Time to change tubes? Which tubes? Here's my situation...

My Quicksilvers have the following tubes:

2 12FQ7's
2 KT-88's
2 5AR4 tubes.

The guy who sold it to me gave me a new set of 5AR4's and told me the rest of the tubes were OK.

I'm not so sure. The KT-88's have a mirror surface on their sides, as if someone had painted them silver on the insides. The 12FQ7's look normal...

Then, I began checking out what tubes these amps had when new. Apparently, the unit has the same tubes it had some 10 years ago (except for the 5AR4's, that is).

The sound is GREAT when used with small speakers. Nice bass, nice mids, nice highs (5 1/4" woofer, 1" tweeter). But when I use my towers (3 5 1/4" woofers, 1" tweeter), the bass sounds sloppy, weak, and a bit distorted. They have plenty of volume, but the sound quality goes down.

I suppose I should replace the tubes, but I was wondering if I should replace everything at once, or try to replace the KT-88's with a nice set of Sovteks first...

What's your opinion?

 

I think that's normal; it's the getter.

You might as well buy a set of KT-88's and swap them in to see what difference it makes. If no difference, then you'll have a set of back-up tubes.

My experience with small signal tubes like the 12FQ7's is that they last for a very, very long time.

 

Yes, the silver on the side is perfectly normal. If the vacuum is ever broken, it will turn white. (In which case the amp would most likely self destruct )

 

First, I must say that most of my tube knowledge comes from using guitar amps. That being said, I found it somewhat odd that the onlly tubes being replaced were the rectifier tubes. Rectifiers can last for 20 or 30 years if of good quality (such as Mullards, etc), and don't really need to be replaced unless they burn out--old or new, as long as working should sound the same. Power tubes and preamp tubes on the other hand can effect the sound of the amp when they begin the wear out. Another thought: Maybe the amp isn't powerful enough to drive your towers and this has nothing to do with tubes. The towers may be inefficient and need more than the 20 watts or so per channel your amp is providing. Just a thought. . . Good luck.

 

Yes, it sounds like the amp may be underpowered for the towers to me too. What you are describing, Javier, is exactly that sound (I had the same problem until I went to a more powerful amp).

 

Thanks for your help!

I don't know if the amp is underpowered... it delivers 60W RMS per channel. I'd think that's enough for my towers... I also connected them using the 4 Ohm tap.

I think I'll replace the KT-88's first!

 

Good idea! Welcome to the world of tube rolling!! You will be amazed at what a difference tubes can make!

 

6550's are a direct swap for KT88's. You might want to try those as well to see if they make that much of a difference.