Classic Quad II Valve Amplifier - Help on what to look out for.

[vishalk]

Hi All

Hoping some of you who are owners of these lovely legendary amps can help me with a few queries.

I took the plunge and bought a pair, now i have been searching for the right pair at the right price and these i couldn't say no to.

There are a many out there for sale which for the money are molested, in bad condition etc. I thought i was very lucky to find these:

Pictures don't really do these justice as they really are in a beautiful condition.
Whether they are original or been refurbished, i am not sure. Looking at the internals it looks good?

Would love your thoughts?

It came with Chinese matched kt66 Electron tube valves, the others a Mullard.

They do sound wonderful, i had them running today for 4 hours.

Can i have tips on what to look out for and what tubes you guys recommend?
Any help would be appreciated

Keith-Snook.info. — QUAD II Buying —

This was a great source of information.

Thanks!

 

[Shoog]

Looks like it has been partly refurbished. The top most resistors below the yellow cap are new and that cap looks new as well.
As such its probably good to go. The only thing to look at in detail is if the main filter caps are original and whether they are still good.

Shoog

 

[lisoformio]

All that old resistors, too. Ageing they drift a lot.

 

[llwhtt]

I have lots of experience with Vox and Selmer guitar amps which used the same ceramic tube resistors, they surely have drifted. Get a DMM and check them.

Craig

 

[lexx21]

I would actually just go ahead and replace the old carbon comp resistors to be honest. They do drift in value over time just because of how and of what they were made. I use carbon film in all of my builds and they work well.

As far as tubes, as long as what you are using are matched and they sound good the way that they are, keep going with what you have until you need to replace them. If you decide to go all NOS Mullard you will pay a FORTUNE for them.

 

[stokessd]

I've got three pairs of them. One pair I replaced the original power supply caps with a PCB and modern snap-in electrolytics. Seen here: Sheldon’s World >> Blog Archive >> Quad II Amplifiers Join The Family

I lso did one with all film caps in the supply, but I didn't write it up as a blog entry though.



Sheldon

 

[Cookj]

QUAD II Valve Power Amplifier Information

Regards
John

 

[Tubologic]

There are so few parts in a QUAD II that it's better and easier to replace them all. The main electrolytic filter cap block is know to be failure prone and should be replaced, yours looks original if it hasn't been re-stuffed. Don't exceed 32 µF per section.
From your picture it can be seen that your amps are currently wired for 16 ohms speakers, if you have 8 ohms speakers you can easily convert the amp for 8 ohms operation by removing the link betwen R-S and bridging Q to R and S to T on the OPT tagboard.