Newb first amp build

[sluckey]

I have continuity all over my output jacks; from lead to lead to tip to chassis, just everywhere.

Don't worry about that. That's normal. You're reading thru the secondary winding of the OT and that's just a long piece of big wire wrapped in a coil. It's very low resistance.

[HotBluePlates]

I noticed that I have continuity all over my output jacks; from lead to lead to tip to chassis, just everywhere.

And it should. The hot wire solder to the jack tip runs through the output transformer secondary and becomes the speaker jack ground wire. The secondary resistance is small enough that you will read continuity.


I think you're fine on that one.

[rakkassan34]

Thanks guys, I was really concerned about those output jacks. I still haven't plugged it in and to resist the temptation I left it at work which I won't be at till tuesday. That'll give me enough time to study and decipher first startup procedures and checks. I really don't want to disconnect my transformers and all that but I also don't want to just plug it up and hope the fuze will blow before anything else if something's wrong.
Biasing is another unknown art to me. I've downloaded a chart to write my voltages and other readings down on but again I just want sooo bad to plug it up turn it on and turn the bias until it sounds good but I know that's the wrong answer so I really need these few days to calm down and study.
wish me luck!

[labb]

lightbulb limiter is your friend.

[rakkassan34]

I built a lightbulb limiter but the first startup instructions I've found are telling me to unsolder my transformers first then check voltages here n there, then start wiring in one transformer at a time to check again and again. It just keeps going on and on looking like it'd take all day to safely start it up.
Anyone ever just say heck with it and fire it up using a light bulb limiter and skipping all that other stuff? does anyone actually do all that other stuff?

[labb]

Remember you must have the output of  a tube amp connected to a speaker when ever it is turned on.

The Paul Ruby startup guide is the safest way to do it but it is best if you were following it during construction. For what it is worth: I usually pull all of the tubes, plug the amp into the light bulb limiter and turn it on. The bulb should only glow after the initial charge of the power supply caps if it is on at all. If all is well I then start installing one tube at a time and checking. If all seems good with all of the tubes installed I unplug the amp and disconnect the light bulb limiter. Then I pull the power tubes, plug the amp back into the mains, turn it on and check the bias voltage at pin 5. Even without the power tubes installed the bias voltage will be very close to what it is going to be. (I am assuming this is a fixed bias amp). Adjust the bias to maximum negative voltage. In stall the power tubes and complete biasing the amp. This is a pretty good article on how to bias: www.duncanamps.com/technical/lvbias.html
When you are through biasing the amp, plug in guitar, turn volume up, hit a cord and scream "It Works" like bloody hell when the cord comes blaring out of the speaker. Best feeling in the world every time I do it and I have built a bunch of amps.

[Willabe]

Anyone ever just say heck with it and fire it up using a light bulb limiter and skipping all that other stuff?

Yes we all do.


              Brad   

[John]

The Paul Ruby startup guide is the safest way to do it but it is best if you were following it during construction.

Amen!
One of the few things I got right on my first build was just that, I installed the PT, checked voltages (thru limiter), then each successive step in the power supply did the same thing.


Still didn't keep me from mis-wiring the last filter cap and sending most of the audio signal to ground, though. 

[rakkassan34]

I know y'all said not to worry about the output jacks but I'm still scratching my head as to why the tip and chassis have continuity, the sleeve and chassis have continuity, and the sleeve and tip have continuity. Transformer causing all that?

[sluckey]

I know y'all said not to worry about the output jacks

We also told you why. Read replies 50 and 51 again.

[rakkassan34]

Y'all have been a great help. I didn't expect it to work perfectly upon first power up due to my lack of experience but I got nothing but a buzz that was hard to hear and that was it. No power light, nothing. I plugged it up again same thing as soft almost in audible buzz then a small whisp of smoke. I'm gonna dig into it today n troubleshoot it starting from the power cord n make my way through it.
Thanks again all

[g-man]

Deleted

[rakkassan34]

I've got the power transformer out now. One of the green leads going to the pilot light has a bare spot on it, no burnt look but more like it melted and grounded out on the transformer.

[rakkassan34]

I think I've found the problem. I have a center tap which I grounded but I also grounded both leads of the pilot light, no resistors just two wires straight to ground. With a center tap grounded I don't ground the pilot light do I?

[eleventeen]

"I think I've found the problem. I have a center tap which I grounded but I also grounded both leads of the pilot light, no resistors just two wires straight to ground. "

What happened to the two resistors you showed from either side of the pilot lamp to ground? In the picture 8 or so posts back that shows your transformer and the two yellow circles. That isn't direct---it's through resistors. Are you now saying you've grounded EVERY WIRE of the 6.3 winding? The center tap AND either side??
Yes, we would call that a complete short. Use either method, not both. But both won't hurt anything.

"With a center tap grounded I don't ground the pilot light do I?"

[/color]What do you mean "ground the pilot light"? The frame, the metal body of the pilot light? No, not needed, it is screwed to the chassis and thereby grounded. And now I guess I have to ask you, when you say "I have a center tap which I grounded but I also grounded both leads of the pilot light, no resistors just two wires straight to ground."  [/size][/font]
[/size][/size]Are you saying that the center tap which you grounded is green-yellow-----or red-yellow? [/font][/color][/size]

My friend, you are not making this any easier. Do not shun certainty. Embrace it.[/color]

[rakkassan34]

I removed the resistors and just ran ground wire shorting it out. I just found out the green yellow wire from the transformer got hot too I guess cause it pulled away from the transformer. I'm going to try n solder it back on but I got a feeling that transformer ain't gonna work anymore

[eleventeen]

STOP! you're killing me (but you, worse)


When you say "I removed the resistors and just ran ground wire shorting it out. "

[/size]Shorted WHAT out? You have no business using unreferenced pronouns! Nobody can know what you mean by that sentence! Shorted WHAT? The CT? The 6.3 winding? The frame of the pilot lamp? Both sides of the pilot lamp? Both sides of the pilot lamp with the green wires attached? 

[/size]You've now apparently desoldered the CT (the green-yellow wire) of the green----green-yellow---green winding with the heat caused by shorting out ALL THREE WIRES of the 6.3 winding to ground. We will leave what your intention was in doing that for some other time. Or maybe not.

[/size]You have one chance to save this power transformer. And that is to reconstruct the synthetic center tap using the two resistors. But before you do that, just connect the two green wires (you don't have the green yellow any more) to the pilot lamp assy and see if you light up the bulb. If you can light up the bulb, leave the amp on for a while and see if the transformer survived. 

[/size]

[rakkassan34]

eleventeen you've given me hope, hope that I can still use this transformer. I had a synthetic center tap but replaced the resistors with wire, why I don't know, not one person here said to replace the resistors with wire they recommended that I remove the synthetic tap since my transformer had a center tap. I had the green/yellow and the red/yellow from the power transformer grounded and both leads on the pilot light grounded. Tomorrow instead of taking the transformer apart and trying to solder that green/yellow back on I'll put the synthetic tap back in, disregard the green/yellow wire and connect the two green ones to the pilot light. I should ground the red/yellow CT wire from the transformer right? I've also disconnected the power wires going to the rectifier board too, can I put power to the transformer with those not connected to anything? 

[eleventeen]

eleventeen you've given me hope, hope that I can still use this transformer. I had a synthetic center tap but replaced the resistors with wire, why I don't know, not one person here said to replace the resistors with wire they recommended that I remove the synthetic tap since my transformer had a center tap. <<Exactly!! "Remove" = snip-snip. Or in this case snip-snip-snip. Period, done, end. 

I had the green/yellow and the red/yellow from the power transformer grounded <<<Correct, but green/yellow does not exist any more. It's gone. Forget it.


.....and both leads on the pilot light grounded. <<<Why?? How can it get the volts to light it up if both sides connect to the same thing, eg; ground, your left index finger, or a Chevy out on the street??

.....Tomorrow instead of taking the transformer apart and trying to solder that green/yellow back on  [I very seriously doubt you'll be able to do this successfully] I'll put the synthetic tap back in, <<NO!!! Not yet! Just see if you can light up the pilot lamp and have it cook for an hour without the tranny emitting smoke and stink or getting overly hot. If you can not, then you need a new tranny and >>IT<< will likely have a center tap. So, no synthetic CT needed.

.....disregard the green/yellow wire and connect the two green ones to the pilot light. I should ground the red/yellow CT wire from the transformer right? <<Ummm, this is how you can drive me and anyone who is trying to help you thoroughly batty. In all your prior posts and in the third sentence of the post right above this one, this red-yellow wire is ALREADY connected to ground! Why is it now a question?

You
can
not
work
this
way.

You cannot start to build a brick wall and once you get midway through the third course, you start chipping away at the bottom course.

....I've also disconnected the power wires going to the rectifier board too, can I put power to the transformer with those not connected to anything? <<Yes. Put some tape or some insulated tubing over the wire ends so you don't zorch yourself. 

[rakkassan34]

Success!!! I hooked the power transformer up as per eleventeen's advice and it's working fine. I measured output voltages again all within range. I left it on for an hour and no smoke, heat or anything unusual. I'm soooo happy. I'm also no longer in a hurry to complete this thing. I'm taking my time and triple checking all I do from here on out

[rakkassan34]

Does anyone know what the letter "A" on the layout represent? I circled them on the attachment.

[sluckey]

Does anyone know what the letter "A" on the layout represent? I circled them on the attachment.

There should be a wire connecting those "A"s together. If you don't connect those points then you will not have any sound from the BASS channel.

[TeslaRect5150]

Just learned the same lesson about the 6.3volt CT stuff. Hooked up some DC heaters, added the 100 ohm resistor artificial center-tap, and forgot to disconnect the CT wire coming from the power transformer. Flipped power, Funky blue smoke and I fried a bridge recto. Then my father informed me that I can't have the CT connected...DOH! Lesson learned.
There is something about seeing that power light shine for the first time. Awesome right?
Sometimes on a first power up I will flip the power on....test voltages....let the light shine and walk away for a while, just to come down from the excitement....then I remember I have another switch to flip...the Stand-by! The light bulb limiter dimming down...then coming back up. I'm sick...I know. 

Peace
Aaron

[rakkassan34]

Thank you Sluckey. I just noticed those today. I haven't powered on my amp yet cause I'm triple checking things as I said I would. I have the same sickness staring at the pilot light when I was checking my power supply. I can't wait to hear it but I'm real nervous.

[eleventeen]

[/size]"[/color][/size][/font][/size]Flipped power, Funky blue smoke and I fried a bridge recto. "


May all your cooked parts be so cheap!

[rakkassan34]

IT'S ALIVE!!! And it sounds beautiful! Clear as a bell not one bit of hum! I'm soooo happy thanks to y'all for helping me have this moment. I must admit I can't find any 1 ohm resistors to set the bias and I've been checking over things for 3 days now n it was driving me crazy not hearing it so I said to myself just turn bias pot all the way down n try it which I did and luckily it sang to life. I connected the two "A's" on the board but no bass at all. I'll have to check that again. Normal sounds crystal clear and can get loud as hell.

[navdave]

Do you have a light bulb current limiter to protect the amp and you if there's  a dead short?
Build looks great for your first one cheers!

[Willabe]

IT'S ALIVE!!! And it sounds beautiful! Clear as a bell not one bit of hum! I'm soooo happy thanks to y'all for helping me have this moment.

      

I must admit I can't find any 1 ohm resistors to set the bias

Our host Doug sells them in his on line store, here's a link;

http://hoffmanamps.com/MyStore/perlshop.cgi?action=template&thispage=Resistors&ORDER_ID=632450164


             Brad     

[rakkassan34]

Light bulb lids limiter was used upon first power up but not while playing guitar. I know our host sells the resistors, I just got impatient.

[HotBluePlates]

Congrats!!

I would bet you're now officially hooked!

[rakkassan34]

Yes I am hooked! I got the Bass channel working and Done more testing today tried to get it to break up which we did. Plugged into high gain it breaks up about mid volume. Plugged into low gain it can stand a little more volume. lower volumes it is sooo clean and clear it gives me goose bumps. I'm thinking that too much voltage is the problem. I'm getting 470V into the board and the tubes not the 420V on the schematic. How can I lower it? Diff resistor on rectifier board? diff resistors on main cap board?

[sluckey]

I'm getting 470V into the board and the tubes not the 420V on the schematic. How can I lower it?

See the red wire that connects between the rectifier board and the main board? Replace that wire with a 500Ω/10W resistor. Recheck your voltages. Increase the value of that resistor if you want to lower the voltage even more. Decrease the value of that resistor if it decreases the voltage more than you want.

Biasing the amp hotter will cause the voltages to decrease. Maybe even enough to satisfy you.

Using a PT that will give you lower voltages to begin with is a better but more expensive way to drop the voltage.

But... if you are using 6L6s, 470V is not unreasonable on Fender amps.

[eleventeen]

Your voltages are a tad high....but instead of entering into an exercise of reducing them.......if you have a 12AX7 as your first preamp tube, try a 12AY7 or a 5751 for the first tube. Those have rather lower gain than a 12AX7 that could solve your problem, it's 100x easier just to use a lower gain 1st preamp tube than to get into circuit mods. This will affect both channels.


It would probably be nice to chop 40 or 50 volts out your B+ as a matter of having your tubes last longer and the thing running a little cooler, but as much abuse as we have handed you during your build, maybe it's better that you enjoy the amp for a while as it is.


The easiest way to reduce those volts is to install a power zener diode or two in series with the B+, and there have been a couple of threads quite recently about doing this. This is easy in some ways but not necessarily so for a newb; these diodes will require a heatsink which need not be fancy but it has to be there.


Should you make that reduction you *may* want to change your V1 back to a 12AX7...or not.

 

[rakkassan34]

but as much abuse as we have handed you during your build, maybe it's better that you enjoy the amp for a while as it is.

I deserve the abuse cause a guy with no experience or knowledge in electronics shouldn't be building an amp like this heck I don't even know how to play a guitar. I don't know why I even attempted this, I should've started with a simple 1tube amp or something. I can say it was well worth it though. This thing sounds so clear and good at lower levels. I asked a buddy to bring a couple of his guitars in to give me his opinion and stress the amp out. When he plugged his Gretsch in and gave it a strum he looked at me and said I just sold it (which I have no intentions of doing cause it's now my fav toy to tinker with). He beat on it with his Gretsch and Fender for over an hour and kept wanting to play but I didn't want to take the chance of burning something up with the high voltages. Once I get the bugs worked out I'll post some sound clips.
Keep the abuse coming I am grateful to y'all for taking your time out to give me a hand. 

[eleventeen]

In the "reduce the 470 volts to 420 volts" department, Sluckey's way is easier (and cheaper) than what I suggested. Just leave a bit of room around that resistor -- it will get warm. Not hot, just warm.


By the way, you opined that you probably should have started w/a one-tube something, eg; a Champ. Tell you what, reading this forum, I have seen plenty of folks who have had problems with Champs, many more than I would have thought. People who have been building stuff for years and years forget what it's like for newbs. I'm sure my early stuff was hit & miss. Electronics has a funny way of letting you know whether you done it right or you done it wrong.

[terminalgs]

RE: lowering voltage.

But... if you are using 6L6s, 470V is not unreasonable on Fender amps.

This option should be the most appealing!!

later Bassman amps used a very similar circuit and bumped voltages to at least 450 or 460v.

You started another thread and mentioned 'bad breakup' at high volumes.  Are you still having that trouble?

[rakkassan34]

It's still breaking up and when I say breaking up I'm not talking a little distortion. It sounds like the speaker is getting punished to the point of exploding, loud crunching sounds from cutting in and out, like it's getting wayyyy to much power in from the guitar. I haven't tried any fixes yet. I've been putting all other stuff aside to build this amp and I decided to take this weekend and catch up. Just finished putting new struts on the stang and I have a pile of vintage electronics I bought at a flea market to go through and maybe I'll have the parts I need to try n fix this one.

[eleventeen]

I note that your 6G6 design uses a 12AX7 as the phase inverter---thus I assume you don't have any 12AT7. Most (more recent) Fenders use a 12AT7 in that spot, thus I was going to reco placing that 12AT7 in your V1 position to reduce the gain from the first preamp stage. I'd again urge you to try that, even better, go get a 12AY7 or 5751 tube for V1.

[rakkassan34]

I'll order a 12AY7 and try that. Wish me luck

[terminalgs]

It's still breaking up and when I say breaking up I'm not talking a little distortion. It sounds like the speaker is getting punished to the point of exploding, loud crunching sounds from cutting in and out, like it's getting wayyyy to much power in from the guitar.

If you built a 6G6 without extra gain stages (which I think is the case),  then something is wrong.  You might be able to "fix" it by lowering overall gain (like replace all 12ax7s with lower gain tubes), but that won't fix the problem..  you'll just lower the total possible gain below the threshold of 'broken'... ("the steering wheel shakes violently at highway speeds"... "staying off the highway fixed it!")

One thing to clarify: at this high volume  knob setting, is this noise (exploding, loud crunching..) present regardless of instrument play?  or is the amp quiet until the instrument is played?

[HotBluePlates]

It's still breaking up and when I say breaking up I'm not talking a little distortion. It sounds like the speaker is getting punished to the point of exploding, loud crunching sounds from cutting in and out, like it's getting wayyyy to much power in from the guitar.

What is the speaker? Is it rated to handle 100w?

100w for a pair of 6L6's sounds excessive. But assume the pair of 6L6's can output 50w RMS of clean sine wave. The peaks of the sine waves touch 100w, but are offset by all the time the wave is not at its peak. Now imagine the sine wave is distorted so severely as to produce a square-wave.

The square wave has a non-changing positive peak, which then drops to a non-changing negative peak. If this square wave's peaks are the same amplitude as the sine wave's peaks, RMS power is now 100w (instead of the 50w for the sine wave).

So to be certain the speaker won't be damaged by distorted output, the total speaker load should be rated for double the clean RMS sine output power.

[rakkassan34]

One thing to clarify: at this high volume  knob setting, is this noise (exploding, loud crunching..) present regardless of instrument play?  or is the amp quiet until the instrument is played?
[/quote]

It's quiet as a mouse without a guitar plugged in. Plug in a guitar it's still quiet until you start playing. With the volume at say 3 and under it sounds great, no distortion, hum, buzz, anything, just clean clear notes. Turn the volume up and it's cutting out/breaking up I don't know how to describe it. I found out with the guitar plugged into the low input jack you can turn the volume up a little more than you can when it's plugged into the high input jack. That's what has me thinking it's getting too much input from the guitar and the higher volts are causing it. Remember I haven't biased it yet also. I'm just taking a break to catch up on things for a few days. Once I bias it I'll post some sound clips.

[rakkassan34]

It's still breaking up and when I say breaking up I'm not talking a little distortion. It sounds like the speaker is getting punished to the point of exploding, loud crunching sounds from cutting in and out, like it's getting wayyyy to much power in from the guitar.

What is the speaker? Is it rated to handle 100w?

100w for a pair of 6L6's sounds excessive. But assume the pair of 6L6's can output 50w RMS of clean sine wave. The peaks of the sine waves touch 100w, but are offset by all the time the wave is not at its peak. Now imagine the sine wave is distorted so severely as to produce a square-wave.

The square wave has a non-changing positive peak, which then drops to a non-changing negative peak. If this square wave's peaks are the same amplitude as the sine wave's peaks, RMS power is now 100w (instead of the 50w for the sine wave).

So to be certain the speaker won't be damaged by distorted output, the total speaker load should be rated for double the clean RMS sine output power.

I'm using 5881's not 6L6's but I still shouldn't be having this issue. I tried a single peavy 4ohm speaker cabinet and a 4 speaker cabinet both with the same effect. I'm only using the 4ohm output on the output transformer currently and I have the speakers plugged into the speaker out jack. not the output speaker jack. I don't know if there's any difference between output jacks or not.

[g-man]

Deleted

[rakkassan34]

Finally got around to putting 1 ohm resistors in to bias the amp. I am taking measurements from pin8 where the resistor is attached and ground. Turned all control knobs all the way down. Turned bias pot until I got 35mv is that correct?
I do know that whenever I touch the plate and screen grid to take voltage readings (which are at 465v) I can hear my test lead touch through the speakers. Same thing when I take Voltage measurements inside the chassis I get that tapping/popping sound through the speakers. All knobs are turned all the way down when I'm doing this. Is that normal?

[eleventeen]

"I do know that whenever I touch the plate and screen grid ...."            Yeah, a little pop is normal.

With no signal applied to the amp, 35 mv, implying 35 ma plate current per tube is IMO a touch on the highish side, but that is my opinion, as one who wants a cleaner sound and not that concerned with maximum wattage output. Let me be clear, it is within spec. You have 465 volts * .035 which is 16.27 watts at idle. Max rating is in the low 20's, so this implies that full-blast is a mere 25-40% over idle when we know it is a lot more. Plus, you have 5881's which are usually considered a tad downrated from 6L6GC, you have highish plate voltage, and you are driving a 4 ohm load. All 3 of those things in that last sentence work to stress those output tubes. So considering that, I would crank the bias colder.

[g-man]

Deleted

[rakkassan34]

I'm getting 36 out of one 30 out of the other.
I did just discover what I think caused the breaking up. I have a ceramic disc cap on my treble pot that is micro phonic, I am going to find a cover for it or wrap it with something. I don't think replacing it with a new ceramic disc one will fix it

[eleventeen]

"ceramic disc cap "

Doubt it. They are often noisy when tapped, if that (tapping it) is what's causing the noise that's bothering you. Snip one leg and see if the breakup persists. Where that cap is, is right in front of gain stages, it's not surprising to find it "microphonic" if that's what you want to call it. Those tend to be surprisingly reliable, but go ahead and change it if you think it's evil. You *should not be able* to change its in-circuit performance by covering or wrapping it.

If it were me, I'd be dialing back the bias to "25" which in your case might be something like 22/28. See how you like how the amp plays.

I'm lazy. I tend to try work the controls (which can be put back exactly where I found them, at zero cost) before I warm up the soldering iron.

[g-man]

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