I'm building a Hi Octane, bought everything and done the board. But since I don't have too much experience on building tube amps, I don't know the wire gauge I have to use. The ones I have here are thin, something about 0,8mm2 and 1mm2 (wire gauge, without the insulation), so I think they can't be used - well, maybe I can use them for the wirings but heater wirings. What's the recommended wire gauge for tube amps?
16 to 18AWG on the heaters and 20 or 22AWG on the rest... should be fine. The length of each wire, routing and how they intersect is important! :icon_wink:
Thanks for the info! I will try to find the the wires today. The ones I have are 21 and 19 I think, so I just need the wires for the heaters.
I'm not familiar with the Hi Octane, the layout, or how many tubes it has...but usually there is enough extra wire coming from the power transformer that you can use your trimmings for heater wire between power tube sockets. Then 22 AWG is plenty heavy for the preamp tube heaters.
If you're wiring heaters in an amp with two power tubes in push-pull, run the wires "parallel" like pin 2 to pin 2, pin 7 to pin 7 (twisted of course). This makes the power amp humbucking with respect to heater supply hum.
If you're wiring heaters in an amp with two power tubes in parallel single-ended (not likely), wire them in a cross pattern (pin 2 to pin 7, pin 7 to pin 2) to get the same humbucking effect.
If you're wiring heaters in an amp with four power tubes in push-pull amp, wire the two outside pairs in a cross pattern, then "parallel" between each pair, for a double humbucking effect.
If that makes sense.
If i recall, two 12ax7's and a single EL84 or i suppose 6V6 so not much total heater current.
dave
Quote from: davent on November 01, 2017, 09:01:43 PM
If i recall, two 12ax7's and a single EL84 or i suppose 6V6 so not much total heater current.
dave
For reference, this one:
http://www.ax84.com/hioctane.html
.
The current it's something like 1,5A. Actually, 760mA for the EL84 and 340mA for each 6N2P, which I'm using instead of the 12AX7s.
Quote from: thermionix on November 01, 2017, 08:44:06 PM
If you're wiring heaters in an amp with four power tubes in push-pull amp, wire the two outside pairs in a cross pattern, then "parallel" between each pair, for a double humbucking effect.
This will be useful for an 4 power tubes amp I'll rebuild soon. To make the wirings shorter, can I wire tubes 1 and 2 in parallel, tubes 2 and 3 in cross pattern and tubes 3 and 4 in parallel?
No, that would be maximum hum, no bucking at all. If you want the shortest wires* go straight across all the sockets (I really shouldn't say "parallel", electronically all these heaters are in parallel, but seems you understand what I meant). That would be humbucking once over, good enough hum reduction.
= X = maximum hum
= = = low hum
X X X low hum
X = X minimum low** hum
This is one of those things that was "unlearned" by Fender during the 70's. Many silverface amps have their power tube heaters wired randomly, and it's worth straightening out if you wind up with one. I think the 50s and 60s 4-tube Fenders were wired = = = (good enough).
12Ax7 preamp tube heaters are automatically wired humbucking when connected for 6.3v operation. I'm not familiar with 6N2P tubes.
*Edit: On second thought, either way you connect them the wires are twisted, so no real difference in wire length. Number of twists counts for more than which socket pin.
**Edit #2: Oh jeez, where is my mind. On THIRD thought...probably no real difference in options 2-4 above. You would only get "double humbucking" with X = X in certain specific situations. Probably easiest to just go straight across for any push-pull power amp. But you still don't want = X = or something unbalanced.
> Number of twists counts
Point of diminishing returns past about 2 twists per inch.
I see wires twisted like the rubber-band on a model airplane and I cringe. Just make it so, if the wires were black and white, and the tube had poor eyes, it would see "grey" not white or black.
Quote from: PRR on November 05, 2017, 12:53:47 AM
and the tube had poor eyes
(http://www.beatriceco.com/bti/porticus/bell/images/mirrophone/magiceye.jpg)
Thanks a lot for the lessons!
Quote from: thermionix on November 04, 2017, 06:15:14 PM
= = = low hum
I'll probably go this way.
Quote from: thermionix on November 04, 2017, 06:15:14 PM
12Ax7 preamp tube heaters are automatically wired humbucking when connected for 6.3v operation. I'm not familiar with 6N2P tubes.
6N2Ps are used instead of 12AX7s because they're cheap :icon_mrgreen: at least here in Brazil. The heaters are internally wired in parallel, with pins 4 and 5 powered by 6.3V and pin 9 connected to ground.
https://tubedata.altanatubes.com.br/sheets/113/6/6N2P.pdf
I'm not sure what you'd call the electrode connected to pin 9 (I bet Paul knows). I guess it provides some shielding between the triodes, from the way it's depicted in the datasheet pinout.
I too believe it's some kind of shielding.
Just finished it right now. I didn't tested it yet, but here's two pics of it. It was a repurposed chassis, so that's the reason of the extra tube and switch holes.
(https://s1.postimg.org/2d28gtpjij/dentro.jpg) (https://postimg.org/image/2d28gtpjij/) (https://s1.postimg.org/5wo66mt45n/frente.jpg) (https://postimg.org/image/5wo66mt45n/)
Nice! Those are some big ol' honkin' transformers for a SE EL84!
Thanks. Yeah, I thought they're pretty big for a SE EL84 too. The power transformer looks like it haves the same size as Hammond 269EX (the one suggested by AX84). For the output transformer, the guy who made it said it's oversized - and I believe in him :icon_lol:. Still thinking on using 3mm green leds under the tubes, as it have a green switch and will have green knobs, but I'm still not sure if I'll do the leds.
Last question before I plug it, I don't have any 1A slo-blo fuse. Does a regular fuse do the job, or it's better wait until I find a slo-blo one?
A "fast-acting" fuse should be fine, I guess it offers just a hair more protection than the slo-blo, but at 1A shouldn't blow under normal operation. What is the mains voltage in Brazil?
Some regions (like mine) uses mainly 127V for almost everything but air conditioners , showers and other high consumption electrics, those are powered by 220V. Other regions uses 220V for everything.
I'll try the fast-acting fuse this weekend.
Remind me to never take a shower in Brazil!
> never take a shower in Brazil!
That seems odd to US folks.
In England they have point-of-use water heaters, one on the shower. I assume this is like he has.
https://www.tritonshowers.co.uk/electric-showers/t80z-fast-fit-electric-shower.html
It says an RCD (GFI) is required.
(https://s33.postimg.org/9tvtyukaj/Electric-shower.gif) (https://postimg.org/image/9tvtyukaj/)
There's not a huge difference between that and my 240V water heater in the cellar. Until recently, the hot water pipes were copper, great conductors. (Now plastic in my place, but copper is still common.)
Here at my place we have 127V showers. But there's people who uses 220V showers - even the simple ones like this:
(https://s7.postimg.org/7lhzduo5j/chuveiro-zagonel-master-banho-220v_1_630.jpg) (https://postimg.org/image/7lhzduo5j/)
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.
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.
Quotenever take a shower in Brazil!
Quotetemperature here right now is about 28°C/83°F.
To die or to stink.. that's the question :)
mac
Quote from: mac on November 13, 2017, 09:05:58 AM
To die or to stink.. that's the question :)
Good question! :icon_lol:
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?
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 :icon_rolleyes: I think a lot of times isolating the input jack helps too depending on what you have going. Just shooting in the dark!
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
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.
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.
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.
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
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.
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.
Quote from: Marcos - Munky on November 19, 2017, 08:16:30 PM
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.
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?
Did you try to rotate the power transformer?
mac
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.
QuoteYou 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
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?
QuoteBut rotating it by 4*Pi would just return to it's actual position, right?
In 3 dimensions. In 2D just 2*pi.
QuoteA 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
Sorry for the dumb question, but I still didn't got the 4*Pi. I think I got the 3D part, that is to put it like this (https://s3.amazonaws.com/tubedepot-com-static/marshall18_mb_a.jpg), correct? I'm still bumping my head with the 4*Pi thing...
Take a look at this transformer orientation>
http://www.tdpri.com/proxy.php?image=https%3A%2F%2Ffarm9.staticflickr.com%2F8575%2F16561199240_09f1acaa2e.jpg&hash=1c2824cc8e5fe81957d7d348b25c1fca (http://www.tdpri.com/proxy.php?image=https%3A%2F%2Ffarm9.staticflickr.com%2F8575%2F16561199240_09f1acaa2e.jpg&hash=1c2824cc8e5fe81957d7d348b25c1fca)
Hey Thomas. I can't see the image, but I think it's the same orientation as the one I've linked. I'm just trying to get the 4*Pi part. In my mind I can find only 2 Pi, so there's 2 missing :icon_lol:
You're not the only one who's confused. 4*pi is approximately 12.5. Of what, I don't know.
Sorry to confuse you guys.
2*Pi is the total angle in two dimensions, (XY)
If you rotate in three dimension, space, the angle is 4*Pi, (XYZ)
(https://i.stack.imgur.com/iUU7Z.png)
(http://www.guitarkitbuilder.com/img/chassis-layout.jpg)
What I was trying to say is "unscrew the PS and rotate it in space, not only in the chassis plane"
In the picture, 90° xy --> 90° xz
mac
Yeah, I got the transformer correct position, I just didn't got the 4*Pi part. And now, thinking about it again, I can only get 2*Pi/2 rotation :icon_lol: One 90 degree (Pi/2) in xy and another 90 degree in xz.
Anyway, I can't do this orientation because of the kind of the transformer bracket I've got. But I'm thinking about making another chassis, so I can at least have the correct tubes and transformers positions.
And I'm suspecting my wall outlet ground is not working, didn't tested it yet to confirm this.
QuoteAnyway, I can't do this orientation because of the kind of the transformer bracket I've got. But I'm thinking about making another chassis, so I can at least have the correct tubes and transformers positions.
Just an idea. Do you have some galvanized steel sheet at hand, or candy can, etc?
You can cut a strip of metal to hold the transformer, and drill two holes in the chassis.
But if you...
QuoteAnd I'm suspecting my wall outlet ground is not working, didn't tested it yet to confirm this.
Test it first.
mac
Problem solved! And it was something else that was causing the hum.
The original project calls for an power transformer with no center tap for the filaments supply. Instead, one of the wires are connected to the EL84 cathode, to get an voltage reference. Today I went to the guy who I bought the transformers, and turns out when he made the power transformer he added a center tap for the filaments, but he forgot to tell me that!
So my amp filaments was actually getting two different voltage references at the same time, one from the EL84 cathode and another one from the center tap connected to ground. So we just cut the wire connecting the filaments to the EL84 cathode and left the center tap connected to ground, and all the hum is gone!
IIRC most ax84 amps have the filaments connected to the EL84 cathode.
They must have strong arguments to do this. Not an expert, I wouldn't do it.
Quotehttp://ax84.com/bbs/index.php?id=500257
mac
In almost all the amp schematics I've saw, the filaments have a center tap connected to ground. If this is the "better" way or not, I don't know, but surely it's the most common one.
Quote from: mac on November 27, 2017, 09:10:09 AM
IIRC most ax84 amps have the filaments connected to the EL84 cathode.
I'll keep that in mind next time I build any ax84 amp :icon_lol:
QuoteI'll keep that in mind next time I build any ax84 amp :icon_lol:
I'm planning to fly to Natal late March or April. Build another one and we jam together, caipirinhas are on me :) :)
mac
Wiring the heater CT (real or virtual) to a small positive voltage reduces heater-cathode leakage. Preamp tubes vary a lot here. If the cathode insulation leaks, 50/60Hz on heater leaks to cathode and thus audio. Back-biasing the parasitic diode reduces the leakage. Maybe 1 of 10 preamp tubes, it matters. In mass production of HI gain amps, this technique is often used so the factory does not have to rotate 10% of tubes (leakers) out of the first hole into higher-level stages where the signal is higher and leak is less of a problem. Unless you love swapping tubes around, you should do it also.
With a power stage that is Cathode Biased, the output cathode is a very good "small positive voltage".
BTW: doing _both_ two-100r to EL84 cathodes AND a grounded CT makes those two-100r resistors "added cathode bias" resistors. I think for typical EL84 bias this raises EL84 current a lot, enough to be a Problem. If the PT winder hard-grounded the 6V CT, then you have to go that way. If it is a lead not shared with other grounds, you could take it to EL84 cathodes for small heater bias.
Quote from: mac on November 27, 2017, 03:52:43 PM
I'm planning to fly to Natal late March or April. Build another one and we jam together, caipirinhas are on me :) :)
mac
I've never been to Natal, but I have some friends who did. It's a nice place. Way far from my place, unfortunally. Here in Brazil, sometimes is cheaper to travel to neighbor countries than to travel to brazilian's northwest, where Natal is located.
Quote from: PRR on November 28, 2017, 01:11:19 AM
Wiring the heater CT (real or virtual) to a small positive voltage reduces heater-cathode leakage. Preamp tubes vary a lot here. If the cathode insulation leaks, 50/60Hz on heater leaks to cathode and thus audio. Back-biasing the parasitic diode reduces the leakage. Maybe 1 of 10 preamp tubes, it matters. In mass production of HI gain amps, this technique is often used so the factory does not have to rotate 10% of tubes (leakers) out of the first hole into higher-level stages where the signal is higher and leak is less of a problem. Unless you love swapping tubes around, you should do it also.
I've noticed hum when I turn up the gain. Do you think wiring the heater CT to EL84 cathode helps to get rid of this hum? Heater CT is a lead not shared with other grounds.
QuoteI've noticed hum when I turn up the gain. Do you think wiring the heater CT to EL84 cathode helps to get rid of this hum? Heater CT is a lead not shared with other grounds.
If you connect on side of te heater transormer to the cathode, disconnect the CT from ground. As Paul said, you might have too much current across the power tube.
What about a rectifier bridge with schottky diodes to avoid adding more turns to the heater transformer.
QuoteI've never been to Natal, but I have some friends who did. It's a nice place. Way far from my place, unfortunally. Here in Brazil, sometimes is cheaper to travel to neighbor countries than to travel to brazilian's northwest, where Natal is located.
Same down here.
But Brasil is way cheaper than Argentina. In fact, we are one of, if not, the most expensive country in the world.
I'm planning to move to Natal (or Mallorca) for this reason. Even London, NY or Oslo makes more sense to me :)
mac
Quote from: mac on November 30, 2017, 05:23:36 PM
If you connect on side of te heater transormer to the cathode, disconnect the CT from ground. As Paul said, you might have too much current across the power tube.
What about a rectifier bridge with schottky diodes to avoid adding more turns to the heater transformer.
Yesterday I've tried to connect the center tap to the cathode, and connect the heater to cathode leaving the center tap disconnected. Both gave me the same result as if I've grounded the center tap: hum. I'm almost sure the problem is in my house electrical system. Anyway, I'm thinking about a rectifier bridge, I'll need something that can handles 1,5A. But I'll try to test it somewhere that have a good electrical system before doing anything else.
Quote from: mac on November 30, 2017, 05:23:36 PM
Same down here.
But Brasil is way cheaper than Argentina. In fact, we are one of, if not, the most expensive country in the world.
I'm planning to move to Natal (or Mallorca) for this reason. Even London, NY or Oslo makes more sense to me :)
Here it's not that bad. Well, if you don't consider high taxes and corrupt politicians. Brazil have lots of different places and different landscapes. I wish I can move to somewhere else, it's just that living 30 years at the same place (even the same city) is kinda boring :icon_lol:
Duplicated post.
QuoteYesterday I've tried to connect the center tap to the cathode, and connect the heater to cathode leaving the center tap disconnected. Both gave me the same result as if I've grounded the center tap: hum. I'm almost sure the problem is in my house electrical system. Anyway, I'm thinking about a rectifier bridge, I'll need something that can handles 1,5A. But I'll try to test it somewhere that have a good electrical system before doing anything else.
A simple test.
Get a long wire, connect one side to the chassis, the other to a metal water pipe, water heater tank, etc.
A 20lts paint bucket full of water and some salt sometimes does the job.
mac
I've tried to connect it directly to a "real ground" today: a metal bar buried about 2-3m in the ground. The hum is still there. I'll try to isolate the preamp stages to find where is the problem. Also, I'll change the power supply eletrolytics and use 12AX7s for the tubes. If the hum is still there after all of this, I'll give up and build it again from the beginning in january, using the correct transformers/tubes positions.