Weird circuit in Fidelity record player.

[vampyretim]

Hi all,

I have a Fidelity, record player that keeps taking out 6X4 rectifier valves it also took out the 5 amp fuse in my lamp limiter. I wanted to see if the mains transformer had a centre tap so that once I've found the fault that I could replace the valve with solid state diodes. The mains transformer looks to me to be a repurposed output transformer and is only supplying the heater voltage. The live from the mains goes straight to the anodes of the 6X4 which are both joined together. There's no dropper resistor and I'm a bit confused with the circuit and was looking for a schematic. I can't find anything online about a Fidelity H.F.I or H.F.1. Has anyone worked on one of these before?

Many thanks,Tim.

[TonyDuell]

I don't know this player, but I've certainly come across units where there is a transformer for the valve heaters but the HT is obtained by rectifying the mains.

This means you will have a half-wave rectifier (hence the anode of the 6X4 are linked, putting the 2 diodes in parallel) and a live chassis (as the -ve side of the HT supply is one side of the mains).

What are the other valves in this player?

[Nickthedentist]

Quite a rare machine I'd say. Nice period styling too. No mention on the Radiomuseum site, or on the Trader Sheet or Paul's data. A forum search returns a blank too.

Someone here claims it's got an isolated chassis: https://www.worthpoint.com/worthoped...tro-1694440334

[vampyretim]

Hello,

Thanks for the replies. The other valve is an EL84 which confused me as I would expect to see a UL84 if it was connected directly to the mains.

Thanks again,
Tim.

[TonyDuell]

The EL84 has a 6.3V heater like the 6x4. I am guessing the heaters are in parallel and fed from a 6.3V winding on the transformer. But the HT comes straight from the mains.

[Edward Huggins]

This is an extremely early Fidelity player as it uses a Collaro autochanger - prior to Fidelity thereafter using BSR units. I cannot quite see the Collaro bronze model label - but if the autochanger is a RC54 dates it to late 1955/early 1956 or if it's an RC456, it will be from mid-1956. I have never seen one so early. In my experience these just use a Filament transformer for the valve heaters.

[John10b]

In the link that Nickthedentist #3 provided it says that the amp has a Mains transformers? I tried to find a circuit but was unsuccessful.
Cheers
John

[Nickthedentist]

It does, but it could well just be for the heaters, as EH says.

[vidjoman]

The mains should not be directly connected to the rectifier valve but via a resistor of probably 100 - 200 ohms. I suspect that at some point in the player's history someone (with a ten gallon hat and spurs) has found a burnt out resistor and just shorted it out/removed it and fed the mains straight to the valve. It worked so they thought no more of it but it should not have been connected that way as it will cause failure of the 6x4 valve. I've definitely seen several old record players that only had a transformer for the heaters.

[Nuvistor]

Presume the PSU is similar to this circuit but two anodes strapped together.
Yes a surge limiter would normally be in circuit as per this diagram.

[kalee20]

By 'taking out 6X4 rectifier valves' what does that actually mean? Heaters failing? Hester-cathode shorts developing? Internal leads fusing? I'm intrigued!

[Diabolical Artificer]

Check the caps after the 6X4, are they about the right value and are they leaky, IE acting as shorts. Check they are wired correctly, IE someone hasn't wired them the wrong way round. Check for shorts in general and lastly check voltages of the EL84 and make sure the cathode r & c are ok.

That is a really nice record player, old record players usually leave me cold but that one has a je ne sais quoi.

Andy.

[barrymagrec]

I think that sets with only a heater transformer were reasonably well known at one time, made for much cooler running without the dropper resistor.

[Herald1360]

So did the (cheaper?) tapping on the motor winding approach. Did any RPs use a dropper resistor- I know a few used the motor in series which would be an inductive dropper and more efficient than a straight resistor.

[Welsh Anorak]

This seems like a rare beast so I'd be inclined to make it work as intended with the 6X4. After all - it worked once! Of course you could always fit a solid state rectifier and leave the valve in situ, but I don't really see the point, especially as the slow HT rise is much kinder to the rest of the circuit. I tend to agree with post #9 - maybe it was retired after a resistor was linked out and the valve failed.

[electrogram]

Some Philips players used a dropper, I'm sure there are others. The Collaro microgram of the late 1940s with its 200ma heaters used one too, dissipating a large amount of heat in a cramped space

[vidjoman]

I think you have to look at price as a full mains transformer would push up the costs. Several makers did use a proper transformer and others used what they had available for the cheapest price. I do recall seeing several with mains droppers for the heaters and HT supplies. Date of manufacture played a part as record players became more popular different approaches were used to keep prices/sales going by each maker. As with radios the 'guts' were enclosed and therefore safety was a minor consideration. The metalwork of the turntable usually being connected via capacitor for 'some' isolation. Look how many had their cartridge connection connected directly to a chassis with only a small rubber sleeve covering the pins and could have been live depending which way round you plugged the two pin mains plug into your supply. Tape recorders presented a challenge as external parts, microphones etc. could be dangerous without proper mains isolation provided by a proper transformer.

[FIXITNOW]

I would keep it as is, but add a surge resistor if overly worried of where it would finally end up or with whom. I would find an old radio transformer to suit then I could give it a proper earth.

[vampyretim]

Hi all,

Thanks for the replies. I'm actually away for a week or so and don't have the thing to hand. From memory though the amplifier seemed untouched so I don't think that it ever had a dropper. When I said that it was taking out the 6x4's when I got the thing it had a milky 6x4 with a cracked base so I replaced with a nos one and the amp was working for 20 minutes or so as I was working on the mechanics and I happened to see a flash and the fuse was taken out in my lamp limiter. Looking at the valve it has completely disconnected an internal connection (I think cathode but can't quite remember) of one of the pins. A huge current has been drawn and I was suspecting it to be the power supply caps.

Many thanks.

[John10b]

Further to Nickthedentist post #3, and the link he provided, the seller states the following “The amplifier has a proper mains ransformer (sic) which allows for an isolated, earthed chassis “.
Cheers
John