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Elizabethan Pop Ten restoration
Elizabethan Pop Ten restoration
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Old 22nd July 2021, 12:30 PM   #1
richardleonard is offline richardleonard
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Default Elizabethan Pop Ten restoration

Hi folks,

So I have this turntable & speaker system, it's very old and seems to be very un-documented online. Thankfully the internal circuit is extremely simple with a mains transformer, a metal 2 prong rectifier, an EL84 tube, a 2x32uf smoothing cap and an audio transformer. Additionally a couple resistors and small caps.

I've fully serviced the turntable, stripping down all the mechanics and cleaning them - it runs like a dream. I've replaced the metal rectifier with a 1n4007 diode + a 100ohm resistor. The smoothing cap is in-spec so I left it, as are the 2 resistors and small caps found elsewhere. The EL84 seems fine, but I've got another on hand too - have tested it with both with the same results.

Voltages are good, turntable is good, sound is good - what's the problem?
Well, the mains transformer makes a REALLY loud buzzing noise. I've never heard a transformer make this kind of noise before, it sounds like a ratchet constantly spinning. It's loud enough to make the deck basically unusable for listening to music. Having physically detached the transformer and moved it away from the rest of the deck while keeping it connected by wires, i can confirm that the noise is 100% definitely coming from it and not the rest of the circuit or the speaker.

Does anyone have any suggestions here? I cannot find any information about this transformer online, or schematics for the deck, but the transformer seems to be stepping mains voltage up to about 330v for the EL84. I presume I have no choice but to replace it, but I have no idea how to gather the information I'd need to do this correctly. It has 4 wires on its secondary, two going to the EL84, one going to the rectifier diode (which then goes to the smoothing cap) and one going to the metal chassis. If there's any other solution available please let me know.

I can say one thing - the noise isn't present when you first turn it on. It comes on as soon as the valve starts warmly glowing, after about 10-15 seconds.

I'm testing the device through a dim-bulb tester with a 70w bulb, which barely lights up at all. The buzz happens when plugged directly into the wall too.

R
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Old 22nd July 2021, 12:52 PM   #2
picowallspeaker is offline picowallspeaker  Italy
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Me thinks it's the smoothing caps. If the rectifier consists in only One diode, It Is likely that the caps have to do a lot of job.
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Old 22nd July 2021, 12:54 PM   #3
richardleonard is offline richardleonard
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So you think the caps are making the transformer buzz, in spite of reading in perfect spec?
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Old 22nd July 2021, 01:00 PM   #4
picowallspeaker is offline picowallspeaker  Italy
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Well, if It buzzes it's another thing. A bad cap can leak to ground thus making an abnormal suction of current from the trafo, which would make It buzz
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Old 22nd July 2021, 01:02 PM   #5
as_audio is offline as_audio
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One way rectification puts unbalanced load on the transformer.
Replace with a bridge rectifier and adapt the resistor for equal
voltage. The initial voltage before heat up may be too high for
the existing caps though.
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Old 22nd July 2021, 01:17 PM   #6
richardleonard is offline richardleonard
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Quote:
Originally Posted by as_audio View Post
One way rectification puts unbalanced load on the transformer.
Replace with a bridge rectifier and adapt the resistor for equal
voltage. The initial voltage before heat up may be too high for
the existing caps though.
I'm not sure that I trust my understanding of the circuit well enough to do this...
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Old 22nd July 2021, 01:25 PM   #7
picowallspeaker is offline picowallspeaker  Italy
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well, look at the pulses...
Rectifier - Wikipedia

If what you have described is right ( the transformer has one output to ground and the other to the single rectifier diode ) then the capacitor has to do the job of making that pulses a straight line ( perfect DC ...)
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Old 22nd July 2021, 01:32 PM   #8
richardleonard is offline richardleonard
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Quote:
Originally Posted by picowallspeaker View Post
well, look at the pulses...
Rectifier - Wikipedia

If what you have described is right ( the transformer has one output to ground and the other to the single rectifier diode ) then the capacitor has to do the job of making that pulses a straight line ( perfect DC ...)
Sorry - I do understand this, and have already followed your advice and ordered a replacement smoothing cap. Will follow up when it arrives and let you know if it solves the problem. Though I mentioned the transformer actually has 4 outputs, one to ground, one to diode, two to EL84.

The thing I said I didn't understand well enough was how to convert the circuit from one-way rectification to a bridge, as recommended by 'as_audio'
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Old 22nd July 2021, 01:44 PM   #9
as_audio is offline as_audio
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In the meantime the mains voltage has probably increased,
which may add to the problem. I wonder why this is a one
tube amp without any small signal tube (it must be a capable
pick up). You would expect 250 Vdc for a single EL 84 usually.

Why do you not publish some pictures to assist the forum in
helping you ?
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Old 22nd July 2021, 01:56 PM   #10
richardleonard is offline richardleonard
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Quote:
Originally Posted by as_audio View Post

Why do you not publish some pictures to assist the forum in
helping you ?
Here! Thank you.

Note: The metal rectifier is still there, but it isn't connected anymore. The 1n4007 is under the yellow heatshrink.
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