It's funny you should ask that, because just a few days ago, prompted by a discussion on another forum about hum levels, I made a point of rechecking the hum. Even with my ear up against the speaker (Lowther DX4, about 98dB sensitivity), hum is completely inaudible. I mean literally; no hint of any hum at all. Using my DVM it registered about 0.2mV AC on the speaker terminals, but that is really lost in the noise.
I was quite struck by the fact that someone on the other forum, speaking of a DHT SET amplifier, seemed to regard 10mV AC as perfectly acceptable. I tried an experiment with a signal generator putting 10mV AC 120Hz into a speaker, and the hum was loud enough that I wouldn't want to share a room with it!
Chris
Chris
Appreciate if you can post the audio spectrum of your amp for future reference, what tube brand you use and do they have different harmonics? Here is a free spectrum analyzer that you can pick up the tone from speaker using microphone. Attached is spectrum of my amp (not Tim's)
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The PSU is meant to supply both channels but you could of course use two with smaller transformers. It's unneccessary extra work though. There are a good few months of work in this amp as it is. I found it one hell of an undertaking and I have been building amps for more than 50 years.
Thank you for your advice, because I only see one transformer for the filament of a pair of power tube, so I need to add one more filament for that in order to make it work. Thanks again.[emoji1] [emoji1] [emoji1]
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You need to take into account the different center-tap arrangements for each set of tubes. It is to do with Cathode / Filament voltage limitations. The best thing to do is use 3 transformers in total with different windings and just feed both channels by connecting them in the way outlined in the circuit. So, 4 completely separate windings, as indicated in the schematic for feeding the filaments of both channels together. The tube numbers for the filaments are written on the PSU schematic. Everything on the schematics of this amp needs to be followed exactly or otherwise you will end up in big trouble. I hope I have made sense.
i design and build all my traffos for my projects....
i am not a commercial winder btw, i just make them for my needs...
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thanks, the lessons learned in the audio show will be put to use if subsequent builds...