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4S Universal Tube Preamp Project (12A*7)
http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=4628
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Author:  Suncalc [ 09 Feb 2018, 19:44 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

Reaper996 wrote:
Here is my latest iteration of the 4S using the 12BH7 tube, the chassis is Padauk and top plate hand-punched and sanded.
Looks awesome! Love that padauk chassis.

Author:  mwhouston [ 09 Feb 2018, 21:06 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

Good to know

Author:  Chris65 [ 09 Feb 2018, 21:36 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

mwhouston wrote:
Good to know

Good to know..........what???

Soundbrigade wrote:
If the question hasn't been asked yet (or if it has), I just wonder - what about parallelling the triodes in each glass bottle. I have a chassis that was used for another preamp (the Elektor from mid 80's) and all are in place - transformer, rectifier (at least) socket, psu details, connectors .... and TWO holes for preamp tubes. Was considering using 6N2P.

Or you could try the cathode follower version.
http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=5186&hilit=4s+cathode+follower

Author:  mwhouston [ 09 Feb 2018, 23:58 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

Chris65 wrote:
mwhouston wrote:
Good to know

Good to know..........what???

Soundbrigade wrote:
If the question hasn't been asked yet (or if it has), I just wonder - what about parallelling the triodes in each glass bottle. I have a chassis that was used for another preamp (the Elektor from mid 80's) and all are in place - transformer, rectifier (at least) socket, psu details, connectors .... and TWO holes for preamp tubes. Was considering using 6N2P.

Or you could try the cathode follower version.
http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=5186&hilit=4s+cathode+follower


Parralel tubes. Good to know

Author:  Soundbrigade [ 10 Feb 2018, 02:39 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

Chris65 wrote:


Will check that one up. The good thing with cathode follers are the higher SMACK!, but I could achieve that with parallelled tubes or use a 12BH7A (Russian 6N6P).

Author:  oloppolo [ 11 Feb 2018, 05:06 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

Hi, I'm a beginner. can I power the anode with 110 volts DC?

Author:  Geek [ 11 Feb 2018, 07:53 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

oloppolo wrote:
Hi, I'm a beginner. can I power the anode with 110 volts DC?


If you mean rectifying the line voltage, this is EXTREMELY dangerous and is not to be done :hot:

Author:  Suncalc [ 11 Feb 2018, 11:42 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

oloppolo wrote:
can I power the anode with 110 volts DC?
As Geek said, if you're talking about direct rectification of the AC mains without a power transformer, this is a very dangerous approach, and any such design is very tricky to get right. I strongly recommend against this approach. Now, if you have a transformer power supply that just returns lower voltage, this won't work with the 4S because the preamp really requires about 220 to 230 Vdc to work properly.

Since you say that you're a beginner I will offer this one piece of advice. If you want to work with vacuum tubes, the power transformer is kind of "the price of admission". There are some specialized projects that work with B+ voltages less than 100Vdc, but they are the exception, not the rule. And if you want to build anything to drive a speaker with more than a watt or two, you'll need to get that power transformer. This doesn't necessarily mean it has to be new or expensive, but you really do need one to move forward.

Author:  mwhouston [ 11 Feb 2018, 12:16 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

With the use of an appropriate tranny, if a low voltage one, a voltage doubler cct. should work here.

Author:  Soundbrigade [ 11 Feb 2018, 12:43 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

oloppolo wrote:
Hi, I'm a beginner. can I power the anode with 110 volts DC?


I haven'┬Ęt examined the design that thorougly so I can give an answer directly, but if you're looking for tubes that may work on lower voltages, look at ECC88/6DJ8 or ECC85/6AQ8/6N3P (Russian). I think the latter is actually made to run on lower voltages.It's not the most linear tube in the wworld, but it is often seen in preamps running on 30+/-10 Volts.

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