[Milsurplus] AT-12 Photo - 814 vs 807

[Kenneth G. Gordon]

On 8 Mar 2017 at 15:52, Richard wrote:

> The 814 has a small 5-pin base, the same as an 807, so it's an easy 
> change.  However, the 814 is a beam-power tube, which is not so 
> sensitive to plate voltage, and will probably work fine down to 500 
> volts.  Overall efficiency will not be great when you're putting 32.5 
> Watts in each filament.

Well, in point of fact, the 807 is also a beam-power tube.

However, the 807 has a plate dissipation rating of 25 watts, while the 814's is 65 watts.

Big difference.

But in my opinion, the big problem is that the 814 is a "filament" type tube with no separate 
cathode, while the 807 has a cathode.

Now, since the 807's cathode is connected to pin 4, and the suppressor grid is internally 
connected to pin 4 in the 807, while the suppressor grid in the 814 is ALSO connected to pin 
4, substituting the 807 for the 814 may be fairly easily "do-able" but one would have to 
connect whatever is connected to the 814's "cathode" to pin 4 in order for things to work 
properly.

But, since I don't have even a remote clue what the AT-12's schematic looks like, that issue 
may already be taken care of....or not, as the case may be.

In any case, I cannot see how the 807 can be a direct sub for the 814...

Ken W7EKB

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