DAC90A with a faulty volume control – no surprise!
I tried one of the Cricklewood pots. They are quite small, the shaft is round (plastic) not the 'D' profile. Measures 5mm in diameter. The bush is smaller too. They should work OK but would need to be used with screw fixing knobs rather than push on types. Due to the smaller diameter shaft the control knob would be slightly eccentric if that makes sense. Good value though.
__________________
Howard |
3rd Aug 2019, 9:30 am | #9 |
Rest in Peace
Join Date: Mar 2011
Location: Basildon, Essex, UK.
Posts: 4,100
|
Re: DAC90A with a faulty volume control – no surprise!
I have never heard of a 5mm shaft, are you sure it was not 6mm. The DAC90A knobs have a locking screw which you access through a hole in the base of the cabinet. So I would file a small flat on the shaft, in the correct place, and fit the knob.
Mike |
3rd Aug 2019, 9:44 am | #10 |
Dekatron
Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 5,761
|
Re: DAC90A with a faulty volume control – no surprise!
Ordinarily, modern pot shafts are 6mm, older ones are 6.4mm (1/4").
__________________
David. BVWS Member. G-QRP Club member 1339. |
3rd Aug 2019, 9:57 am | #11 |
Hexode
Join Date: Mar 2012
Location: East Yorkshire, UK.
Posts: 354
|
Re: DAC90A with a faulty volume control – no surprise!
Apologies, the shaft is slightly tapered at the top which threw me, yes it would be 6mm
Some DAC 90's do have push on knobs though, the gold tuning scale ones which have the knobs with the clear plastic skirt.
__________________
Howard Last edited by Half a Mullard; 3rd Aug 2019 at 10:02 am. Reason: Brain not in gear |
11th Aug 2019, 6:20 pm | #12 |
Hexode
Join Date: Aug 2014
Location: Dartford, Kent, UK.
Posts: 435
|
Re: DAC90A with a faulty volume control – no surprise!
Thank you all for your help. I finally managed to get new replacements from Blore Edwards and fitted one but it did NOT cure the problem!!!!
With the volume turned to minimum I still get a reasonably loud signal from the speaker. The radio has had all of the capacitors replaced as part of the restoration. So I read the other messages about replacing the bypass IF capacitor, which I believe to be C13 100pf, and replaced it with exactly the same results. And before you ask - yes I have changed the UBC41 and checked the resistors. There is 0 ohms between the wiper and feed so I cannot figure out how audio is bleeding through - yet. The original pot also displayed exactly the same symptoms so I don't think that it is a POT shielding issue and the earthing strap is in place. Any practical ideas on this one? |
11th Aug 2019, 6:46 pm | #13 |
Dekatron
Join Date: Aug 2007
Location: W.Butterwick, near Doncaster UK.
Posts: 8,932
|
Re: DAC90A with a faulty volume control – no surprise!
There has to be something high resistance here,if not a res than a joint? Check R 6 and R9. C16
__________________
G8JET BVWS Archivist and Member V.M.A.R.S Last edited by HamishBoxer; 11th Aug 2019 at 6:51 pm. |
11th Aug 2019, 11:55 pm | #14 |
Dekatron
Join Date: May 2010
Location: Greater Manchester, UK.
Posts: 18,715
|
Re: DAC90A with a faulty volume control – no surprise!
That's not necessarily a symptom of a faulty pot. I would first suspect that the cathode resistor of V2 (UF41) has gone high. R6, 220ohm on the Bush sheet.
__________________
-- Graham. G3ZVT |
12th Aug 2019, 10:11 am | #15 |
Dekatron
Join Date: Aug 2007
Location: W.Butterwick, near Doncaster UK.
Posts: 8,932
|
Re: DAC90A with a faulty volume control – no surprise!
As I thought,see above.
__________________
G8JET BVWS Archivist and Member V.M.A.R.S |
12th Aug 2019, 10:16 am | #16 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
|
Re: DAC90A with a faulty volume control – no surprise!
The common cathode resistor is 330 Ohms according to what I'm looking at (Trader sheet)
Lawrence. Last edited by ms660; 12th Aug 2019 at 10:26 am. Reason: To avoid any confusion |
12th Aug 2019, 11:12 am | #17 |
Dekatron
Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 5,761
|
Re: DAC90A with a faulty volume control – no surprise!
It's also shown as 330 Ohms on the Bush data, where it's referred to as 'R8' (rather than 'R6' shown on Trader Sheet 1161).
__________________
David. BVWS Member. G-QRP Club member 1339. |
12th Aug 2019, 11:37 am | #18 | |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
|
Re: DAC90A with a faulty volume control – no surprise!
Quote:
In my original post I did mention R8 from the manufactures data (which I have a copy of au fait) but decided to edit and delete that bit so's to avoid any confusion. Hope that helps. Lawrence. |
|
12th Aug 2019, 1:23 pm | #19 |
Nonode
Join Date: Jun 2007
Location: Coulsdon, London, UK.
Posts: 2,163
|
Re: DAC90A with a faulty volume control – no surprise!
The metal case of the volume potentiometer is 'strapped' to the chassis.
However the anti-clockwise terminal of the potentiometer should not be connected to the chassis in this circuit. In this design it should be connected to the cathode of V3. |
12th Aug 2019, 1:28 pm | #20 |
Dekatron
Join Date: Aug 2007
Location: W.Butterwick, near Doncaster UK.
Posts: 8,932
|
Re: DAC90A with a faulty volume control – no surprise!
Strange I had R6 on my sheet, not sure which one.
__________________
G8JET BVWS Archivist and Member V.M.A.R.S |