Weber 6A40 issues...

[lowell]

This is true about none of those mentioned amps being cathode biased circuits... however how can we explain that he's hearing compression in those amps? Especially SF fenders. SF Fenders are always hard and clean to me... except for the first version of the SF Twin Reverb. That amp actually had some mojo IMHO. I'm surprised that rmj134 finds those amps to have what his does not. The only way I could GUESS at it is that those other amps have old components changing biasing and voltages throughout those amps... or even transformer brand..?? I really don't know, I'm just throwing this out there. The main point here is that if it's compression rmj134 is after, then not trying cathode bias before selling the amp is a mistake. Oh and as far as losing 10w goes I wouldn't worry about it. My diy 5E3X2 has a cathode/fixed bias switch and I don't hear any noticeable difference in power when playing gigs w/ a full band. I'm not saying there isn't, but it's not noticeable to me.

[Five_E35]

I agree about typical SR's not running anywhere near that hot. To me BF distortion, especially with a SR, is that fairly bright swirly crunch of highs & lows that occurs just before the power tubes dim and the amp begins to sound like it's going to explode. Good NOS preamp tubes are partly responsible for that. I hope you're not basing this comparison based on settings, as it's likely the tapers on the weber pots are different from those in an original. Also the Weber schematic shows an .02uf tone cap where most BF SR's amps had a .033uf and most BF amps have a .047uf. The weber schematic also has the mod where the vibrato intensity control switch itself out of the circuit, a mod that adds gain, but also some muddiness to the sound.

But if running the power tubes hot is the solution, you could always find some JAN 7581A's and abuse them. It's the same tube as the 35 watt STR version of the 6L6 used by Fender in the 135 watt Twins and by Mesa in the early 100 watt Boogies. They're getting expensive lately, but last a long time, sound great, and can take all kinds of abuse. I'm not sure if there's a modern day equivalent. Some of the older Russian tubes can take the abuse but don't sound as good doing it.

[mhjensen]

I just built a 5f4, and it sounds really good, but it also doesn't compress quite as much as a vintage amp. I'm building a 6A40 right now, and noticed that on the layout diagram, the connections are wrong for the plain channel bass pot, vice the schematic, and Fender's old aa763 and ab763 schematics. The two wires going to the pot from the board need to be moved to the left by one terminal. Check the super reverb ab763 layout on schematicheaven.com. It would still work like the 6a40 layout shows, but the whole tone stack would probably behave differently than it's supposed to. It might make the bass muddy.You might want to see if your bass pot is wired wrong on the plain channel. The speakers in the old bf fenders were rather inefficient, which sounds like some natural compression over modern speakers, although the weber signatures in the kits sound pretty sweet, IMO.