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Old 15th Apr 2019, 6:29 pm   #1
Kalee21
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Default Fidelity HF25 resistor wattage

Hi
I’m trying to find out what wattage the large 330ohm resistor is
I’m guessing it’s 3 or 5 watts but not sure when tested I got a reading of 448
The rest of the amp looks to be very good even the large capacitor is reading okay.On the meter it was reading good if less than 200uf for both 32uf
The other issue I’ve got is earthing the record deck it’s a twin core and if you look at the photo you’ll see the pickup Cable isn’t attached to the deck
So I’m guessing I can just attach the Earth cable straight to the deck
But I’m guessing it’s not going to be that easy hence why am asking for your information and help
Thank you
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Old 15th Apr 2019, 7:26 pm   #2
ms660
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Default Re: Fidelity HF25 resistor wattage

Warning...Your record player is of the live chassis design, do not connect a mains earth lead to the record deck....Reason...the pickup leads are not isolated from the amplifier's chassis.

If you want to replace that 330 ohm resistor (the cathode bias resistor) replace it with a 2 watt job.

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Old 16th Apr 2019, 9:02 am   #3
Kalee21
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Default Re: Fidelity HF25 resistor wattage

Thanks for the information I don’t think it was going to be that easy is there any solution I could use that would make it a safer record player
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Old 16th Apr 2019, 9:15 am   #4
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Default Re: Fidelity HF25 resistor wattage

What I do with similsr record players is to replace the original two0core mains lead with a length of modern (Blue & Brown cored) Mains lead, ensuring that the Blue (Neutral) lead is connected to the Amplifier Metalwork. Under No Circumstances should a3-wire mains lead be fitted to any 'Live Chassis' Player or Radio. Other members may feel that the pickup leads, both signal & screen should be connected to the deck metalwork via suitable 'Y' Type Capacitors and the amplifier metalwork likewise connected to the deck chassis via a Y type capacitor. Some old record players did have isolating capacitors wired in the above manner.
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Old 16th Apr 2019, 12:05 pm   #5
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Default Re: Fidelity HF25 resistor wattage

Quote:
Originally Posted by 'LIVEWIRE?' View Post
Other members may feel that the pickup leads, both signal & screen should be connected to the deck metalwork via suitable 'Y' Type Capacitors and the amplifier metalwork likewise connected to the deck chassis via a Y type capacitor. Some old record players did have isolating capacitors wired in the above manner.
Would that isolate the cartridge connections from direct connection to one side of the mains? And what about the shunting effect of the capacitors across the cartridge output?

For general info, according to some schematics I've been looking at, the Dansette Prince, the Conquest MK11 and the Transit (mains only version) are live chassis designs with a mains earth connection and a tape socket, in those the mains earth is connected directly to the record deck metalwork, the signal and ground from the cartridge are connected to the amplifier via 0.01uF capacitors in the Prince and Conquest MK11, also in the Prince and the Conquest MK11 the mains earth is also connected to the amplifier chassis via a 0.0018uF capacitor and a 2.2megohm resistor in parallel, In the Transit there's no parallel RC network connected between mains earth and the amplifier chassis and the signal and ground from the cartridge are connected to the amplifier via 0.0018uF capacitors.

Lawrence.

Last edited by ms660; 16th Apr 2019 at 12:22 pm. Reason: addition
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Old 16th Apr 2019, 2:06 pm   #6
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Default Re: Fidelity HF25 resistor wattage

You did well to seek the excellent advice you have received there Kalee21! It's a big worry that quite a few new members don't realise that older equipment [without a Mains Transformer] is going to have a live chassis if the live and neutral supply is reversed-say at the plug. The metalwork is then 240v positive instead of at neutral. It can't be earthed as that would blow the fuse! It wasn't a major problem domestically "back in the day" as everything was kept isolated and insulated. Record Players are a particular concern [as opposed to Radios or TV's]. Ironically, the main risk is for the person attempting to work on the RP or perhaps the record deck itself ending up live when in use. There's lots of threads on this subject as people regularIy ask how do I earth this record player? Sometimes it even gets mixed up with earthing issues re the Cartridge. Take care.

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Old 16th Apr 2019, 2:13 pm   #7
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Default Re: Fidelity HF25 resistor wattage

Hi having done a continuity test I discovered that the record deck is completely isolated from the amp but I think my main concern now is having tested the volume and tone controls I’ve discovered that they’re not isolated from the live chassis and with them protruding slightly I think it would be safer to use this machine for spares it’s just not worth the risk of someone removing one of those plastic knobs and getting a electric shock
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Old 16th Apr 2019, 2:21 pm   #8
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Default Re: Fidelity HF25 resistor wattage

It's admirable that you are being cautious and methodical Kalee but it was probably "safe to sell" originally so, perhaps, see what those more experienced than either of us have to say first?

Dave
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Old 16th Apr 2019, 2:46 pm   #9
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Default Re: Fidelity HF25 resistor wattage

Thank you Dave Walsh it would be nice to use the player it’s like new I believe the family who bought it from new used it for about six months and then put it away and forgot about it
It’s just the first time I’ve come across a amplifier that uses a metal plate as a circuitboard
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Old 16th Apr 2019, 3:07 pm   #10
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Default Re: Fidelity HF25 resistor wattage

The deck metalwork can (and probably should) be connected to mains Earth, with a maximum 10nF class Y rated capacitor between it and the amplifier chassis (which is connected to either Line or Neutral of the mains).

Metal potentiometer spindles should not be electrically connected to anything under normal circumstances, but could conceivably become live under fault conditions. Unless the knobs come off easily, the player probably is safe enough. You could fit a plug with built-in RCD for "belt, braces and sticky knickers" protection.
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Old 16th Apr 2019, 4:42 pm   #11
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Default Re: Fidelity HF25 resistor wattage

As Julie says, it's a fault if the spindles are live Kalee but I suppose you could insulate them and the edges of the metal with tape if it's concerning you. The knobs are plastic. Older AC/DC live chassis sets sometimes have metal grub screws to the spindles that had to be countersunk and insulated. That doesn't apply here! Perhaps two points to note. There can sometimes be different opinions about whether to try to earth live chassis amps or not [as far as I can tell] but the general principle [ie "don't] still holds good. For example, you do need to use the Y rated special caps for this mains isolating purpose [as already indicated] not just any at hand. They are built for the job!

My thought is that the original arrangement should be safe and satisfactory enough.... [in theory and if that's what you've got] but I'm not as experienced as many others. A neon screwdriver is handy I find to check things out but some people don't have confidence in thoseWhatever you do, check in for advice if uncertain. There might be disagreement with this remark but of course, any concerns are more acute if the equipment goes to someone other than yourself. I'm sure most of us do temporary hook-ups we wouldn't advise for the unaware.

Dave

Last edited by dave walsh; 16th Apr 2019 at 4:49 pm.
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Old 16th Apr 2019, 4:46 pm   #12
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Default Re: Fidelity HF25 resistor wattage

Quote:
Originally Posted by Kalee21 View Post
Hi having done a continuity test I discovered that the record deck is completely isolated from the amp but I think my main concern now is having tested the volume and tone controls I’ve discovered that they’re not isolated from the live chassis and with them protruding slightly I think it would be safer to use this machine for spares it’s just not worth the risk of someone removing one of those plastic knobs and getting a electric shock

There's plenty of vintage equipment about that is no more "safe" than this RP. In reality it's no more dangerous than when sold and it is perfectly reasonable to use it (or sell it on) provided it is in original condition.
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Old 16th Apr 2019, 4:47 pm   #13
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Default Re: Fidelity HF25 resistor wattage

Re-reading my comments in post #4, and following other members' comments, I'm not sure, Lawrence, but , IIRC some Record players were fitted with isolating capacitors (obviously not 'Y' types as they weren't around between 50 & 60 years ago!) connected as I describe in my earlier post, although some, like the Fidelity, didn't have any isolating caps.
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Old 18th Apr 2019, 8:43 am   #14
Kalee21
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Default Re: Fidelity HF25 resistor wattage

Thank you for all information I don’t think I’ll be scrapping the player it’s in too good a condition for that and I think I’ll go down the line of installing the Y type capacitors.

Having said that could someone put a link to a suitable Y capacitor for that player I’ve been looking online getting quite dizzy with the amount on there I would rather go for a tried and tested one.

Again thank you for all the help
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Old 18th Apr 2019, 9:03 am   #15
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Default Re: Fidelity HF25 resistor wattage

'Y' (and 'X') capacitors are stocked by all the leading suppliers such as RS, CPC, Farnell, Rapid Electronics, etc., all of whom have websites with details of available values. Buying from one or other of these long-established companies is the best way to go. As Lawrence (ms660) has said in post#5, 0.01uf (10nF) capacitors were used by Dansette and others 'back in the day' so would, IMHO, be a good choice. The nearest available value to 0.0018uf available today would be 0.0022uf.
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Old 18th Apr 2019, 1:03 pm   #16
Kalee21
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Default Re: Fidelity HF25 resistor wattage

Thanks once again for the information having nothing to go off I’m assuming a voltage of 300 V or higher for a Y class capacitor would be better
Thanks
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Old 18th Apr 2019, 7:03 pm   #17
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Default Re: Fidelity HF25 resistor wattage

Class X or Class Y implies a voltage rating, so there won't be an actual voltage marked.
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