5E3 Scratch Build

[David Root]

+1 and thanx for reminding me! I read that a long time ago and I guess that went in one ear and out the other (no surprise, just ask my wife).

As it happens I'm doing a cathodyne on my current build which is a DeArmond R-15 w/4x6V6. Like a 5E3 w/an extra pair, but not identical, a very interesting circuit.

I need to retrofit that into my harp amp too, which is a modified 5E7 Bandmaster.

[rp]

OK, but before I wash up and don the surgical gown, anyone try this and not like what they heard? Or just preferred the blocking distortion (have I got that right?) w/o the mod?

[dave g]

Frequency doubling distortion

With the extra resistor, the sound is smoother and less "grubby". If you don't like it, it's just as easy to remove as it is to install.

I strongly recommend soldering the 470k directly onto the tube socket pin.

[Lonely Raven]

All the parts have arrived, I just need to find some time to clean my bench off (I have a Magnatone 280 with a collapsed cabinet taking up all the limited space), then break out the donor cab and start laying out the parts.

Again, I'm using this amp as a learning tool..I'm finally taking the time to understand where the signal passes, which parts to what, and how those parts effect the circuit. I understand I might be asking some inane questions, but please bear with me, I'm fishing for knowledge and I understand some of you feel I'm barking up the wrong tree. I do appreciate all your opinions though.

That said: I've already got a large assortment of caps to play with, but I've also got some resistors to play with. So I'm looking for some guidance as to what I should and shouldn't do.

For example, I have some PRP 1/2 watt, Takman (pink) 1/2 watt, some cheap metal film from Weber, and some vintage Carbon Comp I picked up at a garage sale. So are 1/2 watt applicable for this circuit? (except in the power section I understand) But would 1 watt be preferable? Which are "important" resistors that carry the signal and I should consider swapping out with different types to get an idea of the sound change? Or would I have to swap every resistor out? Which resistors *should* absolutely be metal film and don't effect circuit?

Sorry that's a lot of questions...I'm just trying to get some tips from those of you who have been down this road. I really can't afford to experiment as much as I'd like, both $$ and time wise. So it would be nice if I could focus on what changes are worth the effort. For example, using carbon comps in the power filter section vs metal film...I'm pretty sure it doesn't make a bit of difference...so I can build that part of the amp correctly and just forget about it - then keep my focus on whatever *does* make a difference.

I figure a 5E3 is a great amp to do this experimentation on. And what I learn here I hope to carry into an Xits X10 build if the forum figures that one out. I also have an empty Super Reverb chassis to build up, as well as a Dripline Super Reverb and afore mentioned Magnatone 280 to rebuild!

Fun stuff!

[Lonely Raven]

OK, so looking at the schematic, am I correct in drawing out the signal path? Are the components in this path the ones I should be focused on for component swaps, or are there more?

Note: I just realized as I'm typing this, I don't understand how the signal goes through the tone knob.

[img684]http://lonelyraven.zenfolio.com/img/s3/ ... 9357-5.jpg[/img]

[jjman]

"Signal path" is open to interpretation. I consider the cathode caps to be signal determinators. Current flows thru them and that current's modulation is essentially the same modulation seen on the signal. Input resistors and tone knob are also in the path for sure. Grid leaks also conduct currents (to ground) that have the same “modulation” as the voltage that appears on them. That voltage is the signal going on down the path. But I would not say that grid leaks are “in the path.”

[dave g]

I agree, "signal path" doesn't really mean anything. Analog circuits are like trampolines...

[Lonely Raven]

I don't follow what you mean by trampolines...

That said, are you saying that (same for same) all resistors in the circuit will effect the tone? So if I used carbon comp in the signal path but metal film on the cathodes that it would sound different than carbon comp all over?

[vibratoking]

I added a 470K grid stopper on the cathodyne. I did not put a scope on it to verify the waveforms as shown in Merlin's document. I did not hear any difference during a 4 hour rehearsal last night. I'll have to listen more closely in a quieter situation.

I also added a false center tap for the heaters. BIG difference.

Thanks for the info guys.

[Big Jim]

I added a 470K grid stopper on the cathodyne. I did not put a scope on it to verify the waveforms as shown in Merlin's document. I did not hear any difference during a 4 hour rehearsal last night. I'll have to listen more closely in a quieter situation.

I also added a false center tap for the heaters. BIG difference.

Thanks for the info guys.

I may try this on my 5E3 as well. It's certainly easy enough to do. From reading the document I would be expecting a dramatic improvement. I will still probably give it a try.

[Lonely Raven]

So I spent two hours cleaning up my "office" (which is nothing but a computer desk and work bench in a corner of the basement surrounded by 2X12 and 4X12 cabinets) and making room to start my 5E3 retrofit into a Fender 1X12 transistor donor cabinet and chassis. After cleaning, I go into storage and pull out the 1X12 donor cabinet, and I was pleasantly surprised to see the 1X12 speaker still in there along with a reverb pan! But then I realized...WTF, the chassis is not there.

I'm going to dig a little deeper and see if the chassis just got stuffed in a box or is in another corner of the storage area...but if the chassis is gone...then this project got nipped in the bud till I can get a 5E3 chassis and build a cabinet for it.

And I was all set to start working on the layout!

[surfsup]

Well as you know I'm a noob, but it seems to me everything affects the "signal" by contributing noise, filtering highs, lows, RF, picking up RF, ground loops, it is a vicious cycle! So the question I would ask myself is what would I want any component "altering" to actually do?

Plates:
Not necessarily the "signal" but if you follow the power supply lead across the smoothing caps horizontally across the middle of the schematic. This lead has leads off it upwards to the plates. The four Rs, three 100k and one 56k plate resistors, see high voltage and usually these would be 1W and some prefer CC here because of the higher voltage. CC offer warmth but CC could be noisy, you can go CF. 1W carbon films might be a nice balance between CC and MF, I dunno.

Input:
Metal film R at the input jack (I got a IRC 2Watt 1M Metal Film glaze for my next build and two more for the PI) because they are quieter than CC or CF and a larger size will be quieter as well. So an extra $0.25 for an extra watt might make a difference. Also the build quality of the resistor.

In addition to your highlights, also the cathode caps and resistors. Just my two cents.

[David Root]

Lonely Raven, the conceptual "signal path" as you highlined it on the schematic should show the yellow line coming also out of the phase inverter cathode (V2B), on thru that .1 coupling cap to the other 6V6 grid. You are showing the 220K bias grid leak resistors as the inverter, 'tain't so.

As others pointed out, there is more to this than that however.

[Big Jim]

I added a 470K grid stopper on the cathodyne. I did not put a scope on it to verify the waveforms as shown in Merlin's document. I did not hear any difference during a 4 hour rehearsal last night. I'll have to listen more closely in a quieter situation.

I also added a false center tap for the heaters. BIG difference.

Thanks for the info guys.

Me neither! maybe my ear isn't that good, but I really couldn't hear an improvement. The amp doesn't sound any worse though.