PT Problems, Seriously frustrated

[DIYDeluxe]

 My problem is this, I built a 5E3 Hoffman last year everything went pretty well, I recently thought I'd look inside just to see what I have and I noticed that I had two or the pre-amp cathode caps in the wrong place. The higher value one should have been on the Normal channel and the lower value on the Bright. After I got it done, I went to power it up and check some voltages, I noticed the plates volts were quite a bit higher than my original measurements. This brought the bias up to what I calculated to be 98%, wow, just about then, I heard a faint,,, Pssst. and noticed the pilot was off. I unplugged and found a blown fuse. So, I started checking a few things, I decided to check the Wall AC and unbelievable it was at 137 Volts. I never saw that so high anywhere. I'm still not sure if this would've changed the bias, being cathode biased I thought it balanced itself out. ???   I ended up loosening the board enough to take a look under to see if there was anything wrong, like leaking solder from a turret to the chassis or any stray strands of wire. Nothing that I could see was wrong. I did a bunch of testing and reading double checked a few things. I did some testing on the  PT but from RG Keen's site, which I do like, I couldn't figure out what he was talking about with testing one lead to ground then both leads to ground, I wasn't getting anything from those readings. I was able to check the PT windings with basic continuity test and it appeared it was still okay. I went through this whole dis-connect all the  secondaries and test, long story short. Turned out that even with No Secondaries attached it still blew the fuses. I'm bummed. From what I gathered this definitely means a blown PT. or short in the Mains. I did everything I could to ensure the PT still good. I now assumed the PT is blown due to the high AC. I ordered a new one from Weber, which I've heard good things about and it was cheaper. Another long story, short, I went through the initial connect and checking the new PT from the very beginning, Now even with No Secondaries connected, it continued to blow the fuses. I connected a light bulb limiter, (finally figured out how to wire it correctly) The limiter appears to being doing it's job, but the PT is questionable. I once again checked everything but removing the entire board which I fear is next. The light stays full bright, even with now Secondaries connected, I'm stumped, I honestly cannot figure out where the problem is, I guess I need to remove the board and go through every component and connection from beginning to end and hope I find the problem. I am not so sure that anything I've done on the Pre-amp side would cause this type of problem, it seems like some sort of dead short. Help. I will post a few pics. I'm not sure you can see well enough to tell anything, I appreciate any help, advice or comments in advance.

[DIYDeluxe]

I can't post the pics, they're too large. I can email them if anyone's interested. Thanks

[sluckey]

Disconnect the PT primary leads. Does the fuse still blow?

[HotBluePlates]

... I built a 5E3 Hoffman last year ... I recently thought I'd look inside ... found a blown fuse. ...

The amp has been working fine for some time until you opened it up? Are the preamp cathode bypass caps the only thing you touched inside the amp?

It would seem likely that the fault lies with anything you might have messed with in the amp. This could be indirect, too, as in a loose solder blob or chunk of wire loosened from messing in the preamp making its way to the power section of the chassis and shorting something out.

... I noticed the plates volts were quite a bit higher than my original measurements. This brought the bias up to what I calculated to be 98% ...

This may not be a problem.

The original Fender 5E3 schematic does not have voltages listed, but the 5C3 layout does. The 6V6 plates are shown as 350vdc, and 18vdc across the 250Ω cathode resistor.

18v/250Ω = 72mA  --> 36mA per 6V6.
350v - 18v = 332v
332v * 0.036A = 11.95w  -->  99% rated dissipation (using the 12w rating)

So idling hot does not appear to be a problem as long as you don't see redplating during use.

... I decided to check the Wall AC and unbelievable it was at 137 Volts. ...

Do you have a true RMS meter, like some of the Fluke meters? If not, and the wall voltage wave was distorted, you might read a high voltage.

Alternatively, the meter could be out of calibration. Or the wall voltage could be really high in your area... You might have to check it over time or with different meters to have a sense of which is the case.

I doubt the high wall voltage caused the blown fuse on its own. I've already shown that ~100% idle dissipation by itself is not necessarily a problem. I've also seen amps with real bias problems where I've measure 150mA+ (and climbing) idle draw through a single tube before I could reach the power switch to shut down; even then, the mains fuse did not blow in that situation.

... I went through this whole dis-connect all the  secondaries and test, long story short. Turned out that even with No Secondaries attached it still blew the fuses. I'm bummed. From what I gathered this definitely means a blown PT. or short in the Mains. ... I went through the initial connect and checking the new PT ... even with No Secondaries connected, it continued to blow the fuses. ...

It is highly unlikely that your new PT is bad out of the box.

Leave the secondaries unconnected (but do heatshrink/insulate the ends). So Red wires not connected, Green wires not connected, Red/Yellow wire not connected, Green/Yellow (if present) not connected. You tell me what you still have connected (like power cord, switch, fuse holder, etc).

You should not have to mess with anything elated to the board, as none of that is in the circuit if you do not have any of the PT secondaries connected to anything.

... I will post a few pics. ...

I can't post the pics, they're too large. ...

Got a Windows machine?

• Open "Microsoft Office" (or "Microsoft Office Tools")
• Find/open "Windows Picture Manager", navigate to your pictures
• Select the picture
• Select "Edit Picture"
• Select "Resize"
• Select "predefined width x height"
• Select "Document Small" or "Web Large"
• Click "Ok" and "Save As" with a new name to have small version and big version.
• Post the small version as an attachment here.

[Willabe]

Sluckey and HBP are right. If you put in a new PT and have all the secondary's disconnected then the problem has to be on the primary side's connections. Your eyelet board has no B+ and signal going to it with the PT secondary's not hooked up.


             Brad     

[DIYDeluxe]

Disconnect the PT primary leads. Does the fuse still blow?

The primaries are not connected, the fuse still blew. I want to check it again without the limiter, but my last fuse is in there now. ???

[DIYDeluxe]

Here's the PT

[sluckey]

The primaries are not connected, the fuse still blew.

Earlier you said it blew fuses with SECONDARIES disconnected. With the primary disconnected the only thing in the circuit is the power cord, fuse, and switch. Should be pretty easy to find now.

Is your wall voltage still 137VAC??? If so, you need to address that. Could be other stuff in your house that's also messed up.

[g-man]

Deleted

[DIYDeluxe]

Yes it was still blowing the fuse with all the primaries, including the green filament wires going to the pilot lamp. The only thing that was still connected was the primary, which is: the black & white wires coming from the AC going to: black to fuse, then out to power switch, then out to black of the PT's primary. You know, I'm really confused, I undid everything, pulled out the board and found I had pushed a wire in through a turret at the point where the 250 Ohm Resistor is. I obviously did this when I decided to clean things up a little, must've pushed it a little too far, and it appeared that it was far enough to touch the chassis under the board. I thought I had it solved so I carefully attached everything back. I had a little trouble being that the Weber PT has a Black wire as the lower primary and the Hoffman White to the White of the incoming AC, and the Weber has a Brown, (120 Volts) and the Hoffman had a Black to the Black incoming AC. So, with this the new Brown from PT will actually attach to the Power switch, the Black actually attaches to the White of the incoming AC, this had me seriously confused. I thought they would all be somewhat standardized colors. I felt I had it attached all correct and with no tubes, it once again blows the fuse. I'm out of answers, I really don't what to do with it, I'm so disappointed that I couldn't have left well enough alone and ended up with such a dismal mess, and no working amp anymore. I will take a little mental health break from it to re-group. May just have to build another board. I wish I could find someone with the same Weber PT and see exactly how they have it wired. I'm done for a while. I think it may be just an analogy of my life right now, problems that I absolutely don't have and answers to. See ya. thanks for your help.

[HotBluePlates]

... I had a little trouble being that the Weber PT has a Black wire as the lower primary and the Hoffman White to the White of the incoming AC, and the Weber has a Brown, (120 Volts) and the Hoffman had a Black to the Black incoming AC. So, with this the new Brown from PT will actually attach to the Power switch, the Black actually attaches to the White of the incoming AC, this had me seriously confused. ...

You mentioned before that you were having high wall voltage.

Take a deep breath and look at the information you posted for your power transformer from Weber. You can wire it for 120vac input or 125vac input; given you were talking about having 137vac from your wall, you want the 125vac wiring, so you use the black wire and the blue wire, marked "125".

It doesn't matter which of the power cord wires connects to which of the PT primary wires: make life easy on yourself and connect black-to-black, and white-to-blue. Done. By "black-to-black" I mean power cord black wire to the fuseholder, switch and then to the PT black wire, as you'd wired it before.

[DIYDeluxe]

I had been posting about my 5E3 troubles. I just used the diagrams from the hoffman layout along with the Weber 5E3 layout for the  PT connections. I still can't figure it out. I thought I had it  when I discovered I had pushed in the lead at the 270 ohm Output tube cathode resistor down, it looked like it could possibly be grounding to the chassis. I've been posting that I've had all the Primaries disconnected, what I meant it I've had the primaries connected to only to the Power switch from PT, to 2amp fuse, to the standby switch. And none of the secondaries connected to any part of the circuit. I had the Reds to the Rec. socket, (with no tubes of course) the Yellow HT to rec socket. and the link to the standby disconnected. so I could check voltages, I can't get anything to stay on. the light limiter just shines fully bright. I'm really hoping that I haven't blown the brand new Weber PT $60 down the drain. I may just start again. Unsolder the new PT, disconnect the entire board, take it out and start checking every single connection on it. When I first was building it, I found only one mistake that way and it worked as soon as I fixed the link I had missed. After I do that, put it all back together. One question, can the power, stnby or Pilot light fault cause a problem like this. I checked them they seem to work fine?? Still confused. 

[Willabe]

Go back to HBP"s reply #3, he tells you how to resize the pictures you took so you can post them.

Please give it a try someone here might see what's wrong. I've seen them do this many times before.


            Brad     

[HotBluePlates]

... I've been posting that I've had all the Primaries disconnected, what I meant it I've had the primaries connected to only to the Power switch from PT, to 2amp fuse, to the standby switch. And none of the secondaries connected to any part of the circuit. I had the Reds to the Rec. socket, (with no tubes of course) the Yellow HT to rec socket. and the link to the standby disconnected.

"Primary" is the "input side" of the transformer. For your amp, this is the Blue, Black and Brown wires than connect to the a.c. cord, switch and fuse holder.


"Secondary" is the "output side" of the transformer. You have Yellow wires (5v); Green & Green/Yellow wires (6.3v) and Red, Red/Yellow & Red/White wires (680v CT, 540v CT) for your secondaries.


You said "primaries" at least once where you may have meant secondaries. This caused confusion.


Do the Following:
1. You mentioned you really had the primary to the power switch, fuse holder, and standby switch. Unsolder the Red, Red/White, Red/Yellow, Green, Green/Yellow and Yellow wires from the PT to the first thing they connect to. Insulate them (wrap end end with electrical tape or heatshrink or wirenuts); make certain none of these loose ends can contact anything.

2. You only 1 primary tap. You will use Blue and Black, because you reported high wall voltage. The Brown wire must have its end insulated (heatshrink preferred, or electrical tape or wire nut) and tucked out of the way. It will not be connected to anything inside your amp.


3. Connect the a.c. cord black wire to the tip of the fuseholder, connect the side-contact of the fuseholder to one lug of the power switch, connect the Blue wire of the PT to the other contact of the power switch. Solder the white a.c. cord wire directly to the Black PT wire. This connection should be well-insulated with heatshrink or electrical tape.


4. The Standby switch is not connected to anything.


5. Install a fuse and turn the amp on, with your lamp limiter. Pilot will not turn on, nor will anything else. You will not have any d.c. volts in the amp, because there is no output from the PT (its secondaries are not connected to anything). The lamp limiter should faintly glow and the fuse should hold.


We are trying to eliminate variables, and what I described only has power cord, fuseholder and power switch wiring in place. If the fuse blows, it will be because there is a fault in that wiring, in the PT itself, or because you're allowing the secondary wires to contact something (they must be insulated and not contacting anything to get a valid test).

[DIYDeluxe]

Okay, I did all of that. A quick re-cap, All secondaries dis-connected and wire capped or insulated well with shrink wrap. My wall voltage has been consistant again at right at 117V AC. So, I will just go ahead and use the brown wire. for 120. I'm not convinced the AC up swing would've cause this problem. If the AC went up that may increase the overall Volts through the PT but I would think that would have the whole thing completely short out. My understanding is that if the output DC to the HT were higher and also higher out of Rectifier, higher volts at the Power tubes, also means higher volts through the cathode, equaling everything out. Is this correct?    Okay, so now I guess I can one by one, either check individual voltages, first: green filiment volts, 6.3 or a little higher due to no load, then re-insulate them, then: Red 5 volt lines to Rectifier filiment.  Then HT high volts. Let me know, I prefer to have verification from you guys at this point, because I have had so much trouble narrowing this down. Thanks, once again.

[HotBluePlates]

Yeah, just hook up the primary (using whichever voltage tap you feel comfortable with), insulate the secondaries, and turn on the amp. Does the fuse hold, or does it blow?

... If the AC went up that may increase the overall Volts through the PT but I would think that would have the whole thing completely short out. ...

No, higher volts should not make anything short out. Only a wiring error (or severely damaged part) should create a short-circuit.

You are correct though that too-high wall voltage would create a higher B+, which should pull more output tube current, which will create more voltage across the cathode resistor, which will increase bias voltage, which will turn off the tube. To a limited extent, this should all balance out.

As long as the B+ d.c. volts doesn't exceed the filter cap rating, and the output tube isn't redplating, this may be a non-issue.

So we'll wait to hear if your fuse holds up with only the primary wired. No secondary voltage measurements are needed or requested (at this point).

[DIYDeluxe]

Thanks for you replies. Yeah, I'm still really confused. Now I'm even questioning if my light limiter is working correctly, with the light limiter, and all of the above done, light shined pretty bright still, 60 Watt bulb. The fuse held. So, I tried the same and measured the green filament wires, from one to ground, nothing, from the other nothing, from one to the other nothing. So, just to check I would check without the limiter, fuse blows. I just don't know or understand how to check to find out for sure if One: The new Weber PT is no good, or Two: My original Hoffman PT is possibly still good. ??? I don't think it's any use in checking anything further, if I can't even get any filament voltage. Can't see how anything else could possibly be working. Does this indeed mean that the new Weber is blown, with no secondaries connected and lines only going from incoming line to fuse holder to power switch, to brown of PT, unless it's the actually the fuse holder, or the Power switch itself, how likely is that? Thanks

[sluckey]

then: Red 5 volt lines to Rectifier filiment.

I have never ever seen the color red used for a rectifier filament. And the pic you posted of the Weber PT clearly shows the 5VAC rectifier leads are yellow.

[HotBluePlates]

I think at this point you need someone there in person to walk you through checking this out.


If the fuse blows with nothing connected but the primary (and not using the lamp limiter), then either the PT is bad or your wiring is bad. We've seen no pictures of what you're working with, and my crystal ball is cloudy. I'd want to see the amp in the flesh to know what's going on.

[bnwitt]

Here is another layout of the Hoffman 5E3 which might help you figure out your wiring issue.  The first difference in the PT transformer shown in this layout from the Weber trannie is there is no green/yellow filament center tap on the PT in this layout and an artificial one has been created with the two 100 ohm resistors on the pilot light.  You wouldn't have that as your filament center tap wire would just go to ground.  The Red wires and red/yellow wire would wire as shown as would the yellow wires.  Of course you could be using the red/white wires of the weber PT instead of the red wires if you are using the 540V output.  The center tap red/yellow would still be used with the red/white wires.  The last difference in the Weber PT is the dual primary taps.  You have black for the common and a choice of 125V in on the blue wire and 120V in on the brown wire

[smackoj]

here is a handy device I located on a new forum I joined, ssguitar.com. It is called a 'Shorted Winding Tester'. I have not tried it but appears legit.

good luck,