Fidelity HF 23

[kirstyd]

Yes I know it's a box of junk and sounds awful but my mum bought it new way back in 1962. I keep it for sentimental reasons. Recently i borrowed its UL84 for another project. Weeks went by and when I came to put the Fidelity back together I mistakenly put an EL84 in. When i switched on the rectifier lit up like a Xmas tree for a few seconds then everything went dead. I put the UL84 valve back and a new UY85 and while that restored power there was virtually nothing from the speaker [just a faint hum and a little sound when playing a record. After checking everything I found all voltages were correct. I came to the conclusion that the OP transformer was dead. I found a transformer from an old radio [forget what model] and connected it up the player now works but the volume is not very loud. It's not the cart because I have tried the unit with an old CD player connected the results are the same so I am stumped. The service sheet says the output should be around 3 watts [I think that may be wishful thinking] but at full volume i would say it's just at a comfortable listening level . It certainly doesn't have that awful loud ear splitting sound it used to have. Any ideas folks. There can't be much wrong with it as there's hardly anything to its very basic amplifier

[AndiiT]

Hi, my first thought would be that the primary of the replacement output transformer is not a good impedance match for the UL84, do you know what output valve was in the radio your replacement transformer came from?

Andrew

[Station X]

Originally Posted by kirstyd

After checking everything I found all voltages were correct.

Strange that all voltages were correct, but the output transformer was faulty. Where was the UL84 getting its anode voltage from?

I wouldn't have thought that fitting the wrong valve would have done much harm, especially as the rectifier burned out instantly. The UL84 and EL84 have identical pinouts.

[G6ONEDave]

Perhaps a problem with the filiament/heater circuit now being low volts. I've not checked the circuit yet so just a suggestion.

Dave

[Station X]

Easily checked. According to the service sheet the HF23 derives its heater voltage from a tap on the motor winding.

[kirstyd]

From what i remember the transformer came out of an HMV radio with an EL84 output valve.

[kirstyd]

The transformer is a lot bigger than the original [about twice the size ] it's far too big to go where the old one was. I have mounted it next to the speaker using one of the speaker's fixings to secure it.

[Edward Huggins]

The OPTX in this generation of Fidelity models is perilously small. I would have thought that with the one now fitted there should be no apparent difference in output power and there would be a slightly better bass after warm up. Maybe the replacement is of itself faulty?

I would go try one those RS Components transformers (with multi-tapped primary and secondary) to optimise it. They cost c.£14-00. Depending on the condition of the cartridge, the output power of a UL84/EL84 is limited to around 1.5 watts - but that's plenty loud enough for average listening. I well remember at our Youth Club, a 1955 Dansette "Automix" using a single UL41 and fully stacked with 78s, could fill the small, packed, Hall with that R&R sound!

[kirstyd]

Originally Posted by Edward Huggins

The OPTX in this generation of Fidelity models is perilously small. I would have thought that with the one now fitted there should be no apparent difference in output power and there would be a slightly better bass after warm up. Maybe the replacement is of itself faulty?

I would go try one those RS Components transformers (with multi-tapped primary and secondary) to optimise it. They cost c.£14-00. Depending on the condition of the cartridge, the output power of a UL84/EL84 is limited to around 1.5 watts - but that's plenty loud enough for average listening. I well remember at our Youth Club, a 1955 Dansette "Automix" using a single UL41 and fully stacked with 78s, could fill the small, packed, Hall with that R&R sound!

Hi Edward
the replacement transformer came from a scrap HMV radio that had an EL84 valve and a 3 ohm speaker .I thought it might be a good replacement for the old unit . The sound is much better[nice and clear without that blaring tinny sound it usually makes ] but its just not loud enough. I will go through it again just to make sure i haven't missed anything not that there's much to miss in one of these. My mum [who is now 89 ] told me an interesting story about this machine .back in 1962 [i was only 5] my dad had gone to load more records onto the record player that was on the draining board in the kitchen [the only room big enough for dancing] .he accidently touched the Ascot geyser and got electrocuted .Dad took the recordplayer back to the shop who simply replac3d it with another

[kirstyd]

Well i have just gone through the whole thing again and all i could find was resistor 2 330 Ohms is a little high at 400 Ohms .I then examined the three replacement caps that i had installed some years ago .The smallest at 25 UF 25volts didn't look quite right and when i moved it one of its wires came right out of the cap body so i replaced it with a new 33Uf 25 volts and switched on not expecting any change .I was rewarded with a good loud [comforting ]hum .Once the pickup leads were reconnected the hum was reduced somewhat .I put on a 78 and was amazed by the sound .Lots of volume but not only that the sound quality is much improved and as Edward remarked [more Bass] could that larger transformer really make that much difference? .

[Fidelity Fan]

I am pleased to see that you have made progress with the HF23. The HF23 uses the same amplifier chassis as the HF25. Often the cause of low volume is the crystal cartridge which are difficult and expensive to source nowadays. Fortunately you have been very lucky.

I remember that when I was about 12, my grandma had an HF25 with a failed UL84. I did the same trick as you and put in an EL84 and got very frustrated when it wouldn't light up, but the UY85 lit up like a Christmas tree! I even tried another UY85 that I'd salvaged from a radiogram, but obviously it made no difference! The printing on both the UL84 and EL84 had got rubbed off which, caused the confusion between the two. I am surprised that the 330 ohm resistor going high in value or the parallel 25uF 25v electrolytic going o/c caused low sound, but all credit to you for sorting it out.

On later production, the UY85 surge resistor was changed from 82 ohms 2 watt to 130 ohms. In fact, the UY85 data sheet states that this should be at the minimum 100 ohms.

Later on, I had another HF25 and I caught one of the 32uF 300v HT smoothing capacitors when unplugged. I got the biggest electric shock that I've ever had! That is one to be aware of!

[Station X]

Originally Posted by kirstyd

The smallest at 25 uF 25volts didn't look quite right and when i moved it one of its wires came right out of the cap body so I replaced it with a new 33uF 25 volts....

A capacitor rated at 25 Volts would be the cathode bypass capacitor. If it was open circuit I'm not surprised the output was down.

[kirstyd]

Originally Posted by Fidelity Fan

I am pleased to see that you have made progress with the HF23. The HF23 uses the same amplifier chassis as the HF25. Often the cause of low volume is the crystal cartridge which are difficult and expensive to source nowadays. Fortunately you have been very lucky.

I remember that when I was about 12, my grandma had an HF25 with a failed UL84. I did the same trick as you and put in an EL84 and got very frustrated when it wouldn't light up, but the UY85 lit up like a Christmas tree! I even tried another UY85 that I'd salvaged from a radiogram, but obviously it made no difference! The printing on both the UL84 and EL84 had got rubbed off which, caused the confusion between the two. I am surprised that the 330 ohm resistor going high in value or the parallel 25uF 25v electrolytic going o/c caused low sound, but all credit to you for sorting it out.

On later production, the UY85 surge resistor was changed from 82 ohms 2 watt to 130 ohms. In fact, the UY85 data sheet states that this should be at the minimum 100 ohms.

Later on, I had another HF25 and I caught one of the 32uF 300v HT smoothing capacitors when unplugged. I got the biggest electric shock that I've ever had! That is one to be aware of!

I have replaced the 82 ohm resistor for a bigger one

[kirstyd]

Originally Posted by Station X

A capacitor rated at 25 Volts would be the cathode bypass capacitor. If it was open circuit I'm not surprised the output was down.

Well replacing it did the trick and the sound is so much better .

[kirstyd]

I recently got hold of a Fidelity HF26 that was working but sounded terrible. The problem was the high output cartridge that someone had fitted. I removed it and fitted it to this HF23 with great results good loud output. I then put the Medium output cart from the HF23 into the HF26 also with very good results. What's the chances of that happening again?

[Fidelity Fan]

I can't remember the original cartridge fitted to the HF26, but it uses an ECL86 valve, so I would think that a medium output cartridge would be adequate. However, the HF23 and HF25 use a single stage UL84 amplifier and need an high output crystal cartridge.

A BSR X5H or Acos GP91-3SC were commonly used replacements for the original TC8 turnover cartridges used in these.

[Edward Huggins]

Originally Posted by kirstyd

I recently got hold of a Fidelity HF26 that was working but sounded terrible. The problem was the high output cartridge that someone had fitted. I removed it and fitted it to this HF23 with great results good loud output. I then put the Medium output cart from the HF23 into the HF26 also with very good results. What's the chances of that happening again?

Well it will happen again, and it will everytime you match the correct cartridge's output to the sensitivity of an appropriate amplifier. Put simply, all single-stage amplifiers need a high-output cartridge. But do not confuse a single valve with a single-stage. In your case a UL84 is an ideal single-stage output valve, but an ECL86 is ideal as a two-stage valve for medium output cartridges. This is because the single glass envelope actualy contains two valves - one as the AF amplifer and one as the output valve.

[kirstyd]

Originally Posted by Fidelity Fan

I can't remember the original cartridge fitted to the HF26, but it uses an ECL86 valve, so I would think that a medium output cartridge would be adequate. However, the HF23 and HF25 use a single stage UL84 amplifier and need an high output crystal cartridge.

A BSR X5H or Acos GP91-3SC were commonly used replacements for the original TC8 turnover cartridges used in these.

The high putput cart that was in the HF26 has no markings on it [Its the turnover flag type] It looks like a Ronnette clone .Whatever it is it drives the UL84 in the HF23 very well in fact along with the bigger op transformer and the cart the old thing has never sounded so good.The HF26 now has a BSR x5M in it