Amp just started drawing extra current...possible why's?

[ALBATROS1234]

I built a simple circuit very similar to my last couple.was testing it out the other night and it was sounding good with a 6sl7 and 5881 single ended. Seemed to work fine did some power tube substitutions to compare tone and was working fine. One small board has the input and cathode resistors with bypass caps the other is a bridge with filter caps with resistors in between very typical stuff. Anyway last night I am playing around with it and I wanted to test if tone would change if i swapped out power transformers. Suprisingly it does slightly. Any way I am playing thru one and I smell the smell of transformer melt down so I go unplug it and the power cord is quite warm as well. It was a smaller xfrmr so I figure that's the deal since I had the 5881 in and it worked with lower current tubes last night.well I plug in another transformer and the lights dim so I unplug it and notice this transformer was warm to the touch. I must say at this point this has no power switch that's why I plug it to turn on.at this point I figure something is touching something it shouldn't as there are alligator clip leads jumping everywhere .
  Anyway today I decide to build the thing mount the boards on the chassis and solder it all up.when I turn it on it sounds pretty good as I play  I think maybe I have to change some thing to give it a touch more high end and I the volume starts fading as I then smell that this xfrmr has just melted down. I hook up another xfrmr bypassing the on off switch and I get the old lights dim when I plug in crap.

My question is where could the prob possibly be.  I assume power supply but can't think what would have failed to cause this when it was working fine 2 days ago breadboarded .short of rebuilding the boards what could cause an amp to all of a sudden. Start drawing a lot more current. It's not either of the tubes because the problem continued with different pre and power tubes. As well as following the circuit from jumpers together with different sockets pots input and output jacks etc. The only commonality is the 2 boards descri as above

[rake]

Maybe you've lost your -bias voltage and the tubes are running away? 

[jjasilli]

Use troubleshooting charts.  Tubenit posted some. Or geofex.com > tube amp debug > smoke of burning smell

[Ed_Chambley]

Not sure what is meant by lights dim when I plug in using another transformer.


Seems drawing more current points to not enough current initially and installing a starved tube. Easy check. Using the known good transformer since you seem no not know the specs and install a 6v6.


What exactly is the difference in current draw? And most certainly a power transformer has a lot to do with tone, feel, attack and increasing wattage.


Now do you have a proven schematic you are using. Did you measure the current in each circumstance?


The largest thing to change current in an SE amp using the same power tube is reduce the cathode resistor.

[ALBATROS1234]

By "the light dimmed" I meant the lights in the room that my amp was being plugged into. In other words I plug in power to the transformer and the second the plug made contact in the socket the light bulbs in that room got noticeably less bright. The values of the cathode resistors bypass caps and plate resistor were all average values . Preamp tube Cathode r 1.5kohms bypass cap 22uf plate resistor 220k. Power tube Cath re 330ohm 5watt bypass cap 10uf 50volt .So all very typical average values. That wasn't the problem though it was something on the power supply board . I took the board off the chassis and connected just the power supply stage to the transformer and with a power cord wire nutted to the transformer I plugged it in and lights in the room dimmed . So I rebuilt it with new caps and new bridge just to make sure. When I hooked it up thus time no problem so I hooked it to the circuit and powered it up with no problem. It's soldered exactly the same way with the exact same values just new components. It was either one of the caps or the bridge.thanks for your replies

[sluckey]

By "the light dimmed" I meant the lights in the room that my amp was being plugged into. In other words I plug in power to the transformer and the second the plug made contact in the socket the light bulbs in that room got noticeably less bright.

    You may want to have someone take a look at your house wiring. My lights don't even dim when my hungry air conditioning unit kicks on.

[ALBATROS1234]

I know the breaker works because I have popped it one or twice in the last few months testing transformers the only time it tripped was excessive current  I have to believe that when plugging in the xfrmrs when attached to this circuit it must have instantly pulled close to 20 amps without pulling enough to trip the breaker therefore causing a slight dimming of lights on that circuit.i am not sure which component but whichever it was drawing mains current to ground. When I tested the components they seemed fine on a simple meter test but could be something undetectable without a capacitance tester unit

[92Volts]

Does the amp have a fuse? A fuse should be located immediately after power enters, on the "hot" wire if your local wiring standards define which is hot vs neutral. That way if anything... even your power switch... shorts mains power to ground OR across the mains, the fuse will interrupt it.

Increased light dimming could be from increased resistance in your house's electrical system, not an increase in current. This could be caused by a connection coming loose or even beginning to heat up, which could be a fire hazard. Best to have that looked at.

[PRR]

> My lights don't even dim when my hungry air conditioning unit kicks on.

It varies. My light dim on very modest loads. When we bought, the "inspector" suggested it indicated A Problem. Idiot. The "problem" is the house sits 500 feet from the road and power transformer. The 500 feet of standard gauge wire is overhead in plain sight.

I did go though (mostly replaced) every joint and breaker. I found other problems. Lights still dimmed on the well pump, the old furnace, the microwave, etc.

Detailed calcs of the wire, and running measurements, say there is about 0.4 Ohms in each 120V leg. So a 20A demand is an 8V drop which is a "light dim". (It is a little more complicated because it is 0.15r in each 240V leg and 0.25r in the Neutral leg, so the "other" 120V leg rises a bit; and a 240V load is much less dimmage.)

The place was wired for a trailer. I don't know how a house got here. It was here when I found it. I think it is just past the distance that the utility company would like for a house on standard wire. My neighbor is similar but his 550' line runs at *19,000V* with the transformer near the house. Solid power, but when a small branch dropped on the line last week it "shorted" the ~~20K line impedance and blew the fuse at the street. (Furnace out, cats freezing.)

[ALBATROS1234]

The place where I am staying was destroyed during hurricane Katrina.  So it was completely gutted and rewired it has new breakers a d every thing.  All I know is this is the first time this happened where when I plugged in the lights dimmed. The voltage was spot on but 2 transformers overheated and shit out within moments. One was a 300va the size of a cantaloupe. Since I re did my ps board all is well no dimming.

[92Volts]

The place where I am staying was destroyed during hurricane Katrina.  So it was completely gutted and rewired it has new breakers a d every thing.  All I know is this is the first time this happened where when I plugged in the lights dimmed. The voltage was spot on but 2 transformers overheated and shit out within moments. One was a 300va the size of a cantaloupe. Since I re did my ps board all is well no dimming.

Is there a fuse built into the amp?

It sounds like there was a problem which is now fixed, but transformers were damaged? If you didn't have a fuse, use one, if you did maybe a smaller value. Because I can diagnose/replace blown fuses I use as low as 0.5x what manufacturers put in similar amps. A Champ likely has 1A to avoid "nuisance trips" and visits to a tech for just a blown fuse. But similar circuits will be better-protected with a 500ma fuse. And I have yet to experience an unwanted trip of a down-sized fuse.

[ALBATROS1234]

No it was breadboarded there was no fuse. Actually there still isn't. I am new this is my fourth amp and I always wait until I am happy with the circuit am done tweakingand then solder it in. Right now I have the hot wire cut and wire nutted in that area so all I have to do is break my tap solder the 2 wires on the fuse holder and mount it. I figured it would be a waste of fuses as during the tweaking process things can fluctuate etc. Probably not the way most would be comfortable doing things but I am an electrician so I am used to dealing with voltages and currents etc. Possibly a bad thing in a way because I am so comfortable that's there's very little fear but at the same time I am aware of the damage that can be done.. especially to a person.

[shooter]

I am an electrician

most of my electrician friends have their recepts hanging out wire-nutted
they drive really nice trucks though 

[ALBATROS1234]

Which was my point. When I am designing it looks like a plate of spaghetti exploded . I just figured the fuse would be more of a hindrance than help at that phase so that's the last thing that I attach.

[92Volts]

Well, the fuse isn't the most critical part for electrical safety per se. I'll admit I've tested breadboard or other similar setups without one.

But it can prevent component damage and answers how much current is used, whether it's expected, etc. It's a small inconvenience that can prevent bigger ones!

You can get fuse holders that are easy to wire like this: https://www.amazon.com/First-Source-In-line-Fuse-Holder/dp/B0002KR8EE

Or integrate power hookup/fuse/switch into one module like this: https://www.amazon.com/uxcell-IEC320-Module-Connector-Switch/dp/B01ARKBFZG/
Beware the smaller fuse size than most tube amps, but it could be convenient for a breadboard/out-of-chassis build.

For tests or something low-budget I usually end up using these: https://www.mouser.com/ProductDetail/Littelfuse/03540601ZXGY?qs=gu7KAQ731UQS%2F50SI0XJZg%3D%3D

[sluckey]

If you continue experimenting with 'light dimming' work you may want to get several of these cheap circuit breakers...

https://www.tedweber.com/amps/fuses-circuit-breakers

[ALBATROS1234]

Thanks guys the dimming lights issue ended when I remade my power supply board . I am going to get some of those circuit breakers though. I didn't know they had small value types like this I normally only see 10amp or larger. I appreciate the input