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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 27th Jul 2012, 12:38 am   #81
AC/HL
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Default Re: Bush SRP 31D not producing sound!

Hello again, I've been a little preoccupied for the last couple of days and missed a few postings. Glad to see you've not fried yourself on the on/off switch!

We seem to have established that the amp is working now, but can be intermittent. The noises you describe on switching off can be nothing more than a dirty volume control. Post 75 seems to confirm this.

You'll need to squirt some cleaning fluid into it as best you can (unplugged!) and exercise the pot vigorously. In an emergency I've been known to use aftershave, anything spirit based! With a bit of luck it may be this simple.

Another possibility is a corroded/loose fuse bulb. This could cause the amp to fade out whilst leaving the turntable OK.
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Old 27th Jul 2012, 12:47 am   #82
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Default Re: Bush SRP 31D not producing sound!

You seem a bit obsessed with the electrolytics. My limited experience has found that those red and black Plessey types are usually OK.

Steve
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Old 27th Jul 2012, 1:18 am   #83
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Default Re: Bush SRP 31D not producing sound!

This is true, it's just once I read that those capacitors can go dodgy and I guess I was worried they were. To be honest though, they are probably fine like you say.

As the machine stands at the moment, it produces sound when the co-axial plug isn't plugged into the amp input socket. In fact when you plug it in it just sounds a lot quieter, which is odd. Now, in the circuit, there's only a resistor with a ceramic capacitor (C2, which seems to be a ceramic flat square coated in a waxy substance which I think is odd) connected in series to the resistor (R2) and then the potentiometer.

Could there be an issue along this line? (although I suppose the potentiometer leads to anywhere in the amp!) also I was advised by Glowing Bits to change the coupling capacitors and one is wired to pin 1 of valve 2 which if you remember was reading 4V instead of 0V. Could this be the reason?

As for the fuse bulb, I changed it as the last one overloaded and blew when I first tried to measure the rectifier. I changed it, swapped it from my SRP31.

Last edited by Spencervs; 27th Jul 2012 at 1:26 am.
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Old 27th Jul 2012, 7:49 pm   #84
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Default Re: Bush SRP 31D not producing sound!

With the co-ax plug out you will only get one channel of the stereo. With it in you should get mono, but the volume should not change. If it does there is a problem with the cartridge wiring.
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Old 28th Jul 2012, 10:00 pm   #85
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Default Re: Bush SRP 31D not producing sound!

OK, I played with the wires and found the right combination! I now have it working.

It also had a rubber protection for the connections but it squeezed the tags together it seems, which is why it would stop making sound suddenly, so I discarded it and it's OK like that but surely this wouldn't cause sound to phase out? Should I change those decoupling capacitors like advised by glowing bits? I suppose it won't hurt to?

Thanks for the help so far.
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Old 28th Jul 2012, 11:07 pm   #86
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Default Re: Bush SRP 31D not producing sound!

ohhh ok, it still fades out... oh by the way, I cleaned the volume and treble potentiometers and they work so well now! also took the time to give the dials a nice little clean up too
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Old 29th Jul 2012, 12:01 am   #87
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Default Re: Bush SRP 31D not producing sound!

Check the co-axial plug. Make sure the screening is not shorting against the inner conductor, and that the latter is properly soldered to the pin. Next, look at the socket it plugs into. Make sure the inner tube is gripping the pin tightly. You may need to tighten things up with long-nosed pliers.
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Old 29th Jul 2012, 1:09 am   #88
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Default Re: Bush SRP 31D not producing sound!

When you say Fades, is it a gradual fade like the end of a record, or just going off when it shouldn't?
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Old 29th Jul 2012, 2:40 pm   #89
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Default Re: Bush SRP 31D not producing sound!

It fades like the end of a record. Like someone's turning it down gradually, normally to nothing or sometimes to a barely audible sound
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Old 29th Jul 2012, 3:47 pm   #90
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Default Re: Bush SRP 31D not producing sound!

Do the heaters look brighter than normal when it fades?
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Old 29th Jul 2012, 5:18 pm   #91
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Default Re: Bush SRP 31D not producing sound!

It's interesting to know exactly how it fades, as has been described.
When it fades, is the anode (metal plate seen when looking at a glass valve) starting to glow pale red?
When it fades, of rather, before it fades, is there a clicking sound?
Better still, it could be the valves worn out/low emission, although this would normally result in low output full stop but not fading.
If the valve is starting to red plate, it would then be time to attack the valve pins with a multimeter while the set is powered!
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Old 29th Jul 2012, 5:24 pm   #92
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Default Re: Bush SRP 31D not producing sound!

I was thinking of an intermittent short on the last valve in the heater chain or an intermittent open circuit on the entire heater chain.
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Old 29th Jul 2012, 5:36 pm   #93
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Default Re: Bush SRP 31D not producing sound!

Quote:
Originally Posted by Refugee View Post
I was thinking of an intermittent short on the last valve in the heater chain or an intermittent open circuit on the entire heater chain.
That's another possibility, although I would expect to find an intermittent heater connection on a set using the chassis as heater return.
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Old 29th Jul 2012, 6:06 pm   #94
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Default Re: Bush SRP 31D not producing sound!

I have had a quick look at the manual and would still go for a heater problem.
It now looks like a bad connection on a valve heater pin would be most likely.
The best check it to unplug the power and check the valve socket pins with a small probe and make sure they are secure on both sides of the bit that holds the valve pin. They sometimes become cracked and loose. Sometimes pins can be salvaged from an old holder. Otherwise a new holder will have to be fitted.
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Old 29th Jul 2012, 6:29 pm   #95
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Default Re: Bush SRP 31D not producing sound!

Quote:
Originally Posted by Refugee View Post
I was thinking of an intermittent short on the last valve in the heater chain or an intermittent open circuit on the entire heater chain.
This model uses parallel wired 'E' series valves so I would expect an intermittent heater short to heavily load the power supply resulting in either a blown fuse or other components drawing current heavily.

From what has been said in some of the OP's original posts, I would still suspect either a problem with the wiring (and connections) somewhere between the 'AMP'/'STEREO' sockets and the Volume control.

Regards
Andrew
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Old 29th Jul 2012, 6:30 pm   #96
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Default Re: Bush SRP 31D not producing sound!

Or try wobbling each valve when the problem occurs, to see if the sound comes back.

Obviously, you must keep your fingers clear of all the wires and terminals when doing this, Spencer!

N.
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Old 29th Jul 2012, 7:08 pm   #97
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Default Re: Bush SRP 31D not producing sound!

After my manual check I confirmed that it has E series glassware and see that the triode sections are both used in the front end and that either of them could cause it to fade out before distortion sets in from the pentode section cooling off if indeed it is a loose valve holder pin.
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Old 29th Jul 2012, 7:48 pm   #98
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Default Re: Bush SRP 31D not producing sound!

Quote:
Originally Posted by AndiiT View Post
Quote:
Originally Posted by Refugee View Post
I was thinking of an intermittent short on the last valve in the heater chain or an intermittent open circuit on the entire heater chain.
This model uses parallel wired 'E' series valves so I would expect an intermittent heater short to heavily load the power supply resulting in either a blown fuse or other components drawing current heavily.

From what has been said in some of the OP's original posts, I would still suspect either a problem with the wiring (and connections) somewhere between the 'AMP'/'STEREO' sockets and the Volume control.

Regards
Andrew
One must agree with the heater blowing something statement.
Another thought, what is the chance of a faulty ground wire somewhere in the audio chain (turntable to pre-amp wiring) causing the problem?
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Old 29th Jul 2012, 8:55 pm   #99
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Default Re: Bush SRP 31D not producing sound!

Hi,
I would have expected a faulty ground wire to give rise to hum via the amplifier and not loss of sound in the way previously described.

As the player is sometimes working this suggests an intermittent contact somewhere, either in the signal circuitry or on the Valve heater or HT supply rail.

Another possibility is that there is an intermittent short circuit on the signal leads between the screened cable coming from the AMP/STEREO co-axial sockets and the amplifier input.
This could probably be proved by connecting something like an MP3 player to the AMP socket and then waggling the screened cable between the sockets and the amp; I suggest an MP3 player as, due to the player design, it would be difficult to perform the "waggle test" whilst playing a record.

Andrew
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Old 30th Jul 2012, 1:07 am   #100
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Default Re: Bush SRP 31D not producing sound!

Found something suspicious! Had it open and watched the valves when it was on and the heater for V2 glows but it dims down and sometimes comes back and V1 doesn't glow at all when it's gone quiet! What can cause this? I thought I checked the valves with the multimeter to find that they were outputting ok! So confused.
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