Speaker Impedance Question. . . . .

[Erich]

Howdy, all, great resource, by the way.....

I have recently acquired a Jet City PicoValve convertible amp (2 watts & 5 watts). It has 4, 8 , 16 ohm outputs. I bought it because I need a nice low-wattage practice amp and it sounds awesome. It is STILL a bit too loud, though and I was wondering if I could use the 8 ohm speaker in the 16 ohm output on the amp to reduce the volume a bit more.

I know doing this on a SS amp could be fatal. I am a very technical guy but have just begun working on tube amps and don't want to damage the plates or tubes. The amount of disparate information available via the "webernet" is more than confusing.

The speaker I have is an old Jensen cast-frame 8" speaker at 15 watts so there is no danger so I should have plenty of headroom at the 2watt setting, even at full volume (where tubes run free).

I have owned several tube amps from an old Gibson 10 watt "stanker" to the Laney AOR Pro Tube 100 and Mesa I currently have. I love this little amp and want to make it last years and years and just don't want to do anything that would reduce the life of it. Any help you fine folks can provide would be greatly appreciated. . . . . . Erich

[HotBluePlates]

... I was wondering if I could use the 8 ohm speaker in the 16 ohm output on the amp to reduce the volume a bit more.

I know doing this on a SS amp could be fatal. I am a very technical guy but have just begun working on tube amps and don't want to damage the plates or tubes. ...

Welcome Erich!

Yes, you can mismatch the speaker load by putting the actual 8Ω speaker on either the 4Ω or 16Ω jacks. It should reduce output power slightly, but probably not as much as you'd expect from your experience with solid state. Tubes generally have an ideal load for a given supply voltage, so mismatching in either direction reduces power output; this is different from solid state where going up you expect to reduce power but going down you expect to increase power (until you increase it so much the output transistors burn out).

The fatal move in a tube amp is driving a signal into the output stage with no speaker load (open secondary), as that causes voltage spikes which can damage the output transformer. However, a tube amp will survive just fine with shorted output terminals (also opposite of what solid state amps do).

[Erich]

THANK YOU! I was pretty sure of this. I'm building tube heads, now, and had am getting pretty familiar with the analog circuitry but still have "solid state" hangover haha. I've owned tube amps for years and have biased several. I knew there was a rudimentary difference in the output stage, just couldn't connect the dots! Thanks, again, I just need to reduce the total volume at "10-10" by 15%, or so, to keep the sound in my studio (and keep peace with my very patient wife). This thing sounds awesome. I've not messed with class A valve heads much and I think I'm in love hahahahaha!!!!

Rock on! (I'm going to  )