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Quad II rebuild.

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I have a couple of Quad II amps that had been sitting in the shed for a year or two doing nothing until this week when I finally got around to getting them going.

So far I've replaced the coupling caps, checking all the resistors and re-tubed with old stock KT66's, GZ32's and EF86's.

 

Underneath the chassis is mint, however the top has some light surface rust which I'm debating if I should re-paint or just polish/wax and leave original.

 

I personally would like them to be nice and shiny but would a re-paint decrease their appeal later on if I decided to roll them to pay for another HiFi aquisition?

 

PS. They're never going to be in my main system on show, just an option for the man cave while they hold interest.

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Ooeee,...MM!

 

Leave them original paint I say.

 

I seem to recall that NZVRS published a Quad II restoration article a few yrs back.

 

Pics plse!

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Here's some initial pics.

Underside is fairly clean, both are exactly the same.

 

They seem to perform nicely, 14VRMS @8ohms 0.4% distortion = 24.5WRMS unless I've mucked my calculation up

Attached files 161320=7809-DSCN0752.jpg 161320=7807-DSCN0753.jpg 161320=7808-DSCN0754.jpg

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Yep, I know...UGLY yellow caps but it's no secret they have had work done on them.

I do have NOS Hunt caps in the drawer but reluctant to use them as they have a fairly bad reputation from what I've read.

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Very nice. Mr Joe Hunts reputation for the quality of his capacitors is richly deserved IMO. Often used to see the leaky POC with cracked cases in some of our telecoms gear in the bad old days.

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Mr MFM,

Please tell us a bit about your test gear... I think I see a fairly modern scope, freq counter, audio generator, distortion meter...?

 

PS. I have not much problem with modern caps (axial of course) but PIO prob sounds good in this vintage (& most) amps.

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Hi, did you add the capacitance to ground as it had originially?

 

"The coupling capacitors C2 and C3 are mounted on the KT66 bases and clearly do not have the capacitance to ground that the metal bodied originals provided — This capacitance possibly required for loop control is provided by the twisted Orange and Violet wires that now form a small capacitor between the anodes of the EF86 valves V1 and V2"

http://www.keith-snook.info/QUAD-II-power-amp.html#QUAD_II_coupling_capacitors_C2_and_C3

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paul300b: No, I didn't... However the original Hunts caps didnt either, although they were bolted down they had a thick plastic sleve over them what would isolate them fairly well from the chassis.

I would say that they are the original caps going the condition and melting temp of the solder.

I may add those twisted wired just in case, thanks for the heads up.

 

Owen: Fairly simple test rig and can't afford a Neutrik.

What you can't see on the top are 2 Sig Gens, one is a modern 10Hz to 100Khz with a digial readout, sine/Square wave, great for a quick signal but no where as good as the Levell Sig Gen which has a very low output distortion and 1hz to 1Mhz range.

 

Next down (you can just see the bottom of it) is a Leader LSG 215 Sig Gen AM/FM/FM St. and CW from almost 0.1Mhz to 115Mhz, good for testing & aligning old radios.

 

Beside that is a Leader 50W 8ohm twin dummy load which I switch the amp output from speaker to the test rig.

 

The unit with 2 meters is a National Distortion analyser and RMS Volt meter, not a bad unit for a quick test, but it only measures in 2 ranges (400hz and 1Khz), beside that is a more accurate Trio RMS volt meter.

 

Next down is the Hewlett Packard 334a Distortion analyser, a lot more tricky to use but quite accurate, again it measures RMS Volts and distortion levels from 30% down to 0.002% readable and AC voltage down to 0.0003v.

 

On the Bottom shelf is a Hitachi 20meg dual trace scope and a Philips frequency counter, both are good solid performers and never fail.

 

The rig is set up so the sig gen outputs to the frequency counter and 1 channel of the scope, out of the rig via a connection block to the amp, then the output of the amp comes back to the switch block (Rig or Speaker), back to the scope and the volt meters and distortion analyser.

So in effect I can figure out an amp's distortion level at whatever frequency/ output level I want.

The scope is great for seeing what's happening to the signal and picking up power supply, hum, matching or other problems in the amp.

 

From there I have a PC which sits beside the bench which I made up a bunch of macro's in exel where I can get enter in data from the test bench and get output ratings, transformer turns ratios and a whole bunch of other stuff which is useful.

Haven't yet gone down the data capture side of things yet but maybe in the next year or two.

 

Probably the most useful piece of kit in the whole shed is my dim light setup, it's saved my bacon many, many times.

Rather than winding up the voltage slowly on a variac and watching the current rise I use a serier of 3 lamps (15w, 60w, 150w) and switch each one in parallel to get several combinations.

For those who haven't used one before, these are great if you are plugging in an amp/radio for the first time when you don't know what's going to happen, If there's a short circuit, the lights just glow brightly..

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Yes I like the series light bulb concept, I should use one more often myself!

 

I have a Dummy Load box, 100W... & I need to spend time practising its use.

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Steve.H;161356 wrote:
Very nice. Mr Joe Hunts reputation for the quality of his capacitors is richly deserved IMO. Often used to see the leaky POC with cracked cases in some of our telecoms gear in the bad old days.

 

Hunts capacitors are reputed to have contributed more to the decline and fall of the UK HiFi/radio industry than all other reasons combined, including the Japanese.

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Yes, I had an old 50's amp with reformed hunts power supply caps in them. Worked ok, then some time later 20mins after switch on one cap blew up, fired up and made a 6 cm hole in the ceiling. I never trust reformed caps anymore. Timebomb.

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These smoked GEC kt66 worth alot in the market now!!! pewwww... My previous Quad II was bought in rebuilt+ re paint condition. Due to this, my resale value drop termendously.

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Wan Weng Yeap;161777 wrote:
These smoked GEC kt66 worth alot in the market now!!! pewwww... My previous Quad II was bought in rebuilt+ re paint condition. Due to this, my resale value drop termendously.

 

Thanks for that feedback, that's firmly help me make the decision to leave them as-is cosmetically.

All the other components seem to be within tolerance so I'll leave them in their current state.

 

Pricing for Kt66's is bananas now-days, I think I recall seeing some on trademe for $250 recently?

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While we're talking matters Quad, I'm on the hunt for a Quad 11 power transformer - and I don't care if it doesn't work or is 110 volt input as all I really need is the metal can. (I have a few old Q11s kicking around and some pillock has replaced the power tranny on one with a gypsy one and it is as ugly as sin).

M

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