Power Transformer

[John]

If that PT is like the ones I'm familiar with, your primary wires will be coming out of one hole, and the secondary will be coming out of the other hole.


AC volts are the ones you measure *before* the rectifier. Anything after the rectifier (either the diodes or a tube rectifier) will be DC. When you're measuring your filter caps, that's DC.


When you're new, even the simplest things can be confusing. So again, go very slow, be very careful. Do NOT rest one hand on the chassis while you're measuring voltages.

[taylorc315]

Why does the diagram show the black wire between the red board diodes look like it goes to ground?

[taylorc315]

That black wire has 110 volts ac coming from it.

[John]

If you're on the primary windings, they're what get hooked up to your on/off switch. So, if that switch is on, and hooked up right, that black wire *on the primary side* will have about 120 volts ac on it. I'm assuming you're on 120 wall voltage, not 220/240 European.


The black wire on the secondary side is the center tap for the high voltage winding. Those 2 red wires get hooked to your rectifier. If you're using diodes, a red wire will go to each one. That black wire then gets bolted to ground. The PT is probably a 325-0-325 or something like that. The red wires are the "325" and the black wire is the "0".

[taylorc315]

This is great information I will make sure I have the right black wire before I run it to ground. Thanks John.

[taylorc315]

When I try to ground the black wire it lights up my current limiter. This is the wire that is in the bundle with the red wires.  It is showing around 66 vac with the meter. I have the black and orange wires connected to the heaters,I just can't figure out where it goes.

[John]

Hmm. Maybe the black wire bundled with the red wires actually goes to the heaters, and the black wire you have on the heaters actually is the CT? Since you're using a lamp limiter, switch them and see what happens. You're disconnected from the filter caps, correct?

[taylorc315]

The black that I have hooked up to the heater is right at 3.2 vac and when I check across the orange and black I get the 6.3 vac that the heaters call for. Very confusing, in the other bundle that has the black and blue wires, I have the blue wire hooked up to line voltage through the switch and fused and the black wire to the neutral side, this is how it shows in the diagram that is correct right? I will recheck everything to make sure that I'm not just doing something stupid and simple.

Thanks
Tracy

[sluckey]

Your PT is connected properly. And that third black wire must connect to ground as shown on the layout. The fact that your lamp limiter lights up when you connect the black wire to ground does not indicate that the black wire is faulty. It indicates that something else is not connected properly in the high voltage supply.

I see a green/yellow wire connected to the bottom side of your rectifier diodes. Where does the other end of that wire connect? Hopefully it connects to a fuse. Most people would use a red wire for that.

PS... Pull all your tubes until this is resolved.

[taylorc315]

Yes the green/yellow wire goes to the fuse, sorry there was so much red and black that I switched it up a little.

[sluckey]

The color of the wire is not the problem. But that wire will have high voltage dc on it if you ever get this thing working. Red is a color that most people associate with high voltage dc. Green with a yellow stripe is most often associated with low voltage heater center tap or AC mains safety ground.

Measure resistance from that green/yellow wire to chassis. What do you get?

[taylorc315]

I'm at work right now, as soon as I get home I will measure the resistance and post, also I will change that wire to red.

Thanks

[taylorc315]

Resistance is 0 from green/yellow to chassis.

[sluckey]

Resistance is 0 from green/yellow to chassis.

That's definitely a problem! Something ain't wired right. You should be able to find that just by looking.

[taylorc315]

I'm on it,,I will find that damn thing. : )

[taylorc315]

Does 35k sound better? I'm checking the resistance with the power on and the stand by switch on.

[sluckey]

DON'T CKECK RESISTANCE WITH THE POWER ON!

[taylorc315]

Still learning, with no power I have 10.47 m ohm's

[sluckey]

So what changed between the time of the zero reading and 10.47M reading?

[taylorc315]

Still had it hooked up to the fuse through the standby switch with the switch in the off position.

[sluckey]

Still had it hooked up to the fuse through the standby switch with the switch in the off position.

That should be a high resistance reading regardless of which position the standby switch is in.

[taylorc315]

Maybe I need to look at how I have the stand by switch and fuse hooked up.

[sluckey]

Maybe I need to look at how I have the stand by switch and fuse hooked up.

Yes. That green/yellow wire should go to the fuse. The other side of the fuse should go to the STBY switch. The other side of the STBY switch should return to the board at point "A".

But you should also insure that your choke and all cap cans are wired to the board correctly.

[taylorc315]

Thanks I will make sure that I have everything wired correct

[taylorc315]

Should I have continuity between the black and blue wires?

[taylorc315]

The wire that is with the red and white wire's that goes to pin 3 of the power tubes,looks like it goes to board A,is that the filter caps? It seems to be what is causing the limit switch to light up.

[sluckey]

You really need someone to stand by your side while you do this. You are in waaayyy over your head.

[taylorc315]

You're probably right about having someone by my side, but as far as waaayyy over my head, I've done a lot of things that may have been way over my head, but have learned that nothing is more satisfying then getting something accomplished that might have been more challenging than you thought at first. I will figure this out, I do appreciate all the info that I have received from all that have responded.

Thanks
Tracy

[sluckey]

My replies tend to be short and direct. I don't mean to discourage you. I should have explained that when I said "need someone to stand by your side" that I meant someone with some electronics background and some experience with building amps. Someone that could see exactly what your questions mean and to give an immediate answer. Someone that can put their hands on the amp, rotate this way and that way, examine the wiring, and say "this wire really needs to go here" or "you must put a jumper between the bias range resistor and the AC input of one of the rectifier diodes" and explain why on the spot.

A lot of amp building issues can be solved over the net, but problems that would take an experienced technician a few minutes to solve if he had the amp in hand can and often do take days to solve over the net just due to time lag between posting replies. And when there is a lack of basic electronics knowledge involved, simple issues such as "how to connect a transformer" become major issues.

Things like your last question (The wire that is with the red and white wire's that goes to pin 3 of the power tubes,looks like it goes to board A,is that the filter caps?) would be so much easier to understand and respond to if you attach a high resolution picture that clearly shows exactly what you are looking at. I think you are referring to the OT primary wires but I'm not clear on what the actual question is. That question could be answered in a few seconds by someone at your side, but over the net, and with no picture, it's probably gonna be a long time before anyone knows for sure what you are asking.

I really want to help with your project (heck, we all do), but we really need more info and pics to do so.

[taylorc315]

No worries, I wish that there was someone around here that I could lean on, heck I would even travel just to gain more knowledge, I will defiantly get some better pics loaded somewhere so that you may be able to see what I have going on. as far as the wire it's the one that connects to board A with the choke.

Thanks
Tracy

[sluckey]

There are actually 4 things that must be "electrically" connected to point A on the board. The primary center tap wire of the OT, one wire from the choke, a wire from your blue filter cap, and a wire from the standby switch. There are several ways to physically connect these 4 components but they must be electrically connected.

I want to repeat this... Don't put any tubes in the amp until you have the power supply working. That includes the bias supply too.

[shooter]

heck I would even travel just to gain more knowledge

What state/country are you in?, someone here might be your neighbor

[taylorc315]

I live in Cedar Rapids Iowa, that would be great, like I said I would be willing to take a road trip as long as wasn't to crazy far.

[John]

Taylor, I backed out when Sluckey chimed in because he's forgotten more than I'll ever know, and he's really good at getting you (me) to think about what you're doing. :)


Anyway, I was looking at your pics, and it appears you have lots of extra wire coiled up coming from your PT, which is good. That allows you to disconnect and start over, should you want to do that. If it was myself, that's what I'd do. I have, in fact, more than once. When I'm hooking up a PT, even a simple one, here's what I do:


Hook up the primary to the off/on switch. Plug into limiter, test secondary AC voltages.


Connect secondary center tap, connect secondary high voltage wires to rectifier, either diodes or tube. Test DC voltages coming out of rectifier.


Connect heater CT and heater wires. Check AC voltages.




Connect high voltage DC wire, coming off your rectifier, to your first filter cap. Check voltages. At this point I still don't have anything connected past that first filter cap.


Try that if you've not found the problem yet, and let us know what you've got. Cheers!

[taylorc315]

Thanks John, I am going to start at the beginning, and do exactly what you suggested. And again I appreciate everything you guys have done for me and the knowledge that I have gleaned from you.

[taylorc315]

I think that I might have damaged the pt I only have around 17/18 vac coming out of one of the red wires. I'm going to order another one and start over, I don't know what if anything I did but obviously I have done something. Thanks I'll be back.

[John]

If you had it hooked up to your limiter, it shouldn't have gotten damaged. Usually damage is accompanied by a lot of smoke and a nasty smell. How much AC voltage do you measure across the 2 red secondary wires with the center tap grounded?

[taylorc315]

No smoke or smell at all, I will check ac voltage across the red wires and see what I come up with. Thanks

[taylorc315]

I've got 745vac across the two red wires, that seems  about right doesn't it? Nevertheless I have another pt coming

[John]

Yes, it does. Don't be in a hurry to hook up that other you've got, I don't think there's anything wrong with this one. So, now that you've got your 745 across the 2 red, you know where they get hooked up, right?

[taylorc315]

Yes I have diodes, so I will connect them to the diodes.

[John]

Excellent!


Plug into limiter, measure the DC voltage coming out. If anything is weird, then the problem is downstream of the rectifier (probably).


As Sluckey instructed, check the connections on your filter caps and all that. If your limiter shines bright without tubes in, you've got a short... or something miswired... after the rectifier/diodes.

[Willabe]

Plug into limiter, measure the DC voltage coming out. If anything is weird, then the problem is downstream of the rectifier (probably).

As Sluckey instructed, check the connections on your filter caps and all that. If your limiter shines bright without tubes in, you've got a short... or something miswired... after the rectifier/diodes.

Yes, agree.


               Brad   

[taylorc315]

I have 509-512 vdc coming from the filter caps, the DC side of the diodes is at 512volts. Also nothing is lighting up the limiter which is good. So maybe the problem is in the tubes. Should I just insert one at a time and see if I get the limiter to light up?

[taylorc315]

What I don't understand is that I had resistance on the DC side of the diodes yesterday but today I have nothing.

[sluckey]

Don't plug the tubes in until you verify that you have  approx. -40v (or more) on pin 5 of BOTH output tubes.

[taylorc315]

Thank you

[taylorc315]

I have -46.5 on both tubes

[John]

So far, so good. Now what do you measure across your filament wires?

[taylorc315]

6.9 vac