[ARC5] Solid State 6AL5

[Kenneth G. Gordon]

On 5 Feb 2018 at 12:17, Bill Cromwell wrote:

> Hi Wayne,
> 
> I have not tried that approach for signal diodes. I wonder if there are 
> substantial differences between tube and solid state circuits for agc 
> detectors, AM detectors, etc. If I remember, when I get time I will 
> look. One obvious (to me) difference is the reverse voltage (avalanche) 
> and reverse leakage in the solid state devices. That could make a big 
> difference in the required circuits.

I have tried using diodes in place of both the 6AL5 and the 6H6. In neither case did that 
work very well, and as you say, Bill, it has to do with the reverse voltage. There is simply too 
much leakage "backwards" in the diodes for them to work well in those high-impedance 
circuits.

> I have mounted rectifier diodes on octal plugs and directly plugged them 
> into sockets in place of 5U4*, 5Y3*, etc power rectifier tubes. 

Yes, but that is a different story. 

> Discounting the different forward voltage drop in the vacuum devices the 
> solid state devices perform as expected. If we pay attention to that 
> reverse leakage and breakdown factor it *should* work for signal diodes.

It works in lower-impedance circuits, but it does NOT work well in high-impedance circuits, 
especially in those AGC circuits which were originally designed for tubes.

I had an almost new RCH/SLR-F receiver once which used a 6H6 as the detector/AGC, and 
tried using a pair of 1N34s in a plug-in octal socket.Although the diodes withstood the 
voltages in the circuit quite well, the output was not good.

This was at least 50 years ago, and I don't remember all the details, but I do remember 
putting the 6H6 back in as I was not satisfied with the results of using the SS circuit.

However, this is only one data-point...

Ken W7EKB

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