refurbishing a set of Quad 57s

[Fran]

Hi all,

well recently I picked up a set of quad 57s at a very reasonable cost (barter actually). I knew in advance that they would need some TLC and maybe more - so I went in with my eyes open.

When I picked them up, I saw right away that they grilles were fairly dented - and the previous owner hadn't loved the sound.... that could only mean that there was something wrong!!!!

So when I get them home and plugged in, right enough the sound was well off the mark - almost no bass from one speaker with the soundstage thrown right off. On the whole the sound was thin too. A little further investigation showed that the serial numbers meant these were a very early pair, from 1959 in fact! A common enough cause of lack of bass is a deterioration in the high voltage bias supply which means the bass panels don;t get the 6000V they need to work right. The bass panels are rarely harmed, but the treble is the one easily damaged. So I set about opening them up:

Here's a pic of the newly opened 57, at this stage the rear cover and front grille are removed. The bass panels are the outside ones, the treble is in the middle:

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You can see the dust and dirt on the cover. Looking at the panels I thought they looked a bit new - and further investigation showed there was a service done by Quad themselves in 1985....

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Very reassuring to see that!! Also, there was no arcing marks on the treble panel - also a very good sign. One of the problems with buying quads is that you can't exactly whip off the panels to take a look - theres about 30 screws holding the rear and front grilles in place.

When I started to look further, I saw another problem - one of the wooden frames that holds the mylar dustcover on the back was broken - potentially causing a problem with dust getting in, and also maybe HV leakage from the panel.

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contd:

[Fran]

So just the way it worked out, I set about fixing the dustcover first. I disassembled the frame from the panel and repaired the broken piece and took a piece of mylar and fixed it to a table top - stretched as evenly as I could manage. I used some double sided tape on the dustcover frame and then placed it down on the mylar. Lastly, I cut it free by using a hot iron to cut the mylar (can't use a scissors or knife for this)

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And here's the rest of the panel:

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This was the rear dustcover (front was fine) and it was a little more awkward because there are 3 heavy gauge, extremely stiff wires that need to be fed through the mylar, through a panel to 3 terminals (bias, ground and signal).

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And here's the reassembled panel with the 3 wires poking through:

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The dustcover/panel assembly is just held together with tape!

[Fran]

Then on to the EHT rebuild - the bit that delivers the 6kV.

The EHT is encased in a small bakelite box near the mains transformer and the circuit board is potted in beeswax. You can see it in this photo:

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I desoldered the wires, and put the 2 EHT units in a bowl in the oven at 150 degC to melt out the wax. Towards the end, I organised to hold the circuit boards above the wax to any residue would just run off. Some 57s were encased in resin - if you have one of these then you can't do this - you need new circuit boards. This is what the board look like out of the wax:

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The word out there is that in the 57s the caps never go, but the diodes become leaky. Again there were 2 types, ones with 8 diodes and ones with 16 diodes. Apparently the 16 diode ones are more reliable. So you can see that these were 8 diode versions and I decided to revert back to the 16 diode version. Here's the rebuilt board:

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Lastly I gave the grilles a really good scrub in the shower, dried them thoroughly and managed by a little bit of coaxing and gentle persuasion to get virtually all the dents out of them. There were one or 2 chips of black paint gone which i touched up(impossible if you have bronze grilles) and you would never know....

Excuse the poor light, but here they are in front of my other set:

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Lastly I powered them up - and hurray!! no big explosions. It took the panels at least an hour to come up to full speed, but once there were bang on!! Yaaay, it worked out!


The real goal here was to get a second set to stack 'em!

Fran

[fergus]

Excellent Fran....as ever I am in awe of your talent!!!

[Fran]

The only other stacks I had ever seen in the flesh were barry robins..... and since I heard them, I knew it was on my list of things to do....

I consulted the internet and Barry and basically a plan was put together to make a wooden frame to hold them. Of course they would be bloody huge, so I wanted to face them off with some nice wood. Also, I wanted to leave some provision for putting a grille cloth or screen on them later if I wanted - one of my sets is bronze, the other black, so thought they might not look great.

I decided to use some 5 by 1/1/2" for the uprights (thats door frame in hardware speak) and 3x2 for everywhere else. So, I made some basic frames from this material:

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and I decided that they would lean back, clean at the front (no legs sticking forward) and with some easy adjustment on the back so I could tilt them. You can see here the frames with the legs... and assistant!

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So I simply painted these frames satin black as they would be largely hidden - no need for fancy joinery skills, these were screwed together and a brace added from the top to back leg for rigidity:

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So the quads would fit in each space, and are held there by 3 screws on each side where the wooden cheeks normally go. Now, I had some southern yellow pine (like clear or parana pine) to hand and decided to use some of this to smarten up the fronts.

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and the 2 together in the workshop (excuse the mess)

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Then after finishing the timber, inside to fit the first set of speakers - hoping they would fit!

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phew, it does! Those bloody quads are heavy and awkward when trying to fit them in.... but we got there:

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[Fran]

Thanks Fergus...

So heres how they look, roughly positioned:

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There's quite a bit of experimentation going on right now, with angles and so on - and I've yet to even start looking at drive amplification. A big bonus is that when paralleled, they present a much kinder load to the amp, so although you might need more watts, its more amp friendly. As I write this, I'm using an EL84 amp at about 10WPC, and have yet to try my Pass F5 amp (about 25 WPC). Other possibilities yet to try are either a second EL84 as a monoblock setup or maybe a EL34 or 6L6 amp. That would all cost $$ of course.


Fran

[fergus]

I have just noticed the reel to reel in the background....that little project also worked out fine I see!

[Fran]

Ah, what sharp eyes you have!! Yes, the R2R worked out AOK. The SQ is surprisingly good, but the motor noise is fairly noticeable when playing - nothing through the speakers, just the actual motor is noisy enough.

Fran

[barry robin]

beautiful stuff, fran. good tutorial, too.

though i know you're loath to build more stuff-amps, in this case-may i suggest using push-pull amps of about 30-50 watts per channel. gives a nice, smooth response and it's easy on the load swings. me, i'm a monoblock kind 'o guy-and you've seen mine. if you like the sound they made, you might want to check out the amps...

it's a site called DIYTube that sells it's own updated kit version of the old Dynaco valve amps; ST-70's and ST-35's. if you used the ST-35 version it would give you 35 watts per channel bridged as a monoblock (17 1/2 watts x 2).

hers the link:

http://www.diytube.com/phpBB2/index.php

-b

[paulb]

if you want to give it a try you are welcomed to borrow my 6l6,20 w , let me know