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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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31st Jul 2010, 8:03 pm | #41 |
Octode
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Re: Bush BAC31 motorboating
There was continuity on all valve pins from the top of the pin to the end of the component leads connected to ensure any breakages would be picked up.
Finger on volume control brought in nothing. On the DL94 I had 1.2 volts and on other valves one had 0.9 v and another had a few millivolts. I then switched off due to my filament bypass bulging again... I have also noticed a small buzz from the mains transformer so I hope that's ok.... Josh (who is not liking this radio much anymore!) |
31st Jul 2010, 8:26 pm | #42 |
Dekatron
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Re: Bush BAC31 motorboating
Only just coming back on line. A week away and back to the physio...
The filament voltage these takes is 7.5v. There should be 2.8v on the DL94 and 1.4v on the others. Check the heater smoothing cap and the other one as well as the resistors in the area. On the Bush sheet these are C23. C22, R13, R14, R15 and R16. Make sure these are OK and also don't overdrive these valves at all. HT is 90v. Try it on batteries first before playing with the Power Supply. If the filament bypass is bulging or getting hot, then I would be inclined to suspect those capacitors listed above. On the Bush Power Unit, check those resistors and the wiring. Cheers, Steve P.
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31st Jul 2010, 10:08 pm | #43 |
Octode
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Re: Bush BAC31 motorboating
Hi Steve, Glad your back with us
Are those part numbers the same as on the Trader sheet? That's what I'm working off. Sadly I don't have enough batteries to make up the 90v and my eliminator is currently out of action..... Cheers, Josh. |
31st Jul 2010, 11:17 pm | #44 |
Dekatron
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Re: Bush BAC31 motorboating
OK having fitted a new DVD writer in the PC I can now run the DVD and look at the circuit!
For test purposes only I would fit a higher voltage rating capacitor for the filament smoothing C28. Use 100V or higher...it can be put back to the lower voltage when the fault has been found. At least this will enable you to carry out some voltage checks without getting covered in capacitor goo! OK chassis to point 8 (I'm using the Trader sheet), you should be measuring about 7 to 7.5 volts (may be a bit less if your reccy is low). If it's higher than this, then there must be an open circuit somewhere along the way. The voltage across C25 should not exceed 25V. If it does (I think you said about 50V) then it suggests and open-circuit on the lower end of R21. That could be wiring or perhaps S9(M) switch. As there is no load I would expect the HT to read high as well. SB
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1st Aug 2010, 8:35 am | #45 |
Nonode
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Re: Bush BAC31 motorboating
Here's the filament circuit from the manufacturers manual. which is a little clearer than the trader sheet.
Check the voltage on pin 7 of the DL94. This should be 6.5v according to the Bush service sheet. If its significantly lower check the 700ohm resistor of the PSU (R21 on the trader sheet). If it's significantly higher check the filaments and the connections on the valve holders. Keith |
1st Aug 2010, 6:44 pm | #46 |
Octode
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Re: Bush BAC31 motorboating
C28 has about 71 volts on the positive, no signs of heat or bulging yet though. It's a 50volt rated original capacitor.
I get 27vdc on Point 8 Pin 7 of DL94 measures 50vdc All filaments and valve holders have continuity. Looks as though it may be R21 then Josh. |
1st Aug 2010, 7:01 pm | #47 |
Heptode
Join Date: Jan 2004
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Re: Bush BAC31 motorboating
50V on pin 7 of the DL94 is not consistent with the filament string having continuity!
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1st Aug 2010, 7:26 pm | #48 |
Octode
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Re: Bush BAC31 motorboating
Everything tests ok though
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1st Aug 2010, 7:26 pm | #49 |
Nonode
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Re: Bush BAC31 motorboating
There looks to be a break in the filament chain
Check on each pin in the filament chain. At some point it will change from 50v to 0v. That's where the break is. I had a faulty pin on a valve holder in the filament chain on one of mine. Fortunately there are unused pins which can be used as replacements. Keith Just a thought is the PSU chassis bolted to the receiver chassis as the ground connection is made through the bolt. |
1st Aug 2010, 7:27 pm | #50 |
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Re: Bush BAC31 motorboating
Now that is worrying. With the set on, quickly measure pins 1 and 7 on ALL valves. This should point us in the right direction.
Cheers, Steve P.
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1st Aug 2010, 7:46 pm | #51 | |
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Re: Bush BAC31 motorboating
Quote:
SB
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1st Aug 2010, 7:50 pm | #52 |
Octode
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Re: Bush BAC31 motorboating
Yes it's screwed together. Will check valve filament voltages tomorrow.
Josh. |
2nd Aug 2010, 4:51 pm | #53 |
Octode
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Re: Bush BAC31 motorboating
OK, here goes:
V1- DK92 Pin 1: mV Pin 7:mV V2- 1T4 Pin 1: 46v Pin 7: 46v V3- 1S5 Pin 1: mv Pin 7: mV V4- DL94 Pin 1: 49v Pin 7: 49v |
2nd Aug 2010, 5:18 pm | #54 |
Dekatron
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Re: Bush BAC31 motorboating
I'm scared stiff of 50V anywhere in the filament system!
There must be a defective joint / bad valveholder contact / whatever. but if you see this voltage, and start wiggling things till the joint makes good, then your 50V-charged electrolytic capacitor will discharge through the valves. Goodbye one or more! Can you get a 10V Zener diode to tack across the filament supply to clamp the voltage, until you have found the fault? |
2nd Aug 2010, 5:56 pm | #55 | |
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Re: Bush BAC31 motorboating
Quote:
Best thing is to disconnect it from the mains, switch you meter to ohms and put one prod on the DL94 (think pin 7), leave this on pin 7 and work your way through the filaments...so measure pin 1 of DL94 next, then measure pin 1 of 1T4 ( leaving the other prod on pin 7 DL94), then pin 7 1T4, then pin 1 of 1S4, then pin 7 1S4 and finally pin one and then pin 7 of DK92. This way you measure each part of the filament chain in turn and somewhere you should find a break. Try it and come back. Whatever you do DO NOT try wiggling the valves in the hope of finding a loose connection....as Kalee said bye bye filaments! SB
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2nd Aug 2010, 6:57 pm | #56 |
Nonode
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Re: Bush BAC31 motorboating
It looks as if there is a break in the wiring between V2 & V3. If the filaments were open circuit there should still be some continuity because of the resistors across the filaments.
Try removing all the valves with the set switched off and the measure the resisatnce between V4 pin 5 and ground. There should be approximately 1020ohms. If it's open circuit move down the filament chain. You should get the following result if the filament chain wiring is intact. V4 pin 5 1020ohmsI suspect there will be an open circuit between V2 pin 1 and V3 pin 7. Keith |
2nd Aug 2010, 7:06 pm | #57 |
Octode
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Re: Bush BAC31 motorboating
Ok, thankyou to you both
Will give this a shot either tomorrow or day after tomorrow. Thinking logically? Me? Josh. |
2nd Aug 2010, 8:11 pm | #58 |
Octode
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Re: Bush BAC31 motorboating
Here are some results (coursework is boring.... ):
With what Sideband suggested: With one multimeter lead connected to pin 7 of DL94 I got: DL94 Pin 1: 16.2 ohms 1T4 Pin 1: 25.5 ohms 1T4 Pin 7: 16.5 ohms 1S5 Pin 1: 4.5 Mohms, keeps growing 1S5 Pin 7: 5.5 Mohms, keeps growing DK92 Pin 1: 5 Mohms, keeps growing DK92 Pin 7: 4.72 Mohms, keeps growing With what KeithsTV suggested: DL94 Pin 5 to GND, should be 1020 ohms, measured 4.5M + DL94 Pin 1 to GND, should be 550 ohms, measured 4.5M + 1T4 Pin 7 to GND, should be 550 ohms, measured 4.3M + 1T4 Pin 1 to GND, should be 330 ohms, measured 4.8M + 1S5 Pin 7 to GND, should be 330 ohms, measured 17.4 ohms 1S5 Pin 1 to GND, should be 150 ohms, measured 8.9 ohms DK92 Pin 7 to GND, should be 150 ohms, measured 8.9 ohms DK92 Pin 1 to GND, should be 0 ohms, measured 0.3 ohms V1- DK92 V2- 1T4 V3- 1S5 V4- DL94 So a breakage somewhere between 1T4 and 1S5 I guess (like what you both said ) Are there any components I should check as well as wires going between the two? Josh. |
2nd Aug 2010, 8:22 pm | #59 |
Dekatron
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Re: Bush BAC31 motorboating
Wires and valveholders. Even a piece of wire can hold a fault you know.
Please either put a zener in or use batteries for the 7.5v supply. Cheers, Steve P.
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2nd Aug 2010, 8:53 pm | #60 |
Octode
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Re: Bush BAC31 motorboating
I don't think I've got any Zeners anywhere (I'm sure I had a couple somewhere )
Could someone send me a link to a suitable one on the RS site please? (Just had a look and there's loads....) Or failing that if anyone has one to spare..... I will test wires etc for continuity tomorrow. Will also check all valve holders again. Josh. |