Quad FM1 questions

[Luxman1050]

Well
all voltage readings more or less spot on in ref to schematic.
Could be KT66 valves although they test good.

Still lack of volume and distortion very frustrating. I think it's going to be the pre amp so will need to go over that although everything has been changed using good quality caps and resistors, plus all solder joints re soldered, pots cleaned etc. Re wire where needed. So where do you start ha. Already done.

Could be FM tuner as nothing has been changed since it was made all original and falling apart. Could be cause? Then again could be anything really.

Must admit getting bit bored with this one.

[Nuvistor]

What test equipment do you have? A scope and audio signal generator will make this job easier to test the pre amp and power output stages.

If the circuit you have doesn’t tally with the amp then perhaps draw your own circuit.

[Luxman1050]

Hi Frank
no I don't. I have a 70s venner oscillator. But would not be helpful as it's a dial as opposed to a screen.
I've checked everything on mono block and everything is spot on all wired correctly took a while as needed spec sheets for the valves as there not in order number wise on schematic.

P is on winding of the output tranny not marked but sits bottom end of Q winding.

The output on speakers more or less spot on reading 8.25ohms either side so cannot see that causing any form of distortion. Changing the Russian pio caps seems to have made slight difference. I have 2 in the pre amp so will remove those and put some polys in see if any improvement there.

Now the choke which I had brand new one made up on mono block is wired to the two turrets on opposite side of C5 and R12 I think that's the right way round not 100% sure as when I removed it it was covered in tar and wires broken off so was nothing to compare original connections to. So C5 and R12 not physically attached to choke. Would you know if that's right.

Anyhow thanks for advice Frank.

Cheers Chris

[Nuvistor]

I can only go off the circuit I have, C5 and R12 are in the cathode circuit of the KT66’s, I presume the choke is the one in the HT circuit so there should be no connection between these parts.

[Luxman1050]

Sorry guys here we go again.
Managed to sort out quad2 pre amp still bit of a mystery but I'm back on this FM quad tuner. This model I think is their 1st version so the schematics I can only get on lineare for the 2nd model.
Does anyone have the schematics for my model? Be great help as I'm working blind. Have attached pics of base and schematic I have as you can see completely different.
The other thing the hunts 8uf electrolytic cap is can negative. Now I opened up the can and put in a new cap with negative soldered to the can. But radio does not work just a hiss. I also tried soldering negative to chassis ground and still the same. On schematic it looks like negative is going to the top mounted 5k resistor which goes to pin 4 on HT lead. But original can has no such physical connection.

Any pointers most welcome.

Cheers Chris

[ms660]

Originally Posted by cdm1christopher

On schematic it looks like negative is going to the top mounted 5k resistor which goes to pin 4 on HT lead.

On a schematic I'm looking at the +ve of the electrolytic (C38) is connected to the 5k resistor.

Lawrence.

[Luxman1050]

Yeah that's what I have but if you look at the underneath of my tuner the layout is completely different and does not fully tally at all with the schematic I have hence this must have been their 1st model. Heavens knows! Yeah it connects to the 5k via the rail which has resistors and capacitors also attached not on schematic! But on schematic it looks like it runs straight to the 5k resistor?
Plus negative seems to be running to v6 then onto chasis ground on schematic. But the can is negative so is grounded that way I think straight to chasis. But here is no physical wire connection via the capacitor negative. So cannot understand since I have soldered negative to the can and that is secured to and touching the chasis it is not working. Unless the new cap has to have the negative physically grounded. Tried that but no difference. Just hissing. But put original can back in and it's fine? So something needs connecting on the negative side. Never encountered this before as I usually always clean out cans and put new caps in although this is the first one which has only the positive terminal to the base normally a negative there as well.

[ms660]

C28....-ve to chassis, +ve to the HT rail that supplies the valves, that's it so far as I can make out on the schematic and in your photo's of chassis bottom side.

Lawrence.

[Luxman1050]

helps if you plug in the aerial Lawrence ew. Seems to work now ha ha ha.

But schematic definitely different to this model must be an early one.

[ms660]

Originally Posted by cdm1christopher

helps if you plug in the aerial Lawrence ew. Seems to work now ha ha ha.

But schematic definitely different to this model must be an early one.

You should always check the simple things first. I looked for an earlier schematic but no joy so far.

Lawrence.

[Synchrodyne]

Re the Quad FM schematic, I have those corresponding to what appear to be the four major iterations of this tuner, as detailed below. I don’t think that I should post them here, but please send me a PM and I’ll email them to you.

Series A, to S/N 4000:

Original circuit, with 6BJ6 RF amplifier and 6BH6 1st IF amplifier, (smoothed) AGC from limiter grid to RF amplifier, no AFC, no neutralizing of 1st and 2nd IF amplifiers. Sometimes referred to as the “Acoustical FM Tuner” in Quad literature.

Series B, S/N 4001 to 8676:

AFC added, neutralization of 1st and 2nd IF amplifiers added. From this iteration onwards referred to as the “Quad FM Tuner”.

Series B, S/N 8677 to 19061:

RF amplifier changed to 6BH6 without AGC. 1st IF amplifier changed to 6BJ6 with "fast" AGC from limiter grid.

Series C, S/N 19062 upwards:

MPX switch added, to allow direct connection of the MPX decoder without the need to disconnect the de-emphasis components.


I am not sure if Quad ever retroactively referred to the “FM” as being the “FM1”, or whether the latter is simply an unofficial designation. It did retroactively refer to the original Quad amplifier as the “Quad I”, so it might have done the same with the initial FM tuner, although if so, “Quad FMI” might have been more likely than “FM1”, given that the initial stereo FM tuner was the “FMII”, although sometimes referred to in marketing literature as the “FM Stereo”.

The prototype design (by Geoffrey Horn) goes back to 1952, and was recorded in Wireless World (WW) 1952, July, p.257. J.D. Collinson of Quad finished the design for production in 1955, that work including the addition of the twin-neon tuning centre-channel indicator, as described in WW 1955 September p.428ff. It is said that Collinson derived that from a similar device he saw in an American magazine. This might well have been from the Sonocraft FM tuner, which was reviewed, with a description of its tuning indicator, in Audio Engineering 1953 January, p.56. The twin neon indicator was subsequently also used by Jason and Beam Echo. The solid-state era twin-lamp derivative was used quite widely.


Cheers,