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

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Old 1st Dec 2017, 2:05 pm   #81
Station X
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

Your diagram isn't clear enough for me to give a definitive answer.

You could replace two caps with one so long as the originals both had their negative side connected to the chassis. This seems to be the case for most electrolytics in the set, with the exception of one of the caps on the mains transformer secondary.
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Old 1st Dec 2017, 2:16 pm   #82
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

NO. You cannot.
Graham, his picture clearly shows the + of one going to the - of the other, these caps are on the rectifier diodes at the bottom of the circuit.
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Old 1st Dec 2017, 2:22 pm   #83
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

OK thanks.
2 separate caps it is!

Glad I asked

here is a close up of that part of schematic:
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Old 1st Dec 2017, 2:30 pm   #84
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

Be very careful. you have 2 red wires, they are NOT the 2 positives, this is a voltage doubler circuit. Ensure that you put them back in exactly the same places as they came from. see your original photo.
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Old 1st Dec 2017, 2:48 pm   #85
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

Thanks, It's back as it was but just using one of the + on the double cap.
I'll be looking for a separate axial replacement for the 100uF in the clip underneath.

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Old 4th Dec 2017, 8:52 pm   #86
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

ok... Caps all sorted.
I have one more little thing to deal with please:
the headphone output loading...
I'm looking for a half decent pair of headphones to use with this amp now, however modern headphones seem to be too sensitive. I have a pair of 100ohm Senn HD26 that work ok with an impedance reducing cable that I had made up, but looking at the schematic I'm thinking it might be worth adding something where the 56ohm R23/R123 are. ..what would I need to solder in here and in what sort of configuration in order to dispense with the cable and plug in any newer set of cans? I'm really struggling with the way 220ohm headphones are more sensitive than 50ohm. The lower the number .. the greater the load... is that right.? and to reduce that number I have to wire resistors in parallel? Many thanks for your help again guys.
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Old 4th Dec 2017, 9:42 pm   #87
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

I've now read this...http://nwavguy.blogspot.co.uk/2011/0...explained.html

and kind of understand a bit more. especially resistance and impedance being very different.
Is there a way to measure the output impedance of the headphone socket with a multimeter? it isn't specified in the user manual but as it's a direct tap off the speaker output circuit I'm guessing it's 8 - 16ohm?
the two resistors are just reducing the voltage to the headphone socket. right?
And I'm now thinking I should be looking for HIGH impedance / low sensitivity headphones.
It's all very confusing.
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Old 5th Dec 2017, 1:17 pm   #88
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

Others will be much more expert on this than me but dredging up A level physics from many years ago a basic explanation of impedance and resistance would be that resistance is the measure of the resistance of a material to the flow of a direct current. This is caused by the ease or otherwise of the flow of electrons through that material caused by the atomic make up of the material itself and can be measured by an ohm meter.

Impedance relates to alternating current. If alternating current is passed through a coil, say, then the wire from which the coil is made up will have a resistance, but the current will also set up a magnetic field which will resist the flow of current. The amount of this "resistance" or reactance is dependant on the frequency of the current as well as the physical make up of the coil (number of turns etc). The combination of the two makes up the impedance of the coil. There is a similar explanation for capacitors and circuits that have both. I seem to remember that the square root of -1 was involved in the calculation! You need a special impedance meter to measure it.

I hope that is right!

Edit.

Regarding impedance matching I imagine a signal as pulses of water flowing down a pipe. If two pipes of the same diameter are joined the maximum amount of water will flow through and the "signal" will remain. If the second pipe is narrower then the signal will still remain but less water will flow and some of the signal may be reflected back up the pipe to interfere with the signal coming down it. If the second pipe is much wider than the first one the water will flow but the pulses or signal will be less apparent. To me that is similar to an electric signal in a wire. To get the most signal and best power transfer the the impedances must be equal. You will still get a good signal but less power if the load impedance is higher that that of the source ad you won't get a good signal if the impedance of the load is less than that of the source. It may not be the perfect analogy but it works for me!
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Old 5th Dec 2017, 5:59 pm   #89
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

Many thanks Paul,
I have been doing a bit of web research and am now hoping my local retailer can get in a set of Beyerdynamic DT880 600ohm for me to audition on my amp. they are by all accounts hard to drive, which I think is what will work best with my amp.
Tim
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