speaker suggestions based on OHM load

[selloutrr]

I stumbled across a Traynor Mark 3 head a few months back... It offers a 4ohm load and came loaded with JBL k120's in the combo version (dual 8ohms parrallel to 4ohms).
I also came across a matching empty 4x12 traynor cab. I've been going rounds about what speakers to use I'd like to keep it stock, or at least in the same voicing that complimented the heads voicing at the factory. I'd like to load it with JBL k120's or celestien G12h-30's (which were, reportedly stock? in some of the 4x12 cabs) (marsland speakers where stock in the PA series and 15" bass speakers, they didn't work for guitar amps as the 12" was only capable of 15 watts). either way they are both an 8 ohm speaker so 4 speakers will end with an 8 or 16 ohm load. what ill effects will the missmatch of a 4ohm head threw an 8ohm cabinet really do?

[Structo]

It really depends how robust the output transformer is.

The old Fender amps could go all day on a one step mismatch either way, up or down.

From what I understand, using a speaker with a higher impedance than the amp can cause flyback voltage which can damage the OT or power tubes.
Going the other way is harder on the speakers from what I gather.
But other than that I guess you either have to talk to somebody that has done it with the same amp or just try it and try to feel how warm the OT is getting after playing awhile.

[Markusv]

The OT's on the Traynors are huge Hammonds
Especially on the mark 3's
I'm sure a 1 step mismatch will do very liittle. Not sure if the volume you play at makes a difference but the YGL mk3's at moderate volume are already very loud so likely you'll be OK

My $ .02 FWIW

[jaysg]

What are the output tubes? It matters...he used 6L6s, 7027a's and EL-34s in the big amps. Worry about EL-34s.

[Markusv]

In Mine, it is el34's

Why do you say that you worry about them? - I thought they are pretty robust?

[jaysg]

Z mismatches can create higher voltages in the tubes. In the case of real EL-34s (not GE/Sylvania 6CA7s), those can exceed the mechanical limits...in other words, you can get internal arcing on peaks. It's best to get the right impedance match with EL-34s. The US tubes (6L6, 6V6, et al) are more forgiving. This is apparently why the Canadian JCM800 amps don't have 16 ohm settings. I believe Marshall used the same OTs, but terminated the 16 ohm taps inside the bell.