DIY Audio Projects Forum

tube amp information
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Author:  sergiobattistini [ 29 May 2019, 10:22 ]
Post subject:  tube amp information

I'm starting with a new hobby. to Mount my first tube amp, and I have a doubt that I would like some information.
What diference to use 6,3Vac for filament or 6VDC. This affect the sound quality?

Author:  ILoveHiFi [ 30 May 2019, 05:04 ]
Post subject:  Re: tube amp information

Not much diffrence, the only diffrence is how you bias up the valve heaters and ground them to reduce noise.

Author:  sergiobattistini [ 30 May 2019, 15:33 ]
Post subject:  Re: tube amp information

Eu entendi. Obrigado pela sua informação

Author:  Gab [ 31 May 2019, 06:56 ]
Post subject:  Re: tube amp information

It can make a huge difference, but not in every cicuits or stages. It is mostly used in preamps and phono stages. I don’t know the exact reason, but Small signals in input stages are more sensitive to the AC currents. I guess that the AC current can couple into the cathode from the heater. Preamplifiers take small signals and amplifies them a lot, so small noises presented to the input get amplified too and become more audible than the same noise presented to the output stage of a power amplifier, for example. Especially phono stages, and even more if it is for an MC cartridge.

As in everything else, there are exceptions. DC heaters are also used for directly heated output valves like the 300B or 2A3.

There are many members here that are more knowledgeable than me and they might have a better explanation as to where and how to use DC heaters, but I wanted to contribute !

Do not hesitate if you have more questions. Also, have a look at the technical articles and links in the project section of this website. You’ll need to read a lot to complete your project, as I had to do when I first started

Author:  ILoveHiFi [ 01 Jun 2019, 01:45 ]
Post subject:  Re: tube amp information

I have zero exprience with direct heated valves, not going to go in that but there you wanna use dc since the cathode is connected to the heaters

For indriect heater AC is king for best sound, however DC is better overall because the heater voltage can be locked on fixed and heater voltage changing only 0.1V will have large impact on sound quality and life span.

However AC has lowest noise because avrage voltage = 0. Then you use capacitors on the cathode and connect them to ground of the HV supply, this means the heaters are grounded in AC(audiable frequency) any noise will be directly shorted to ground via capacitor, thus zero heater leakage or very little is possible.

DC there will always be some cathode to heater voltage potnetial diffrence causing white noise.

The diffrence between the two is too little so you really want to do what ever is easiest and cheapest to heat them up.

Capacitance to ground of minimum 100uF is recomended. Any more than 1000uF is over kill and negltible perfomance gains.
The capacitor from heater to HV ground means the heater is connected by a wire to ground meaning no noise can appear on it

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