Tube Question

[Barrey78]

About 9 months ago I took my 68 Twin Reverb into a shop to get a tune up. They replaced the tubes (with pretty {censored}ty tubes). About two weeks later the power switch broke. It sat in my space for about 6 months, then I decided to try and fix it myself because I have no money.

 

I replaced the switch for 5 dollars, which is a repair that I got quated at about 100 dollars, plus cab fare two ways (40 dollars, I live in NYC), and it works again.

 

One of the tubes broke when it rolled off my table. My question is : will I be alright if I just buy a new set of matched tubes and just replace them all, or can I just buy a matched pair, and replace the two inside, or outside.

 

Or, do I absolutely have to get it biased and all that jazz. I would like to get this done for as cheap as possible. Thank you.

[jonny guitar]

I believe that you can get away just fine with replacing inner or outer 2. Are they rated tubes (like groove tube, mesa or svets that have the number on the base)? If they are you might be able to just buy one with the same rating....this will allow you to just pop it in and go.

I have run amps 4 tube amps with different duets and not had any problems.

Consider this a bump for someone to confirm this.

....good for you fixing your switch!

[Barrey78]

Thank you,

Ill look to check out if they are rated, I still have the boxes of the old tubes.

It sounds really good at half power. Can I damage the amp running it on half power?

[jonny guitar]

You need to adjust the impedance if you are only running two tubes.

Follow this

"In amps with an impedance selector, when pulling two tubes the amp should be set to half the cabinet impedance, that is, set the amp at 8 ohms for a 16 ohm cabinet, 4 ohms for an 8 ohm cabinet, etc. to preserve the impedance match. "

It is okay for short term but I would crank your amp like this forever.