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Old 5th October 2014, 02:11 PM   #1
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Default Quad II amplifier needed for parts

Hello,
My Quad II mains transformer is overheating, so I am looking for a replacement. I have been discouraged by transformer experts in my attempts to repair the faulty winding because the tar used to pot it is extremely messy and smelly to remove!
Preference given to members from European Union Countries as customs duties in Portugal are heavy on items from non EU countries!
Alternatively, I would like to acquire a non working Quad for parts as the chokes and transformers are not easily available. The condition of the valves is not important as I am using the Russian made 6P3S that are much cheaper for everyday use.
Thanks in advance.
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Old 5th October 2014, 08:44 PM   #2
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Are you sure it is the transformer at fault?
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Old 5th October 2014, 08:47 PM   #3
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Did you take the tubes out to see if it still gets hot?
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Old 6th October 2014, 12:13 AM   #4
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I will try the amp out tomorrow without the tubes!

One of the center tapped windings of the secondary, marked as the HT terminals of the secondary windings, measures 8 Ohms between one of the HT terminals and ground compared to the the other HT terminal to ground reading of 80 Ohms. On my good amplifier, each HT terminal to ground measures 80 Ohms.

The valves are OK because they have been exchanged with those on the good amplifier which continues to play and maintains its transformer warm to the touch. The valves I am using are the Soviet 6P3S and R12 (originally 180 Ohms 3 Watts) has been replaced by 220 Ohms 7 Watts to alter from bias of KT66 valves to 6L6 Russian equivalennts.
All capacitors have been changed: Russian vintage Paper In Oil K40Y-9 and K42Y-2 & one large and long Tube Amp Doctor TAD Can Capacitor 50uF + 50uF / 500VDC plus Nichicon axial 22uF electrolytics. (I had to buy a decent quantity of each capacitor to compensate for shipping costs, so if interested in buying any or all capacitors, send me a PM) .

The explanation given to me by one gentleman by the name of Manfred Mornhinweg (link to his motivational transformer theory and practical winding articles under electronic projects tutorial section http://ludens.cl) is that the shorted winding is heating up and causing the tar inside the transformer to melt and carbonize hence the smell of tar within a couple of minutes after power on!

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Old 6th October 2014, 02:17 AM   #5
kevinkr is offline kevinkr  United States
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It does sound like the high voltage secondary is shorted; classic symptom is as you describe.

I know the tar is messy to deal with, but I almost hate the thought of cannibalizing a potentially restorable amplifier for a power transformer. Winding a new one to install in the old case might be preferable from a reliability standpoint as well.

I assume it can be unpotted with some care in an appropriately hot oven. I have done this with Heathkit and other transformers in the past. Wear gloves! Ventilation.. LOL
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Old 6th October 2014, 09:55 AM   #6
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Yes, I do see your point. However there are 2 things I am also taking into account apart from having spare parts:

The most discouraging of all is the removal of the tar from the old transformer and its can. I have it on good authority that it is messy, smelly and something to be done outdoors. I have in the past, unpotted a transformer that had beeswax, but the tar is a different beast altogether!

After putting new capacitors in my amplifiers, I sold the faulty originals to collectors. It seems there are people who want to restore Quads with original parts for cosmetic reasons and not for personal use! I could do the same with the faulty transformer, that way a collector somewhere feels good and so do I. Nothing from a Quad is suppossed to end up in the rubbish bin!
There also is a supplier in the UK that makes a replacement transformer that fits on top of the amplifier but not in the old can, but it is an expensive alternative!
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Old 13th October 2014, 04:57 AM   #7
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Don't put it in the oven!!!! Put it in the freezer wait over night then bang on all sides until the tar breaks up... It's like glass when cold and you can clean all of it out if you take the time to keep refreezing it.. Hope that helps good luck..
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Old 21st October 2014, 07:21 PM   #8
405man is offline 405man  Scotland
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I have just removed my transformer from the freezer and removed the core in about 5 mins, brilliant idea, no more smell or mess, thanks very much for sharing

Stuart
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Old 21st October 2014, 08:00 PM   #9
srian is offline srian  Sri Lanka
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you can remove most of the tar by prying off with a screwdriver and a pointed knife.(keep these pieces of tar to re pot it later after rewinding)
soak and dissolve the residual tar (pitch) useing gasoline as the solvent.
get it rewound.

once rewound connect it to the amp to see every thing is okay.

repotting has to be done carefully.

transformer is to be heated in an owen.
bieng careful not to overheat it so that the insulation is damaged.
melt the tar in a pan outdoors being careful it does not catch fire.
pour the molten pitch to the hot transformer in the can.
observing the correct orientation.
let it cool.
you can add a small amount of dry sand hear and there when filling to compansate for the lost amount of tar while you were removing.

if not comfortable get it done by a proffesional.

i have done it many times to quad opt's and power transformers as they get
damaged due to the green oxide which forms in the copper wire due to the age.

once done properly they sound like the original.

srian.
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Old 21st October 2014, 09:36 PM   #10
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Glad I could help with the tar although it wasn't my idea a friend showed me that.. Good luck with your project.
Jason
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