Bush BAC31 motorboating - Page 4 - UK Vintage Radio Repair and Restoration Discussion Forum

KeithsTV · 2nd Aug 2010, 11:12 pm

There's decoupling cap from V3 pin 7 / V2 pin 1. Have you replaced this and inadvertently cut one of the other wires on the pin?

To prove the connection is open check the resistance between V3 pin 7 & V2 pin 1.

From the resistances measured, which I assume were with the valves in place, the filaments are still intact.

Keith

JoshWard · 3rd Aug 2010, 3:38 pm

Well I checked where the capacitor is and tugged at a few wires and sure enough the wire which then goes onto V2 wasn't connected

It looked as if it was, tucked up right by the joint and indeed when I first redid that joint it still crackled etc so must have been brushing up by the joint then when I redid the one next to it I must have knocked it out the way slightly causing the o/c!

It's now gone back to crackling healthily with HT sitting at about 73 volts on the output transformer so I'm going to go back redoing joints (and connecting all the wires back on.....

)

Josh.

KeithsTV · 3rd Aug 2010, 6:13 pm

That's better although 73 v is a little low, the manual states 80v. What's the voltage on pin 7 of V4? It should be 6.5v according to the manual.

It's possible that the DK92 will need replacement. Try picking up the local oscillator on another radio.

Shouldn't be too long before it's going.

Keith

JoshWard · 3rd Aug 2010, 6:22 pm

I'll try voltages in a sec. First of all I need to know where the blue wire on the wavechange switch goes (originally a black wire). I've got it connecting to a terminal which then goes to ground.

JoshWard · 3rd Aug 2010, 6:44 pm

I get 5v on pin 7 of v4 using the EZ41, and 4.7v using an EZ40.

Sideband · 3rd Aug 2010, 7:38 pm

Oh that's good news Josh! See it had to be something simple. At least the valves have survived. So now we are basically back to the beginning of this thread...full-circle in fact

.

Now as Keith said, try and pick up the oscillator on another set. I think you tried this before with no joy but no harm trying it again now that the filaments are working. If you still have no joy then it's time to sub a DK92. Your HT is a bit low anyway but will probably work with good valves.

It might be worth looking on eBay for valves. There are quite a lot being advertised on there at the moment so you may be lucky.

SB

JoshWard · 3rd Aug 2010, 7:42 pm

So that's about 3 pages due to a loose wire

I will try picking up the oscillator sometime this evening (soon hopefully). My DK92 worked fine before back in the days of the radio working so I wonder if something is just bringing the HT down?

Josh.

Sideband · 3rd Aug 2010, 7:46 pm

Quote:

Originally Posted by JoshWard

I get 5v on pin 7 of v4 using the EZ41, and 4.7v using an EZ40.

Total filament supply should be 7 volts so you are about 0.5V down on each valve. That's pushing things to the limit with these. Maybe someone can help you out with a good reccy.

SB

KeithsTV · 3rd Aug 2010, 7:59 pm

Quote:

Originally Posted by JoshWard

First of all I need to know where the blue wire on the wavechange switch goes (originally a black wire). I've got it connecting to a terminal which then goes to ground.

The blue (black) wire from the centre terminal of the switch should be connected to ground.

As a quick check you could change the mains tapping to the 220-230 setting and monitor the filament voltage. If it changes to close to the correct value leave it while you check the local oscillator. May be worth checking your mains voltage.

As SB has said if the filament voltages are low, especially on the DK92, the performance will be affected.

Nearly there now (fingers crossed)

Keith

JoshWard · 3rd Aug 2010, 9:08 pm

I just don't know what to do anymore...

I tried it on 220-230 volts and I couldn't hear House Of The Rising Sun above all the foreign stations that were coming through and I tried but couldn't find that signal anywhere else

Looks as though it's a low reccy then, as it works brilliantly on medium and long on the lower voltage setting.

Josh.

mickjjo · 3rd Aug 2010, 9:25 pm

I have a BAC31, I found that the EZ41 has to be in perfect condition for correct operation as it supplies the 50 mA series heater supply as well as around 10 mA of H.T. current, the poor little thing is only rated at 60mA so has a very hard life!

http://www.r-type.org/exhib/aaa0126.htm

Regards, Mick.

JoshWard · 3rd Aug 2010, 9:29 pm

It must have expired fairly recently. It was working ok before we moved and I retested all my sets and that was with leaky old capacitors in it.

Anyway, a replacement is on its way and I will keep the other as it may prove useful in a less demanding set! If not it joins my workshop windowsill of knackered valves....

Josh.

KeithsTV · 3rd Aug 2010, 9:53 pm

What's your mains voltage? If it's low that could give rise to these symptoms. Also check the heater voltage of the EZ41 on the 240-250 setting. This should give you an idea whether your mains is low

Keith

JoshWard · 3rd Aug 2010, 10:01 pm

The time I've been working on it it's been connected to the Variac at about 236 volts.

I will put it on the mains tomorrow (too lazy to fit a plug...!)

Josh.

Sideband · 3rd Aug 2010, 10:08 pm

Hopefully a happy ending!

These sets work well and sound every bit as good as a mains only radio. Good point about your mains voltage. Now you've moved, it may be lower than at your old address. 10 volts will make a difference to these sets especially if the valves are borderline.

Well done...got there in the end. How about a 'Success Story'?

SB

JoshWard · 3rd Aug 2010, 10:11 pm

Yes they do sound good, I remember it when it was working before although it sounds a bit nicer now.

We were in the middle of a town before and I think it was about 240 volts there. Will have a check here, now we're in the middle of a field (I would go out to the workshop now and have a go but there's a big spider that lives in the firewood store next to my workshop

)

Just got to put it all back together and tidy up the cabinet and the success story should be along in the next few days...

Josh.

G8UWM-MildMartin · 3rd Aug 2010, 11:13 pm

Ah, now you're in the middle of a field, the mains regulation might not be so good, depending on who else is on your supply and when they do the milking or whatever...
A zener (or a couple in series plus the odd ordinary diode to get the voltage "spot on" (plus a little bit to compensate for ageing valves if needed)) across the heater string, as already suggested and using the lower mains tap sounds like a good idea.

KeithsTV · 4th Aug 2010, 8:12 am

When I had my first BAC31, must be 35 years ago, I modified the power supply with a regulator for the filament chain. I don't know if that helped as my parents were using it until they got a new radio some years later. I think the DK92 was probably failing as I had to replace it when I got round to restoring it a couple of years ago along with completely rebuilding the power supply which was devoid of most of the components after I'd stripped out the regulator.

Don't forget that these sets were designed to run off batteries which would not be constant voltage. Mine would run with the HT down to about 65v and the LT down to about 5.5v.

Adding a zener would probably work but may increase the current through the EZ41 which is almost on the limit of its rated current. A replacement EZ41 and DK92 may be the answer.

Keith

JoshWard · 4th Aug 2010, 7:04 pm

Getting about 245 volts and it's running OK at the moment. When the new reccy is here I'll try that and keep it for if I ever move somewhere with lower mains voltage! (Or for when the original reccy expires as I daresay there's not a huge amount of life left in it)

Thanks for everyone's help.... will post a success story after tea!

Josh.

2nd Aug 2010, 11:12 pm	#61
KeithsTV Nonode Join Date: Aug 2007 Location: South Bradford, West Yorkshire, UK. Posts: 2,574	Re: Bush BAC31 motorboating There's decoupling cap from V3 pin 7 / V2 pin 1. Have you replaced this and inadvertently cut one of the other wires on the pin? To prove the connection is open check the resistance between V3 pin 7 & V2 pin 1. From the resistances measured, which I assume were with the valves in place, the filaments are still intact. Keith

3rd Aug 2010, 3:38 pm	#62
JoshWard Octode Join Date: Dec 2005 Location: Near Stowmarket, Suffolk, UK. Posts: 1,962	Re: Bush BAC31 motorboating Well I checked where the capacitor is and tugged at a few wires and sure enough the wire which then goes onto V2 wasn't connected It looked as if it was, tucked up right by the joint and indeed when I first redid that joint it still crackled etc so must have been brushing up by the joint then when I redid the one next to it I must have knocked it out the way slightly causing the o/c! It's now gone back to crackling healthily with HT sitting at about 73 volts on the output transformer so I'm going to go back redoing joints (and connecting all the wires back on..... ) Josh.

3rd Aug 2010, 6:13 pm	#63
KeithsTV Nonode Join Date: Aug 2007 Location: South Bradford, West Yorkshire, UK. Posts: 2,574	Re: Bush BAC31 motorboating That's better although 73 v is a little low, the manual states 80v. What's the voltage on pin 7 of V4? It should be 6.5v according to the manual. It's possible that the DK92 will need replacement. Try picking up the local oscillator on another radio. Shouldn't be too long before it's going. Keith

3rd Aug 2010, 6:22 pm	#64
JoshWard Octode Join Date: Dec 2005 Location: Near Stowmarket, Suffolk, UK. Posts: 1,962	Re: Bush BAC31 motorboating I'll try voltages in a sec. First of all I need to know where the blue wire on the wavechange switch goes (originally a black wire). I've got it connecting to a terminal which then goes to ground. Attached Thumbnails

3rd Aug 2010, 6:44 pm	#65
JoshWard Octode Join Date: Dec 2005 Location: Near Stowmarket, Suffolk, UK. Posts: 1,962	Re: Bush BAC31 motorboating I get 5v on pin 7 of v4 using the EZ41, and 4.7v using an EZ40.

3rd Aug 2010, 7:38 pm	#66
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,580	Re: Bush BAC31 motorboating Oh that's good news Josh! See it had to be something simple. At least the valves have survived. So now we are basically back to the beginning of this thread...full-circle in fact . Now as Keith said, try and pick up the oscillator on another set. I think you tried this before with no joy but no harm trying it again now that the filaments are working. If you still have no joy then it's time to sub a DK92. Your HT is a bit low anyway but will probably work with good valves. It might be worth looking on eBay for valves. There are quite a lot being advertised on there at the moment so you may be lucky. SB __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

3rd Aug 2010, 7:42 pm	#67
JoshWard Octode Join Date: Dec 2005 Location: Near Stowmarket, Suffolk, UK. Posts: 1,962	Re: Bush BAC31 motorboating So that's about 3 pages due to a loose wire I will try picking up the oscillator sometime this evening (soon hopefully). My DK92 worked fine before back in the days of the radio working so I wonder if something is just bringing the HT down? Josh.

3rd Aug 2010, 9:08 pm	#70
JoshWard Octode Join Date: Dec 2005 Location: Near Stowmarket, Suffolk, UK. Posts: 1,962	Re: Bush BAC31 motorboating I just don't know what to do anymore... I tried it on 220-230 volts and I couldn't hear House Of The Rising Sun above all the foreign stations that were coming through and I tried but couldn't find that signal anywhere else Looks as though it's a low reccy then, as it works brilliantly on medium and long on the lower voltage setting. Josh.

3rd Aug 2010, 9:25 pm	#71
mickjjo Rest in Peace Join Date: Jul 2004 Location: Dartford, Kent, UK. Posts: 1,661	Re: Bush BAC31 motorboating I have a BAC31, I found that the EZ41 has to be in perfect condition for correct operation as it supplies the 50 mA series heater supply as well as around 10 mA of H.T. current, the poor little thing is only rated at 60mA so has a very hard life! http://www.r-type.org/exhib/aaa0126.htm Regards, Mick.

3rd Aug 2010, 9:29 pm	#72
JoshWard Octode Join Date: Dec 2005 Location: Near Stowmarket, Suffolk, UK. Posts: 1,962	Re: Bush BAC31 motorboating It must have expired fairly recently. It was working ok before we moved and I retested all my sets and that was with leaky old capacitors in it. Anyway, a replacement is on its way and I will keep the other as it may prove useful in a less demanding set! If not it joins my workshop windowsill of knackered valves.... Josh.

3rd Aug 2010, 9:53 pm	#73
KeithsTV Nonode Join Date: Aug 2007 Location: South Bradford, West Yorkshire, UK. Posts: 2,574	Re: Bush BAC31 motorboating What's your mains voltage? If it's low that could give rise to these symptoms. Also check the heater voltage of the EZ41 on the 240-250 setting. This should give you an idea whether your mains is low Keith

3rd Aug 2010, 10:01 pm	#74
JoshWard Octode Join Date: Dec 2005 Location: Near Stowmarket, Suffolk, UK. Posts: 1,962	Re: Bush BAC31 motorboating The time I've been working on it it's been connected to the Variac at about 236 volts. I will put it on the mains tomorrow (too lazy to fit a plug...!) Josh.

3rd Aug 2010, 10:08 pm	#75
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,580	Re: Bush BAC31 motorboating Hopefully a happy ending! These sets work well and sound every bit as good as a mains only radio. Good point about your mains voltage. Now you've moved, it may be lower than at your old address. 10 volts will make a difference to these sets especially if the valves are borderline. Well done...got there in the end. How about a 'Success Story'? SB __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

3rd Aug 2010, 10:11 pm	#76
JoshWard Octode Join Date: Dec 2005 Location: Near Stowmarket, Suffolk, UK. Posts: 1,962	Re: Bush BAC31 motorboating Yes they do sound good, I remember it when it was working before although it sounds a bit nicer now. We were in the middle of a town before and I think it was about 240 volts there. Will have a check here, now we're in the middle of a field (I would go out to the workshop now and have a go but there's a big spider that lives in the firewood store next to my workshop ) Just got to put it all back together and tidy up the cabinet and the success story should be along in the next few days... Josh.

3rd Aug 2010, 11:13 pm	#77
G8UWM-MildMartin Heptode Join Date: Jan 2004 Location: Stockport, Greater Manchester, UK. Posts: 827	Re: Bush BAC31 motorboating Ah, now you're in the middle of a field, the mains regulation might not be so good, depending on who else is on your supply and when they do the milking or whatever... A zener (or a couple in series plus the odd ordinary diode to get the voltage "spot on" (plus a little bit to compensate for ageing valves if needed)) across the heater string, as already suggested and using the lower mains tap sounds like a good idea.

4th Aug 2010, 8:12 am	#78
KeithsTV Nonode Join Date: Aug 2007 Location: South Bradford, West Yorkshire, UK. Posts: 2,574	Re: Bush BAC31 motorboating When I had my first BAC31, must be 35 years ago, I modified the power supply with a regulator for the filament chain. I don't know if that helped as my parents were using it until they got a new radio some years later. I think the DK92 was probably failing as I had to replace it when I got round to restoring it a couple of years ago along with completely rebuilding the power supply which was devoid of most of the components after I'd stripped out the regulator. Don't forget that these sets were designed to run off batteries which would not be constant voltage. Mine would run with the HT down to about 65v and the LT down to about 5.5v. Adding a zener would probably work but may increase the current through the EZ41 which is almost on the limit of its rated current. A replacement EZ41 and DK92 may be the answer. Keith

4th Aug 2010, 7:04 pm	#79
JoshWard Octode Join Date: Dec 2005 Location: Near Stowmarket, Suffolk, UK. Posts: 1,962	Re: Bush BAC31 motorboating Getting about 245 volts and it's running OK at the moment. When the new reccy is here I'll try that and keep it for if I ever move somewhere with lower mains voltage! (Or for when the original reccy expires as I daresay there's not a huge amount of life left in it) Thanks for everyone's help.... will post a success story after tea! Josh.