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4S Universal tube preamp
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Author:  mwhouston [ 18 Feb 2016, 18:46 ]
Post subject:  Re: 4S Universal tube preamp

PCR wrote:
I have to 24V AC @ 1A tranni. Going to use one of them as 24 V AC Wall Wart and one of them as PT1. Can it be a problem above 150 mA of PT1?


I wouldn't go below 150mA but yes bigger is OK.

Author:  PCR [ 31 May 2016, 00:36 ]
Post subject:  Re: 4S Universal tube preamp

My build is proceeding. I have two questions if you don't mind Mark. I am at very beginning and this is my first. But learning.

1) In the schematic of preamplifier section 10k res goes to grid, 1k2 goes to cathode and 100k goes to plate right? But where the heater is connected to? And also where the heater center-tap (pin 9) connects to?
2) In the schematics of preamplifier section do all the signal grounds unite? And if so where is the uniting point? And does signal ground unites with chassis ground? I assume chassis grounds are only present in the power supply section and they all unite and connect to chassis, but what about signal ground points?

Thank you in advance.

Image

Author:  mwhouston [ 31 May 2016, 04:32 ]
Post subject:  Re: 4S Universal tube preamp

The heater pins are 4 and 5. Pin 9 is the centre tap for the heaters. At pins 4 and 5 apply 12V but if you short 4 and 5 together then apply 6V at 9 and 4 and 5 shorted.

The negative of the input and output signal go to PS ground. Not sure about some of your questions. Bring all grounds to one point, signal and PS.

Author:  PCR [ 31 May 2016, 13:34 ]
Post subject:  Re: 4S Universal tube preamp

Ok i understand clearly and apllied. In the power supply schematic, after PT1 there are four 0.01 uF caps connected to every pin of bridge rectifier right?

Author:  mwhouston [ 31 May 2016, 17:37 ]
Post subject:  Re: 4S Universal tube preamp

Rectifier ridges are generally more noisy then ultra-fast soft recovery diodes. To reduce noise in the bridge 0.01uf 630V poly caps are placed across each pole on the bridge. This means that each diode part in the bridge has a cap across it. It is the same with electrolytic caps. They should have 0.1uf high voltage polies across them.

Author:  gonzalo guerrero [ 31 Oct 2016, 07:25 ]
Post subject:  Re: 4S Universal tube preamp

Suncalc wrote:
Well, I have another update to the tube list for the 4S Universal. This is a special case because you can only use this tube if your heater supply is capable of putting out a full 600mA into the filament. If so, the 12BH7 tube will expand your tube rolling capabilities. This tube is halfway between the 12AU7 and the 12AV7 from a gain perspective and is very low distortion. I don't have any on hand but if someone tries it, be sure to let us know how it sounds.

with the 12bh7 i got some hum...i snubbed all the filter section with 0.1/630v mallory and the hum just gone...sounds like12au7,but more open and better highs.

Author:  mwhouston [ 31 Oct 2016, 16:56 ]
Post subject:  Re: 4S Universal tube preamp

gonzalo guerrero wrote:
with the 12bh7 i got some hum...i snubbed all the filter section with 0.1/630v mallory and the hum just gone...sounds like12au7,but more open and better highs.


This addition does expand the 4SU's tube-roll roll. I wonder if there are any more out there but even with the original list, Matt kindly put together, there are plenty of choices.

Author:  gonzalo guerrero [ 01 Nov 2016, 01:01 ]
Post subject:  Re: 4S Universal tube preamp

mwhouston wrote:
gonzalo guerrero wrote:
with the 12bh7 i got some hum...i snubbed all the filter section with 0.1/630v mallory and the hum just gone...sounds like12au7,but more open and better highs.


This addition does expand the 4SU's tube-roll roll. I wonder if there are any more out there but even with the original list, Matt kindly put together, there are plenty of choices.

marvelous!!!

Author:  famousmockingbird [ 02 Nov 2016, 11:35 ]
Post subject:  Re: 4S Universal tube preamp

I still don't understand this preamp design?

You can't just plug a 12AU7 into a 12AX7 circuit they are completely different, this is ridiculous. The only similarity is pinout and heater characteristics, that's it. The circuit can only be optimal for one tube so why plug anything else into it?

I see uneducated guitar players doing the same thing, substituting a 12AU7 or a 12AT7 into a 12AX7 circuit. Dumb.

Author:  mwhouston [ 02 Nov 2016, 17:16 ]
Post subject:  Re: 4S Universal tube preamp

famousmockingbird wrote:
I still don't understand this preamp design?

You can't just plug a 12AU7 into a 12AX7 circuit they are completely different, this is ridiculous. The only similarity is pinout and heater characteristics, that's it. The circuit can only be optimal for one tube so why plug anything else into it?

I see uneducated guitar players doing the same thing, substituting a 12AU7 or a 12AT7 into a 12AX7 circuit. Dumb.

You can roll many tubes because the design is NOT optimised for any one tube. It's a universal design. But the design may slightly favour one tube over another.

The original 4S designs are optimised for a specific tube not the 4SU.

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