Hello dai H,
If not already obvious I'm not the chief guru on all this insanely complex stuff.
But I do have a brain that can think outside the well worn attenuation game and from all I've read and the experience gained from building a lot of different ideas has proved attenuation has limitations.
Some attenuators work ok,,, but HEy I wanted Fantasticly Stunning Sonic Heaven.
If attenuators work for you then great but obviously you are already inside the guts of the Palmer wondering how to improve it?
If you where truly happy with the Palmer you would not be asking.
I wish you luck trying to work out all the maths. BTDT,,Meantime I'm off playin my guitar and having far more fun than sitting over a hot soldering iron.
I admit I fell for the tecky game and started chewing all the attenuator maths inducky stuff but once I heard and also understood the Guytron GT 100 was just a simple resitive load on a small Amp into a second BIG amp. WOW DING!!!
A little bell rung in my guitarded brain that said hang on a mo,, if a simple resistor can pull such a fantastic tone why waste time on these attenuators.
Plan B materialized in a short space of time. Probably not quite as slick as the Guytron sound but still I'm miles ahead of attenuators.
Except for a dud socket in the load box I've never had any issues in 5 years and I play every 2 weeks for 6 hours at a local club. When I built that little Amp I ran it through an 8 Ohm soak test for 3 days flatout. I hardly ever touch it or worry about it as it gives me no sign of problems.
I run a Derated well setup but simple PP cathode biased 10 watt Amp.
Signal path thus;
Small tone box of tricks> 10 watt tube amp> Load box/Lineout > GraphicEQ > 120 Watt SSamp.
As to the Marshall load;
Well I've read more than once that *The Ultimate Attenuator* uses a 30 Ohm Load.
So your best bet is to ask folks that own the UA and a big Marshall?
An 8 Ohm resistive load is a very different animal when compared to an 8 Ohm speaker.
An 8 Ohm Resistive load puts a fair amount of stress on an Amplifier output,, much more than the speaker does.
Remember one is R and the other is Z.
R is the same load at ALL Freq whereas the speaker is a constantly changing load at different frequencies.
My best guess is 30 Ohms is a compromise between the two extremes.
There is nothing new under the sun
Heck if you search Tube schematics for long enough you will find that some old stuff used a *Safety resistor*. Maybe 50 Ohms across the speaker out socket.
This is there as a backup load so if the speaker is unplugged the amp won't run open circuit and try to push an infintite R causing major damage.
(A very smart idea,, some Amp builders could learn a lot by checking the real old stuff)
****Point being that R load can be higher than Z load and be quite safe.****
Marshall's have had problems over the years because they don't protect the *screen grids* enough. (King TUT gives a very indepth explanation of the old Marshall meltdown problems covered in his book TUT 2)
It's just that under stress for long enough (i.e. like running flat out through an attenuator) will show up the flaw in the Amps design. **This has absolutely Nothing to do with the attenuator**,,, but of course the ignorant will blame the attenuator,, not the sacred Marshall,, Winky.
My advice is get your BIG Amp checked out by one who knows how to derate for such use.
Frankly you will be far better served by using a $small tube $Amp and $soak that. $ cheaper
**Then** use the Marshall as the second Amp. (a couple of hot wire tricks can bypass V1 in the Marshall as you will likely have to much signal now)
Remember you have to carry 2 amps now!! Do you really wish to carry a great big heavy 100 Watt Amp when a small one does the same job?
Of course if you Are EVH you can have it all done for you while you sit back in your Limo.
Cheers, Phil.