New power transformer?

[chuckb]

Well guys, I've installed the new Hammond power transformer in my 64 Princeton 6g2 and the tranny is still getting hot. I have no tubes installed and I can't figure out what it can be. The amp keeps blowing fuses? I'v swapped out the bad screen resistor 1k/5w for a new and heavier one ,still no luck. I tried swapping the filters in the power section and still nothing. anyone else got any ideas?

Chuck.

[eschertron]

Well guys, I've installed the new Hammond power transformer in my 64 Princeton 6g2 and the tranny is still getting hot. I have no tubes installed and I can't figure out what it can be. The amp keeps blowing fuses? I'v swapped out the bad screen resistor 1k/5w for a new and heavier one ,still no luck. I tried swapping the filters in the power section and still nothing. anyone else got any ideas?

Chuck.

Blowing fuses with no power tubes? pull the rectifier tube and measure your voltages on the primary and secondaries. You might be pulling enough power on your filament windings (if they're shorted, or some such thing) to overload the primary side. Do youy have a lightbulb limiter to use?

[bob p]

A light bulb current limiter is a smart idea. Put one of those in front of the amp and post a voltage table for the amp. That would help to determine what's happening.

A line meter like a Kill-A-Watt might also be helpful.

When you say that the PT is getting hot, how much of a temperature rise are you talking about? If you have an IR thermometer it would be helpful to know the magnitude of the rise in temperature above ambient.

Just thought I should ask -- what kind of fuses are you popping? Are they slow-blo fuses or fast-blow fuses? A 2A slow-blow fuse shouldn't pop on power-on, but a fast-blow fuse might pop due to the inrush current as the transformer is energized.

[chuckb]

Well i don't have a light bulb current limiter. The tranny gets quiet hot to touch, then after a minute or so the fuse bows. i was using 2a slowblow.I don' have any tubes in it at the moment not even the rectifier tube. The last thing I did before installing the new tranny was to hook up a three prong wire for power. Green to ground, white to on/off switch, black from PT to other side of on/off switch,PT black to fuse and black from power-cord to fuse.

[eschertron]

Well i don't have a light bulb current limiter. The tranny gets quiet hot to touch, then after a minute or so the fuse bows. i was using 2a slowblow.I don' have any tubes in it at the moment not even the rectifier tube. The last thing I did before installing the new tranny was to hook up a three prong wire for power. Green to ground, white to on/off switch, black from PT to other side of on/off switch,PT black to fuse and black from power-cord to fuse.

Can you post a schematic? With NO tubes in the amp, and NO diode rectifier, my fist assumption is that your PT should be drawing no load current.
A couple of thoughts:
Does the tranny have multiple primary taps? There's an opportunity to pick the wrong number of windings.
Have you checked the secondaries to make sure that there isn't a short on a set. Check your voltages as bob said above.

I built my light bulb limiter with a spare line cord, a duplex outlet, and a box. I plug whatever lamp I have handy into one plug, the amp into the other. The duplex plug has had the tabs broken off and the plugs are wired in series. Great little tool, easy to make it go hide when I don't need it.

[bob p]

If you're popping slow-blow fuses then you have a serious problem. The first thing that I would do would be to build a simple light bulb current limiter like the one shown here:

http://www.geofex.com/article_folders/spo_test.htm

Using a low-wattage lamp like a 25W bulb will help to limit your current enough to provide you with the ability to perform voltage measurements that will be helpful diagnostically.

If you're not sure exactly where the current problem is coming from, you could start disconnecting nodes off of the B+ power supply to determine which node is feeding the problem.

[bob p]

It's normal to draw a small amount of current when there's no load on the secondaries. That amount would be the magnetization current of the transformer. It's a pretty small amount.

[52 Bill]

With the tubes pulled, there are only two things that can cause the PT to heat, a problem with the rectifier tube socket wiring or a problem with the 6 volt filament wiring.

Check the rectifier tube socket wiring and for any signs of carbon tracks on the insulator body.

Check all of the 6 volt filament wiring to the tube sockets and the tube sockets as well for carbon tracks. If you unhook the winding from the transformer, you can try measuring the resistance of the filament wiring to ground to see if you can find a short.

[Tom Phillips]

You can also cut to the chase and disconnect all the secondary leads. Then power up and if the transformer still gets hot then the problem is in the transformer itself. If you can measure the AC current drawn by the primary with all the secondaries disconnected I'd expect it to be less than 250ma for that transformer. If it is higher then there is something wrong inside the transformer.

Also - Does your Hammond transformer have a dual voltage primary? If so, is it configured correctly for your line voltage?

[Enzo]

Amen, a miswired dual primary could easily cause this.

[Tom Phillips]

Another big clue that has been mentioned is that this new transformer is exhibiting the same symptoms as the one it replaced. Based on that fact I'd check for shorts at the pilot light holder as suggested in the other thread.

[chuckb]

inside pics of 6g2


Here are some inside shots. One of the heaters is grounded to the chassis?

[bob p]

Fuse Blows

[chuckb]

The fuse don't blow right away, it may take 3o seconds and the transformer is getting hot. Could the b+ be causing this problem and not the power tranny?

[Enzo]

Do what Tom suggested several posts ago. Disconect all the secondary transformer wires - leave them in mid air. Now power the thing up with only the primary wired. Does it still get hot and blow fuses? If so, you have a bad transformer. If not, then start reconnecting wires. Start with the yellow ones. ANy change? Now the red ones. Any change? All that is left are the green heater wires.