Princeton Reverb blowing fuses RESOLVED

[makingnoise88]

Hi guys, This is my second build I'm using a hoffman turret board but have changed a few things.
I am using a deluxe reverb output transformer, and added a mid knob.
I got the amp all built but It is EXPLODING the fuse so I have done something wrong but I keep going over it and can't seem to find anything wrong. Im attaching pictures of the build. I didn't wire in the foot switch connecter as I want to use a 1/4 in instead of the standard RCA style jacks. If you have info on wiring that in as well would be helpful! Also I am using an LED instead of the standard lamp, I didn't have a 180k resistor on hand so I wired it to a 100k and a 68k to get me close. Is that to incredibly ignorant? haha as I'm sure you can see I am very new to all of this but I'm having a blast learning! Thanks so much for any help in advance.

[Planobilly]

Hi,

Take all the tubes out and see if the fuse still blows. I assume there is a tube rectifier. I have not looked at a schematic. If you are still up I will stick around for a few min.

Cheers,

Billy

[makingnoise88]

I pulled all the tubes and The fuse still exploded!
Thanks for your help I really appreciate it

[Planobilly]

ok...with the tubes out HT power only goes to the rectifier tube socket and heater voltage to all the tube sockets. So..the issue is in the power transformer it self or transformer wireing. I assume you are running it on 120VAC. Be sure you have the AC power to the transformer ( two black wires in most cases) wired correctly. If that is correct then disconnect the the heaters ( both green and yellow) and High voltage ( red wires and I assume a red wire with a yellow stripe to ground).

Bottom line, you need to test the power transformer without it being hooked up to anything. If it still blows the fuse then the power transformer is shorted and no good.

Be very careful messing with this and keep you hands off the chassis. I can not do CPR over the internet...lol

Cheers,

Billy

[makingnoise88]

haha this is true! I am sure I have it hooked up correctly As this was my first thought and I have been over it a dozen times! I will unwire the power transformer and I will test tomorrow. I will post and let you know whats going on then.
Cheers

[Planobilly]

See you tomorrow.....it is after midnight here....

Cheers,

Billy

[tubeswell]

And, when you have the PT secondaries unhooked for testing, make sure the bare winding ends aren't touching each other or anything else (even the chassis).


With everything unhooked, the fuse should not blow (unless the problem is a short on the primary side of the PT (like a shorted mains-voltage lamp or something - if you are using a mains-voltage lamp that is).


If the fuse doesn't blow with everything unhooked, then you will know to either look for a short from the B+ to ground somewhere, or a short from one of the heater pins/wires to ground or to something else.

[sluckey]

I see what appears to be a blue transformer wire connected to chassis at a transformer bolt. I bet that wire should not be connected to chassis.

[makingnoise88]

Slucky, the blue wire you see is blue/black it's the ground for the 120v

[sluckey]

Transformers don't need a ground for the 120V.

What PT did you use? Where did it come from? Can you provide a data sheet?

[makingnoise88]

Wow I feel really dumb....
The black blue is 100v white 120v and black is zero
With this being the case what would the solid black be for?
I need to swap the black/blue with the black and do what with the black? Seal it off?

[sluckey]

There are six wires on the primary. NONE OF THESE SIX WIRES WILL CONNECT TO CHASSIS. You will use the black wire. You will use the white wire. The other four wires will be taped off and not used.

The black wire will connect to your power switch. The white wire will connect directly to the NEUTRAL lug on the IEC connector.

[Planobilly]

Connecting the primary to ground would surely do it! One of the reasons I told you to be careful what you touch.

Anytime I have an amp that is blowing a  fuse I take extra precautions in how I touch things.

Good luck.

Cheers,

Billy

[eleventeen]

Yes, I have made single ended fuse blowers and push-pull fuse blowers. Never made a primary fuse blower.

[makingnoise88]

Well I pulled the blue/black wire taped it off and it's still blew the fuse!
So I guess the next step is testing the transformer!

[dude]

Maybe you blew the PT with that 100v blue primary to ground...?

[eleventeen]

Just so it's clear:
You feed your 120 VAC into two transformer wires. Black and white.
Any and all of the 4 unused primary wires are:


A) Not used for anything. Not connected to anything.
B) Not connected to the chassis
C) Not connected to each other, meaning INSULATED from each other.
My next test would be:


Either bring the thing up on a variac, OR light bulb limiter, in this case the light bulb limiter might actually be better; good excuse to build one if do not have such a thing and you want to do other builds or fix other gear.


Connect up the power transformer in temporary fashion (eg; tack-solder it) as if you were running your amp on 240 VAC.
That would be:


Leave alone the black wire.
Disconnect the white wire from wherever it is now connected and tape it off.
Wherever that white wire went, use the black/red instead with a temp solder connection, don't tie up your wires.   


Now, you are connecting the tranny up as if it expects 240 VAC, but still of course only feeding it 120 VAC. That means it will be getting only half-powered. I really doubt you blew it up; trannies are quite rugged, the previous fuse(s) did their job and blew rapidly if not instantly.
Measure output volts on the various secondaries. They should be half of what's expected.

If it still blows the fuse and the secondaries are disco'ed from anything, then my opinion would change and shift towards yeah, you blew it up.

[makingnoise88]

Perfect! I'll try this tonight!
I can't thank you guys enough!

[2deaf]

It appears in the picture that black (0V/Common) is connected to what is ordinarily neutral in US house wiring.  White (117/120V) is connected to one end of the fuse with the other end connected to what is ordinarily hot.  Neutral connects to ground in a properly wired US house.  With the 100V tap connected to ground, there would have been a complete circuit to run the wall power from the 100V tap to the 117/120V tap.  With way fewer turns than from 0 to 120V, you would expect the load to blow the fuse.  With the 100V tap removed from ground and all unused taps insulated, you would expect everything to be hunky-dory.

I would like some DMM readings before tearing everything apart.  While disconnected from the wall, what is the DC resistance across the external pins of the IEC connector with the power switch on and a good fuse installed? 

[makingnoise88]

Ok. So i finally have some time to sit down and test some stuff on this amp.
I have the power transformer completely unwired to test but as I said before this is my second build and I have no clue what settings I need on my multi meter or what I'm looking for. Does anyone have any resources on how to test this transformer?
Thanks in advance

[VMS]

I suggest you read this page first:


http://paulrubyamps.com/info.html

[makingnoise88]

Ive pulled the transformer completely and took some measurements!
Please let me know if I'm right or wrong in how I'm measuring and I will adjust.

DMM Setting = 200 ohms
Black and white wire = 05.8
Yellow wires = 00.4
Green wires = 00.5
DMM Setting = 2000 ohms
Red wires = 256

[eleventeen]

That looks very in the ballpark of a power transformer. Both heaters are practically short circuits. The other readings are pretty typical, at least in my experience.

[makingnoise88]

I'm gunna reinstall and try again!

[tubeswell]

Hook the primary up with a mains fuse from the Active/Phase wall wire, then the mains switch, then the Pt primary. Return the other end of the primary to the 'neutral' wall wire. Install the PT in the chassis, and have the chassis firmly bolted to the earth wire. Don't let any of the secondaries touch each other nor the chassis, nor anything else. Clip your insulated 'gator leads/test clips across each secondary winding end and measure the VAC across each winding when you flick the power switch on. Switch of the PT off each time you go to change the clips to another winding.

[eleventeen]

Do like Tubeswell said.....


The only tweak I would add is...many multimeters don't like >600 volts. My old Fluke 77 is one. So, when measuring the HV winding, measure from one side to the CT, not across the whole winding. Do it again, other side of the HV winding.


In all cases, your test leads are CLIPPED ON, and your hands are nowhere near the thing.


If you are in a partially built amp and have line cord > AC entry > fuse, fine. Power it up that way.


With a raw tranny, I don't mind sticking the primary wires into the female end of an IEC cord. Why? Because even though it may seem hairy, it forces my hands to be away from the tranny wires, holding a rubber/plastic thing. I could understand if that seems scary for Hallowe'en.


It's also easy to do the "remote turn on" using one of those 6-way outlet strips.


Know that the voltages will be high since they are all unloaded. Thus, 6.3 volts could be 7, 7.2.


5 volts could be 5.8


That's why your HV winding (designed to be say 350-0-350 = 700) might be closer to 800 volts (750-775) when unloaded, esp if your line volts are highish. Some meters will not like that.   

[SILVERGUN]

Is it me or does he have one leg of the filament winding connected to ground in this picture?
 
Or is that a bung'd up way of doing an artificial CT mixed with a current limiting resistor?...either way, it ain't good

[sluckey]

Is it me or does he have one leg of the filament winding connected to ground in this picture?

I noticed that too, but it's kinda hard to tell from that angle. I figured I would mention it if he ever gets the PT primary hooked up correctly.

[SILVERGUN]

Is it me or does he have one leg of the filament winding connected to ground in this picture?

I noticed that too, but it's kinda hard to tell from that angle. I figured I would mention it if he ever gets the PT primary hooked up correctly.

OK, I feel better knowing you're still lurking...
Even if it aint going to chassis, those resistors are just a dead short across that winding....I'll bet that LED was really bright for a split nano-second 
 
 
 
While I was at it, I spotted this as well...
Nothing connected to bias supply (maybe that's what the BLUE wire is for- usually on new Hammond xfmrs)
But also, the bias supply is going through a front panel pot and I'm scratching my head as to why, and where those other 2 pot wires are going.
Is this a fancy master volume?...of course it is
I've been away for a while...maybe it's me?
 
EDITED- If it really is the Mojo PT posted in pic, then I'm obviously wrong about the blue wire
EDITED AGAIN- so as not to confuse OP
 
 

[sluckey]

I'll bet that LED was really bright for a split nano-second

Nah. Those current resistors for the LED are parallel 100K and 68K. That LED ain't never been lit. The only thing that's been bright so far is the line fuse.

Nothing connected to bias supply (maybe that's what the BLUE wire is for- usually on new Hammond xfmrs)

The blue (actually blue/black) in a primary voltage tap. There's a data sheet for the PT up above. He will eventually have to connect the bias supply to pin 4 or 6 of the rectifier socket.

the bias supply is going through a front panel pot and I'm scratching my head as to why

Look at the PR schematic and the truth will be revealed. 

[SILVERGUN]

the bias supply is going through a front panel pot and I'm scratching my head as to why

Look at the PR schematic and the truth will be revealed. 

Ahhh, so that one was me....kinda
 
I'll go away with red face and check back for updates.
Please don't keep it on my permanent record...

[sluckey]

No promises. This forum is RIGGED!      

[makingnoise88]

Ok. So i was able to get the transformer hooked up correctly and power tubes and lighting up nicely!
As far as the led it was just floating in the air, I figured I would rewire it permanently after got the amp up and going.
I did forget the bias Tap so I added that from the 3w 100k resister to pin 6 of the rectifier.
So it looks like everything is correct at this point but I'm not getting any sound what soever so I'm going to go back over my schematic with a fine tooth comb and see if I find anything! If anyone sees anything please let me know! This has been an incredibly awesome thread I can't thank you guys enough!

[sluckey]

Your resistors for the LED are way wrong. Hoffman likes a bright LED and uses a 180Ω resistor. I find that about 1K to 5K gives me plenty of shine. But 100K and 68K wont even light at all.

Click on the link in my signature line at the bottom of this reply for a good method to verify that your wiring and component values are correct.

Measure the voltage on all 4 of the filter caps. Then measure voltage on every pin of each tube. Post these voltages (even to zero voltages). Hoffman has an online chart for this purpose that makes sharing your voltages easy. Or you can just post in a reply.

[makingnoise88]

Perfect! I'll do this. I want as bright of an led as possible! If I didn't use any resistor would that be a problem?

[tubeswell]

Also make sure pins 4 and 5 are tied together on the pre-amp tube sockets (for 6V heater operation)

[sluckey]

I want as bright of an led as possible! If I didn't use any resistor would that be a problem?

Absolutely!

[makingnoise88]

So 180ohm is the best choice for the brightest led?

[PRR]

> If I didn't use any resistor

No resistor, current goes to "INFINITY", LED blows up.

> 180ohm is the best

On 6V power it gives around 20mA, which is the Max rating of most small LEDs.

20mA in a modern LED is very bright. Many people favor 1K, 5K, even 10K or more.

But it would have to be Halloween Midnight to see an LED with 68K (~~0.05mA) resistor.

[makingnoise88]

Ok so I had sometime to sit down and take voltage readings across the amp and I've definitely found a problem!
My heaters are not lighting up and rightly so seeing as they are getting 1.1 volts ac. So here are all the voltage readings and if you can give me a starting point as what to look for and try that would be amazing!

Both 6v6s read the same.
6v6
1. 0       
2. 1.1 ac       
3. 1  .     
4. 1  .
5. -25.0
6. -25.0
7. 1.1 ac
8. 0

V1. reads
1. 354
2. 9.6
3. 0
4. 1.1 ac
5. 1.1 ac
6. 0
7. 0
8. 0
9. 1.1 ac

V2 reads
1. 400
2. 0
3. 0
4. 1.1 ac
5. 1.1 ac
6. 400
7. 0
8. 0
9. 1.1 ac

V3 reads
1. 352
2. 0
3. 0
4. 1.1 ac
5. 1.1 ac
6. 352
7. 0
8. 0
9. 1.1 ac

V4 reads
1. 330
2. 0
3. 0
4. 1.1 ac
5. 1.1 ac
6. 1  .
7. 0
8. 0
9. 1.1 ac

[SILVERGUN]

Take another look at the picture I attached in reply#26.
How did you resolve that wiring error?
(A close up pic would do wonders for our curiosity)

[makingnoise88]

I added the bias tap, but everything else's is the same. The diagram shows that wire going to the intensity pot for the trem.

[sluckey]

Measure voltage between pin 2 and pin 7 of a 6V6 socket. What have you?

[eleventeen]

If your tubes are not lighting up...they can not work...and they thus cannot draw/pass current. That's why you have huge volts on your preamp tubes. Are you using a tube rectifier and is *IT* lit up?

[makingnoise88]

6.3 on both the power tubes are lighting up as well as the rectifier tube. So if 6.3 isn't  passing through to the pre amp tubes that would mean a cold solder joint?

[sluckey]

Probably a bad connection of some kind, cold joint, broken wire, etc. Should be easy to find.

Measure voltage between pins 4/5 and pin 6 of each small tube socket.

[makingnoise88]

Reading 4/5 and 6 with ax voltage I get 0 across the board.

[sluckey]

Reading 4/5 and 6 with ax voltage I get 0 across the board.

Crap. My mistake. That should be "Measure voltage between pins 4/5 and pin 9 of each small tube socket."

Sorry

Be sure there is a jumper between pins 4 and 5 on all those little sockets.

[makingnoise88]

 I should've figured that's what you meant. When testing individually I get 1 to 1.1 but when testing together this is zeros on every one.  So I would've steam since V4  he's first in line for the 6.3 V it would be somewhere between 6V6 and V4  I reflow the Sauter with no change at all so I assume I would need to change those wires out?

[SILVERGUN]

Take another look at the picture I attached in reply#26.
How did you resolve that wiring error?
(A close up pic would do wonders for our curiosity)

I added the bias tap, but everything else's is the same. The diagram shows that wire going to the intensity pot for the trem.

I was referring to REPLY#26

Sluckey got you straightened out on the LED resistor value, but how do you have it wired?
You should have created an artificial CT with 2 100ohm resistors (which is why I thought you had 50ohms feeding that LED )
Sluckey picked up on the values (100K and 68K - because he is forum "establishment")

Did you incorporate an artif. CT and how did you wind up wiring that area in the circle of my posted pic?

Here's an adjusted schematic snip: