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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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Thread Tools |
6th Dec 2018, 12:11 pm | #21 |
Pentode
Join Date: Jan 2014
Location: St Albans, Hertfordshire, UK.
Posts: 215
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Re: 1957 PORTLAND record player
Sorry about that. I got side tracked when the rectifier was suggested as faulty.
I plan on re-doing the wireing today and just noticed a resistor getting very hot so will have to work out what it's doing, it appears to go to another transformer, but don't know why that transformer is there.? There is three transformers, never seen that before, wish I had a circuit diagram. I am going to sit down and try and work out the circuit, it can't be that difficult, I think it's going to be the only way to sort this set out, it's been a while, 30years, since I worked out circuits. |
6th Dec 2018, 2:41 pm | #22 |
Rest in Peace
Join Date: Mar 2006
Location: N.W. Oxfordshire(Chipping Norton)
Posts: 7,306
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Re: 1957 PORTLAND record player
I don't know the circuit of this particular player, never heard of 'Portland' until I saw this thread, but there are two possibilities as to why there are three 'transformers', the first being, hence my quotation marks, that one 'transformer' is actually an A.F. choke. If so, it will be wired between the reservoir and smoothing capacitor positive terminals. This is rare. Usually a resistor, which may be the one getting hot, was used for reasons of cost. The other possibility is that a transformer was used between the preamplifier and output stage - in which case it's primary will be connected between the anode of the pre-amp. valve and HT, and it's secondary will feed the control grid of the output pentode. This, too, was unusual due to the extra cost involved, but I can't think of any other reason for three transformers to be fitted to a mono amplifier.
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6th Dec 2018, 5:17 pm | #23 |
Dekatron
Join Date: Sep 2015
Location: Southwold, Suffolk, UK.
Posts: 8,302
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Re: 1957 PORTLAND record player
I have never heard of an inter-stage transformer or a smoothing choke ever used in a budget "U" series single-stage amp. Is the OP sure they are transformers?
Maybe there is one in-lieu of a motor winding tap to provide a 90V heater supply? And yes, the smoothing and surge resistors will run hot.
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Edward. |
6th Dec 2018, 6:12 pm | #24 |
Dekatron
Join Date: Nov 2003
Location: Heckmondwike, West Yorkshire, UK.
Posts: 9,637
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Re: 1957 PORTLAND record player
There's nothing in your photo to suggest this, perhaps more photos could help us to understand.
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