Replacing the guts on a Tube Depotkit build to an authentic build - advice needed

[d. spree]

I have a new project and will need some advice – starting this while I wait for some components on the problematic champ build I am helping a friend with.
This new project is a 5e3. I have built 3 of them and they have all been problem free and the build went well. The first build I ordered a kit from TubeDepot as I was worried about having very clear step by step instructions. But it bothers me that this build is really not an authentic 5e3 and doesn’t have the same qualities and richness that the two later build s (from Mission) have. It also bothers me that this has a very modern printed circuit board even though nobody else knows what’s inside. It’s an aesthetic thing. So I am gonna remove the board and replace it with the real deal and with cloth covered wire and top notch caps etc. For this one I also will experiment with using carbon comp resistors (my other builds used carbon film resistors). I want to see if there is any truth to the “mojo” of carbon comp theory.

So my questions relate to some of the differences between the TubeDepot stuff and the “usual” 5e3 components.
The major issue is that (for some totally unknown reason) Tube Depot used a black faced deluxe reverb PT, not a 5e3 PT. I would prefer not to have to buy another PT but to use the one already in the amp.

The spec sheet for the BF deluxe reverb shows the high voltage rating to be 700V CT @ 120mA. The 5e3 PT shows 660V CT @ 120mA. The green filament leads on the black face show 6.3V CT @ 1.65A and on the 5e3 PT 6.3 V @ 3 Amps. The yellow on the blackface show values of 5V @ 3A compared to 5V @ 2 Amps on the 5e3. Also the TubeDepot kit came with a GZ34 rectifier which I replaced with NOS 5Y3 GT as the voltages were too high across the board – this has worked well.

So the specs on the PT are different and I presume that is why some of the resistor values on the board (especially the B+ resistors) are different so as to address the need to drop the voltages and there is also an additional resistor attached to each of the power tubes.

Here’s the detail: (1)The first resistor on the B+ rail is 4.7K Ohms / 3 watts compared to my Mission builds which are 5K Ohms /2 Watts. Second resistor on the rail is 22K Ohms/3 watts compared to Mission 22K/1 Watt. I presume that if I use the resistor values from the original Tube Depot specs that will be fine.

(2) Another difference is that the Tube Depot build had me wire additional resistors on the output tubes. Specifically the sockets are wired with a 470 Ohm / 2Watt resistor on each tube from pin 4 to pin 1 – pin 1 being unused on standard 5e3 layouts. Is this also to adjust for the PT voltage differences?

(3) The third difference I see in the layouts is not to do with the PT but with two feedback resistors a 47 Ohm resistor and a 2.7K resistor (labeled feedback resistors)> I presume I can simply omit these are the original deluxe design didn’t include them?

So my thought is use the same values as the original TubeDepot board, keep the tubedepot output socket wiring with the extra resistors the same, and ignore the feedback resistors. Does this sound sound?
The only other differences are in the grounding scheme – I will use a brass plate and ground as per my mission builds.

[Enzo]

Power transformers need to supply the circuit they are in. 700CT vs 660CT is not a huge difference, when you split the thing by grounding the CT, the one is 20v higher.

6vAC. 6V6 tubes draw 0.45A for heaters, and you have two, so .9A there. You also have two preamp tubes at 0.3A each, so 0.6A there. Total is 1.5A, so a 1.65A winding is fine. The extra current th 3A winging provides doesn;t go anywhere. Your 5v winding does only one thing, power the rectifier heater. Your 5Y3 needs 2A current at 5vAC. SO either the 2A or the 3A transformer works just fine.

Your details:
1. 4.7k versus 5k? Those two parts are essentially the same thing. 300 ohms difference doesn't matter much. Using the higher wattage resistor will not hurt anything. You can use Ohm's Law to determine how much power those resistors dissipate, so you can see how much headroom they have in the circuit.
2. 470 ohm screen grid resistors. You need to know what each part does. The original 5E3 had no screen resistors, but I think they are a fine idea. MANY fender amps have 470 ohm screen resistors. It protects the tube. Pin 1 on the socket is not used by the tube, so it is free to be used by the amp maker as a convenient place to solder something, like the other end of a resistor to pin 4. Though usually we use pin 6 as the tie point instead of 1. it has nothing to do with the voltages.
3. the negative feedback was not part of the original, but that doesn't make it a bad idea. The Tube Depot drawing points out that it was not original and what to do if you don't want it. In fact they have a jumper there so you can turn it off and on. For the price of two resistors, why not keep it, and jumper it in or out as you prefer.

You mention a tonal diference. I see the Tube Depot kit includes a Jensen MOD 12. What speaker did you put in your Mission kits? That right there can make a huge difference in sound. I am not saying the amp chassis sound identical, but speakers make the largest change in an amp's sound.


A printed circuit board may not appeal to someone's vintage sense, but we rarely have layout issues with circuit boards like we do with hand wired stuff.

[d. spree]

Power transformers need to supply the circuit they are in. 700CT vs 660CT is not a huge difference, when you split the thing by grounding the CT, the one is 20v higher.

6vAC. 6V6 tubes draw 0.45A for heaters, and you have two, so .9A there. You also have two preamp tubes at 0.3A each, so 0.6A there. Total is 1.5A, so a 1.65A winding is fine. The extra current th 3A winging provides doesn;t go anywhere. Your 5v winding does only one thing, power the rectifier heater. Your 5Y3 needs 2A current at 5vAC. SO either the 2A or the 3A transformer works just fine.

Your details:
1. 4.7k versus 5k? Those two parts are essentially the same thing. 300 ohms difference doesn't matter much. Using the higher wattage resistor will not hurt anything. You can use Ohm's Law to determine how much power those resistors dissipate, so you can see how much headroom they have in the circuit.
2. 470 ohm screen grid resistors. You need to know what each part does. The original 5E3 had no screen resistors, but I think they are a fine idea. MANY fender amps have 470 ohm screen resistors. It protects the tube. Pin 1 on the socket is not used by the tube, so it is free to be used by the amp maker as a convenient place to solder something, like the other end of a resistor to pin 4. Though usually we use pin 6 as the tie point instead of 1. it has nothing to do with the voltages.
3. the negative feedback was not part of the original, but that doesn't make it a bad idea. The Tube Depot drawing points out that it was not original and what to do if you don't want it. In fact they have a jumper there so you can turn it off and on. For the price of two resistors, why not keep it, and jumper it in or out as you prefer.

You mention a tonal diference. I see the Tube Depot kit includes a Jensen MOD 12. What speaker did you put in your Mission kits? That right there can make a huge difference in sound. I am not saying the amp chassis sound identical, but speakers make the largest change in an amp's sound.


A printed circuit board may not appeal to someone's vintage sense, but we rarely have layout issues with circuit boards like we do with hand wired stuff.

Thanks Enzo for a thoughtful and very concise response. part of my wish to rebuild this one was also to continue tp learn about how the guts of an amp work. I posted once here some time ago that having built my first 3 amps (all 5e3s) I realized I still understood little about how they work. So I agree that a printed circuit board is somewhat foolproof as I just had to follow the very detailed instructions (solder wire X to point A etc) and I was delighted to have a working amp. That's why I went with teh Tube Depot build the first time. However, the PCB was was a complete mystery and it made it hard to understand the actual circuitry. The next two build using a traditional grommet board make the circuits very evident. So that's a downside to the PCB. I still find I am learning how the damn things work and feel very much at the beginning of that - for instance I just helped a friend build a Champ and there were some faulty components and that took a while to figure out. And that is as simple a build as it gets. I must admit I am still stumped by schematics and am trying to learn to read them. I've read the other more obvious materials such as Dave Hunter's book.

So I followed your advice and went ahead and rebuilt the Tube Depot build from scratch. Rewired everything- put together a grommet board, improved the grounding scheme by fabricating a brass plate, and used "better quality" components (nothing wrong with the Tube Depot supplied parts but I wanted something a little closer to the originals). I have to say I am blown away by how quiet (as in zero hum) this amp works. It sounds great. The earlier build was much "hummier." This amp has no hum even when I plug in my self-built P90 equipped Les Paul. I also added two humbucker mods on toggle switches so that I can be happy with any of the guitars I use So I am happy to know what's inside, and with the overall quality.

Oh and yes there was a difference in speakers used - this one has a Weber Blue Dog and my later builds I switched to Weber 12A125As. They break up nicely a little earlier and seem less stiff than the blue dogs - but both are great speakers. However, I did try the original Tube Depot build with the Weber 12A125A.

So again, thanks for your response - sorry it took some time to acknowledge it (had computer access problems over the last few days) and you responded so quickly which freed me up to start - but the bottom line is you response gave me the go ahead. The rebuild went very fast - is really "clean" and has worked out great.

[CharlieP]

I know about 8 mos have passed but just wanted to comment on the 5V 2A vs 3 A PT. 3 A allows use of 5U4, 5Y3 or Gz34 a feature worth keeping.

[d. spree]

yeh, didn't swap out the PT. She sounds superb