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Old 15th June 2006, 02:31 AM   #1
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Default Some HMMM on my SRPP

Dear DIYAudio Friends,

Tomorrow I was finished my Pr amplifier, with the simplest topology of SRPP. The pre-amplifiers tubes
is russian 12au7.

The power supply is two 12+12 2A back-to-back transformers. The 220vAC is Full Bridged and Filtered with a 330uf capacitor.

The power supply of the Filaments is a 12+12vAC retified and Filtered with 3300uf, and regulated with a 7812.

I haven't noise on the output, the pre-amplifier is opering okay, but I have some HMMMMMMMMMMM.

Thanks,
Felipe Navarro
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Old 15th June 2006, 05:54 AM   #2
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Watchout for h-k breakdown on that top tube.

Use of two tubes for stereo, one top tube, the other the bottom. Float the top tube and bypass it to ground with a cap for noise (2.2 to 4.7uF OK). If you lift the bottom tube's heater 30V or so, AC or DC makes little difference unless the heater insulation is leaky. Since the top tube is a CF, I found that lifting its heater above cathode voltage doesn't make a difference.
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Old 15th June 2006, 01:11 PM   #3
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Hey Geek,

I stay using one tube per channel.

Why I need to float the tube's heater to 30v? How I do this? A friend asked me to make a B+ refference and put this refference in the GROUND of the Tube Filament.

Is this correct?

Thanks in advance.
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Old 15th June 2006, 04:32 PM   #4
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You really do need to change your arrangement so that one valve is used for the lower triodes and the other valve for the upper triodes. It's because you have approximately 150V on the cathode of your upper triode, but at the moment your heaters are connected to 0V. That means that the upper triode has 150V across its heater cathode insulation and that is exceeding its rating. If you use one valve for the upper triodes, you can use a separate heater winding to heat it and connect that winding to +150V. Even better, connect it to +180V to switch off the unwanted diode between the cathode and the heater. Keep the lower triodes fed from their existing heater connected to 0V.
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Old 15th June 2006, 05:04 PM   #5
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Hi Friends,

I will modifier mine amplifier to this schematic how I put in this post.

This will work fine? Without HMMMs?

Thanks in advance,
Felipe Navarro
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Old 15th June 2006, 05:43 PM   #6
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I have puted a referece of the B+ on the Filament GND. How the schematic I has posted on my last post.

The HMMM persists...



Oh My God.

What I Do?
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Old 15th June 2006, 05:52 PM   #7
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Try a 47uF 250V capacitor across R6.

Of course, the hum could be something else entirely. Post a photograph of the underneath...
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Old 15th June 2006, 06:00 PM   #8
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A photograph.

I will put a 47uf 200v on the R6.

And call the results in here.

Thanks
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Old 15th June 2006, 06:16 PM   #9
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We need a slighter looser shot that shows more of where all those wires go...
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Old 15th June 2006, 06:27 PM   #10
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Friend,

In this photo you can see best than other a best vision of all circuit.

I have putted a 47uf 200v on the R6 and the HMMM persists.

This is a old photo without the Referece of the B+ on the Filament Supply.

Thanks,
Felipe navarro

PS: Congratulations for the U.K. soccer team. The team stay playing well, and GOD SAVE THE QUEEN
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