Modern 5E3 build questions

[JoeK]

Why! oh Why! do people want to change something that works and has been proven to work thousands of times over? I don't know I can't help myself and I like some of the ideas others have shown me. So I'm just planning a 5E3 head and looking at a few changes others have done.
I was interested to see if anybody likes/dislikes the idea of separate cathode resistors-caps on the power tubes, or how about a 470k grid stopper on the phase inverter to clean up distortion, heresy?
I'll use a turret board but have grid stoppers on tube pins, shielded wire, star ground to keep filter cap nodes supply and return together etc.

[Enzo]

Unless you propose a circuit the flat out won;t function, do whatever you like. But know this: tube engineering was a mature industry 75 years ago, guitar amps have been around as long. There really is nothing you can come up with for these amps that has not already been done. Not saying don;t try stuff, please do and have fun.

Separate cathode resistors on the power tubes? Been done, go ahead. What benefit are you hoping for? That is the standard question. What do you want it to do differently?

You have a common cathode circuit on the input, you could make them separate like a zillion other fenders. You can try eliminating cathode bypass caps here or there. You could go to one input channel and parallel the two input triodes on it. Nothing that I can think of either that will not already have been done. Look at the body of work in the Fender file, all the variations on power tubes, on phase inverters, on tremolos, tone stacks, etc.

[Chuck H]

+1000

If you're familiar with the 5E3 then consider what you might like to change, add or subtract. Then do that. Or, if you don't know how, ask here.

I think the point is, why would you choose to use separate cathode circuits on the power tubes? I'm not saying there's nothing to it, I'm just asking why YOU might want to do it.?. If you don't have a clear and good reason, there's no reason. The stock circuit works fine.

Just as an example I'll tell you what "I" would change if I were building a 5E3 for myself. I'd series the input triodes and make the second tube a LTP. Then I'd change the rectifier to a 5ar4. But now it's not even close to being a 5E3 anymore, is it.?.

Build what you want. Don't make the mistake of building something that isn't what you want and try to make it what you want. The best you could hope for is that it'll end up "more like" what you want.

[JoeK]

I was asking about the dual cathode resistor as I saw it used on another 6V6 cathode biased amp and wondered if it would give an imbalanced set of power tubes an improvement in shared current draw. I was also wondering if builders had tried the grid stopper on the PI grid and found it OK or changed the character of the distortion of the original. Cheers Joe.

[pdf64]

'I was asking about the dual cathode resistor as I saw it used on another 6V6 cathode biased amp and wondered if it would give an imbalanced set of power tubes an improvement in shared current draw'
Yes, I find that a cathode bias resistor (and bypass cap) per tube is helpful in allowing non-matching tubes achieve a reasonable static current balance.
I think that power resistors, and especially electrolytic caps, were expensive back when these things were designed, so there was a benefit to reduce the numbers used.
All else being equal, I can't hear a difference between shared and individual methods.

'I was also wondering if builders had tried the grid stopper on the PI grid and found it OK or changed the character of the distortion of the original'
I've put one into my 5E3 based amp but didn't notice any difference / improvement. Perhaps there would be with a better regulated B+ but on a 5E3 there's so much sag, with a consequential reduction in gain and voltage swing, which both act to mitigate the blocking distortion / frequency doubling that the 470k stopper is intended for.
Pete

[Dave H]

Yes, I find that a cathode bias resistor (and bypass cap) per tube is helpful in allowing non-matching tubes achieve a reasonable static current balance.

I tried that on my EL84 amp when I didn't have any matched EL84s. The same two tubes had a 12mA difference with a common cathode resistor but only a 3mA difference with separate resistors. I'd guess that in fixed bias the difference would be somewhere in between (6mA?).

They really did go to great lengths to save a couple of resistors or caps back then. How else could you explain those stupid back to front volume controls on the 5E3? It makes a log pot perform like a reverse log pot. It's flat out at '2' and there's little change above that. I'd change it to the more usual set up and reduce the bass. I prefer an LTP PI but I can live with the cathodyne in the 5E3.