35Z5-GT Tube Questions

[Wil_Bloodworth]

Hello All!

This is my first post so I apologize in advance for the newbie level questions!  I recently decided to start restoring antique radios and my first project is a 1946 Mason 45-4.  I was unable to find a schematic but I did find the schematic for the Mason 45-1 which has been "some" help.

My first question is about the 35Z5-GT tube.  According to its data sheet, pin 1 is "No Connection" which I assume to mean it is not used... even though it physically exists.  Is there an actual purpose of pin one coming from the tube itself?

The second and less trivial question is, shouldn't pins 2 and 7 have continuity if the tube is good?

I can clearly see that pin 1's jumper has wires soldered to it but I am not sure the original assembler was simply using this terminal to join other things together instead of intending the actual usage of the tube pin.



Thanks in advance!

- Wil

[Emo]

Hi Will, Yes, between pins 2 and 7 should be continuity. It almost looks as if the specs mentioned in your picture contain errors and/or if these specs are depending on the brand.  In the data it says between pin 3 and 4 - 3 and 6 which cannot be OK.
Are the markings on the tube still visible and is it a general electric build tube?

Eric

PS pin one is indeed only a mechanical stand. Often used in tube designs

[TimFox]

Tube data sheets usually distinguish "no connection" (as for the 35Z5GT) and "internal connection-do not use" for button-base tubes, where there is an internal connection holding up something inside the tube, and therefore it cannot be used for a terminal, unrelated to the tube, the way your photo for the 35Z5GT socket uses it.
The phenolic 8-pin octal base has wires from the glass bulb soldered individually to the pins, while button-base tubes have rigid rods sealed into the glass for pins.
Here is a good data sheet for the 35Z5GT:  https://frank.pocnet.net/sheets/093/3/35Z5GT.pdf
Note the two recommended connections for the heater on the bottom of page 2, depending on if you use the panel lamp option.

[med6753]

Pin 1 is indeed no internal connection and can be used as a tie point for other components under the chassis. This is a common practice for half wave rectifier tubes which have few internal connections and the extra unused pin insures the tube seats tightly in the socket.

There should be continuity between pins 2 and 7. You could pull the tube and place approx 20 - 25VDC across the pins and see if the filament glows. If it doesn't it's open.

[Wil_Bloodworth]

Thanks everyone!

Yes, @Emo, it is a genuine General Electric bulb and all the markings are clearly visible both on the body of the tube as well as the glass itself.  And there is zero connectivity/continuity between pins 2 and 7.  In fact, there isn't any continuity between any of the pins... so I'm assuming this tube is dead and I'll have to replace it.

@TimFox:  Thank you for the link to the much nicer data sheet!

@Eric:  I agree about the specs.  Although I know about as close to nothing as one can get with regards to reading tube specs, it seems a bit "off" logically when I read through it.

And the panel lamp was wired up directly to pins 2 and 3 as the data sheet suggests... but there wasn't a shunt resistor anywhere to be found.  The sheet says, "Shunting resistor required if DC output current exceeds 60 mA" so it sounds like the manufacturer is telling the consumer of the bulb, "Hey, I don't know what your intended purpose of this bulb is, but if...<condition>, add a shunt".  I'm guessing Mason's design did not expect the DC current to meet or exceed 60 mA but I don't think it would hurt anything to add a shunt anyway.

Much appreciated!

- Wil

[Wil_Bloodworth]

I have been pulling my hair out figuring out what the heck they were thinking when they assembled this radio.  . It turns out that the tube on the right in the first image has the tube socket oriented top to bottom with pin 1 and 8 being the bottom... BUT then they rotated the socket to the left of it 180 degrees.    I've been thinking that pins 1 and 8 were at the bottom just like the tube on the right this entire time and NOTHING made sense.  Rotate it 180 degrees and magically... it all makes sense now.

This is probably why Mason didn't stay in business... shoddy workmanship.  Or maybe it's just me!

- Wil

[TimFox]

Varying the orientation of the socket around the tube's axis is normal:  sometimes it makes the wiring shorter or neater.
Octal sockets have the orientation key, 7- and 9-pin miniatures have the gap between extreme pins, and all are numbered clockwise from the bottom.

[Wil_Bloodworth]

Clearly, I should have been paying more attention!

- Wil

[Wil_Bloodworth]

First off... I HATE eBay. I ordered a replacement 35Z5-GT from eBay... which arrived today.  There is no continuity between pins 2 & 7. Ugh!

- Wil

[TimFox]

My usual source:  https://www.tubesandmore.com/search/node/35Z5?categories%5B0%5D=Vacuum%20Tubes
Their 35Z5GT is a bit pricey:  $23.90

[Wil_Bloodworth]

Yes, I'm sure this $20 radio is going to cost me about $750 to repair... assuming I can actually get it done.

- Wil

[Roehrenonkel]

Hi Wil_Bloodworth,
 
....remember: Tubes/Valves use Bottom-view.
Can't belive you got a dead tube, but on epay everything is possible.
I have here in my stock four 35Z5 (and 1000s US-tubes 0....117)
but i'm in germany.

Good luck

[fmashockie]

Sorry to hear that you got a bad tube off eBay.  I can vouche for tubesandmore.com.   I grabbed a few different tubes from that site to restore a 1930s Grunow super heterodyne.  All of them new old stock in great shape.