Fidelity HF35T (Transistor version).

[HRichard]

Guys
I have been given a Fidelity HF35 (transistor version, not valved) and have stripped, cleaned and lubricated.
It is all working now except there is no sound from the speaker.
I can hear playback directly from the cartridge, but obviously very faint.
Any ideas which component needs replacing please?
PS. I was here a few years ago but couldn't remember my login details, hence re-registering.
Thanks all, speak soon.

[Station X]

Have you tried a buzz test to check if it's a cartridge fault?

I believe the circuit is very similar to that shown here:-

https://www.vintage-radio.net/forum/showpost.php?p=494885&postcount=11

[HRichard]

Hi Graham
If by buzz test, you mean tapping the cartridge, then yes, tried that and nothing......

[Techman]

You could easily use the search box at the top of the page to search for "buzz test" and find all the information you require, but I'll tell you anyway. Just touch each of the cartridge electrical connections in turn at the rear of the cartridge with the blade of an insulated screwdriver and with the volume control turned up to full and one of the connections should produce a load 'buzz' from the speaker. If there's a 'buzz' then this proves that the fault is with the cartridge. If there's no 'buzz' then the fault is with the amplifier side, or the connections to it.

[HRichard]

Thanks Techman. I can confirm, NO buzz.

[Techman]

So as long as you made a good electrical connection with the screwdriver blade to each cartridge tag (there's often an insulating sleeve on the cartridge tags) then it sounds like there's an amplifier or speaker fault, or possibly one of the interconnections in between. Can you hear any hum at all with your ear to the speaker?

[HRichard]

Techman, I have tried a different speaker, there's no power on "thud" and no hum from the speaker. The only sound is the unamplified noise from the record surface.

[Station X]

Time to get your meter out and check out the power supply. Best checked by measuring the DC voltage across any electrolytic capacitors.

Can we have some pictures of the amplifier please so we can be certain which version it is. Does it look like the one in this thread:-

https://www.vintage-radio.net/forum/showthread.php?p=1059388

[HRichard]

Different version of the same system Graham.
I'll get some pics up tomorrow.

[EmleyTim]

Likely AC176 and AC128 with consequent tin whisker problem.
Regards, Tim

[Edward Huggins]

These types of transistors are not used in this very early, crude circuit.

[HRichard]

Some pics of the board.

[HRichard]

The cap bottom left 0v
Big cap in centre 27v
Cap near right 0v
Cap far right 27v
Top transistor 27v
Bottom transistor 0v
Bottom right horizontal resistor 0v
Other resistors in that area all have voltage.

[Brains1]

From your photos, this looks like the AC176 and AC128 transistors version as mentioned in #10.

If it used the MJE340 etc transistors, I would expect 90V supply with 85V at the MJE340 Collector.

Regards

[Station X]

No transformers as far as I can see so I guess it must be powered from a tap on the motor winding.

[Station X]

The circuit may be similar to the Bush SRP52.

See post #7 in this thread:-

https://www.vintage-radio.net/forum/showthread.php?t=31591

[julie_m]

With a multimeter on 200V AC (~) range, measure the voltage on the two white wires coming from the motor windings to the amplifier board. (It shouldn't actually be anything like as high as 200; if it's below 20V, feel free to switch to 20V~ for an extra decimal place.)

Now switch to 200V DC (==) and measure the voltage on the other two pins of the rectifier (the blue component to wich they connect, that looks like a painted stack of metal plates). As before, if it's less than 20V, you can switch down to 20V== for an extra decimal place.

NB: The record player will need to be powered on, and the motor running, for these tests. (This record player uses an extra winding on the motor as a power transformer.)

[Techman]

Originally Posted by julie_m

The record player will need to be powered on, and the motor running, for these tests. (This record player uses an extra winding on the motor as a power transformer.)

Did you miss post #13 Julie? He's already proved voltage from the power supply, so doesn't really need to do this test.

Sounds like it might be output transistor problems.

[julie_m]

Ah, right. It took me a while to write my post, so I could well have crossed over.

27V DC isn't too unexpected. Let's test some voltages on the output transistors, then! (Those are the ones in the tubular metal cans with the copper thing clipped to them.)

With the negative meter lead held on the point marked "C" and the meter on 200V DC (==) range, measure the voltage at each of the points circled and marked 1, 2, 3, 4, 5 and 6 on the attached picture. Again, if any of the readings are smaller than 20V, you can switch down to the 20V range.

(NB: If all the readings come out negative, try again with the positive lead on C and mention this alongside your readings.)

[HRichard]

Voltages as per image above:
1 - 0
2 - 0.03
3 - 0.18
4 - 0.18
5 - 0.03
6 - 27.0