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Old 26th Jul 2010, 11:27 pm   #21
Biggles
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Default Re: Bush BAC31 motorboating

Hi Josh. I've got a couple of these sets if you want me to compare voltages on mine with yours I could power them up for you.
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Old 28th Jul 2010, 2:01 pm   #22
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Default Re: Bush BAC31 motorboating

With the EZ40 instead of the 41 I still got about 73 volts HT.

I started redoing some joints, then when I redid the one which has a chassis connection for the on/off/volume control I started getting about 120 volts HT!
I have tried redoing that joint several times but each time I get the same result....
At 120 volts it's also lost all crackling etc.....
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Old 28th Jul 2010, 7:24 pm   #23
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Default Re: Bush BAC31 motorboating

Hi Josh. I can not actually remember the cure that I did on my Bush BAC31 radio. I do remember that some resistors were out of tolerance by a great deal. I did earth the frame of the volume control to chassis, and I added a screening can from a B7 valve, which was formerly used in a G.E.C radio, to the first audio amplifier. Maybe you could try out these suggestions ?
Regards
Mike
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Old 28th Jul 2010, 7:56 pm   #24
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Default Re: Bush BAC31 motorboating

Quote:
Originally Posted by JoshWard View Post
then when I redid the one which has a chassis connection for the on/off/volume control I started getting about 120 volts HT!
At 120 volts it's also lost all crackling etc.....

Ouch!! If that reading is correct, then it's waaay too high and the filaments are in danger of popping as well. I hope that the loss of crackling isn't due to the fact that the fillaments have already popped which, incidentaly would also make the HT high as there would be no load...

Careful voltage checking is in order I think.


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Old 28th Jul 2010, 8:12 pm   #25
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Default Re: Bush BAC31 motorboating

I will check the filaments first. The filament bypass capacitor had over 50 volts across it! I changed it for a modern one before this and it started bulging so just put another one in (rated at 25volts as the original was) and naturally that gets boiling hot.

I'm really annoyed with this... I can't see any of my work being bad, I've checked every joint for continuity yet it has turned from a working radio into a nightmare! It's been a long while since it motorboated and produced a signal

I redid a whole tag strip of joints that I had previously made and checked after each one. There was life after each one apart from the end one which is where the volume control connects to the tag strip connecting to the chassis along with a 4.7M resistor and two capacitors. I've redone this joint about three times now....

I find voltage checking in this set very difficult as there's so little room to work. I don't think Bush made this set very well at all, nearly every original joint is just layer soldered as well.

Thanks for your patience in helping me get this sorted out. It really is appreciated.

Josh.
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Old 28th Jul 2010, 8:40 pm   #26
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Default Re: Bush BAC31 motorboating

Agreed they are not the easiest of sets to work on. Have you seen this account of my repair?

https://www.vintage-radio.net/forum/...ad.php?t=52754


May give you some tips. The only way to work on these is to take everything out of the cabinet, including the frame aerial.

It's possible you have valveholder problems. These B7G types are not the most durable and broken pins are common.

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Last edited by Sideband; 28th Jul 2010 at 8:50 pm.
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Old 28th Jul 2010, 8:50 pm   #27
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Default Re: Bush BAC31 motorboating

Bit of inspiration there As you can see I commented when you posted that saying I was looking forwards to doing mine.... How naive I was...

Luckily my HT leads to the output transformer are in good condition and quite long. I have the frame aerial connected via croc clips.

Anyway time to do some filament checking....

Josh.
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Old 28th Jul 2010, 8:54 pm   #28
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Default Re: Bush BAC31 motorboating

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I have the frame aerial connected via croc clips.

Josh.
I wonder if that was affecting the aerial tuning resulting in no signals.....


I also edited my last post to mention the valveholders. Check the primary of the output transformer as well in case that's gone O/C....


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Old 28th Jul 2010, 9:01 pm   #29
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Default Re: Bush BAC31 motorboating

Well there's no life now so I don't think the croc clips will make any difference but good suggestion anyway, never thought that might have affected it.

Once I've finished my ice cream i'll go out to the workshop and have a look....
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Old 28th Jul 2010, 9:27 pm   #30
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Default Re: Bush BAC31 motorboating

Primary of the output transformer measures 580ohms, Trader sheet says 540 so that's alright.

All filaments seem ok.

HT sitting at about 112 volts.
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Old 28th Jul 2010, 9:49 pm   #31
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Default Re: Bush BAC31 motorboating

To prevent damage to the filaments while you're checking the PSU you can remove the valves and fit a 150ohm resistor between the LT+ connection on SK1(pin 3) and the chassis.

What is the mains voltage setting set to? It's possible to compensate for a failing DK92 by changing the mains voltage setting. I know as I did this 30 odd years ago on my BAC31. This will increase the HT and the LT.

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Old 28th Jul 2010, 9:53 pm   #32
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Default Re: Bush BAC31 motorboating

I think its on the max setting. I'll stick it down one tomorrow and give it a shot. I just can't figure out why my HT has leapt so much and why I've lost all crackles etc.

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Old 28th Jul 2010, 10:00 pm   #33
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Default Re: Bush BAC31 motorboating

Try it on the 240-250v setting. That should give the lowest HT & LT. Are you measuring the HT at the EZ41 cathode or at the HT rail on the receiver chassis.

There should be about 106v at the EZ41 cathode.

Keith
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Old 28th Jul 2010, 10:23 pm   #34
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Default Re: Bush BAC31 motorboating

I've been measuring it on the o/p transformer.

Will see what's on the reccy tomorrow.

Josh.
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Old 28th Jul 2010, 11:13 pm   #35
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Default Re: Bush BAC31 motorboating

That suggests its on the lowest mains setting, 200-210v. You'll probably find the DK92 will need replacing once you've got the voltages right.

Keith
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Old 30th Jul 2010, 9:07 pm   #36
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Default Re: Bush BAC31 motorboating

Voltage is set on 240-50 and has been since I bought the set.

I get about 114v on a DMM on the EZ41 cathode, similar to what I'm getting on the output tranny.

Maybe a resistor in the power supply has gone so the voltage isn't dropping enough?

Josh.
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Old 30th Jul 2010, 9:23 pm   #37
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Default Re: Bush BAC31 motorboating

If the filaments aren't lighting because of an O/C somewhere (not necessarily and O/C filament but possible a valveholder with a duff pin) then the HT will be high as well. Is there any life at all from the audio (finger on middle contact of volume control)...buzz?? What are the volts across each individual filament (pins 1 & 7)? If the filament bypass cap has over 50 volts across it, there is an O/C somewhere.


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Old 30th Jul 2010, 9:26 pm   #38
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Default Re: Bush BAC31 motorboating

All filaments tested ok the other day, will try some contact cleaner in the valve sockets and will clean the pins.

Haven't tried finger on the volume control yet.

Will do those and check filament voltages tomorrow.

Josh.
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Old 31st Jul 2010, 12:05 am   #39
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Default Re: Bush BAC31 motorboating

Contact cleaner on the pins may help if they are just tarnished. The problem with these B7G holders is that the pins break internally. Sometimes you can swap unused pins from one holder to another. Otherwise you have to change the holder......!


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Old 31st Jul 2010, 9:17 am   #40
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Default Re: Bush BAC31 motorboating

I'll do a continuity test on them then (when it has stopped raining and I can get outside!)

Josh.
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