Are the forty a different design to II? My Quad II are ultra reliable and need no tubes, they still run with the original NOS ones....
Quad II/forty problem solved
The last few years I have had an all Quad system (except sources - SME 10 table, SME V arm, London Decca Reference cartridge, Ayre C5xe) using the Quad II/forty amps, QC-twentyfour pre-amp and QC-twentyfour P phono amp, along with ESL-2905 speakers. Over the last year, I have had fuses blow frequently in the power amps, to the extent that I bought a box of 100 slow blow 315mA fuses on eBay. My excellent dealer suggested it would be the rectifier tube at fault, and eventually I was sent a pair of ElectroHarmonix 5U4G tubes to replace those that came with the amps. Twenty minutes into the first session with the new tubes, the right amp started to emit smoke and was turned off. The two green capacitors under the socket for the rectifier tube were very hot when I got the bottom plate off and seemed to be the problem. You can see the two wicked smokers roughly in the middle of the photo here:
http://drmoss.ca/IMG_0317.jpg
(Yes, that's one of my backup Audio Electronic Supply 811 monoblocks in the background waiting to go into service to avoid a house fire!)
So I replaced the rectifier tubes again with NOS GE tubes, thinking there must be a fault with one of the ElectroHarmonix tubes. This let the amps play without smoke arising from the right side, but the right amp was still much hotter than the left - hot enough that touching the rear casing would burn your fingers. Facing the thought of sending these amps by courier at vast expense to Ontario (I'm in Nova Scotia) for a service, I decided to try one last thing - replace all the other tubes in case one of them was at fault. I got ElectroHarmonix KT88's and GE 6SH7's from thetubestore.com and put them in place. No excess heat any more on the right side! I don't know whether it was a 6SH7 input tube or a KT88 output tube at fault, but one or the other was making the amp overheat. I have asked my dealer to forward the story to Quad in case it will help another owner having problems. Any knowledgeable types out there able to say which was likely at fault?
Chris
http://drmoss.ca/IMG_0317.jpg
(Yes, that's one of my backup Audio Electronic Supply 811 monoblocks in the background waiting to go into service to avoid a house fire!)
So I replaced the rectifier tubes again with NOS GE tubes, thinking there must be a fault with one of the ElectroHarmonix tubes. This let the amps play without smoke arising from the right side, but the right amp was still much hotter than the left - hot enough that touching the rear casing would burn your fingers. Facing the thought of sending these amps by courier at vast expense to Ontario (I'm in Nova Scotia) for a service, I decided to try one last thing - replace all the other tubes in case one of them was at fault. I got ElectroHarmonix KT88's and GE 6SH7's from thetubestore.com and put them in place. No excess heat any more on the right side! I don't know whether it was a 6SH7 input tube or a KT88 output tube at fault, but one or the other was making the amp overheat. I have asked my dealer to forward the story to Quad in case it will help another owner having problems. Any knowledgeable types out there able to say which was likely at fault?
Chris