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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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25th Nov 2005, 12:32 pm | #1 |
Nonode
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Bush MB60 not sounding too good
Hi,
I've had a quick try of my MB60 but the reception isn't very good. The stations seem week and there is a lot of hiss. If I tune just past Virgin I get a loud thumphing noise?. If I attach a small length of wire to the aerial socket the reception is greatly improved (still with hiss). However as this is a portable radio shouldn't it work ok without an external aerial? I admit to having no experiance with portable valve radios so maybe this is how they sound? Any ideas Thanks David |
25th Nov 2005, 12:50 pm | #2 |
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Re: Bush MB60 not sounding too good
Most battery valve sets don't perform as well as mains sets but you shouldn't be hearing thumping noises! The first thing to check is the RF alignment - just move the coils along the ferrite rod until you find a peak.
If that doesn't help it's just down to standard fault finding I'm afraid. The aerial coils can become disconnected, the wavechange switch may be giving problems, or one of the valves may be low emission (battery frequency changers and IF amps are much more likely to fail than mains types). You should expect good reception of strong stations such as BBC R5. Good luck, Paul |
25th Nov 2005, 1:12 pm | #3 |
Nonode
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Re: Bush MB60 not sounding too good
Thanks Paul,
I've attached a photo of one of the coils which initially looks like it's moved? However if it has it's done a very good job of re-attaching itself Thanks David |
25th Nov 2005, 1:23 pm | #4 |
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Re: Bush MB60 not sounding too good
Hi Dave, the thumping sounds like some kind of instability, I've had similar before with battery sets. Look out for decoupling capacitors gone low in value or leaky, particularly the AGC decoupler. (0.1-ish paper capacitor down to chassis on the agc line), otherwise, as Paul says. I would tend to avoid moving any coils unless you have exhausted all other possibles though. e.g valve substitution is a good idea.
Biggles. |
25th Nov 2005, 1:57 pm | #5 | |
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Re: Bush MB60 not sounding too good
Quote:
I'd leave all the other coils and IFTs alone at this stage though, especially if they look undisturbed - as Biggles says, it's better to exhaust other alternatives first. Good luck, Paul |
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25th Nov 2005, 2:29 pm | #6 |
Nonode
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Re: Bush MB60 not sounding too good
Oh well, it's not going to be easy. I've moved the coil back to where it looks like it should be and it's made no difference. The problem is confined to MW, LW works very well!
All the Hunts caps have been replaced so I guess I'll just have to look for something else Thanks David |
25th Nov 2005, 2:57 pm | #7 | |
Dekatron
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Re: Bush MB60 not sounding too good
Quote:
Rich.
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There are lots of brilliant keyboard players and then there is Rick Wakeman..... Last edited by Sideband; 25th Nov 2005 at 3:02 pm. |
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25th Nov 2005, 3:53 pm | #8 |
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Re: Bush MB60 not sounding too good
Hi Dave, Just checked inside my MB60, Looks like those aerial coils would need a blowlamp to shift them, stuck with lots of wax. Worth checking the LT and HT voltages in case the metal rectifier is getting tired. Are the stations appearing at the correct points on the dial?,Usually worth tweaking the aerial trimmer and possibly the oscillator one, but mark the original positions first. Another possibility would be those 110pf capacitors inside the IF cans may have drifted off value, upsetting the alignment..... .
Regards, Mick. |
25th Nov 2005, 4:59 pm | #9 | |
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Re: Bush MB60 not sounding too good
Quote:
There should be a very obvious peak as you slide the coil along the ferrite rod. You can confirm this with the (working) LW coil. If the MW coil is open circuit you can substitute most scrap coils, even from trannie sets, so long as they're the right diameter. The tuning may not track perfectly across the whole waveband but it'll probably be 'good enough'. Good luck, Paul |
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25th Nov 2005, 5:14 pm | #10 | |
Nonode
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Re: Bush MB60 not sounding too good
Quote:
Thanks David |
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25th Nov 2005, 6:07 pm | #11 |
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Re: Bush MB60 not sounding too good
Hi David
My MB60 is quite sensitive - it has an extra IF stage to most D-series valved battery/mains sets. As Paul says, there is something funny happening to the aerial coils. I am sure that there is a market if you record the thumping!
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25th Nov 2005, 9:00 pm | #12 |
Octode
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Re: Bush MB60 not sounding too good
If the thumping is caused by LF instability, you might find a decoupler on the HT+ line is the culprit. There's C36 (Trader sheet ident) which is a 0.1uF. Try replacing it: you never know.
-Tony |
26th Nov 2005, 11:42 am | #13 |
Nonode
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Re: Bush MB60 not sounding too good
Paul, your a genius, the MW aerial coil had 3 broken coils which I managed to solder back together.
However.... I turned the radio on and it sounded really good, all the stations were there and no "thumping" noises I did notice that the volume control didn't turn down properly, it's (was) actually quite loud with the volume off. It played it on Amber for half an hour but when I tried tuning through the stations again Virgin had disappeared. As I fiddled with the tuning Amber vanished too, then they all went. All I'm left with is a slight hiss. HT and LT seem to still be Ok.... Thanks David |
26th Nov 2005, 11:46 am | #14 |
Octode
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Re: Bush MB60 not sounding too good
Sounds possibly like your local oscillator has packed up. May be the valve, may be low HT+. Check for latter, try replacement valve for former.-Tony
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26th Nov 2005, 12:08 pm | #15 |
Nonode
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Re: Bush MB60 not sounding too good
Brilliant, I changed the DK96 and it's working again. It's strange but it tested OK yesterday, but then again it was made by Pinnacle!
The only problem now is the volume, any ideas why it does'nt turn down fully? Thanks David |
26th Nov 2005, 12:13 pm | #16 | |
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Re: Bush MB60 not sounding too good
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Glad you're making good progress with it. Best regards, Paul |
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26th Nov 2005, 1:13 pm | #17 |
Nonode
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Re: Bush MB60 not sounding too good
Ok I've given the volume control another squirt, It actually works very well with no crackles and with a multimeter attached to the wiper it reads nicely from 0 to 400 ohms.
The earthy end of the track is connected via a 10K resistor which checks out Ok too Unfortunately the volume is still too loud when it should be off Thanks David |
26th Nov 2005, 3:21 pm | #18 |
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Re: Bush MB60 not sounding too good
Hi Dave, The circuit in R+TV servicing for the MB60 shows a 1k resistor in series with the bottom end of the volume control. I think this is a deliberate design feature to still give some output when the volume control is at minimum, This may avoid running down the batteries unintentionally by users turning down the volume, The on/off switch of course is combined with the tone control on these sets. I'm not sure why your set uses a 10k resistor though . Maybe you could experiment with the value to give an acceptable minimum volume setting? .
Regards, Mick. Last edited by mickjjo; 26th Nov 2005 at 3:39 pm. |
26th Nov 2005, 6:27 pm | #19 | ||
Nonode
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Re: Bush MB60 not sounding too good
Quote:
Quote:
Many Thanks David |
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26th Nov 2005, 7:30 pm | #20 |
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Re: Bush MB60 not sounding too good
The 1k resistor is there because the negative feedback is fed back into the bottom of the volume control. This would mean that the volume will not go down to silent, but it should go down to very quiet (somewhat lower than normal listening level).
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