DIY Audio Projects Forum

300B SET Design Project
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Author:  Citation19 [ 31 Aug 2020, 18:21 ]
Post subject:  Re: 300B SET Design Project

Mouser delivered today....

Now have 2x275R 25w wirewounds in series in place of the 47R. Bolted and thermal pasted to the HV shield on the underside of the chassis. Only powered up for around 30m and I would say it got very WARM, maybe just this side of hot.
I am going to roll with it for a bit. If anything goes poof, I'll post the death toll.

Also changed Second power supply resistor from 27kR to 20kR 3watt metal oxide.

Voltages now : B+ 414 / 6SN7 supply B++ 293.4 / Plate (to ground) 403.5 / Cathode ( to ground ) 67.5 for 90ma .... I think this results in 30.24 watts plate dissipation for the 300b's ?

Will do listening tests this weekend... Yet I do not have any 300b or SET listening experience under my belt.

More pics to follow as I button things up.

** As a side note... Even though this amp is pretty much dead silent ( smallest amount of buzz if I stick my ear all the way into the speaker. We are talking say ear 1" away from the phase plug of 8" Tang Band full range 96db efficiency speaker) the amp induced a small hum into a powered sub that was plugged into the same outlet. Will switch power cords around and see what we get.

Take Care all.

Author:  Citation19 [ 01 Sep 2020, 18:43 ]
Post subject:  Re: 300B SET Design Project

Hello all ...

External image of the amp mounted in its case.

Scratch the previous messages mention of subwoofer hum being caused by this amp. The sub buzzes on it own with nothing else powered up.

Take care..

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