Quad 11 Problem !

[pre65]

Hi-i have got round to repairing my Quad 11 amps now,and having replaced the faulty resistors and caps have now powered them up without valves to check the basic voltages.
the HT and 6.3 heaters are spot on BUT i have a problem with the 5v supply.
i have measured the voltage of both terminals to earth and then both terminals together.

Amp 1 0.07/5.6 = 5.1
Amp 2 15.1/14.9 = 5.1

Amp 1 is the "good" amp and Amp 2 is the one that had red valves and lost a bit of black gunge from the transformer (not a lot).

anyone make sense of this ?

Philip

[pre65]

Hi again-just checked the 5v in the same way with the GZ32 in position and i get 994/994 = 5.1 on BOTH amps.

bit more confused now !!!

Philip

[pre65]

Hi-ive tried it with old speakers and everything seems ok.

they are now back in their rightful place in the main system and it's nice to have them back.

there is something about them i love,they were re-resistored and capacitored some years ago and have Jibbles russian KT66.

Long live Quad 11's

Philip

[andrew ivimey]

I had Quad2s a long time ago (sold them and a few other bits and bobs inc. ESL57s and lived off the proceeds in USA for a few months just travelling around, 25 years ago or so - it was a far trade)

Quads sound good but what is so speical about them? The preamp is regarded as 'not that good', but I liked it, in context. And the power amps have a certain magic but why oh why oh why?

And although I put together a push pull jobbie that I can put any old pentodes in (right now lovely old Brimar 6V6s - and why not!), I massively prefer the three dimensional beauty of SE rather than the wall of power I get from PP.

A thousand years ago I thought the Quad11s were huge! Apart from T-amp, the amplifiers I now play with dwarf Quad11s;

they also sound hugely better ;-) wicked.

[pre65]

Hi-how hot should the mains transformer be ?

on both amps you can only put your fingers on for about 4-5 seconds before it hurts !

never really noticed before.


Philip

ps-put my digital thermometer on top of transformer-39.9 degrees C

[andrew ivimey]

This is a feeling I know well .....

[pre65]

Hi-do any other members run Quad 11 's,and if so how hot do yours get after a couple of hours use ?

Philip

[Basil]

Hi

I used to run a pair before I converted to a WAD KAT 34 and they ran very hot after a few hours, in fact one more than the other - a drop of moisture on the transformer case would quickly evaporate. Original GEC valves were fitted for most of the time but I carried out a minor mod that allowed me to use cheaper EL 34's which tightened up the loose bass. Unfortunately, the side effect of this was to make the amps to run hotter due to the increased heater current. However, they are still working well 3 years later with their new owner.

Basil

[pre65]

Thanks Basil-its nice to know that that is the norm and they are not faulty (fawlty ?) sorry about that !
i have got an article somewhere that details the changes needed to run EL34 but i like the sound as it is with Jibbles russian KT66.

Philip

[Franquin]

A bit late but better then nothing
Quad transformers doesn't heat until the room temperature gets to approx 24C. It is reaaly sensible. When this temperature is passed, transformer have the bad habit to reach a 45C after 2 working hours. This is approximation of course but it in no case should burn you finger.
The reason why is the proximity of the tubes GZ32/34 ant KT66, they heats the pot all simply (you can notice that putting your hand opposite side of the pot, it is quite cool). It is by the way amazing to notice tar leak on that side only. When summer comes, just put a piece of silver paper between the iron and the tubes and it will help (not very sexy but...).

Now if you notice the iron gets hot very quickly (1/2 h or less) whatever the conditions are, it is technical problem and they finally reach a very high temperature that you couldn't keep your hand flat on the pot.
1/ Old tranformers have inductance leakage and spend (waste) much more than necessary (by their own). In that case, change them. But before check the following
2/ Could be the head cap (2x16uF). DC leakage on old ones pull a lot of courant from the transformer. Change with a 2x32uF (JJ or LCR) but never put a 2x50uF as you can read sometime. Kills the rectifier quickly and time constant gets to high, your amps could sound lazy
3/ An other reason is the bias of the KT66 making them pulling hard. Measuring cathode bias must be aroun 26V +/- 5%
4/ Most of the Chinese tubes draw too much Ih, I don't know about you Russian one. This could be a problem as well.

WARNING: If you are not use to handling tube amp problems, do not try to put your hands in. High voltage and tension can kill you. Sorry to end up this note that way.

Best regards
Pierre Franquin