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Oddwatt Push Pull Tube Amplifier Projects
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Author:  Danny [ 11 Jun 2018, 13:03 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Forgot to mention that I used Russian FT-3 teflon caps, which complicated things due to their size.

Author:  gofar99 [ 11 Jun 2018, 15:20 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hi, Nice case. Makes my efforts with wood look like making orange crates. Anyhow, Some hiss is normal. I too have sensitive speakers (96dbw). A very slight amount of noise right at the speaker is common with tube amps. However, yours may be more than it ought to be. It may be from the driver tube. Not all are quiet and some actually quite noisy. There is another "trick" that may help. In some of my high gain phono preamp circuits I found the following can cut the noise by 2-3 db. It involves adding a capacitor from the heater circuit to signal ground. A 47uf seems to work best ...if it does anything. Sometimes nothing happens. Try both sides of the heater circuit one often is better than the other. This will only work if you are using DC heater power. I personally don't find it necessary as the slight noise is not audible at more than about 2cm from the tweeter. Let us know what you find.

Good listening
Bruce

Author:  Trackhappy [ 11 Jun 2018, 18:02 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Very nice!

Author:  Danny [ 12 Jun 2018, 10:40 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Bruce,

Thanks for suggesting to add a 47uf capacitor from the driver tube's heater circuit to signal ground in order to try to remove the hiss.
But to be sure, I have a question since the heater circuits are not grounded. Is this how it should be placed?

Thanks,

Author:  poty [ 12 Jun 2018, 10:47 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

The heater circuit is AC grounded - the 2.2u Poly which is right above the 47u you added.
I doubt the 47u will help to lower hissing, I too think it is a noisy driver tube.

Author:  gofar99 [ 12 Jun 2018, 14:02 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hi, On AC heaters I have not found the extra cap to be of any value. My experience with tubes has been that some are really noisy. Even new right out of the box.

Good listening
Bruce

Author:  Danny [ 12 Jun 2018, 14:42 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hi. I am using DC heaters. Look at the image above. My question is if the placement that I show is correct.

Thanks,

Author:  Trackhappy [ 12 Jun 2018, 17:46 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hi Guys,
Looking at the schematic shown above, there is a note that "the capacitor immediately after the LR8N should be the same size and type as the ones in the main amplifier". The schematic I have shows a 4.7uF on the output of the LR8, and a 1uF at the socket. Can somebody please advise which is correct? What type of capacitors should the 4.7 and 1 be? Also, the schematic I have shows a 1K from the 100uF capacitor feeding the 47uF filter capacitor. The diagram above shows a 33k. Which is correct?

Thanks,Glenn.

Author:  poty [ 13 Jun 2018, 02:46 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Danny wrote:
My question is if the placement that I show is correct.
Yes, the placement is right. Bruce mentioned that you should try both wires of heating power supply (you connect the capacitor to the "+" wire, you should try the "-" wire too and choose the connection with the best result).

Author:  poty [ 13 Jun 2018, 02:53 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Trackhappy, it depends on what schematic you are reffering to. Could you provide a link to the schematic you use?

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