5u4g for 5ar4 mesa rectifier

[zm01]

hey, been a while since ive posted here.
ive recently been trying to replace all the tubes in my mesa dual rectifier solo head(2 channel). so i went to the local music store. however when i asked the guy if he had any 5u4g rectifier tubes, he gave me two 5ar4 tubes. i told him i didnt think they would work, but he assured be they would and said something about them "clipping faster"(????). anyhow, i have yet to put them in. i was wondering if what he said was true(although it sounds like [img]/images/graemlins/bs.gif[/img]) and if not, what kind of damage could that cause my amp? i cant return them, but i would still like to have a little ammo to throw at the guy.
Also, on another note, i have a bias switch on my amp to switch from el34 to 6l6 and was wondering what kind of tonal differences there would be switching from my 6l6's. any help would be GREATLY appreciated. thnx in adv. [img]/images/graemlins/confused.gif[/img]

[fabamp]

Re: 5u4g for 5ar4 mesa rectifier

Yes you can use 5ar4 in amps calling for 5U4, but not the other way around. This is because 5ar4 draws less heater current(1.9amps), so your amp will prolly run a bit cooler. In amps calling for 5ar4 you could overload the VA of the power trafo because of the 3 amp draw by 5U4.
The sag maybe increased because the effective plate-supply impedance/plate for 5ar4 is about 200ohms opposed to the about 21 ohms in 5U4.
6L6/EL34 boils down to taste. Let your ears decide but generally EL34 has earlier breakup and stronger mids. 6L6 may give you thicker tone and a bit more headroom.
Hope that helps.