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

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Old 14th Nov 2018, 1:58 am   #21
Chris55000
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Default Re: Fidelity HF29

Hi!

Will this do with a 2M2 added across the ends of the track?

https://www.ebay.co.uk/itm/Vintage-E...UAAOSwSKtaf371

A single transistor amplifying stage could easily be added to your HF29 amplidier chassis on a piece of tagstrip, use a BC557 with upper base resistor 22k to supply –ve, a collector resistor of about 4k7 to supply –ve, a 6k8 from base to chassis, with an emitter stabilising resistor of 1k5, bypassed by 10uF to chasses (+ pole of cap to chassis – the foregoing assumes your amplifier is +ve earthed to chassis which will almost certainly be the case in a 1960s unit!

I/P and O/P couplers of 2.2uF (input cap –ve pole to base and O/P cap –ve pole to collector) will be fine!

The values suggested will give about three times voltage–gain which should be enough for most of the replacement ceramic cartridges you can find nowadays!

Chris Williams

PS!

If you run into bother with that tiny mains transformer, a 9–0–9V one with a 250mA secondary with a 115V primary (use a dual–primary one with primaries in PARALLEL) fed from the 90V taps and neutral of the original motor will give just about the right voltage!
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Last edited by Chris55000; 14th Nov 2018 at 2:09 am.
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Old 14th Nov 2018, 10:08 am   #22
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Default Re: Fidelity HF29

That would be O.K., but 1Meg Log pots. with D.P. mains-rated switches should be available, either from eBay sellers or the likes of C.P.C. and others.
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Old 14th Nov 2018, 11:23 am   #23
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Default Re: Fidelity HF29

The input impedance of that single stage common emitter amplifier will be far too low for a ceramic cartridge. Bass will be non existent!

Use a simple op-amp circuit- the chip will only cost a few pence- little more than a transistor.
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Old 14th Nov 2018, 11:35 am   #24
ms660
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Default Re: Fidelity HF29

The OP's amp looks like a 4 transistor job to me.

Lawrence.
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Old 14th Nov 2018, 12:20 pm   #25
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Default Re: Fidelity HF29

Is the amp original to the player? It appears to be held in place by four different screws. The wooden mounts are crudely cut pieces of block board which haven't discoloured like the plywood panel. I'm not sure that block board would have been available at the time the player was made and surely the cabinet makers would have had lots of small offcuts of plywood available from speaker holes etc?
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Old 14th Nov 2018, 3:28 pm   #26
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Default Re: Fidelity HF29

I can only see 3 transistors Lawrence.
Click image for larger version

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ID:	172793

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Old 14th Nov 2018, 4:05 pm   #27
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Default Re: Fidelity HF29

What's the Black? object between the volume pot and the large yellow capacitor? Then look at the print on the print side directly below the bottom of the resistor that's next to the green mains earth wire.

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Old 14th Nov 2018, 6:20 pm   #28
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Default Re: Fidelity HF29

For something to do...1st attempt at reverse engineering a schematic, scanner's clipped a bit of the RH side where the motor and on/off switch is

'scuse scrawl

EDIT: I missed a dot!

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Last edited by ms660; 14th Nov 2018 at 6:49 pm.
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Old 14th Nov 2018, 6:35 pm   #29
Chris55000
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Default Re: Fidelity HF29

Hi!

Your diagram looks close enough for me to say you've got it right and it just needs the component values adding!

If you show us a close-up picture of the thermistor in the O/P transistor base circuit I can probably root out its data, but I'd make a tentative guess at Mullard VA1040 to begin with!

Chris Williams

PS!

I did have a look myself for a 1M log. pot with DP switch and I couldm't locate one new or used from any of the UK sources anywhere - it seems high-value controls are hetting much harder to find today, what with everything being fancy-menu-and-button-operated!
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Last edited by Chris55000; 14th Nov 2018 at 6:51 pm.
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Old 14th Nov 2018, 7:46 pm   #30
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Default Re: Fidelity HF29

Is that the 4th transistor in the lower image?
The top image has been "mirrored"
Click image for larger version

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ID:	172813

I have to admit I never studied the copper side of the board I assumed the pots were bolted on with normal threaded collars. I have not having seen any pots mounted like that.

Where are the control spindles?

Some better photos would maybe help.

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Last edited by crackle; 14th Nov 2018 at 7:53 pm.
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Old 14th Nov 2018, 7:54 pm   #31
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Default Re: Fidelity HF29

Quote:
Originally Posted by crackle View Post
Is that the 4th transistor in the lower image?
The top image has been "mirrored"
Attachment 172813

Some better photos would maybe help.

Mike
Yes Mike, so far as I can make out.

Also I didn't include the 100k? input resistor to the pot in that R.Eng'd schematic as it appeared to be shorted out by the wire link.

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Old 14th Nov 2018, 8:32 pm   #32
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Default Re: Fidelity HF29

Quote:
Originally Posted by Station X View Post
Is the amp original to the player?
I wondered that, they usually use metal brackets, but if you look at the external views online it puts the controls in the right place. Presumably using removable plastic extension shafts. It would help if one of these had been seen before!
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