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:
(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?

First off I think the parts you are referring to are resistors not capacitors. My guess it was one of the KT88's but that is a WOG (wild ass guess.) Is it possible for a KT88 to be bad or fail in a way to make it draw and abnormal amount of heater current?
Have similar issue. After 6 mos of normal operation one of my forty mono blocks blew a fuse and killed the 5U4G rectifier. I placed the rectifier from the other block and now after 20min it blows the fuse. So far did it twise but did not kill the rectifier. Got 2 EML 5U4G mesh to replace the TAD rectifiers but I am afraid to put this one on the block that i have this problem in case it burns it.
These amps were serviced by a Quad dealer in Germany and want to avoid the trouble of sniping this one for service. Any suggestions?

Thanks, Peter
There may also be a solid state rectifier for another supply in that amp that may be shorted. It's also possible that a power supply cap is partially shorted or one of your output tubes is pulling too much current over time that causes the fuse to blow. I have seen output tubes pull too much current and force the rectifier tube to fail.
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....