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Old 8th July 2015, 08:59 AM   #1
Katch is offline Katch  United Kingdom
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Join Date: Dec 2011
Default My Quad II and 22 restoration

So, some of you may remember this thread from a few years ago;

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

Click the image to open in full size.

My great uncle gave me his old Quad gear including a pair of untouched Quad IIs and the 22 control unit.

A house move, a kitten, a puppy, a wedding and a baby later, I've finally had a chance to look at them again.

After a few shandies and feeling cocky - I decided to take a gamble and plug the whole lot in. I know, I know, reckless - but I knew the risks and thought I'd roll the dice.

Long story short - they work. I wouldn't say they are healthy but they definitely work and I've had them driving my speakers for a short period.

Which brings me to the restoration. I've been keeping an eye on eBay prices for these for the intervening years, and restored Quads that are ready to play definitely command a higher price. So my mind is made up, I am going to restore them and listen to them for a while before ultimately rehoming them.

Hence why I am posting here today as I am after some advice from you all about various decisions that will form the path of this restoration.

Here are my objectives.

First off - I want them to be 100% electrically safe.

I want to replace old components with contemporary equivalents that will have a long service life ahead of them.

I want to keep as much of the "Quad sound" as possible.

The Plan

Replace all resistors
Replace all capacitors
Replace speaker outputs with binding posts (can be done without drilling)
Add chassis earth from the bulgin plugs (possibly change to IEC)
Add single RCA input
Clean casing and respray if deemed necessary

Resistors

I'm planning to go with 1w metal oxide for R1 - R11. Yes I could be more faithful and choose a modern carbon comp or NOS carbon comp resistors but I feel the risk to the rest of the amp is too great. Using metal oxide should give the units the best life expectancy possible.

R12 - I'm going to use a 10w wire wound resistor.

Capacitors

Now here is my main conundrum. What to use what to use...

I'm going to pull the grey can C4/C5 and replace with an ARS 32uf+32uf

https://www.watfordvalves.com/produc...il.asp?id=2889

C1/C2/C3 - I'm thinking about replacing with these 0.1uf 630v Mallorys

https://www.watfordvalves.com/produc...il.asp?id=3146

C5 - looking at using Ansar 22uf

Ansar Supersound Audio Polypropylene Capacitors | eBay

C2/C3 replacements are non-conductive cases so don't have the impedance that the original circuit is designed to have. I have seen some restorers appear to wrap the cases in copper tape. Is this a viable way of recreating that impedance?

Why no PIO NOS? I've thought long and hard about this. NOS always worry me. The O means old, and even unused capacitors can degrade with age. It just doesn't seem worth the risk to me. Objective 2 is a long service life ahead of them.

Notes & Feedback

I will be labelling and bagging all the original parts as I remove them so that when I come to sell them - all the original parts will be included.

I'd really appreciate some feedback about my capacitor choices and any recommendations and suggestions for them before I start purchasing parts.

If I make it through the Quad IIs then we can start thinking about the fiddly 22 Control unit.

Thanks for reading.

Last edited by Katch; 8th July 2015 at 09:08 AM.
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Old 8th July 2015, 09:51 AM   #2
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I have a pair like that somewhere in a box, so will be following your progress with much interest!
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Old 8th July 2015, 10:06 AM   #3
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Location: New Zealand
hi Katch
This site looks at many aspects of restoring the Quad 2
quad2powerampmods

and Keith Snook has some great information too
QUAD II Valve Power Amplifier Modernising and Modifying

I have a feeling you will end up keeping them

Cheers / Chris
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Old 8th July 2015, 11:20 AM   #4
msdin is offline msdin  United Kingdom
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I would stay with good quality carbon film resistors in the Quad II amps the sound changes with metal film.

Here is a link to the modification I did to my Quad 22.

Quad 22 Preamp Challenge. - pink fish media

Sharif
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Old 8th July 2015, 11:27 AM   #5
Katch is offline Katch  United Kingdom
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Join Date: Dec 2011
Quote:
Originally Posted by msdin View Post
I would stay with good quality carbon film resistors in the Quad II amps the sound changes with metal film.

Here is a link to the modification I did to my Quad 22.

Quad 22 Preamp Challenge. - pink fish media

Sharif
Any suggestions for resistors? Trying to find all 12 from the same series is proving difficult. What voltage rating do I need to meet - Keith Snook suggests 500v - is this overkill?
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Old 8th July 2015, 11:55 AM   #6
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Location: New Zealand
Hi
If you follow your own objectives
"First off - I want them to be 100% electrically safe.
I want to replace old components with contemporary equivalents that will have a long service life ahead of them.

I want to keep as much of the "Quad sound" as possible."

They should guide you to agree fully with what Keith and msdin suggests.
Alternatively you can do extensive research on ESR applying to high voltage
equipment, you will find there is more to component ratings than just
steady state conditions.

Cheers / Chris
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Old 9th July 2015, 08:15 PM   #7
Katch is offline Katch  United Kingdom
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Limbering up... Quad 303 resurrected from the grave. It had no output on either channel. Replaced the PSU caps (output caps on back-order...), the electrolytics on both channels and replaced all the trimmers.

Click the image to open in full size.

Just letting it burn in for an hour or so before resetting the bias. Gonna be using a pair of these to biamp my system while I get these Quad IIs back up.

Back on topic;

Having a little difficulty finding a supplier for the resistors in my Quads. Can't seem to find a brand and series that do all the values I need and don't fancy mix and matching. Any suggestions?
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Old 10th July 2015, 01:18 PM   #8
Katch is offline Katch  United Kingdom
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Started ordering some bits today;

Smoothing caps are being replaced with these ARS 32uf+32uf cans

Click the image to open in full size.

ARS 32UF+32UF/500V RADIAL

And the coupling capacitors are being replaced by these Mallorys

Click the image to open in full size.

Cap-Mal-150-.1uF/630 volt

Both from Watford Valves.

Still choosing what to use for C1 and C5.

Still struggling to get the resistors.
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Old 12th July 2015, 07:51 PM   #9
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Location: Pretoria, South Africa
A few points:

Resistors: I stay with 0,5W (alt. 0,6W) metal film resistors, mostly because the physically smaller 1/4W types look rather silly!

I would caution regarding trying to be too 'grand'. Respectfully, as an EE I cannot support the subjective experience that metal film changes or diminishes the sound, or an overrated fixation with boutique coupling capacitors. There is no good reason to replace with carbon resistors - sorry. Materials have developed with great strides over the last 6 decades; carbon resistors have been used only because at the time it was all there were.

If the original appearance is part of your goal and you do not mind doing some 'tinkering', one can replace the twin electrolytic filter capacitor inside the case with two modern ones*. One can unsolder the bottom of the square container and remove the cap inside. What with newer smaller sized capacitors it is fairly easy to replace with two separate 32F 450V units in the same space and bring out the connections topwise. (I use brands like Hitano, Trec, Jamicon and other reliable brands - no affiliation with any brand). The inside can be filled with some urethane foam or similar to keep the caps in place and the bottom returned. One does have to do a respray job to restore the appearance.

Finally there is a slight effect from replacing C2, C3 by non-metal canned polyester types. The slight (about) 18 pF of capaciy to earth thus forfeited can be compensated for by placing a 1 NF cap across (in parallel) with R11.

Technically this causes a lead phase shift correction within the NFB loop, improving stability - the effect can be seen when viewing a square wave response on a 'scope.

One can also substantially increase C5 to 1000F or even 2200F 35V, thus causing fixed bias conditions for the KT66s (the so-called 'music power' conditions), again taking advantage of the modern smaller size formats. With the h.t. at about 340V for our mains supply I could get 18W music power from a Quad II before clipping.

Finally: Do move C5 away from the hot R12! Over the years I have found just about every C5 a sorry dry emaciated wreck from having lived in the heat to R12. (Heat is the enemy of particularly electrolytic capacitors.)

Best wishes; Do keep us informed of your progress.

PS: Not attentive here! You could use the exact same capacitors for C1, C2, C3.
__________________________________________________ _______

*Apology. I have just noticed that you have already ordered some components. Fine then; perhaps a suggestion to other would-be restorers.

Last edited by Johan Potgieter; 12th July 2015 at 07:57 PM.
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Old 13th July 2015, 08:52 AM   #10
Katch is offline Katch  United Kingdom
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I'm not massively concerned with retaining the original appearance; how often do you look at the inside of your amp when it's playing?

I'll be keeping all the original parts in original condition should a future owner want the original look.

I've gone with a set of metal oxide resistors ordered in kit form from an eBay seller.

I've also picked up some WIMA caps for C1.

In fact - everything needed is now ordered and should arrive this week - so stay tuned.
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