Way too high bias voltage...blown transformers?!... I think I may have screwed the pooch...

[whopperplate]

Thanks for your help everyone

So I am building up a new 50 watt super lead amp with a PPIMV, I was troubleshooting oscillation in the phase inverter and chopsticking wires and I inadvertently discovered I hadn’t soldered the bias voltage wire to the output tube grid wires, and I subsequently knocked it loose off the post blowing the HT fuse in the process

I of course soldered the connection, but seemingly too little to late

I am afraid I may have really messed things up as now the bias voltage is reading insanely high negative volts at -287 and 800+ volts in the ht circuit

I removed all of the tubes and checked the transformer side of the rectifier and I am getting nothing, and after the rectifier reads too high to even measure

The bias is reading over 700+ volts before the diode and -287 after

Did I possibly blow my power transformer? I am really kicking myself for my negligence on this one

My volt meter may have taken a hit in the process of measuring these things, as it seems a resistor may have burnt out and it smells , so I am going to grab another tomorrow and double check the amp again , but at this point that’s my only variable

Thanks for any help, I always come crying on the forum for something I screwed up, appreciate you all immensely

[glpg80]

First off, I’m glad you are safe during this test. Loose wires and high B+ are a dangerous combination regardless of what it was.

Let’s take a step back first. Definitely get another voltmeter. Sounds like that one took a hit in the process and cannot be trusted.

Second, what are the voltage ratings of the capacitors you’re using? My first concern is that they have been over voltaged even in series if you’re reading high B+. For safety sake I would be removing them to check their capacitance value, ESR, and any physical changes to make sure they are still safe to use assuming of course your voltmeter is valid.

A transformer that’s suspected to be shorted in a secondary is a dangerous thing because windings that have the enamel protection removed can then not only short to another winding next to it if the insulation is compromised, but also to the grounded core in a worst case scenario.

There is a way to back out the winding ratios of each tap of the transformer, but you’ll want it out of circuit to do so.

Let’s start here and determine where to go accordingly.

[whopperplate]

Well thank goodness, went and fogged over the cash for a 1000v voltmeter, fired her up and everything seems kosher voltage wise in the amp

Those high voltage readings were likely the faulty meter. I found the burnt out resistor by smell and eventually sight on the circuit board.

It was deceiving as the other voltage settings were reading fine, but I realized after a simple 9 volt battery measurement on the high voltage setting that was reading twice the volts it should it was definitely screwy

Going to take step by step and will update the post for educational purposes as I go.

At this point let this serve as a lesson to double , triple, and quadruple check all connections, especially in the high voltage line, and always have a backup meter.

Thank you for the care and the quick reply, I truly owe everything to this forum for getting me into building amps over a decade ago, and let this go to show you are never too experienced to make mistakes