Replacing EL34 valves

[The Grand Wazoo]

You're both right.
Triode valves do exist.
The valves you need are pentodes. All EL34/6CA7 valves are pentodes.
Your amp has valve sockets which are wired in a triode configuration. This is a kind of kosher bodge.
The valves will be fine - they are exactly what you need.

[NRG]

Well they are electrically equivalent! The 6CA7 is the American version of the EL34 but its a beam tetrode not a pentode, they will sound subtlety different. I would stick to the same valve as the others you have.

[Ali Tait]

I had an EL34 amp for a while that came with cryo'd Shuguang valves. Sounded very good to me, and they are not silly money. I have four matched RFT valves I'd let go if you are interested, say £80 for the set.

[The Grand Wazoo]

......... but its a beam tetrode not a pentode,

Yes, apologies - I stand corrected - I knew that!