will this work? 5e3 to Harvard conversion

[tubescent]

i have a 5e3 clone that i want to tame and make a bit more like a Harvard 5f10.
looking at the schematic there doesn't seem to be much difference. i have edited a weber 5e3 layout - will this work?
http://i936.photobucket.com/albums/a...ayoutedit1.jpg

do i have to change the cap coming off v1/pin1 to 0.022uf or will it be ok with what is there (0.1uf)?
also the cathode bias resistor coming off v1/pin3 should now be 1.5k rather than 820 - what will sticking with 820 sound like? otherwise can i combine the cathode bias resistors of v1 and v2 as in the green wire connection?

and one more thing: a lot of amps use a switch to change values of these cathode bias resistors on the v1/1st triode preamp stage. can this idea be applied to the cathode bias resistors of other tubes? ie. power tubes with a switchable bias resistor? or the next 12ax7(v2)?
is this what is going on in the angela schematic with the "vox twang switch" on the 6v6 here - Angela Super Single-Ended 6V6 Guitar Amp Project

[petemoore]

The SSE Guitar schematic 'deep/bright' switch switches the cathode AC coupling capacitor value. The two caps paralleled is a larger value, supplying the cathode with more uumph for amplifying bass.
Another way to get an idea of kinda how it works is to use a Jfet @9v, substitute the cathode for the source, the gate for the grid and the drain for the plate connections.
Mess around with the source plays role of cathode, experimenting with various R/C combinations to ground...anything else...safely. This little booster is a useful and nice booster.

[MWJB]

I don't really see the point of converting a 5E3 to the layout you posted, basically your layout shows a 5E3 with just a bright/inst. channel. There will be change in tone/how fast the volume pot ramps up because the the Harvard (like nearly all other amps) uses the volume controls wired as voltage dividers (signal in on the ungrounded tag, out on the wiper) and the 5E3 does not (sigal in on the wiper, out on the ungrounded tag).

Either 0.022 or 0.1uf will work as the coupling cap, go with what sounds best.

When both halves of v1 share a single 820ohm cathode resistor, it is the same (or near enough) as giving each half/triode a 1500ohm cathode resistor. Running a single 820 for one half of the tube will give a raspier, fuzzier tone & the tube may be under biased when hit with a large signal that will make it choke.

I would not have V1 & V2 share the same cathode resistor as the 2 stages are out of phase with each other. A shared 1.5K is the equivalent of giving each triode a single 3K cathode resistor...this will result in higher voltages on the preamp tube & a cleaner tone.

Not much point in having switchable cathode resitors on the power tubes, cathode bias functions well over quite a range (say 30-40mA per tube in this case).

In the Angela schem the 6V6 cathode resistor is normally unbypassed, with the Vox Twang engaged a bypass cap is now in the circuit.

You could try splitting the cathode resistors at v1 so that pin 3 & pin 8 have their own resistor & cap. You could also try Bruce Collins 5E3 vol/tone mod which will allow tweaking of the bright caps for both channels & give a smoother ramp up on the vol controls.

[MWJB]

"The SSE Guitar schematic 'deep/bright' switch switches the cathode AC coupling capacitor value. The two caps paralleled is a larger value, supplying the cathode with more uumph for amplifying bass." Not really. The switch just gives the option of 25uf vs 0.68uf. If you put the 25 & 0.68 in parallel (25.68uf) it would sound the same as 25uf.

[tubescent]

i don't really like the two volumes thing so if this makes it more of a standard amp then i'm happy - also i want to make space to use the extra diode for reverb (+ another tube).
i got mixed up with regards to the cathode resistors - yes even if i joined v1 and v2 to the 1.5k that would be 3k. i'll just replace the 820.
still don't quite understand what the vox bright switch is about but maybe i'll just have to do some more reading and it'll become clear.
cheers