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I only play closed back cabs so I can't draw any direct comparisons with Fenders. However the clean modes on it are fantastic, smooth, deep and with a nice sparkle if you dial it in for a brighter sound. Personally I think it has the nicest cleans on any high gain amp I've tried. The main negative with it IMO is how picky it is about cabs. I honestly think the matching Rectifier V30 cabs make all the difference for it. I've not tried them, but I'd imagine the clean channels would sound great through the Lonestar cabs too.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Just because I don't care, doesn't mean I don't understand." - Homer Simpson
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Just because I don't care, doesn't mean I don't understand." - Homer Simpson
Yes ICBM, that "progressive linkage" stuff came about from my Fender clean amp discussion and your recommendation to look at the Blue Angel. Thanks for the recommendation. I haven't deserted that thread, but this one seems to have taken over for now. I found a clip on YouTube of an amp for sale some time ago with worse pot issues than Jimi Hendrix. But while it was working right it sounded sublime. Now that has both 6v6 and EL84 power sections. Complexity, and flexibility, and great engineering, that is right up my street.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Just because I don't care, doesn't mean I don't understand." - Homer Simpson
So I have to ask for an explanation. What is the effect of impedance mismatch, how would you describe its character and extremes ? This is another area of unknown valve territory for me, so it will be good to breakdown some more boundaries.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Just because I don't care, doesn't mean I don't understand." - Homer Simpson
Putting some numbers on a cathode biased stage might shed some light on why it is hardly ever used for output stages past about 30watts.
If we take an EL34 and wish to bias it to a modest 50mA* the grid voltage would be around 30V and so the bias resistor, for one valve, 600Ohms. Guitar amp op stages always share a single resistor so, twice the current, half the resistance=300 Ohms. It is simple to show the resistor would dissipate 3watts and so a 5W, better 10W component is needed. It will still get quite hot so need to be kept away from other components, especially electrolytic caps.
A pair of 34s so biased with say a 300V HT would probably put out 20-30watts. To get more power we would have to increase the HT to 400, 450 even 500**volts.THAT would mean anode current would rise and the grid voltage needed to bias it back even higher and that means Rk is higher in value and thus dissipates even more power. We lose more and more output voltage swing to the cathode. Connecting the cathodes to earth, neg HT, and generating a negative bias voltage elsewhere improves efficiency greatly.
*I nave NOT looked up the curves so I don't know if a 50mA bias is feasible but surely the numbers will serve for "demonstration"?
**500V actually hits the 25W anode dissipation limit for the EL34 and 50mA Ia.
On the subject of different output valve "sounds"? It is often overlooked that different types have very different drive requirements or sensitivities (gm). For instance the venerable 6V6 and the EL84 are very different in this respect so in an "EL84" amp, V6s are going to make the PI work much harder for the same power output.
Dave.
The Mesa Simul-Class is unusual in that the 'Class A' section is fixed-bias, but I'm not sure if it's true Class A or not - it is low-powered enough that it's possible. It also runs in triode mode which sounds quite different from tetrode/pentode, which may be more important than the class!
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Just because I don't care, doesn't mean I don't understand." - Homer Simpson
Yes! Should have said "almost all" use a common cathode resistor. I did ask once a B's why two are so rarely used but they could not tell me either! I doubt that the saving of one R and cap would be it!
The HT-20 biasing is unusual. About 12 volts of it comes from cathode bias* but there is also a negative supply with setting and balance control. Not sure why they went that way? One advantage is of course that the V loss in the cathode circuit is only about a third of full CB.
One operational advantage is that you can swap the 34s pretty much with impunity and the bias will come up about right. Best of course to get it set and balanced soon as...
*At first glance it looks as tho' the 20 has separate cathode Rs but in fact it is two 7 watters in parallel.
Dave.