[Hallicrafters] Re: Replacing 6H6 with diodes.

[Kenneth G. Gordon]

On 14 Feb 2008 at 9:59, Rodney Bunt wrote:

> Not only high back resistance you need VERY low forward junction
> voltage. A tube diode conducts in the forward direction from a VERY
> low voltage. A diode if silicon needs approx 0.7v forward bias before
> it conducts, a Germanium (1N34) needs 0.3volt forward bias. Today you
> could use Shotkey diodes, but the 6H6 uses very little power and works
> very well. 

Yes.

> An old trick is to reduce the filament voltage, thereby
> reducing the "electron cloud" around the cathode (these -ve electrons
> tend to repel other electrons from leaving the cathode) reducing the
> filament voltage, reduces the "cloud" reducing the forward bias
> voltage necessary to conduct.
> 
> Rodney 
> VK2KTZ

Thanks for the tip, Rodney. And you're absolutely correct. I 
can't see any good reason to change a 6H6 for a pair of SS 
diodes. The SS diodes won't do as good a job, and there 
really isn't much of a savings. The 6H6 is very reliable.

When I changed the 6H6 in my Scott SLR-F back in the 
1960s, it REALLY didn't help. In fact, the change made it 
work worse. I took it out.

Thanks for the info.

Ken Gordon W7EKB