Built my first 5E3! Comments/questions

[mbratch]

OK guys, I really have tried almost everything. Doing the "dual star" as tubeswell suggests, flipping the ground switch, removing the ground cap, changing to Leo's original wiring of the grounding for the output section, moving my CT ground to share the same lug as my other grounds at that location, lifting the soldered ground from the jack side that I currently have, and a variety of permutations of these, grounding everything to the PT side, different rooms, etc.

The most remarkable thing to me is in all these tests, the hum changes very little if any. I would have thought I'd at least have made it worse with some of the things I tried.

The only thing I haven't done is use a brass plate. Unless someone has some other ideas, I guess I'll try that next. But so far I'm just convinced that this baby was "Born to Hum".

[mbratch]

Have you tried different tubes in V1 & V2 or swapping them to see what happens? Sometimes tube shields help, occasionally they make it worse. Is the back panel of the cab shielded and grounded? If not try a heavy piece of foil over the back the chassis, but be extra carefull not to short the standby, power, and pilot light terminals.

In mine, I found it would hum when both volumes were up at the same settings, if the plate voltages on each side of V1 were more than about 10 volts apart. I'm not sure how plate voltage relates to preamp tube matching, but my guess is this has something to do with the shared cathode.

Haven't tried that. V1 is a 12AY7 and V2 is a 12AX7. I don't have a spare 12AY7 but I'll play with that at see what happens...

[tubeswell]

The other thing that occurred to me just now (besides swapping the tubes, which is the first thing you should try BTW), is shielding the input cables from the sockets to the grids of V1. When doing this you have to mount the 68k resistors at the input sockets, and ground each cable shield at the input socket end only.

You probably should also shield the wire from the vol pot wiper to the 1st grid of V2 in the same way.

These wires are the most prone to picking up unwanted stray coupling (from EM radiation from other parts of the circuit) because they are in more sensitive parts of the amp (being around the input stages).

[mbratch]

I had tried the easy ground cable once (from the volume pot) and didn't notice a difference. Since I had seen so many "quiet" builds without the grounded cables, I backed off that idea.

If it comes to that, I'll try it again and also the input jack grounds + 68K resistors.

Many thanks again tubeswell for trying to help me through this. It's a real puzzler for me. I just have this nagging feeling that there's something else wrong going on, but I'm not sure. The fact that the hum hardly changes, if at all, with all the things I tried is strange to me, but maybe that's normal (?).

[tubeswell]

Remember when using shielded cables, you have to ground one end (only) of the cable shield, otherwise it won't work. The idea is to surround the signal wire with metal at ground potential. This eats up stray EM from elsewhere before it can be induced into the signal cable. Shielded cables are very effective if done properly. But you must only ground one end of the cable shield (so as not to create a ground loop).

[mbratch]

Yep, I know about the grounding of one end routine on the shielded cable. Thanks!

[ho-mayed-stuff]

Have you checked your house wiring with a meter or tester?
Have you inspected all of your solder joints looking for a cold joint?
You can eyeball them, use a meter, or re-heat them.
Start in your preamp section then go to the phase splitter.
Also, use a meter to check chassis earth ground against the power chord (hot, ground and neutral), input sockets ground, cathodes to ground, and pot ground.

[mbratch]

I assume you flipped the ground switch, but disconnecting that cap may help. If you intend to keep it, it should be a UL-approved class Y1 or X1 cap. These are designed to fail open, are commonly used in surge strips with noise filtering, so if you plug into one of those you don't really need it in the amp.

My chassis is marked "ground" and my anal nature will compel me to keep it that way for now. But I'll likely go to a 3-way switch and one of those UL approved caps. Are those readily available (like Mouser etc)?

Have you tried different tubes in V1 & V2 or swapping them to see what happens?

OMG! You da man!

I swapped the tubes and the hum vanished. The only hum left is the nearly imperceptible amount that is there even when the volume is down, but that's much more acceptable for now. I also simply tried swapping out the 12AY7 in V1 (an EH tube) with a 12AX7 I had kicking around, and that had the same result. Does that mean the EH 12AY7 is bad or something? Or are they just naturally susceptible to noise? I don't have a spare 12AY7 so I put a 12AU7 which seems to work well. I use the normal channel volume to control the gain on the bright channel. It's a very interesting interaction.

There's also a bit of hisssss (always been there), especially at high volume, but I assume this is normal for this amp.

In mine, I found it would hum when both volumes were up at the same settings, if the plate voltages on each side of V1 were more than about 10 volts apart. I'm not sure how plate voltage relates to preamp tube matching, but my guess is this has something to do with the shared cathode.

Mine hums if either volume is up. Noticeably more on the "normal" volume.

[mbratch]

OK so now that the amp is running with a very, very low idle hum and with a 12AT7 in V1...

I have a question about the lack of linearity in volume controls again. After playing with it a bit, this is VERY non-linear. Volume for the bright channel is no-sound at 2.5 and then at 2.6 I get a sudden onset of sound, but not very loud. Then above 2.8 it's already pretty loud. What's odd to me is the sudden bump in sound, like something somewhere reached some threshold. Is this normal behavior for a 5e3?

[tubeswell]

I have a question about the lack of linearity in volume controls again. After playing with it a bit, this is VERY non-linear. Volume for the bright channel is no-sound at 2.5 and then at 2.6 I get a sudden onset of sound, but not very loud. Then above 2.8 it's already pretty loud. What's odd to me is the sudden bump in sound, like something somewhere reached some threshold. Is this normal behavior for a 5e3?

Depends on the quality of the pots you have. A lot of modern production audio pots are cheaply made with two bits of carbon, and have a 'two-line' taper instead of a log taper. They are susceptible to funny bumps. Best thing would be good quality NOS 1MA pots if you can find some.

[cminor9]

I have a question about the lack of linearity in volume controls again. After playing with it a bit, this is VERY non-linear. Volume for the bright channel is no-sound at 2.5 and then at 2.6 I get a sudden onset of sound, but not very loud. Then above 2.8 it's already pretty loud. What's odd to me is the sudden bump in sound, like something somewhere reached some threshold. Is this normal behavior for a 5e3?

My 5E3 did a similar thing (before I totally changed the input section and tone stack.) Up until about 1.5 there was no sound. Once it kicks in, it was fairly loud, and then it just got a little louder from there. I have tried a few different new production pots and have gotten the same results each time. So I don't think I had any defective pots and suspect you don't either.

I also suspect the 5E3s in the 50's didn't have this problem where for the first number or two on the dial there is no sound. I haven't played an original, but from a consumer standpoint, it would seem like a buggy product. Here's the best I can think of: An ohm now is the same as an ohm 50 years ago. Same with farads, volts, amps, and so on. So the components should be the same value as back then, and probably even better quality today. While voltages are generally higher, and tubes are arguably not as good, I don't see how these factors weigh in here. But one thing that isn't spec'd and could well have changed over the years is the base value for the log pots (when's the last time you bought an audio taper pot with the base value for the log specified?). That just seems to be a likely suspect for this behaviour, and you can probably imagine how a less steep slope (or steeper slope, depending on how you look at it) could cause it. I'd be interested in seeing if Fender's reissue 57 deluxes have this problem, but I haven't played one of those either.

My theory is that it wasn't a normal problem for a genuine Tweed Deluxe. But I'd imagine it IS normal for modern repros.

Tubeswell might be onto something - get an old timey 1M pot and try it. But let's be honest: the 5E3 comes alive at about halfway up the dial anyhow. The lack of low volume never bothered me that much. Is it worth enough to you to trace down a fifteen dollar pot that may or may not fix this? Me, I printed a sign that I hung above my workbench as a reminder. It has on it the old saw "If it ain't broke, don't fix it, idiot!" So, is it really broke?

[mbratch]

Thanks guys. My main concern was to understand whether this was the "typical experience" with a new 5E3 build. I agree that, in practice (no pun intended) it may not turn out to be an issue due to the volume I end up playing at. But the behavior made me wonder whether I did something wrong in the build, or whether I had a defective component, or whether I overheated the pots soldering something to the back of them.

[Five_E35]

Glad you got it working. Sometimes it's the simple things we assume people have already tried. It may be that the tube in V1 is more critical in these smaller amps because we turn them up so much. The same tube in a Bassman or Twin might be fine because we'd be loosening up the drywall with the volume on 11. I originally had a NOS 12AY7 in mine which besides hum was microphonic. An EH I tried was fine, but I've got a NOS 5751 in there now, which distorts quicker but sounds a lot better.


The Secret Life of Pots explains a lot and has some solutions.
http://www.geofex.com/article_folder...s/potscret.htm

I originaly had Alpha 1M audio pots for mine which turned out to be about a 20% taper. Bruce mentioned that the CTS/Mojo 1M audio pots were better, so I ordered some, measured them(they are 10%), and they work about the same as the Fender RI and Victoria versions I've played. The Fender RI does have 10% - shown on the schematic as 1M-10A. Except for linear taper which would be like an on-off switch, I agree about ohms is ohms. The difference between 10% & 20% is about 1 or 2 numbers on the dial, probably most noticeable on the tone control. Fender BF amps have 30% taper pots, so what's right for one kit would be wrong for another. Fender has the luxury of ordering custom pots.

I normally play mine with the volume anywhere between 6 & 10 and turn down at the guitar for clean at the lower settings, so a couple of numbers one way or the other doesn't matter that much. It is usefull to know when one guys 'great' settings don't work the same on someone else's amp.

[mbratch]

Thanks Five_E35.

I guess it didn't occur to me that a pre-amp tube might be originating a 60Hz (or harmonic thereof) hum. I almost feel silly having done, undone, and redone grounding ideas only to come to changing a tube. But in the end: I'm happy! And the knowledgeable, patient, and helpful folks on this forum have given me a lot to learn.

I sent an email to the place I bought the kit from asking what taper pots they are.

I have yet to find my "sweet spot" on the amp and play with doing more guitar-based volume control. To date, I've been playing with a Princeton Reverb or Deluxe Reverb and using pedals for overdrive. I'd like to do more with getting more drive through guitar volume control. More learning for me...

This amp sounds really sweet with the AlNiCo speaker. This one in particular has the Weber Sig 12S.

Off to read about the Secret Life of Pots...

[mbratch]

I assume you flipped the ground switch, but disconnecting that cap may help. If you intend to keep it, it should be a UL-approved class Y1 or X1 cap. These are designed to fail open, are commonly used in surge strips with noise filtering, so if you plug into one of those you don't really need it in the amp.

Any idea where I can get these? I checked Mouser but couldn't find them there. I did a quick Google troll and didn't come up with something, but I could dig further. Wondering if others here have used them and know of a good supplier.