Ideas 5e3 cab and volume

2L man

Tele-Afflicted
Joined
Nov 23, 2020
Posts
1,530
Age
62
Location
Finland
Yeah, but we're talking a 2X mismatch, which shouldn't be so bad.

I've got at least one amp with a 4 ohm tap (only) that I've used with an 8 ohm speaker for the longest time, with no problems with power tube longevity or killing the OT.

I've also got an amp with a DR OT that I use with a pair of 6L6s, into an 8 ohm speaker. Same thing with that one - power tubes last forever, and the OT is fine. In that setup, I'm actually using cathode bias with a B+ that's similar to a 5E3 (~370 VDC), with no negative feedback.

IMO, really the biggest consequence of the mismatch is that it changes the nonlinear frequency response at the output, which may sound better or worse. In the case of my own experiments, I've concluded that it simply 'sounds different'.
Possibly 2x less speaker load is fine but I did measure one 6V6 push pull and there came very high voltage spikes on power tube anodes which did not exist using "correct" load. I think this is because not all the (current) energy there comes to OT is not absorbed to higher impedance loudspeaker and it turns to (voltage) energy.

I have "simply explained" this to myself that when loudspeaker impedance is higher the loadline comes more horizontal and can extend further to the right where the higher plate voltage is. Obviously some of or most of this energy comes from the bias current.

Seeing that it does not surprice me at all if tubes or OT destroy if loudspeaker cable detach when setup is driven high power... but then loudspeaker impedance can be many times higher on resonant frequency. Some speakers easily 20 times higher?
 

11 Gauge

Doctor of Teleocity
Joined
Mar 21, 2003
Posts
12,795
Location
Near BWI Int'l
Seeing that it does not surprice me at all if tubes or OT destroy if loudspeaker cable detach when setup is driven high power... but then loudspeaker impedance can be many times higher on resonant frequency. Some speakers easily 20 times higher?
Yes, that's my understanding, higher at the resonant frequency. Not sure if there's a situation where it would be 20X higher (I honestly don't know), but I have seen a graph or two where an 8 ohm driver resulted in at least a 15 ohm impedance at the resonant freq.
 




Top