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In the Forum: Analog Playback
In the Thread: 7788 tube mic pre design
Post Subject: My experience with 7788 is very different.Posted by Romy the Cat on: 1/13/2008
Jim, I do not know what to say: I never experienced any nose problem with it. A few years ago I built 2 mono phonocorrectors with 7788 at input as a pentode both of them were just nice and quiet and did not give me any problems in noise department. The phonocorrectors are still in service. Over the year I was trying a few different 7788 brands: Philips, Raytheon, Telefunken, Siemens, few otheres and none of them were noisy. I drive the 7788 with DC of course, typical for me SS rectifier with LCRC. The last cap is 80.000uF. The tube has 150V on plate and slightly less on screen, both drivers from the same 400V power supply, SS bridge – LCRC with an enormous last cap. The tube has one ferrite bid on grid, 50R grid stopper and uses Pearl’ shock-mount tube socket. I use as grounded tube cooler around the tube. Pretty much it is all that I did. I have no microphonic at all and noise at 150MHz (~200MHz in realty) scope looks very noise and random (I have no faster scope). I do pick microphonics if I hit the tube but it immediately dies. I never ever seen my 7788 get aroused itself in the way how 417A or 435A did. What is also amassing that all my 7788 were practically identical in gain, plate impedance and etc… Sorry, I am not useful in it as I never develop any experience to fight with 7788 as I never had any problems with it.
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