Bill's Quad woes cont.

[Bufo Bill]

I have a new problem with my QCII, but on the bright side I get to learn more and hopefully you can help me again.

Today's problem is the phono stage. It has just got slowly quieter over the last three days and is now inaudible. The Quad FM 1 still works, good volume at no.2 volume, and loud at no.3. The current pickup is an AKG P8ES, which normally sounds good on no.6 Volume. I have a R7 pickup adaptor.

You've come through for me before, so I'm hoping someone can help with this.
Cheers from Bill.

[PJL]

You are running a mono setup? and the volume from the tuner is unchanged?

The cartridge is very old and so I would start with that. Do you have another turntable you could try?

[Bufo Bill]

Hi, thanks for your help. Yes it is a mono set up, and you have it right, the tuner volume is unchanged.
I don't have another Turntable, I have tried an Empire 1000ZEX cartridge, (which is even older, I must admit), the same result of no volume. I have swapped leads from the tonearm to the preamp too.
Cheers from Bill.

[PJL]

You have the correct R7 adaptor installed (this controls the gain and input impedance)?
You have selected the RIAA compensation?

If it's not these then we need to look inside the box as it may be a poor contact or a weak EF86.

Try cleaning the switches, adaptor contacts, and the EF86 valve pins and socket, then measure the EF86 voltages.

[Bufo Bill]

Cleaned the areas you suggested, no change so far, but the switches were okay, but a bit of dirt on the valve pins, will test the valve later on,
Cheers from Bill.

[vidjoman]

Easiest way to test the valve is to swap with the other channel. If it changes channel- it's the valve. If it stays the same channel - it's a component.

[Bufo Bill]

Hi, thanks for your response, I can swap out the valve for a spare so thanks, will try that later on. Just so we're all on the same page, you mentioned swapping channels, this is a mono system, but useful tip there, many thanks.
Bill.

[vidjoman]

Sorry Bill - read it as 22. Yes try another valve and see what happens.

[PJL]

Bill, measure the voltages as well as that may help us diagnose the fault.

[Bufo Bill]

Hi PJL, I appreciate your help in this. I have swapped EF86, we now have a signal reaching the speaker, albeit at 7.5 on the volume control instead of approximately 6 before this trouble. I haven't yet checked my other pickups.
I shall clean the valve base again and check both EF86 in the circuit. I shall also test my other pick up to be certain that there is nothing there adding to the problem.
I will write again tomorrow.
Cheers from Bill.

[PJL]

The R7 adaptor tries to pull every bit of gain out of the EF86 but it is worth checking the valve voltages as it's also possible it is not being run optimally due to drifted component values.

[Bufo Bill]

Hi, not got round to checking things out today, spent 45 minutes shopping and upon return was told to vacuum "the whole sorry mess". Oh dear.

Originally Posted by PJL

The R7 adaptor tries to pull every bit of gain out of the EF86 but it is worth checking the valve voltages as it's also possible it is not being run optimally due to drifted component values.

Re the valve problem, I believe there is something else to be rooted out here. I ran the turntable for half an hour last night, new valve installed, and there was some deterioration in sound volume by the end. You may well be right.
Will get back to you with the readings.
Cheers from Bill.

[Bufo Bill]

I have re emerged . . .
Sorry for the delay in responding, but two strokes in different branches of my family rather spoiled the fun. Neither was fatal thankfully.
Anyway . . .
Va measures 96.7 VDC
Vg1 couldn't get a fixed reading
Vg2 60.1 VDC
Ia 0.45 mA
That's as far as I got, will get back to it tomorrow.
Sorry again for the delay.
Cheers from Bill.

[PJL]

Sorry to hear about your family disasters which I guess is from Covid stress. The readings look OK, has it had the capacitors replaced?

[vidjoman]

Presume those reading were taken soon after switch on. What readings do you get after it's faded?

[Bufo Bill]

PJL, the capacitors have not all been replaced, C13 and C16 are the original Hunts caps.
Vidjoman not sure what you mean by "faded"?
Cheers from Bill.

[Herald1360]

After the signal has gone down or faded away. Volume controls in mixers may be referred to as "faders". Suspect the term came across from lighting control systems?

[PJL]

How about a picture. C13 in particular and C16 should both be replaced along with any other paper capacitors and possibly the small electrolytics like C15 and C14.

[Bufo Bill]

Pictures below.
Va 97.1 VDC
Vg1 ?
Vg2 62 VDC
Vg3 0 VDC
Ia 0.6 mA
Ig2 0.13 mA
S no reading on mVDC

1 min after switch off.
Va 7 VDC
Vg1 0.01mVDC
Vg2 6mVDC
Vg3 0

[vidjoman]

Originally Posted by Bufo Bill

Vidjoman not sure what you mean by "faded"?

You said way back the sound level drops after a time (fades)- so that is when the fault is present and it's the voltages at that time relative to when you start listening that we need to know. There should be some differences and maybe we can determine whats happening.