Have no filament voltage for my champ amp?

[Dennis Perusse]

Hello all,

I did a search on this but didn't find what I need to know so, hence, the direct approach. I'm re-building my champ amp (again) and for some reason I don't have filament voltage at all on the green wires. I've checked the bulb and it tests fine. Heck I've even put my voltmeter onto the green wires and still nothing. I get voltage for the rectifier and I'm positive that my wiring of the 3 prong cord is right. What could cause a power transformer to do that? My power tranny is a classictone with these numbers 40-18019, 166-1145. Any help here is greatly appreciated. :-)

Dennis

ps I may end up just emailing the manufacturer but I'd rather try here first. :-)

[BobbyZ]

Hate to ask but I've done it. Are you checking with the meter on AC ? Cause that's what filaments are.

Edit.

Before someone posts 500 tube amps with DC heaters yes some are DC.
But not the one's we see.

[t-luxe]

^^^ this.

If not, pics would be helpful...

Be sure your filament winding center tap is grounded, and double check all your wiring from the transformer to the pilot light to the tube sockets, taking VAC readings as you go.

[Dennis Perusse]

Hello,


Okay, the plot thickens. I'm not getting power not only out of the filaments, I'm now also not getting any power out of the other windings as well. My 5y3 tube tests fine in my emissions tester and when I put it into the circuit I get no glow from the tube) At first I thought it was the switch (as I ended up tripping the circuit breaker when I tested a few things) but I replaced that with a known good one. Is it possible that I may have blown out the power transformer? Is there an internal fuse that I should be aware of in the transformer at all?

[BobbyZ]

A bad PT blow the fuse if it's shorted. No fuse in the PT.
Start from the wall plug make sure you have 120AC there then check for 120ac where the cord goes into the amp before and after the switch and the fuse. If you have 120ac going into the PT you should be getting ac out the other side. Only the B+ coming off of the rectifier is dc pin 8. That then feeds DC to the rest of the amp.
Did this work before the 3 wire cord was added?
And if you could post some pics it may help.

[Keyser Soze]

Disconnect all secondaries. Tape off all secondary leads - only remove tape on leads under test.

Plug the amp in, turn main power switch on. Check voltage at the power switch. If you have line voltage proceed to check the voltage on each secondary.

If you read proper voltage on secondaries (with no load they will read about 10% high) then the problem is your wiring.

If so replace all heater wiring. Many people like solid core wire for heaters, I do not. All that twisting work hardens the copper and makes it very prone to failure. Even if it never fails enough to open the circuit it can still be a source of noise.

If you don't read proper secondary voltages then your tranny is shot. Typical guitar amplifier transformers do not have internal fusing.

[Dennis Perusse]

Okay a few clarifications here. I've rechecked my wiring again and, to me, it seems okay. Although I am checking for power off of the green wires these are the ones that come from the transformer. Still no Power so trying to check from any other point where the heater wires connect to would do no good. Plus when I check the rectifier wires the tube has been unplugged so I still should get power to the socket. No power to the socket. :-( I am starting to wonder if I truly did kill the beast?
I am getting power from the wall outlet to the amp as I run a serge protector from the wall socket and I have my clock radio plugged into it so it is getting power.

[hackworth1]

Even with your clock radio functioning on the same power strip, A dead fuse in the amp would kill power to transformer.

Sometimes the simplest things are overlooked. I saw no mention of the fuse in the fuse holder and whether you checked it or not.

[Dennis Perusse]

Hackworth1,


Good call on the fuse. I took it out and looked at it closely. It was burnt. I changed it over and I'm back to the condition that I was in as I have power to the rectifier (both yellow and red wires to the socket) but still no filament voltage. What I'm going to do is get another meter and then check stuff out again as my radio shack meter might not be reading right so let me test it with a another meter to see if I get the same effect. I'll contact people tomorrow and let everyone know what I find. I do appreciate everything people are doing for me in this instance as I'll take a picture tomorrow and post it. :-)

[jchabalk]

t-luxe mentioned the center-tap on the filament, did you check that the center-tap is properly connected to the chassis?

[Dennis Perusse]

Jchabalk,


The red/yellow and the green/ yellow center taps are soldered to a lug which is grounded to one of the nuts on the PT which holds it into the chassis. I still haven't yet gotten around to getting another meter (the snow in my hometown plus foolish drivers aren't making it any easier as of yet to get one) but when I get one I'll take another look at the voltages and go from there. Here is a pic of my amp internals and his a textual reading of how it is wired.

Okay, starting from the power cord the green wire is going to ground. The white neutral wire is going to one of the black wires on the power transformer. The other black wire (from the transformer) is going to one leg of the fuse. The other leg of the fuse is going to the switch. Now the leg of the switch is going to the black wire of the power cord. To my knowledge this is the proper way to wire this up with the red wires going to pins #4 and #6 respectively. The yellow wires going to pins #8 and #2 on the rectifier tube socket which is a 5y3 will be used. The green filament wires are going to the pilot light but that is where I have no voltage at all? Unless I'm doing something really boneheaded {it hasn't been the first time} then something is really wrong on the PT. :-)

[Dennis Perusse]

Hello,


Okay this is where I'm at. I've decided to rebuild this thing from the ground up as I've decided to get some new wire. Obviously this doesn't cure my pilot lamp not turning on but by redoing it I can focus on newer stranded wire and better lead dress. Also the possibility of getting a new board is becoming preferable as my eyelet board upon closer inspection is looking a bit haggard. Plus one of my sockets isn't looking to hot either. I am determined to finish this, as this is my first amp project, but I want to do it with quality and not just slap it together and hope it works. Thanks everyone whom answered my questions. I'll update this as things happen. :-)


Dennis

[BobbyZ]

You have voltage out of the PT but not to the filaments and the fuse was blown.
Look for a short in the filaments. Pull the tubes just incase.
Also at what point did it stop working?

[t-luxe]

The green filament wires are going to the pilot light but that is where I have no voltage at all

If you have voltage to the recto as you say, but none to the pilot light, and your connections (and wire) are good then I'd say bad filament windings. You really should check things over with a meter before you start pulling it apart again.

[Dennis Perusse]

T-luxe,


I probably do have bad filament wires as I checked my pilot light with a regular battery and the light lit up, so I'm gonna rebuild it using better wire (in this sense stranded 20 gauge) instead of solid core wire plus stranded wire. I just ordered some parts from tubedepot like two octal sockets which I know will fit better than my last pair did. I'm debating on doing it with terminal strips which will allow me to better connect the wires up or just go with g10 turret board as I'm not a fan of the eyelets on fiber board, not enough room in that tiny chassis. I tried doing it with a homemade chassis but that was a debacle in an of itself a while back. I'm in the process of checking out all of my resistors too so any that may have burnt out from my past wiring jobs I can easily check and replace. I also have another PT that I might swap in as I rebuild it and then test out the PT that I tried to use for this build and see if it (the filament) is gone or not. Either way, it's still a fun project and I'm not gonna stop until it gets done. :-)

[BobbyZ]

Or you could just check the PT first.

[Dennis Perusse]

Hello,


Okay a quick update on this. This might give some a quick chuckle or a roll of the eyes. I decided to do, on my recently purchased multimeter, to do a resistance check on the PT. Where I tripped the circuit breaker while using my old multimeter I figured that I'd check stuff with a brand new one. The numbers show the following.

Black Primary Wires: 6.3 ohms
Green Filament Wires: .1 ohms
Center tap (green/yellow) .1 / .1 ohms
Red Wires 361.3 ohms
Red center tap (red/yellow) 186. 0 / 175.5 ohms
Yellow Wires .1 ohms

I sent those number to Chad at Triode and he confirmed for me that that is normal and proper for the PT. So these facts are conclusive:

1. The PT seems to be okay according to the resistance values.
2. The bulb in the bayonet works as I tested this with a battery.
3. Still don't know what is causing the bayonet with bulb to not light when I had it connected?

Where I'm still waiting on parts to arrive I'll keep people posted on what's going on. I'm wondering could the chassis be an issue? I realize that this a foolish question but when you eliminate the impossible, whatever remains, however improbable, must be the truth? So I wonder if that could have an effect anywhere? One question I do have for people is about the bayonet. Is the Bayonet isolated when it's screwed into the chassis or does it ground out because it is screwed in?

Again, just more food for thought here as people who are building their champ amps who may run into any similar problems like I'm having. Betcha' that it's something truly under my nose.

Dennis

[Wally]

Reread post #6. Do this before you proceed to any other operations.
LIVe voltages sticking out there....danger. twist on connecting caps might be handier than tape. IF you have good voltages in those tests, then move downstream until you find your problem. IT would be a pity to 'rebuild' the amp and miss the basic problem.....or rather, itmight be alonger learning period to fail to follow Keyser Soze's suggetions. IF the voltages are good, you might siply have a bad solder connection at the pilot light.....or a short on down the line in the filament wiring....or a tube in that line.
AS for those resistances, that is all well and good; but that doesn't show what the windings do with current flowing through them. This is why Keyser's advice is of value.
I recently overhauled a '73 Pro Reverb. I got the basic work done and fired the amp up. Hmmm????? NO pilot light! I checked voltage at the those connections at the pilot light...good voltage....but no pilot light. PRodded with a non-conductive stick and Voila! voltage and a pilot light glowing. I kept messing with the intermittent nature of the circuit and realized that what looked like a perfectly good factory solder connection was in fact no good at all. A quick resolder and the amp works each and every time. I wonder how many times in the last 39 years that amp would either come on or NOT??? After I cleaned the amp up,that PRo rEverb looked brand new....so I am going to guess that it sat around doing nothing much of the time because it was 'unreliable'. (this amp also had an incorrect vetical mount reverb tank in it from the factory! Feces occurum!)

[Dennis Perusse]

Wally,


I'll try that out and let everyone know what my findings are. :-)

Dennis

[CoolBlueGlow]

Your filaments are blown. No offense to your test gear, but unless you are measuring these filament DC resistances with a well calibrated VTVM, your static multimeter resistance readings of the filament windings are practically useless.

I think the "obvious thing" that you are overlooking is that indeed very obvious. Something blew that fuse in the first place. I'm betting it was a shorted filament winding or windings.

Only that agrees with the measurements. You have AC on the primary. You say you've carefully checked your wiring (I believe you) You have plate voltage, you have NO filament voltage. You found a blown fuse.

In my book, that equals blown filament windings.

Sorry for your trouble. Good luck in your rebuild. I think you'll get her going...but you're going to be buying a tranny, methinks...

Cheers

CBG