First time build....and it almost works...(help appreciated)

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dehughes
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First time build....and it almost works...(help appreciated)

Post by dehughes »

Hello again,

Well, first off, many thanks to those of you who have helped me thus far in my amp build. Much appreciated. This is my very first build and I had (and STILL have) a lot of learning to do.

Now, to the point: I FINALLY finished the build today (yay!), and turned it on (didn't explode...), measured some voltages (didn't die), installed the tubes (none melted...), plugged in a guitar AND

bzzzzzzzzzzzzzzzzzzzzz


That's about it. I re-checked the obvious stuff, and nothing was odd except I had the common and the hot wires connected to the wrong prongs of the IEC socket. I corrected that, and kept checking, but nothing seemed odd or obvious. It seems to be an unchanging hum (much like a mismatched pair of power tubes or a 60hz hum, or some kind of "motorboat" sound) that neither increases or decreases in volume. It isn't very loud.... Turning the volume and/or eq knobs produced no noticeable change. Plugging in a guitar changed nothing. The tubes all lit up, and the voltages seem to be pretty close to where I'd expect them to be.

The amp is a two channel creation with CH. 1 being a EF86 AC30/4/AC15ish circuit, and channel two is a full eq AC30/Top Hat/Matchless-ish thing using 12AX7s. Four EL84s for power, and one 5AR4. All tubes are new and/or known to be good. Trannies are Mercury Magnetics Woden clones and a Mercury Magnetics choke.

So, where should I start looking? I can post pics of the schematic too, if that would help.

MANY THANKS! :) It's almost alive....!
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Last edited by dehughes on Sun Jun 25, 2006 4:15 am, edited 2 times in total.
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dehughes
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Re: First time build....and it almost works...(help appreciated)

Post by dehughes »

A few more pics of the layout, in case that helps anyone suggest a possible "fix". THANKS!
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skyboltone
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Re: First time build....and it almost works...(help appreciated)

Post by skyboltone »

Gorgeous Build Mister!
Well, it's apparent that you designed this thing yourself. Not usually a good idea for someone with your experience. And so it goes. Congratulations!

#1 We need to start with a schematic! Draw the sucker up and post it.
#2 We need a full round of voltages!
Plates
Screens
Grids; input stages are at 0 volts. (Do you have a Simpson 60?)
Cathodes; input stages at +1 volt or so.
#3 Post a scope image (if you got one) at each node of the Power Supply with the tubes pulled (with the exception of the rectifier) Check the voltage differences with tubes in and out at those nodes.
#4 What is the current draw between the rectifier and the first cap. You'll have to insert your milliamp meter between (literally, disconnect the rectifier from the rest of the power supply) those points. Check current draw with tubes and without tubes.
#5 Make sure your filaments are above ground by 100 ohms or so.
#6 Plate voltage MUST be higher than screens in the power tubes.

Those are basic checks. After all that stuff checks out OK, then, (power tubes pulled) work forward from the input in your scheme and make sure your voltages are right in amount AND polarity. You've got a miswire somewhere.

Good luck
Dan
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Elcabong
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Re: First time build....and it almost works...(help appreciated)

Post by Elcabong »

First thing, this is one of the nicest built I have ever seen. Very clean!

From what you indicates, nothing get beyond the preamp channels so you could concentrate around the PI and power amp. It is hard without a schematic or a layout to figure out from the pictures what could be wrong!
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skyboltone
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Re: First time build....and it almost works...(help appreciated)

Post by skyboltone »

David: (That's it I think?) Anyway, two things; I'm gonna use your build as a goal for my own work. That is phenominal quality. Two, tube sockets are numbered counterclockwise from the bottom with pin #1 the first one on the right after the gap. Or in Octals after the center pin marker.

Not that I can see anything like that from the pictures, it's just something I found out years ago from experience. Don't make me explane how I found this out!

Dan
The Last of the World's Great Human Beings
Seek immediate medical attention if you suddenly go either deaf or blind.
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dehughes
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Re: First time build....and it almost works...(help appreciated)

Post by dehughes »

Thanks guys. I've worked on this thing for months....taking my time designing, ordering parts, drawing up schematics and layouts, putting it all together, etc.. I knew it was a bit much for a first build, but I had a good feeling about it so I just jumped in. :) The learning curve isn't a curve so much as it is a rock face several hundred feet tall. :)

I'm stoked that it didn't explode, but perplexed as to what's wrong. I'll go check and record all the voltages and get back to you. All I have is a little DMM (no scope, or anything else...), so I'll get to it tonight and finish up tomorrow (been working a lot lately...). I have an older schematic that is close enough to what's here, so that should help.

Again, thanks for your time, and I'll get back here and let you know what I've discovered...
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dehughes
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Re: First time build....and it almost works...(help appreciated)

Post by dehughes »

skyboltone wrote:David: (That's it I think?) Anyway, two things; I'm gonna use your build as a goal for my own work. That is phenominal quality. Two, tube sockets are numbered counterclockwise from the bottom with pin #1 the first one on the right after the gap. Or in Octals after the center pin marker.

Not that I can see anything like that from the pictures, it's just something I found out years ago from experience. Don't make me explane how I found this out!

Dan
Yeah, it's David. You're correct about the tube pin location. :) On my build, in the pictures you see, the nine-pin sockets are situated with pin 1 at the upper right, and pin 9 at the upper left (about where 1 and 11 would be on a clock...). I've situated them that way as it is how my Top Hats are built (their build quality eclipses mine by FAR....it is unreal...and my own personal goal to build them like they do). Brian at Top Hat is my amp mentor, no question.
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dehughes
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Re: First time build....and it almost works...(help appreciated)

Post by dehughes »

IT WORKS! IT'S ALIVE!! :) :) :) You know what it was? I forgot to wire the cathode pin of the PI to its turret connection.....so the PI was just sitting there without anything on the cathode. One little missed wire....and now it works!!! I started writing down all the voltages, etc...but got sidetracked once I FIXED IT! :) I'll catalog the voltages tomorrow and see what I can see, but so far SO GOOD. It sounds like a less filtered version of a King Royale/DC30...which is FINE, as the low gain tones are GREAT. The tone knob has been wired in backwards (don't know how that happened...) as did the CUT knob (easy fix....or just leave it...), but other than that, GREAT! Thanks so much for your help!
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skyboltone
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Re: First time build....and it almost works...(help appreciated)

Post by skyboltone »

Great!
Its much easier to find the missing wires with a methodical voltage check. What I hate is when I've ADDED a wire somewhere that doesn't need one. That'll get you scratching your head!

Well that's just fantastic. What did that build take, about two weeks? Now the tweeking begins for that perfect tone. Still would like to see a schematic.

Dan
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Elcabong
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Re: First time build....and it almost works...(help appreciated)

Post by Elcabong »

Elcabong wrote:... you could concentrate around the PI and power amp.
Sorry, but I could not resist! It is too easy to come after and say " Hey, I told you it was your PI !" :oops: :oops:

I am glad you fixed it and hope you will let us hear how it sounds.

Great work again! :D
dehughes
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Re: First time build....and it almost works...(help appreciated)

Post by dehughes »

Yeah, you told me so! :) I love it, actually, as that's what I WAS HOPING FOR when I posted here. :) That's the goal of asking a question, no doubt, and you guys have been super helpful.

The amp is REALLY quiet except for that annoying little hmmmmmmmmmmmmm, which I believe is either the power tubes or the recto (I have cheap ones in there now...for testing's sake), or the fact that the amp is pretty under-filtered by modern standards. 16 uf caps on all but the first two preamp stages, which are 8uf. I'm starting with the stock AC30 values to get a benchmark, and will go from there. Higher filtering would let the master volume channel be more usable at high gain, low volume settings, but then I want a VINTAGE feel out of this thing, not a modern feel. There is a reason people covet old AC30s and AC30/4s and AC15s....they don't buy them to hack them up and increase the filtering. If they want that, they'll buy a new Matchless or, if they are really discriminating and have great taste (plug for Brian... :) ), they'll grab a Top Hat!

Plus, I have a 50 ohm cathode resistor on the EL84s right now, which is too low, but is the only thing I have lying about now (it is a 10w)...and I didn't want to wait any longer before turning it on. :) I'm going to order some nice 62 and 68 ohm silicone coated power resistors from Steve at Apex Jr., along with some nice caps and a few switches to allow me to pull in some additional filter caps for a more modern feel. :) It'll be great. Now I just need to get a head and speaker cab, and another Alnico Blue (it'll be in a 2x12...).

THANKS!
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dehughes
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Re: First time build....and it almost works...(help appreciated)

Post by dehughes »

skyboltone wrote:Great!
Its much easier to find the missing wires with a methodical voltage check. What I hate is when I've ADDED a wire somewhere that doesn't need one. That'll get you scratching your head!

Well that's just fantastic. What did that build take, about two weeks? Now the tweeking begins for that perfect tone. Still would like to see a schematic.

Dan
I have an older schematic, but nothing current and updated. I don't know exactly how long it took....maybe two months of little by little assembling everything. Most of the time was designing the layout of the parts and the chassis, figuring out what trannies to use, getting the faceplate together, altering the chassis to fit everything, etc... It is a LOT of work...but rewarding.

I just played the hell out of the amp (through a closed back 2x12 with V30s...not the cab I intend to use with the amp...) and it sounded pretty darn good. I didn't get around to checking the voltages...I'll do that tomorrow. I've not been practicing as much lately as I've been building the whole time, so the tinkering can wait a bit. ;)
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dehughes
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Re: First time build....and it almost works...(help appreciated)

Post by dehughes »

skyboltone wrote:
#1 We need to start with a schematic! Draw the sucker up and post it.
#2 We need a full round of voltages!
Plates
Screens
Grids; input stages are at 0 volts. (Do you have a Simpson 60?)
Cathodes; input stages at +1 volt or so.
#3 Post a scope image (if you got one) at each node of the Power Supply with the tubes pulled (with the exception of the rectifier) Check the voltage differences with tubes in and out at those nodes.
#4 What is the current draw between the rectifier and the first cap. You'll have to insert your milliamp meter between (literally, disconnect the rectifier from the rest of the power supply) those points. Check current draw with tubes and without tubes.
#5 Make sure your filaments are above ground by 100 ohms or so.
#6 Plate voltage MUST be higher than screens in the power tubes.

Those are basic checks. After all that stuff checks out OK, then, (power tubes pulled) work forward from the input in your scheme and make sure your voltages are right in amount AND polarity. You've got a miswire somewhere.

Good luck
Dan
Okay. Voltages, with tubes in and amp on, etc...

Rectifier: Pin 8: 344v DC (of course...)

1st cap (16 uf) after recto, before choke (OT center tap): 347v

2nd cap (16 uf) after choke (goes to EL84 screens): 330v

3rd cap (16uf) after 22k resistor (goes to PI plates): 302v

4th cap (16uf) after 10k resistor (goes to cathode follower stage): 290v

5th cap (8uf) after 22k resistor (goes to plate of 1st 12AX7): 313v

6th cap (8uf) after 22k resistor (goes to plate of EF86): 305v

EL84:

Pin 9: 330v
Pin 7: 340v
Pin 3: 11v

1st 12AX7 (1st stage...only one triode used):

Pin 1: 146v
Pin 3: 1v

2nd 12AX7 (cathode follower):

Pin 1: 184v
Pin 3: 1v
Pin 6: 290v

3rd 12AX7 (phase inverter):

Pins 1 and 6: 343v
Pin 8: 57v

EF86:

Pin 1: 111v
Pin 3: 2v
Pin 6: 111v

So, that's what I have. I'm wondering if those voltages are about right....especially the EF86. All the dropping resistors test correctly (100k for the cathode follower, 220k for the 1st 12AX7 plate, 220k for the plate of the EF86, and 1M for the screen of the EF86), so that's good, but I don't know what to look for in terms of optimal voltages at a given stage.

NOTE: Caps 4, 5, and 6 and their respective resistors are in line after the 2nd filter cap....so consider that when I say "after 22k resistor"...


david
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