hi octane wire gauge

[Marcos - Munky]

Here at my place we have 127V showers. But there's people who uses 220V showers - even the simple ones like this:

[PRR]

127V, 220V, 240V is mostly about the available voltage.

The 127V showers seem to be slightly lower Wattage than the 220V ones, probably because the wire-size gets crazy at the lower voltage.

Even the 5,700 Watt is much more power than my electric water-heater. But my 3,500W tank will not make hot water as fast as a shower can use it.

I *also* have a gas-fire on-demand water heater which seems to work out to 30,000 Watt equivalent? It will make a small amount of HOT! water even with our cold Maine well. But if the flow is large it isn't very hot, and if the flow is small it shuts-off cold.

[Marcos - Munky]

The ones at my place are 5500W. We usually don't go above half of the power, temperature here right now is about 28°C/83°F. Our coldest days are about 5°C/39°F, so the 5500W shower at full power is more than enough, at least for me.

[mac]

never take a shower in Brazil!

temperature here right now is about 28°C/83°F.

To die or to stink.. that's the question

mac

[Marcos - Munky]

To die or to stink.. that's the question

Good question!

Well, I've plugged it today, and good things first: it didn't blew off! But the bad thing is I got a loud hum, even with guitar unplugged (input connected to ground) and all pots at min. Any suggestions on where I start to looking for what's causing this hum?

[BetterOffShred]

Wire routing/dressing is key with higher gain amps, and heater wiring.   If you haven't checked out Hoffman amplifier forums head over there and take a look.  Some really really knowledgeable dudes who are happy to guide.   There's always the old wooden chopstick poke and prod technique keeping your hands out of the amp obviously.   Ground loops are pretty common, I've created a couple myself    I think a lot of times isolating the input jack helps too depending on what you have going.     Just shooting in the dark!

[mac]

It sounds like the problems of first Epi Valve Jr.
You can check the mods done to version 1 and 2 of this amp.
Mine is v3 and is very quiet.

mac

[thermionix]

I wrapped up a nightmare Marshall JMP 2203 repair today.  It had been sloppily modded and I basically put it back to stock, but it took me hours and hours to figure out this awful 60Hz hum present any time the master volume was turned up past 2 or so.  Everything I could measure checked out, the grounds were connected same as factory, all electros were new and good quality.  I tried 3 different brand new 12AX7s, two Sovteks and a reissue Tung-Sol, the hum persisted.  I even swapped the socket, after EVERYTHING else had been tried, but still no change.  I was about to go nuts over this thing!  I had the hum isolated to V1b, but could not find the cause.

Well, turns out it was the 12AX7.  All 3 of them I tried.  All made in Russia, I think at the same factory (Reflektor?).  Apparently those tubes have too much leakage from heater to grid to be used in the first spot of some high-gain amps.  I stuck a USA-made 7025 in for V1 and now the amp works fine.  Jeez.  Really earned my pay on this one.  Most repairs take under an hour, this one took days.  In the process the amp got some shielded wires and improved lead dress, so I guess that's a bonus.

Not that this is likely related to your hum issue, but one more thing to look out for.  Tomorrow I drop this amp off at the shop and get paid (whopee!), but at the same time pick up a Marshall DSL (barf!) that came in Friday.  I don't know if you've ever looked inside a JCM2000 series amp, but they're basically designed as a giant middle finger to repair techs.

[Marcos - Munky]

I'll try all those suggestions. But first I'll add a virtual CT to the filaments' secondary to see if this helps. I jsut need to get two 100ohm 3W resistors, I don't have any of them and the next store is about 20Km from my house.

But since the hum happens even with master volume at zero, should I assume the cause seems to be around the power tube? Also, the tubes and transformers aren't at the best positions possible, the EL84 is next to the power transformer, while the 1st 6N2P is next to the output transformer. I was forced to use that position because the chassis I've got was already drilled, but I'm thinking about on doing another one.

Also, forgot to say that I didn't tested it on a grouded wall socket.

[thermionix]

So your filament supply has no CT?  Yeah that would be the first thing to eliminate.  You don't need 3W resistors, 1/2W works fine.  They may burn up in a H-K short, but that can be a good thing, acting like a fuse.  Also, I don't know what the whole workable range is, but 47r is fine, so anything in between too.  Just don't use a pot, like some Fenders and Ampegs did, those regularly fail, and are more expensive to replace than a resistor or two.

For an ungrounded wall outlet, you need a "death cap" unfortunately.  Unless someone knows a better way, I don't.  Use something highly reliable, like a 600v orange drop.

[davent]

Valve Wizard offers 100r @ 1/2w and 220r @ 1/4w for the center tap. Pretty sure i've seen other sources saying down to 33r for the job.

http://www.valvewizard.co.uk/heater.html

dave

[PRR]

Heater centering resistors can be dozens of Ohms to hundreds of Ohms (but both the same 10%), and 1/4W is ample until you get a heater short. I'd do that to prove/disprove a floating heater problem, and get 100r 1/2W on some future order.

[Marcos - Munky]

My transformer have no filament supply CT, like the one the project calls for. Nice to hear I just need 1/2W resistores. I only have 1/4W ones, but I'll try to buy a few of them this week, I need to get some other stuff too.

About the ungrounded wall outlet, the outlet is actually grounded, but the AC cable I've used had the ground pin cut off.

[thermionix]

About the ungrounded wall outlet, the outlet is actually grounded, but the AC cable I've used had the ground pin cut off.

Can you get just a replacement plug?  Sometimes easier and cheaper than replacing the whole AC cord.

[Marcos - Munky]

I can get the AC cord for cheap. It's the next think I'll do.

I got the resistors. The store only had 100 ohm 2W resistors. Anyway, the hum is still there. I did a research, and it sounds like a 60Hz hum. I've checked the wirings again, and there's no ground loops. Tried to change the output tube, and got no results. Same thing for the wooden chopstick poke and prod technique.

Since the hum is present even with the volume pot at zero, should I assume the hum is being generated at the power amp stage?

[mac]

Did you try to rotate the power transformer?

mac

[Marcos - Munky]

You mean rotate it by 90 degree? The guy who gave me the chassis made it so the transformers are facing the same way. I've rotated one transformer by 90 degree, but it was the output transformer.

[mac]

You mean rotate it by 90 degree?

Unscrew the PS and rotate it in space, 4*Pi, not just Pi/4
The PS field can interact with other components of your amp, tubes, wires, etc.

For example, less than a block away from my apartment there two TV stations and a street transformer. The single coil of my guitar is useless, unless it's in the N-S direction, and play it like a lap steel guitar

mac

[Marcos - Munky]

But rotating it by 4*Pi would just return to it's actual position, right?

A question that came to mind: does the connection between the power transformer and live/neutral of the AC cord have any kind of "polarity"? I mean, there's any difference if I reverse the primary wires of the power transformer?

[mac]

But rotating it by 4*Pi would just return to it's actual position, right?

In 3 dimensions. In 2D just 2*pi.

A question that came to mind: does the connection between the power transformer and live/neutral of the AC cord have any kind of "polarity"? I mean, there's any difference if I reverse the primary wires of the power transformer?

I'm pretty sure some of my outlets have the wrong "polarity", but I don't have hum problems.
The rectifier diodes of my amps do not care what outlet I use
If there is some hidden effect the tech guys can clarify, and can induce hum on some amps, I don't know.

mac