[ARC5] Glass or Metal Tubes Preferred for Receivers

[Richard Knoppow]

     OK now it makes sense. BTW, I have not seen a 5Z4 for ages. 
Also, FWIW, the old Super Pro series were excellent receivers. 
The only mods I would suggest are the installation of a VR-150 
for the oscillator B+ and a TC cap on the oscillator tuning cap. 
Hammarlund added the TC cap in the SP-400 series. The VR tube can 
go under the chassis with the plate resistor of the oscillator 
changed from 12K to about 8K. Not perfect but keeps the 
oscillator from pulling when the AVC or RF gain changes.

On 2/6/2018 2:37 PM, Rich Post wrote:
> I ran into the "hot" tube issue when looking over a newly 
> acquired Hallicrafters S-76.I noticed a tube substitution. The 
> 5Y3 rectifier had been replaced by a 5Z4, a metal tube. That was 
> a reasonable substitution voltage and current-wise,.. but wait. A 
> metal tube connects pin 1 to its metal shell. A quick check 
> showed that Hallicrafters had used pin 1 of the rectifier socket 
> as a B+ tie point. Therefore the tube shell would be live with 
> B+, a "gotcha" just waiting for the unwary. I quickly located a 
> proper glass 5Y3GT.
> 
> Rich KB8TAD

-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL