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In the Forum: Analog Playback
In the Thread: 7788 tube mic pre design
Post Subject: Re: 7788 - love the tube!Posted by hagtech on: 2/15/2006
Yeah, so the closeness of the grids results in a higher current gain.  So what?  What is the relationship between gain and sonics?  Are you saying that all high gm tubes sound better than low gm tubes?  And does that include 300B and 2A3?

One problem with these high gm tubes is microphonics.  The close grid spacing demands higher dimensional tolerance, stability, and stiffness.  Parameters drift a lot as the tube warms up and settles.  On the other hand, high gm tubes tend to be much better constructed. 

I am curious, Romy, do you run this tube as a pentode or triode?  I would guess pentode, given the very high gains you are achieving.

I once designed a modem to operate over an old submarine telephone cable.  It used vacuum tube repeaters every 20 miles.  They were pentodes.  And the requirements for linearity were really high.  They were getting 50dB out of one tube!  SNR was also very good.  Wish I remember what tube that was.


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