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4S Tube Preamp with 12AU7 Cathode-Follower Output Stage
https://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=5186
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Author:  ILoveHiFi [ 02 Jan 2020, 19:00 ]
Post subject:  Re: 4S Tube Preamp with 12AU7 Cathode-Follower Output Stage

You add the series resistor of 2-5W at 0.XX ohms to reduce voltage

Author:  lowhifi [ 03 Jan 2020, 18:34 ]
Post subject:  Re: 4S Tube Preamp with 12AU7 Cathode-Follower Output Stage

I put this little network minus the resistors on the heater supply and it reduce the hum (and the voltage) to an acceptable level. A bridge will drop too much voltage i think. Regards.

Author:  mwhouston [ 03 Jan 2020, 19:31 ]
Post subject:  Re: 4S Tube Preamp with 12AU7 Cathode-Follower Output Stage

lowhifi wrote:
I put this little network minus the resistors on the heater supply and it reduce the hum (and the voltage) to an acceptable level. A bridge will drop too much voltage i think. Regards.


You probably don’t need the 100ohm resistors to ground but they can’t hurt also put a 0.1uf poly across the 10,000uf cap. Big caps are noisy and so are diodes. The poly will help suppress that noise.

Author:  lowhifi [ 03 Jan 2020, 20:30 ]
Post subject:  Re: 4S Tube Preamp with 12AU7 Cathode-Follower Output Stage

Thanks, presently only the triodes are DC regulated, should i run the rectifier on DC also? I want to put more capacitance on the high voltage. tizman made an simulation on PSUD but he add 147uf? or 47uf somewhere but i don't know where. Regards.

Author:  mwhouston [ 03 Jan 2020, 20:57 ]
Post subject:  Re: 4S Tube Preamp with 12AU7 Cathode-Follower Output Stage

lowhifi wrote:
Thanks, presently only the triodes are DC regulated, should i run the rectifier on DC also? I want to put more capacitance on the high voltage. tizman made an simulation on PSUD but he add 147uf? or 47uf somewhere but i don't know where. Regards.


Usually the first cap after a rec tube is no more than 30uf. Some tougher tubes may handle 47uf. After the choke, which should be next, 100uf is ok.

Author:  gofar99 [ 03 Jan 2020, 21:35 ]
Post subject:  Re: 4S Tube Preamp with 12AU7 Cathode-Follower Output Stage

Hi Mark, OT for sure...but are you folks ok in Aussi land? It looks horrible from here.

Good listening
Bruce

Author:  mwhouston [ 03 Jan 2020, 22:50 ]
Post subject:  Re: 4S Tube Preamp with 12AU7 Cathode-Follower Output Stage

Bruce, off thread but yes Australia burns with no end in sight. The longest burning fires (months now) are in another state a long way from us but Victoria has its on disastrous fires ranging. Yesterday we had a major flare up only a few miles from us and heavy smoke filled our roads and even in our backyard.

The amount of burnt out area is larger than Belgium and grows every minute. My wife and friends have collected tons of food and clothing for the victims now in shelters. This will be delivered in the new few days. Fortunately local big supermarkets and even smaller stores have given generally.

The fires are so big they cannot be stopped. Only heavy rain would make any difference and that’s a way off yet. Friends who have moved to smaller country towns only recently have been evacuated. Thousands of live stock gone and hundreds of homes burnt to ash. A long way to go yet.

Author:  lowhifi [ 05 Jan 2020, 08:12 ]
Post subject:  Re: 4S Tube Preamp with 12AU7 Cathode-Follower Output Stage

I have a friend who is actually in visit in Australia in the Melbourne area. 10 years ago we had a relatively large forest hundred of kilometers away and i was impressed by the smell and the smoke from where i live near Montreal Quebec. That's a shame i work at the airplane factory where was build the CL-415 water bomber aircraft, despite it's the most succesful aircraft of this type the production was stopped due to a lack of orders. Can i use this power supply with the preamp we discussed here? Regards.

Author:  vixr [ 10 Jan 2020, 08:01 ]
Post subject:  Re: 4S Tube Preamp with 12AU7 Cathode-Follower Output Stage

gosh...this may be the most amazing thread I've ever seen.

Author:  lowhifi [ 11 Jan 2020, 23:40 ]
Post subject:  Re: 4S Tube Preamp with 12AU7 Cathode-Follower Output Stage

We are Devo.

I remplace the 33uf capacitor before the choke for a 45uf and add the DC heater supply with a .1uf cap and now the preamp is very silent. The resistors where already installed at the end of the tube supply. An other successful build. Regards.

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