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Old 25th Oct 2020, 4:04 pm   #1
CarsonQuad
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Default Quad 2 Mod??

Hi Everyone,

I'm wondering about what appears to be a minor mod in my Quad 2 amplifiers. I attached a photo for reference. Looks like maybe an audio input of some kind. I don't see any reference to it anywhere, and haven't seen it in photos of other people's amps.

My questions are:

1) Can someone confirm that this is NOT original?
2) Any idea what would be its intended function?

Ideally I'd like to remove it and repurpose the hole for something else, like a power cable or RCA audio input.

Thanks.
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Old 25th Oct 2020, 4:10 pm   #2
barrymagrec
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Default Re: Quad 2 Mod??

It looks like someone has fitted a Jack socket input in order to use the amplifier without the pre-amp unit or otherwise using the Jones socket input.

Certainly not original.
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Old 25th Oct 2020, 4:13 pm   #3
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Default Re: Quad 2 Mod??

Quote:
Ideally I'd like to remove it and repurpose the hole for something else, like a power cable or RCA audio input.
It does look like an input, why not leave it as a jack type? Much better than the RCA ones all you need is a plug.
 
Old 25th Oct 2020, 4:20 pm   #4
snowman_al
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Default Re: Quad 2 Mod??

1) Not original. Looks as if someone has partly replaced the resistors, but left the coupling cap(s) C2 & C3 and removed the speaker sockets...
2) It connects to pin 2 of the Jones socket. That is the input connection with pin 1 ground. If you do use it for an RCA, do not use the chassis as the ground. Insulate the outer ring from the chassis and add a wire from pin 1 to the ring.
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Old 25th Oct 2020, 4:29 pm   #5
CarsonQuad
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Default Re: Quad 2 Mod??

Thanks for the tips. It was me who swapped the resistors. I also removed the speaker sockets.

I'm planning to use the amp with a different pre-amp, so an RCA-type input would be ideal as it would match the RCA output on my pre-amp.

This feedback from everyone is great. Basically confirms what I thought.

Cheers.
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Old 25th Oct 2020, 7:08 pm   #6
GrimJosef
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Default Re: Quad 2 Mod??

I guess you're aware that the Hunts L45 coupling capacitors are very prone to going electrically leaky, sometimes only after they've warmed up, and that that can have serious or, at worst, catastrophic consequences for the KT66s and/or mains transformer and/or output transformer ? Leaving them in situ is a very brave* thing to do ...

Cheers,

GJ

*To be honest, it's a very risky thing to do.
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Old 25th Oct 2020, 7:53 pm   #7
CarsonQuad
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Default Re: Quad 2 Mod??

I appreciate the warning about the Hunts capacitors. I've decided to replace all the capacitors and resistors. There aren't that many of them and they aren't expensive. I don't like the idea of relying on bits that are 60 years old. For C2 and C3 I'm planning to use the same caps 0.1 uF Polypropylene film caps I used for C1.

Having said that, I may just not touch C4 and C6. They read within 3% of 16uF on my multimeter and replacing them looks a bit more invasive.

After I've done all my work I'm going to hand off the amps to my tech guy and ask him to check everything over and power them up.

Cheers. -Carson
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Old 25th Oct 2020, 8:38 pm   #8
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Default Re: Quad 2 Mod??

Quad did things engineering wise so replacing parts with modern and better ones would please the designers.
 
Old 25th Oct 2020, 8:56 pm   #9
GrimJosef
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Default Re: Quad 2 Mod??

Quote:
Originally Posted by CarsonQuad View Post
... Having said that, I may just not touch C4 and C6. They read within 3% of 16uF on my multimeter and replacing them looks a bit more invasive ...
Yes. However, if the amp hasn't been powered up in the last couple of years then it's wise to 'reform' these capacitors (a search on here will turn up a lot of information about electrolytic capacitor reforming). I keep the current down to a milliamp or less while doing this. The success rate, assuming the capacitors haven't already been blown by someone 'just plugging the amp in', is then very high.

Cheers,

GJ
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Old 27th Oct 2020, 11:58 am   #10
Richardgr
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Default Re: Quad 2 Mod??

Just a thought about those jack sockets. If you would like to keep your Quads close to the speakers, then you have the problem of a long run for the RCA input cable, and you would need to split it so that it was mono to each amp. Using the jack would permit the use of a better quality cable, like a microphone cable, and then you have a splitter on the preamp.

Maybe that was the reason for doing it this way?

I have also recently restored some Quad IIs. I added a 0.1uF capacitor from the input to protect the amp from DC.

Out of interest, using an C14 type IEC socket (to work with a laptop cable), I was able to fit the IEC without drilling the chassis - I use the old fuse hole for the socket, and the input voltage selector hole for the fuses and power switch.

Putting the power input by the transformer means that you keep the power wiring close to the transformer.

I did drill one hole - for the chassis earth, next to the power inlet.

If you are wondering about the tubes - they are 5B/255M with loctal to octal socket adaptors. They work very well, but I did add a 100ohm screen resistor to be on the safe side.
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Old 27th Oct 2020, 12:44 pm   #11
Richardgr
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Default Re: Quad 2 Mod??

The IEC picture was not very clear, and if anyone is interested here is a Swedish Radio version, complete with original cage.

I fitted the fuse and power switch into aluminium balanking plates, then attached that inside the case, with a fillet between the fuse holder and switch, so that it was flush and sealed to the outside.
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Old 27th Oct 2020, 1:08 pm   #12
GrimJosef
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Default Re: Quad 2 Mod??

Quote:
Originally Posted by Richardgr View Post
... Out of interest, using an C14 type IEC socket (to work with a laptop cable), I was able to fit the IEC without drilling the chassis ...
I think that's a C6 chassis plug, not a C14, isn't it ? And the screwholes which are used to secure it do count as 'drilling the chassis' I'm afraid.

Cheers,

GJ
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Old 27th Oct 2020, 1:22 pm   #13
Richardgr
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Default Re: Quad 2 Mod??

Yes, correct on both accounts. I was a bit hasty with the post - it is C6 inlet with a C5 plug.

The holes are just 2.5mm, so easy to disguise, so I had not counted them as 'surgery'.

Having the IEC is convenient, but I think in many cases just having a short lead with a socket on the end is just as good, and even more flexible since the plug does not protrude.

However, having the earth on the chassis is a necessity, so some sort of action is required to make the old Quads safe, especially considering they have 60 year old transformers.
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Old 27th Oct 2020, 2:27 pm   #14
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Default Re: Quad 2 Mod??

I hope you meant a short lead with a plug on the end. In the absence of any qualifier such as male or female, sockets have errr... sockets in them and plugs have pins. You don't want live pins lurking until they bite!

Things get confusing around equipment inlets where you insert the (trailing) socket into the (fixed) plug

And then there're touch safe shrouded and recessed pin plugs just to confuse things even further
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Old 27th Oct 2020, 2:30 pm   #15
GrimJosef
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Default Re: Quad 2 Mod??

I agree about the earth. I tend to bring the mains in at the original end and use one of the existing screw holes to secure the earth.

Cheers,

GJ
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