power tube replacement Mark 5:35 combo

[jaytime]

I recently identified a bad power tube and ordered a set of 4 EL84s. I noticed that all 4 EL84s that are in currently in my amp are "match group GRN" "code 10". The new tubes that arrived are "match group GRY" code "3126". I am wondering if I just can just change out the one "bad" power tube or if it is best practice to change them all out at once. Additionally, do I need to re-order so that I get the "match group GRN" "code 10" power tubes? Thanks in advance for any advice regarding this process.

 

[Tim S]

You’ll want to maintain matched pairs when you replace a bad power tube.

If your bad tube is one of the two outer-tubes, then replaced BOTH GRN tubes from the outer pair with your two new GRY tubes.

But if your bad tube is one of the inner-pair then replace BOTH inner-pair of GRN tubes with your new GRY tubes.

There’s no need to ensure that both pairs of power tubes are the same color — just match the two inner-pair & match the two outer pair. Some people prefer to have all their power tubes be the same color, but it’s not a requirement.

While you can hang onto the “non-bad” tube from the removed pair for later use (as a spare if you ever retube with that GRN color again or use it in an amp that uses a single EL84), it’s now a used tube with enough “road miles” on it to make failure more likely in the near future.