• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Pair Quad II in all original condition... restore or sell

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Restore them well - have a listen and then sell them.
The people who love these are generally not capable of restoring them so will pay good money for having a pair in reliable working condition.
Undoubtedly you will realize enough cash to build something much better as a result.

At least you get to hear them this way before you have to make a decision.

They're in excellent condition under the dust and grime. Little bit of tar leakage but that's normal with these. I could get away with cleaning them gently and not repainting them at all I reckon.

There's a pair on eBay in slightly worse condition than these (missing base plate) that are about to sell for over £800 - YIKES!

Still in 2 minds - I don't want to start the restoration and find any nasty (read expensive) surprises... when I could sell them as is - for that much....

....but then.... the tubes.... ah I want to see them glow and sing...

It's a hard decision.
Yeah, with a restoration, it is mostly about making it work and sound relatively the same way, but with more modern bits. But do all this with safety in mind, I would consider an upgrade in resistors to be metallized or wire wound versus the carbon ones because of temperature drift and safety of it all. Putting NOS 50 year old possibly dried out electrolytics in there is probably a nice thought, but modern electroyltics with a higher temperature rating and voltage rating will clean up the sound (to a degree) and even out the circuit, but again is more about safety. Corroded sockets that can arc over, gassy or worn out tubes that are going to overrun, or crapped out transformers are also not a good thing to have either.

Most of these things listed up there are in the power line side of things, so the audio output side of things (keep the chokes and OPTs if they are still working), that is a whole different matter. If you can keep that as close to spec as possible will still preserve a lot of "that Quad II sound". If your amp has them, then you have to weigh the paper in oil caps versus a modern polyester cap. But again, safety first.

Modification is probably not a good idea if you want to sell it, but safety and updating it is a good idea.

Now that the cart is before the horse, let's decide on the horse; are you going to keep it or not?
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Putting NOS 50 year old possibly dried out electrolytics in there is probably a nice thought......

Caps are an example of restoration practices that allow having both. Since modern electrolytics are much smaller than vintage, it's not unusual to slip a new cap into an old PS housing to maintain original visuals.
Personally I would tread carefully with resistors. Potential customers for that Quad II sound might have strong opinions about metal vs carbon. Paper in oil caps are a little easier, Soviet military replacements are all over E-Bay. With all replacements I suggest unsoldering rather than snipping and selling the amp with a baggie of original ju-ju parts.
Ex-Moderator R.I.P.
Joined 2005
nice !
but you will need effective speakers
I guess preferably simple design
if speaker are not righty, you might even think they sound weird or strange
and don't expect thunder bass
but very refined sound, midrange especially
probably sounds more like a single ended SE than the PP it actually is
and you may need a preamp with some gain
but depends on your source

this seems to be your first post about tube amps
I take you have limited experience, and none with tubes ?
Limited = none yes -

I've built Class D stuff and that's about it - but I have a lot of soldering hours under my belt and even build SMD stuff (Metcal Soldering Station and a Hot Air Rework) - this is mostly for RC Drones etc.

So I'm no bad shakes with a schematic and a multimeter - and lets face it - you couldn't get more simple than the schematic of these amps.

If I do restore - it will be as minimal as I can. I'd swap out the resistors for metal film and update the electrolytics to something contemporary. The rest I'd leave alone so long as it is sound.

I feel I would have to update the power socket to a fused IEC and earth the casing - I would not be comfortable with the stock sockets. I'd also change the fuse holders to something modern and safe.

I'd probably leave the jones connectors in and use a converter plug.

I'm just worried that I might start the restoration and find one of the transformers is shot - or a knackered choke... then the cost of restoration suddenly starts to creep up.
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So you basically know where to start and your own limits. That is good.

Resistors, electrolytics, are the perfect starting points. Tubes would be next because a dead tube is exactly that, but only if you can not find a fellow diyaudio member with a Hickok or EICO tube tester nearby (there is a list somewhere here on-site I believe).

Does the casing need grounding? Something I recall George at Tubelab had mentioned in an incidental way about some companies using (or not using) the grounding of the chassis as part of the feedback. You might want to look through the tubelab section of this website and check that out. If nothing at all, it is also something that you will learn about tube amps.

Sounds like you are going to keep this pair of beasties... you might enjoy them and they might make you change from chips to tubes.

Either way, see it as a journey and have some fun along the way.
Ex-Moderator R.I.P.
Joined 2005
ah, ok... making play first.... with minimal costs and effort, and then decide :scratch2:

yeah, sure, thats how you restore vintage classics
no cosmetic work until its in good mechanical and functional condition

btw, regarding their 'simplicity'
please notice they have rare and special output transformers with taps(winding) for cathode feedback
I would say more like 'sophisticated', and not really so 'simple' at all
Disabled Account
Joined 2010
Its very easy,

To make a complete mess of something like this...take your time and think very carefully before you do anything..resist the erge to grab the soldering iron and then regret it later...

Its a bit like buying a classic car and putting a modern engine in it then finding you don't enjoy the ride any more.

No1 if you sell the amps as updated and in good working condition then you become responsible for the safety...if sold as vintage non tested its different!

So think of making a good job and a safe job and you will have a great set of amps...so what I,m saying is take your time..If your not going to sell them then its a case of what you feel like doing..as long as its safe. :)

The first thing I would do is check the transformers its easy to compare the one amp with the other using a multi-meter on the ohms scale..reason is if the Tx's are stuffed then don't waste your time..if thats all OK then your in a better position to decide..

These amps might not have discharge resistors so be carefull with B+ Ht up after power off..and as stated the PSU caps are probably stuffed.. :)

That all said you might become a valve addict...so can you take the chance of conversion..?

M. Gregg
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Consider it this way -- as far as we know, you didn't spend any money to obtain them. Zero dollars.

None whatsoever.

Nothing other than washing your hands with some strong soap and taking a picture.

No matter what you do, you have found money if you sell the pair as is or found money (didn't pay for them) if you restore them and use them yourself. You will not even be out of pocket one single cent if you decide to give them away for example, to someone like me as I would pay the postage. Right now at this moment, you are out of pocket absolutely nothing and have some potential upside.

Do you have the time to fix and shine them up? Do you want to hear what an original tube monoblock pair sound like?*** Is this your thing or are you more Class A/B transistors and multi-way speakers instead? Could you part with the pair without regret?

Maybe you want to give her a go and the transformer you mentioned does runaway and has a meltdown, means that you will sell as parts partially restored minus one working transformer or further source a part and fix.

Just do what will let you get a restful sleep at night.

*** at the very least, get a variac, test bench speakers, and a cross your fingers
Disabled Account
Joined 2010
Seems I will be the only one going for the sell them right away option, original state is what brings prices up no matter if it means parts would have to be changed to restore it to a working condition.

Score some good cash and build some DIY amplifier design and still have money left over even after requiring suitable speakers.

Your not the only one..I'm in the sell them "as is" camp as well..

Only if someone realy wants Old Quads as a project would I consider restoring them. Probably a good idea to put them on your HiFi rack and see if you could live with them???(before touching them) I would probably build a good DIY unit.:D
As I said what if you mod them all up to spec and don't want them???

M. Gregg
Ex-Moderator R.I.P.
Joined 2005
well, thinking twice about it....I will only buy them 'as is'
now that we know the details, I wouldn't trust you to do it, sorry :clown:

if it were a violin a professional would say...hands off, or you will ruin a good violin
learn how to build one before attempting difficult repair jobs

maybe a swap with another good but properly functioning tube amp would a better idea :scratch2:
There's ample information out there for anyone with reasonable skill to make a more than competent job of restoring one of these using generally available components. If the transformers are bilked then they are next to worthless anyway.
Your market expands significantly if they are properly restored since the number of HI-FI fans who are competent with a soldering iron and know what to do is not massive. My experience is that HIFI fans often have no technical understanding of the products they are buying which is why they are so prone to snake oil salesmen.

I would be more concerned about selling it onto someone who would then power it up without restortation and take down the transformers.

How about this for inspiration;


Or this;


My first foray into valve DIY was to restore a pair of LEAK Stereo 20's, so its not rocket science.

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