The Amp Garage

I’m testing out speakers on my new 5F8A High Power Tweed Twin build. Is it impossible to get smooth breakup with high powered speakers? I’ve run it through some new Celestion G12H75s, a Tone Tubby Amsterdam/4040 and it sounds great cranked, but is somewhat brittle in the early to medium breakup area. Great treble detail, but not a bunch of compression. I’m running the 8 ohm secondary. I understand Joe Bonamassa prefers the Lead 80 with this amp. Short of a 412, I’m finding 212 arrangements to not cover all the bases, yet. What would you recommend?

Is the amp itself transitioning into overdrive nicely? How does it look on a scope?
Too much NFB can cause a sharp transition, creating higher order harmonics that might sound kinda spurious, not blended in with the main signal.
Or it may be only marginally stable, perhaps only flipping into oscillation at a certain conduction angle.

Although it's certainly true that different speakers can significantly affect the tone, loudness, and distortion characteristics of an amp, my experience has been that high-power speakers more accurately reflect those characteristics of the amp itself. One example is D-style amps with EV speakers.

pdf64 wrote: ↑Mon Apr 04, 2022 10:51 am Is the amp itself transitioning into overdrive nicely? How does it look on a scope?
Too much NFB can cause a sharp transition, creating higher order harmonics that might sound kinda spurious, not blended in with the main signal.
Or it may be only marginally stable, perhaps only flipping into oscillation at a certain conduction angle.

Only going on the sound to my ears, it sounds a bit harsh. I have a scope, but don't know how to diagnose overdrive transition. I would imagine as I inject a signal and turn the dials, the clipping shape would indicate. I need to find a good source for reading up on that.

The voltage difference between power tube plates and screens is a volt at best. I've seen discussion of spreading that out a bit by adding series resistors to the choke (which might lower my preamp voltages slightly closer to spec, they're a touch high), or placing larger screen resistors in. I'm eager to understand this more.

I wouldn’t be so quick to assume that high power speakers are the direct culprit , but they definitely can highlight any harshness coming from the amplifier itself .

Achieving “smoothness “ with a g12h75 might prove to be a challenging endeavor . The high mid range is in your face . I only use these speakers when the rest of the band is in a volume competition, otherwise they can be overbearing . Works for Jimmy Page

I don’t know have experience with the tone tubby .

That being said , as your boy JB will attest , high power tweeds are like “afterburners” for his rig. They add all the upper mid clarity that his Dumbles lack . Smoothness isn’t exactly their strongest attribute .

And with all that being said, I personally would love a look around in your amplifier to see the layout and component choices . It all adds up .

v-types might work or 65w creambacks