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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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22nd Oct 2019, 10:57 am | #21 |
Dekatron
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Re: Bush DAC90A - power but no sound
You're right. With no feedback it doesn't (or shouldn't) matter which way round you connect the transformer primary. As to how the transformer is mounted....not sure. Maybe it doesn't matter. All you can do is try it and see.
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22nd Oct 2019, 11:27 am | #22 |
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Re: Bush DAC90A - power but no sound
I mostly use an analog meter. This has a battery inside to measure resistance. This will give a click when connected across the speaker or transformer primary. Use the lowest range to get the most current.
If you do not have an analog meter then use a single cell or battery with a wire brushed over the battery terminal. A scratchy sound when the speaker isenergised shows the peaker is probably OK. If no sound is produced when the transformer primary is energised, then the transformer is faulty. I always measure DC voltages early on to find serious faults. You could do this if you connected a 1k 2W resistance in place of the transformer primary. As said before, do not run the set with no anode current, the current all goes to the screen which will object. |
22nd Oct 2019, 2:36 pm | #23 |
Octode
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Re: Bush DAC90A - power but no sound
My own DAC90A restoration Thread is here - see Post #9 from David G4EBT in particular : -
https://www.vintage-radio.net/forum/...d.php?t=146402 I also had an open circuit on the Primary of the Output Transformer - contact Ed Dinning on this Forum for a rewind or replacement. Please ensure you don't turn it back on without working your way through all the preliminary checks and essential replacements e.g. C18, the audio coupling capacitor. Make sure you obtain the Bush Service Instructions before proceeding.
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22nd Oct 2019, 3:08 pm | #24 | |
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Re: Bush DAC90A - power but no sound
Quote:
UL41's are becoming very expensive and hard to find so you certainly don't want a new one to be subjected to any kind of overload. Make sure you change C18 (audio coupling capacitor) as a priority as well as replacing the output transformer. Even with a new transformer, don't think of switching on the set without changing C18 at least. You should change all of the waxy paper caps at any rate but first things first, lets get the main problem sorted and go from there.
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22nd Oct 2019, 8:14 pm | #25 |
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Re: Bush DAC90A - power but no sound
Looking at the picture in post #7, C22 (0.1 uF) - the RF Bypass capacitor across the mains, is still in place and still intact. Before any live testing is carried out a wise precaution would be to snip the capacitor out or it will become very annoyed and will almost certainly go off with a nerve jangling bang. The set will function perfectly well without it, but if it's desired to replace it, the replacement should be a Class X capacitor specially designed to be across the mains.
Not easy to tell from the picture, but to my eyes, on what wiring I can see, the insulation looks brittle and crumbly. Replacement of the wiring with heat resistant silicone rubber insulated flex, including the speaker connection, dial bulbs wiring and around the voltage selector panel would be high on my list of priorities. These ubiquitous sets are now some 70 years old, so inevitably, have suffered the ravages of time. Do heed the warnings about removing and discarding the spring retaining clips from the valve-holders before pulling out any valves. The springs serve no useful purpose and if left in place pose a high risk of breaking the glass pips on the valves. Good luck in your endeavours.
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23rd Oct 2019, 10:31 am | #26 |
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Re: Bush DAC90A - power but no sound
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23rd Oct 2019, 11:07 am | #27 |
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Re: Bush DAC90A - power but no sound
There are no springs in the valve holders of the DAC90A I'm in the process of repairing. It's serial no. is 73/204886 by the way, if that helps to date it.
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23rd Oct 2019, 1:50 pm | #29 |
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Re: Bush DAC90A - power but no sound
Is it not so, that the springs on the valve bases were originally designed in to ruggedise the valve mounting when used in the stressful environment of car radios, which was one of the primary design applications for some of that series of valves?
Thus redundant in the currently discussed use. - Just another unfortunate trap for the inexperienced and unwary restorer. Tony |
23rd Oct 2019, 4:11 pm | #30 |
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Re: Bush DAC90A - power but no sound
Quite often the springs will have rusted and attached themselves to the skirt of the valveholder which means that as you try to pull out the valve the little locating pip on the side of the glass will shatter and the valve will be no longer any good. Removal of the spring ensures that it ought to be possible with care to safely pull the valve.
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23rd Oct 2019, 4:16 pm | #31 |
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Re: Bush DAC90A - power but no sound
The springs can serve a useful purpose when someone ships a set without first removing the valves and wrapping them in bubble wrap or W.H.Y..
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23rd Oct 2019, 7:17 pm | #32 |
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Re: Bush DAC90A - power but no sound
My DAC90A does not have removable springs, it has riveted skirts as illustrated.
My instinct was to release the tension from the pips using my thumb nail. Interesting that the UL41 and UY41 are valve bases are secured with nuts & bolts, rather than rivets. Only the rectifier is all glass.
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23rd Oct 2019, 7:47 pm | #33 |
Octode
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Re: Bush DAC90A - power but no sound
Here is a close up of mine before restoration and removal of the spring retaining clips: -
@rambo1152 - Not sure what you mean by "Only the rectifier is all glass" ?
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23rd Oct 2019, 8:00 pm | #34 |
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Re: Bush DAC90A - power but no sound
The UCH42, UF41, UY41 etc etc started off with metal rims and pips.
Here's a Philips article about them from 1946 describing the low temperature sealing technique used to seal the bulb to the base: https://www.dos4ever.com/EF50/PTT_ok..._large_eng.pdf Lawrence. Last edited by ms660; 23rd Oct 2019 at 8:14 pm. Reason: added link |
24th Oct 2019, 9:08 pm | #35 |
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Re: Bush DAC90A - power but no sound
I usually lift the spring out of the slot and rest it on the lower part of the Valve holder and then slide it back up into the slot when the Valve has been replaced.
Steve. |
25th Oct 2019, 9:04 pm | #36 |
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Re: Bush DAC90A - power but no sound
I hope 'Justamo' hasn't become disheartened with the radio or thinks it is beyond his ability.
I was eagerly awaiting the next installment.
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25th Oct 2019, 9:39 pm | #37 |
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Re: Bush DAC90A - power but no sound
I wouldn't worry too much about that, Sideband, as from his previous posts I think he just wants to get these radios going as cheaply and as easily as possible so that he can sell them on for a fast buck. I would suspect that a rewound or replacement transformer would work out more than the radio is worth and perhaps a bit of a lesson about the potential issues that can be encountered with these sets.
As a second point, I'm against removing original springs from valve bases in these radios. I've never yet broken the pip off a valve while removing one. Obviously it can happen if you're a bit 'ham-fisted', but if this is the case, then what I always say is that perhaps you shouldn't be working on vintage radios. You just have to release the spring carefully - I sometimes treat them with a very light oiling if they're a bit rusty. We shouldn't pander to peoples carelessness, either get used to handling these old components properly and with care or don't do it at all. Not having a go at anyone - just saying! |
26th Oct 2019, 8:23 am | #38 | |
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Re: Bush DAC90A - power but no sound
Quote:
I remove the spring since I had my 'mishap' and have had no further problems in doing so. I never really liked the rimlock method and glass pip and I wouldn't mind betting that many a good valve met an untimely end when being removed for test. I hope the DAC90A in question doesn't get scrapped.
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There are lots of brilliant keyboard players and then there is Rick Wakeman..... Last edited by Sideband; 26th Oct 2019 at 8:28 am. |
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