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Old 29th May 2020, 12:55 am   #1
tracypaper
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Default Fidelity HF10 circuit diagram please

Hi all.
Any body have a circuit diagram for the mentioned valved record player please.
Gaz.
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Old 29th May 2020, 12:34 pm   #2
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Default Re: Fidelity HF10 circuit diagram please

A couple of mentions in the search box above, but nothing concrete. Is it a another variation on the usual? As always, a photo or two.
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Old 2nd Jun 2020, 10:56 pm   #3
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Default Re: Fidelity HF10 circuit diagram please

Hi.
couple of pictures of the amp. A mate brought it and said it all worked, just very low output, he told me he took out the TC8H cart and replaced it. When I got to look at it the cart he put in was a BSR SC12H, hence low out put.
So.. replaced two waxies 0.02 and a 0.01uf and the 100uf electrolytic, but had a wire loose From out put transformer, and after the initial shock. decided to solder it where it is now, it was the only place it could have come from.. I know.. forgot to test player and take pics before starting.
Hence why asking for Schematic to see if the wire is in the right place?
Any how after staring at it for hours plugged it in.... got hum from speaker, no sound from working higher out put cart and the large 100ohm resistor to the right started to smoke and melt the paint, so turned off.
I'm sure the wire is in the right place and the 100uf is the wright way round, but who knows.
Gaz
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Old 3rd Jun 2020, 1:05 am   #4
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Default Re: Fidelity HF10 circuit diagram please

The SC12H shouldn't be too low on output. It will be about the same as a medium output crystal cartridge, so not ideal, but good enough. There's nothing to that amplifier, so you should be able to work out what's going on from any similar single stage amplifier circuit.
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Old 3rd Jun 2020, 1:58 am   #5
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Default Re: Fidelity HF10 circuit diagram please

Gaz - you need to think about how this type of circuit works. The output transformer primary will be in series with the anode of the output valve. I can't see with just a quick look at those pictures at this late hour, but for a guess I think you've probably somehow got the transformer primary straight across the HT without the valve in circuit, particularly if there was an immediate 'hum' when you first switched on. That circuit looks very spread out on that piece of metal!
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Old 3rd Jun 2020, 9:17 am   #6
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Default Re: Fidelity HF10 circuit diagram please

The red wire from the transformer should go to pin 7 (anode) which also has a small resistor on it - looks like you put it on pin 4 which is heater earth by the looks of it so the tranny is taking the HT to earth. The 2 white wires to the speaker look dangerously close to shorting out.
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Old 3rd Jun 2020, 12:41 pm   #7
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Default Re: Fidelity HF10 circuit diagram please

That transformer looks really big compared to the miniscule OPTX used in just about all the early Fidelity valved record players. Please don't be offended Gaz, but it looks just like a 4 wire (2 in, 2 out) heater transfomer? I know you sussed the BSR SC12H cartridge, but others should not be mislead by that "H" suffix - this will givesa far lower output than most medium-output crystal cartridges.
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Old 3rd Jun 2020, 9:22 pm   #8
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Default Re: Fidelity HF10 circuit diagram please

Thanks vidjoman the red wire was reconnected to pin seven and all worked fine. My mistake here was thinking that when I cut the wires from the two waxies that I had cut the red wire of as well and after finding it disconnected assumed it went on the only other newly soldered tag (pin4), It must have snapped off pin 7 during removal from cabinet. The two speaker wires are close to shorting in the picture but weren't when testing, they have just moved together during many movements of the amp, will be re-connected properly now that the amp is working again.
The TC8H mentioned above was fitted to the player and according to the list has an output of 1.1v, or 800mv The TC8M = 400mv and the SC12H 190mv.
The output TX maybe big Edward but you should see the mains transformer (not offended) two in four out. Is a heater transformer the same as an output transformer?
I wish I knew how this circuit worked, did try to find another amp with the EL84 and EZ80 combo but most of my other players have the UY valves, are these similar amps?
Thanks every one for the input, much appreciated and lessons learnt.
Gaz.
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Old 3rd Jun 2020, 11:25 pm   #9
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Default Re: Fidelity HF10 circuit diagram please

Apart from the low voltage parallel heaters fed from the mains transformer, the circuit will be very similar to the UL84/UY85 amplifiers with series high voltage heaters. There's very little variation in all these players, whatever the make.
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Old 4th Jun 2020, 10:32 pm   #10
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Default Re: Fidelity HF10 circuit diagram please

The amp is now done and back in the player all earthed up and stuff, just the deck to service.
Discovered that the cartridge is a SC12M not H so only 100mv.
Cheers.
Gaz.
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Old 4th Jun 2020, 11:35 pm   #11
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Default Re: Fidelity HF10 circuit diagram please

Quote:
Originally Posted by tracypaper View Post
I wish I knew how this circuit worked, did try to find another amp with the EL84 and EZ80 combo but most of my other players have the UY valves, are these similar amps?
Have a look at the Portogram "Babygram". On RM, even the snapshot of the circuit is legible enough it's that simple.

It's here too:

https://www.service-data.com/product...10/6371/a15010
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