Please check each resistor for right vaue.
One of the problem of these old stuff are the values of resistors ( but also caps) that have a differences from the original value.
I have done lot of checks on this amps ( but the problem is similar to Leak stuff) and after replacing the reisstors and caps the amp return at the best performances.
Then I give to the owner a little bag with the original components, just to remember!
Walter
One of the problem of these old stuff are the values of resistors ( but also caps) that have a differences from the original value.
I have done lot of checks on this amps ( but the problem is similar to Leak stuff) and after replacing the reisstors and caps the amp return at the best performances.
Then I give to the owner a little bag with the original components, just to remember!
Walter
Some useful information about Quad-II problems and modding can be found here:
QUAD II Valve Power Amplifier Information
~ QUAD II Valve Power Amplifier Modernising and Modifying ~
quote:
Resistor R12 is under-rated
The R12 resistor fitted by QUAD is rated at 3W but under the best conditions will dissipate about 3.75W and in some circumstances even more ~ Even if it looks okay it is best to replace R12 with a 5W or a 7W resistor like the TT electronics W22 type shown opposite and at the same time replace C5 with a capacitor adequately rated at a.c. and as well as d.c. (see bad examples in buying guide)
:unquote
QUAD II Valve Power Amplifier Information
~ QUAD II Valve Power Amplifier Modernising and Modifying ~
quote:
Resistor R12 is under-rated
The R12 resistor fitted by QUAD is rated at 3W but under the best conditions will dissipate about 3.75W and in some circumstances even more ~ Even if it looks okay it is best to replace R12 with a 5W or a 7W resistor like the TT electronics W22 type shown opposite and at the same time replace C5 with a capacitor adequately rated at a.c. and as well as d.c. (see bad examples in buying guide)
:unquote
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The heater problem may have been dirty sockets. Get some isopropyl alcohol and some of those inter-dental brushes and give them a good cleaning, if you haven't already.
The Quads don't have a blocking capacitor on the input so any DC from your preamp is likely to pass straight to the EF86s. The inputs are sensitive enough that running it from a phone / cd player directly (to test) works fine.
The Quads don't have a blocking capacitor on the input so any DC from your preamp is likely to pass straight to the EF86s. The inputs are sensitive enough that running it from a phone / cd player directly (to test) works fine.
This is often stated, but in fact I've never seen one fail. It is mounted well up into the breeze where convection can occur, and it's a very sturdy looking component bigger than what it usually gets replaced by, so maybe it was conservatively rated in the first place. Clearly in the application it is well able to handle the wattage.
By all means replace it if you like, mounting it the same way, but neither this resiststor nor any other can possible cause a hum.
I'm basically happy with the sound, and while I am not at all bothered about originality I don't want to change things that work ok. The hum/buzz really bothers me though - does the solution lie in adding an input capacitor to block dc on the Quad II? Or is there a fault with the 33? Hope this topic is not straying too far!
I following Patrick Turners recommendations for the basic mods to the Quad II, for example seperate cathode bias resistors ...
Patrick Turner Quad II
I added the DC blocking capacitor to the input, but initially I missed the extra resistor to ground for the input tube and had some nasty instability if I disconnected an RCA.
It is a great read, that site, and I really hope there is a custodian to take over now that Patrick is no longer with us.
Patrick Turner Quad II
I added the DC blocking capacitor to the input, but initially I missed the extra resistor to ground for the input tube and had some nasty instability if I disconnected an RCA.
It is a great read, that site, and I really hope there is a custodian to take over now that Patrick is no longer with us.
Thank you - I have had a read of his site, and enjoyed it! I am particularly interested to hear of real experiences - theories and recommendations are one thing, but I am not sufficiently qualified or knowledgable to judge on my own. I wouldn't want to modify extensively or 'improve' the Quads but using modern components seems perfectly logical - I'm sure that manufacturers in the past used the best components available (within the budget dictated by the accountants, of course) I would, however, like to prevent the very loud buzz/hum if used with the 33, and add a safety earth connection which doesn't use the signal cable, so any experiences of following recommendations from Patrick Turner or anyone else would be most welcome.
No and no. Hum isn't DC. There is only a fault with the 33 if there is no hum without it.
Is it really a hum (50Hz sine wave)? or rather a buzz (100Hz triangle wave)? Does it happen with no preamp connected?
It's more of a hum, but really loud. With nothing connected to the input there is just the faintest hum, but only audible with an ear almost touching the speaker cone, and there is no earth connection. No more hum than there is from an old Hacker valve amp connected to a 99db sensitive speaker in my main system anyway - and that uses the 33 with an active crossover between it and the amps. With an iPod connected the faint hum is diminished, but with the 33 connected it becomes really very loud!
ok - it's definitely the 33. Cables are good, and I tried others too. I'm still not sure why it was fine with the active crossover and 4 other amps but not the Quad II, but now it makes the same noise with other amps too. I probably won't be able to do anything for a few days anyway, so maybe I'll just have to despair quietly and then start a new thread for the 33.
Many thanks to all for helping!
Many thanks to all for helping!
Good point! It was, however, modified (although now I think about it, that was more than 20 years ago) so that it runs from an external battery, and the M12017 boards have had all capacitors changed for Kimber or Ansar Supersound and resistors are some expensive Vishay items, the M12029 board has had 4 caps changed for modern polystyrenes (but C5 and C6 are still original) The M12019 board has all new caps and resistors (well, not new now!) and the volume and balance pots were changed for ALPS units. No transistors were changed.
I can check all connections and wires, but am otherwise not really sure where to start...
Maybe this should now be a new thread?
I can check all connections and wires, but am otherwise not really sure where to start...
Maybe this should now be a new thread?
I'm guessing there's a problem with the ground connection. If your 33 is on a battery, then there should be no mains hum, but the IIs are almost certainly connected to mains.
So it might be that there is a bad interaction between the ground on the IIs (or other amps) and the 33.
Is the active crossover run by battery as well? Do you have access to an oscilloscope?
So it might be that there is a bad interaction between the ground on the IIs (or other amps) and the 33.
Is the active crossover run by battery as well? Do you have access to an oscilloscope?
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The 33 is grounded to a rack unit containing the batteries and chargers, which also power a DAC. The same unit switches ac power to all other components - turntable, CD player, crossover and amplifiers - so there is just one ground connection to the mains for everything. That said, there is a ground lift switch on the rack unit, and with it connected there is faint hum, so it is usually in the lift position. The Quad II is only grounded via the signal input, although this is something I would like to change.
I examined the 33 and heard a rattle when I moved it - this was traced to the little power indicator lamp behind the front panel. The glass had come off, and there may have been an intermittent short between the contacts. I removed the whole assembly, and the 33 sounds as good as ever with the active crossover. If I connect the 33 direct to one of the other amplifiers it is fine, it is just with the Quad II that there is the loud hum (you can probably hear it, it's that loud)
I don't have access to an oscilloscope, unfortunately, and the news is that the faulty Quad II reverted to only one KT66 glowing, and both EF86s cold - I had already cleaned the sockets and checked the connections, but I wiggled the EF86s slightly and it's working again....
I remain (as ever, really) slightly puzzled - I'll try to get another pre amp to test it.
I examined the 33 and heard a rattle when I moved it - this was traced to the little power indicator lamp behind the front panel. The glass had come off, and there may have been an intermittent short between the contacts. I removed the whole assembly, and the 33 sounds as good as ever with the active crossover. If I connect the 33 direct to one of the other amplifiers it is fine, it is just with the Quad II that there is the loud hum (you can probably hear it, it's that loud)
I don't have access to an oscilloscope, unfortunately, and the news is that the faulty Quad II reverted to only one KT66 glowing, and both EF86s cold - I had already cleaned the sockets and checked the connections, but I wiggled the EF86s slightly and it's working again....
I remain (as ever, really) slightly puzzled - I'll try to get another pre amp to test it.