I'm working on a 6g2 Princeton w/ trem removed and the AC voltage on a brand new PT is testing way high. I am reading 366 VAC on the high voltage winding of the power transformer (according to mercury magnetics this should be 290 VAC). The 5V and 6.3V secondaries are testing within a reasonable range (+/- .3 volts). Hooked up to a current limiter and tubes installed the amp has VERY high B+ voltage. The B+ values I am reading are written in red on the layout diagram below:
Here are pictures of the chassis for reference:
New Transformer - High Voltage AC Testing Way High - Princeton 6G2 Build
Moderators: pompeiisneaks, Colossal
New Transformer - High Voltage AC Testing Way High - Princeton 6G2 Build
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Last edited by lightbath on Fri Oct 23, 2020 11:38 am, edited 14 times in total.
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Stevem
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Re: B+ Voltages Testing High, Signal Dropout When Volume Turned Up- Princeton 6G2 Build
Your V+ voltage is way above what a 5Y3 rectifier can take and it's likely arcing, also it may be too high for the voltage rating on the 3 section filter can as it would need to be rated at 500 volts, not 450, so that could be arcing over also.
It sounds like your power transformer is bad , or it's the wrong one and is wound wrong!
Also the bias filter is likely getting hit in more then 50 volts and that could be going south now too and that would take its toll on the output tubes!
It sounds like your power transformer is bad , or it's the wrong one and is wound wrong!
Also the bias filter is likely getting hit in more then 50 volts and that could be going south now too and that would take its toll on the output tubes!
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Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: B+ Voltages Testing High, Signal Dropout When Volume Turned Up- Princeton 6G2 Build
The filter caps ARE rated at 500 volts AND there are two 25uF/50 volt capacitors in parallel in the bias section so I think I am covered there.
The transformer is brand new. Is it possible the high voltage winding is wrong from the manufacturer? I just installed it today. What else would cause the 6.3V and 5V filament to test fine while the high voltage AC is testing high?
VOLTAGE READINGS ON POWER TRANSFORMER:
6.7VAC on the green heater winding
5.36VAC on the rectifier heater winding
366VAC from the red high voltage winding to ground
Here is a diagram of the power transformer used. A Mercury Magnetics FBPP. I spoke with Patrick at MM and he suggested this as a replacement for an original 6G2 transformer.
The transformer is brand new. Is it possible the high voltage winding is wrong from the manufacturer? I just installed it today. What else would cause the 6.3V and 5V filament to test fine while the high voltage AC is testing high?
VOLTAGE READINGS ON POWER TRANSFORMER:
6.7VAC on the green heater winding
5.36VAC on the rectifier heater winding
366VAC from the red high voltage winding to ground
Here is a diagram of the power transformer used. A Mercury Magnetics FBPP. I spoke with Patrick at MM and he suggested this as a replacement for an original 6G2 transformer.
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Re: New Transformer - High Voltage AC Testing Way High - Princeton 6G2 Build
I have a NOS Phillips 5Y3GT installed now and another GE 5Y3 for backup. The issue is the high voltage winding is already putting out 76 volts AC more than is listed by the manufacturer.
Last edited by lightbath on Fri Oct 23, 2020 3:00 pm, edited 1 time in total.
Re: New Transformer - High Voltage AC Testing Way High - Princeton 6G2 Build
Hello —
Transformer is definitely wrong if you get HT winding voltages that high while well loaded. Send it back.
Best .. Ian
Transformer is definitely wrong if you get HT winding voltages that high while well loaded. Send it back.
Best .. Ian
Re: New Transformer - High Voltage AC Testing Way High - Princeton 6G2 Build
Can we step back for a minute? My first reaction was to say you should call or email MM. I expect they will stand behind their product.
Before you do that, how did you measure 366VAC? I suggest pulling the 5Y3 and putting probes on pins 4 and 6. The PT is 290-0-290. You should see 580VAC +/- 5% depending on line voltage. (I've seen line voltage in my house as high as 129VAC. Yes, just stick the probes in the wall socket and see what it is and adjust expectations accordingly.)
I don't know if MM rates it 290-0-290 with a load or without a load. You might allow another 5% variance if that is for a loaded PT.
If you get a reasonable reading on the unloaded HT secondary, then there is likely nothing wrong with your PT. I'd look elsewhere for the problem. If you see more than about 610V, I'd contact MM.
With the 5Y3 in the socket, I'd expect about 320VDC +/- 5% to 10% depending on loading and line voltage on the primary. If your primary line voltage is up around 130VAC then 366VDC is high, but not all that far off from expected output.
Do that simple test. Tell us what you find on the unloaded pins 4 and 6.
Before you do that, how did you measure 366VAC? I suggest pulling the 5Y3 and putting probes on pins 4 and 6. The PT is 290-0-290. You should see 580VAC +/- 5% depending on line voltage. (I've seen line voltage in my house as high as 129VAC. Yes, just stick the probes in the wall socket and see what it is and adjust expectations accordingly.)
I don't know if MM rates it 290-0-290 with a load or without a load. You might allow another 5% variance if that is for a loaded PT.
If you get a reasonable reading on the unloaded HT secondary, then there is likely nothing wrong with your PT. I'd look elsewhere for the problem. If you see more than about 610V, I'd contact MM.
With the 5Y3 in the socket, I'd expect about 320VDC +/- 5% to 10% depending on loading and line voltage on the primary. If your primary line voltage is up around 130VAC then 366VDC is high, but not all that far off from expected output.
Do that simple test. Tell us what you find on the unloaded pins 4 and 6.
Re: New Transformer - High Voltage AC Testing Way High - Princeton 6G2 Build
Testing the end of each high voltage secondary (red to red, pin 4 and 6) I get 733 VAC. Testing the high voltage center tap to red secondary I get 366 VAC.
The last thing I want to do is contact MM about their product but I can only believe what the meter is telling me. I have tested with multiple meters. I know fluctuation in wall voltage is a factor but I just don't see it being responsible for a 150 V spike in B+ at the first filter cap (the layout diagram in the first post has all the B+ voltages).
Pin 8 tests at 466VDC. Unloaded the voltage is even higher. I was getting up to around 500 V with rectifier only. (315 V on the schematic, I have seen people report up to 380).
I will pull the Recitifer and take a reading. I will get back to you in a moment.
The last thing I want to do is contact MM about their product but I can only believe what the meter is telling me. I have tested with multiple meters. I know fluctuation in wall voltage is a factor but I just don't see it being responsible for a 150 V spike in B+ at the first filter cap (the layout diagram in the first post has all the B+ voltages).
Pin 8 tests at 466VDC. Unloaded the voltage is even higher. I was getting up to around 500 V with rectifier only. (315 V on the schematic, I have seen people report up to 380).
I will pull the Recitifer and take a reading. I will get back to you in a moment.
Last edited by lightbath on Fri Oct 23, 2020 10:02 pm, edited 2 times in total.
Re: B+ Voltages Testing High, Signal Dropout When Volume Turned Up- Princeton 6G2 Build
It's time to speak with Patrick again.
And those two 50V caps in parallel still only have a voltage rating of 50V. Gotta put them in series to increase the voltage rating.
Thanks for pointing that out. I think you are right but I am still reluctant to contact them as a fairly novice builder.
I just don't see any other explanation. The rectifier is pulled and the AC high voltage secondary is still testing high. The only variables appear to be the wall voltage and the transformer.
I emailed MM and he is out of the office until Tuesday. I will post an update when he replies.
I just don't see any other explanation. The rectifier is pulled and the AC high voltage secondary is still testing high. The only variables appear to be the wall voltage and the transformer.
I emailed MM and he is out of the office until Tuesday. I will post an update when he replies.
Last edited by lightbath on Fri Oct 23, 2020 3:58 pm, edited 2 times in total.
Re: New Transformer - High Voltage AC Testing Way High - Princeton 6G2 Build
Well you could wait until every forum member chimes in and tells you the same thing. But by then Patrick may tell you, sorry buddy. Shoulda called sooner. 
Re: New Transformer - High Voltage AC Testing Way High - Princeton 6G2 Build
I would pull the rectifier tube and measure the AC on the red AC secondary leads.
Re: New Transformer - High Voltage AC Testing Way High - Princeton 6G2 Build
Yup. According to OP (see above) done and read at 766VAC, for 383VAC on each. Way way off spec. Unless the meter is wildly miscalibrated there is no way to make close to correct 6G2 around that.
Best .. Ian
Re: New Transformer - High Voltage AC Testing Way High - Princeton 6G2 Build
Yeah, sounds like it's another transformer in Mercury's Princeton line, 360-0-360. Bummer!
https://www.mercurymagnetics.com/produc ... ransformer
Re: New Transformer - High Voltage AC Testing Way High - Princeton 6G2 Build
That's what I was thinking. I ordered a few transformers including a 6G3 PT and I can only assume they somehow mixed the order up? Hopefully everything works out.
Note: above I stated 766 and 366 VDC as the AC voltages. I mistakenly wrote 766 instead of 733 VAC. Still way high but I wanted to correct that.
Note: above I stated 766 and 366 VDC as the AC voltages. I mistakenly wrote 766 instead of 733 VAC. Still way high but I wanted to correct that.
Re: New Transformer - High Voltage AC Testing Way High - Princeton 6G2 Build
I'm sure they will make it right. What does the label on the transformer say? Hey, so in the meantime, what are the mods for your circuit? The switches and extra knob? Looks cool.