5E3 performance

[dfoxdavies]

I have just completed my amp built to a 5E3 schematic. I detailed in another post some of the minor issues I had with the build, but all is running OK now.

So, there are some often spoken facets to the performance of this circuit, some of which my build doesn't seem to exhibit. Like interaction between the volume controls even though just one channel is plugged into, mine doesn't do that. Volume largely peaks out by 3 on the volume control, yep does that. Easily enters into overdrive territory, no mine stays clean pretty much all the way.

I am pleased with the sound (tone) of the amp. It is louder than I was expecting. If it doesn't display these attributes, I'm still pleased with the amp.

Some of the components are not exactly as a genuine '57, so maybe that could be the reason.
1. Power transformer may be a bit beefier, my power rail seems to be running around 390V instead of the 350ish I believe it should be. Transformer is a P-TF41316.
2. Output transformer is a P-T1750J rated at 20W.
3. Rectifier tube is a 5U4G instead of a 5Y3GT. It's what I had on hand
4. First tube is a 12AX7 instead of a 12AY7. This I think gives more volume, but again it's what I had on hand.
5. The coupling capacitor after the tube in the bright channel is only 0.022uF. This I believe is better for humbucker pickups.
6. Speaker is from a Hot Rod Deluxe, I believe. This probably has a much bigger magnet than would have been available in '57.

I had intended to build an uprated version of a Princeton, many years ago. I bought many of the parts back then, hence not necessarily 5E3 parts. Anybody like to comment on this?

[johnnyreece]

The thing that jumps out at me is, your choice of rectifier. A 5U4 will drop much less voltage than a 5Y3, so it's likely a lot of your B+ increase is due to this. A brief look at the PT data sheet says the 5V winding can handle the 3A filament current the 5U4 needs, so you're good there.

[dfoxdavies]

Thanks for the reply.

That's much as I expected the main reason for the higher voltage to be. I'm assuming that would be a big contributor to the higher than expected power output. I would consider making the change if anyone felt it would also contribute to other attributes being met

[cdemike]

mine stays clean pretty much all the way.

It should be possible to overdrive it at some point. Two 12AX7 gain stages should provide more than enough gain to overpower the output section, even with the other changes in the amp. Your elevated B+ is a major contributor to increased headroom, but it should still be possible to overdrive it.

First tube is a 12AX7 instead of a 12AY7. This I think gives more volume, but again it's what I had on hand.

This shouldn't give an overall increase in volume, but rather make breakup happen sooner on the volume knob's travel, so it's even stranger to me that your amp is essentially clean even when dimed. Power supply capacity should be the terminal limiting factor in terms of loudness capabilities in this type of amp. What kind of pickups are you playing through it?

[dfoxdavies]

So far, mostly P90's. Briefly some humbuckers, very briefly. I think I have a 5Y3 rectifier tube I could put in, I may give that a go, see what happens.

I have a Carvin with humbuckers and active tone controls. I'll give that a try, that should send a lot of signal in.

[dfoxdavies]

The volume graduations go up to twelve (that's why it's loud ). Up to 10 it's clean, when you go over 10, the volume drops significantly and there's much ugly distortion. The Carvin does cause some breakup, but it's not the best partner for the 5E3. I prefer the sound of my Partscaster Thinline Tele with P90's.

At some point I will dig out a 5Y3 that I think I have and try that. Meantime, I will keep it below 10.

[cdemike]

That’s very strange behavior, especially for an amp without negative feedback; negative feedback breaking down can cause that kind of very sudden transition to overdrive, but it wouldn’t be consistent with a drop in volume. I gather from your original post and the last post that your amp gets louder from 0 to 3, stays the same loudness from 3 to 10 and does not get overdriven, and past 10 the amp drops in volume and suddenly gets extremely overdriven. Is that right?

What kind of resistors did you use? I’m specifically wondering if you used any carbon comps, since they can drift dramatically from their stated values.

[maxkracht]

Up to 10 it's clean, when you go over 10, the volume drops significantly and there's much ugly distortion.

Sounds like it could be some kinda parasitic problem. Playing with lead dress/ moving some wires around with a chopstick might help you find the issue. Otherwise, you might need a scope to see what's going on.

Edit: didn't notice the part about channels not interacting, possible there is a wiring error on the volume/tone controls? Did you split the cathodes on V1? Unrelated to channel interaction, are you using log taper pots?

[dfoxdavies]

First off, yes audio taper pots.

I have to say that I am a Mechanical Engineer by profession and only dabble in electronics to suit my musical hobbies. Sometimes I have to think a bit about technical terms, more so with tubes than transistors.

When I built the amp I generally followed the build instructions on the Mojotone website, even though it wasn't one of their kits. The turret board is a 5E3 specific part as is the Aluminum chassis. I built my own cabinet to 5E3 design (without the sloping front panel).

When you talk about splitting the cathodes on V1, are you referring to the two 100K resistors which join to the power? These are as Leo intended as is most of the circuit (apart from the differences I mention previously)

I have been re-investigating the channel interaction since I have got the amp running more reliably. What I see now is that the 'unused' channel does have some output albeit around 50%ish of the used channel. It is also a little muffled. Under normal use, operating the 'unused' volume control still doesn't produce any significant change in tone. I am going to try a 5Y3 rectifier soon, maybe that will have an effect. I am thinking that this interaction is caused by linking through the power supply?

Thank you again to all for taking time to think about my problems and offer advice. Dave.

[maxkracht]

I meant the cathodes, pin 3 and 8 on V1. 100k resistors are the plate load resistors. (I'll try and stop using jargon) If it's a stock 5e3 pins 3 and 8 would be connected. Doesn't add much channel interaction anyway, so don't worry about it. I was just curious.

I would double and triple check your wiring on everything connected to the tone and volume pots. If everything looks correct, poke each solder joint and ground connection with a wood chopstick while audio is playing through the amp and see what happens. It's possible you have a wiring error or bad solder joint. There should be noticeable interaction between channels, meaning both volume knobs will change volume/tone regardless of what input you use. The volume control associated with the channel you are plugged into will affect things more, but both should cause noticeable changes. A different rectifier tube won't have anything to do with channel interaction.

[dfoxdavies]

Jargon is fine, I'll get used to it.

Yes, pins 3 and 8 are jumpered. I will get to probing the volume pot wiring sometime over the weekend I hope.

[cdemike]

I really doubt these differences can be explained by the higher B+ and different rectifier tube. What you're describing is a major loss of signal, and it sounds like it's likely between V1 and V2 based on the lack of interactivity between channels. The design must necessarily involve a high degree of interaction between the channels, so if a more-or-less stock 5E3 doesn't have channel interaction, something is wrong. Do you have pictures of the amp's guts?

[dfoxdavies]

I have taken some pictures of the amp. I know my wiring and soldering wont win any prizes, I'm hoping for serviceable, not necessarily pretty.

20240727_112338.jpg

20240727_114138.jpg

20240727_112332.jpg

20240727_112451.jpg

20240727_112509.jpg

20240727_112326.jpg

[dfoxdavies]

So far, I cannot see any incorrect wiring issues, or find any bad solder joints. I have found a 5Y3 rectifier and installed that. B+ is now 366V, but the amp seems just as loud. There may be some overdrive now but it's not significant.

What I have noticed now is that when I attach probes to measure voltage etc, there is an increased hum as soon as the probes get near to the circuit. Also, when I move the guitar close to the back of the amp (it's up on the workbench) there is a loud hum. Maybe I have a grounding problem?

[maxkracht]

So far, I cannot see any incorrect wiring issues, or find any bad solder joints. I have found a 5Y3 rectifier and installed that. B+ is now 366V, but the amp seems just as loud. There may be some overdrive now but it's not significant.

Hard to tell from photos where all the wires go under the board, but nothing looks like it's in the wrong place at first glance. I do see many suspicious solder joints. Also looks like the center and right lug of the bright volume are shorting to ground.

When you are soldering, make sure the iron is touching the lug you are soldering to and any wire(s) you plan to solder to that lug at the same time. Solder should act as a thermal bridge between the components and your iron tip so they all heat up evenly. It also helps to tin your wires before soldering. Sometimes copper wire gets an oxide coating and it takes a bit for the solder to adhere. Flux is your friend, either get some extra rosin flux or keep adding a tiny bit of fresh solder so things flow well.

What I have noticed now is that when I attach probes to measure voltage etc, there is an increased hum as soon as the probes get near to the circuit. Also, when I move the guitar close to the back of the amp (it's up on the workbench) there is a loud hum. Maybe I have a grounding problem?

You might have a grounding problem, but this all sounds normal.