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Filament voltages in old radio

wlgrant6

wlgrant6

AK Subscriber
Subscriber
Hey everybody. Happy first day of spring to you. Don't know about where you guys are, but it doesn't feel much like spring here in Ky. Hope you guys don't mind me asking a question about an old Zenith AM/FM Model T723 table radio. According to the tube placement chart on the radio, and the schematic, it should have the following tube complement. 35C5, 19T8, 12AT7 and 4 12BA6's. If you add the filament voltages up, that comes to 114 volts. The 35C5 has been replaced with a 50C5. That comes out to 129 volts. Is it possible that this was done to lower the filament voltages overall to compensate for high AC line voltages, or someone along the line didn't have a 35C5 to replace a bad one, and just stuck the 50C5 in there. Or maybe it's just my math. LOL. IMG_1104.JPG The radio is working.
 
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Hi wlgrant6,

Your guess of someone not having a 35C5 on hand is likely correct. And as you have found, it will work. As long as the radio sounds OK to you I wouldn't bother changing it, but if it sounds at all weak and doesn't pull in stations well then sure give it a new 35C5.
 
not uncommon to do this honestly, and usually it works out just fine using a 50C5 as a sub.

the other option is to add a resistor in series with the power cord to drop a few volts.
 
If I had a 35C5 on hand, I'd stick it in there along with a CL90 to knock the voltage down a little, but since I don't have one, guess I'll leave it as is. I never work on table radios, so I don't have any spare tubes for them. Picked this up at an estate sale, and it was in use at the time. Liked the looks of it. Bill
 
gadget73 said:
not uncommon to do this honestly, and usually it works out just fine using a 50C5 as a sub.

the other option is to add a resistor in series with the power cord to drop a few volts.
Click to expand...
A thermistor would do this and have the benefit of some added inrush protection.
 
Not sure inrush current is a thing in series-string AA5-type radios, as all the filaments take a minute or so to warm up. Might make any pilot light bulb fed off the 35z5 or 35w4 rectifier tube's filament maybe not flash as bright when switched on. Speculation, I never tried it myself.
 
if its got the bulb run off the tap, definitely make sure its the right one. There is also a trick about bridging it with a resistor so if the bulb fails it doesn't kill the rectifier too but I don't remember the fine points of what value to use.
 
It doesn't have any dial lamps, and I don't remember seeing any bulbs when I was inside of it. The schematic that I have is very poor quality, can't see if there is a bulb in there or not. Someone has already replaced the selenium rectifier with a diode. Bill
 
Catmanboo said:
Not sure inrush current is a thing in series-string AA5-type radios, as all the filaments take a minute or so to warm up. Might make any pilot light bulb fed off the 35z5 or 35w4 rectifier tube's filament maybe not flash as bright when switched on. Speculation, I never tried it myself.
Click to expand...

I wasn't thinking of the CL90 so much for a soft start, as just knocking the voltage down a bit. Guess we can't refer to this one as an AA5, guess we'll have to call it an
AA7 LOL.
 
wlgrant6 said:
I wasn't thinking of the CL90 so much for a soft start, as just knocking the voltage down a bit. Guess we can't refer to this one as an AA5, guess we'll have to call it an
AA7 LOL.
Click to expand...
No need for it if using the 50c5, that'll cool down all tubes a little. If you want a 35c5 though, pm me. I have many & will send you a tested good one for the postage.
 
Catmanboo said:
No need for it if using the 50c5, that'll cool down all tubes a little. If you want a 35c5 though, pm me. I have many & will send you a tested good one for the postage.
Click to expand...

Thanks for the offer, but guess I'll just leave the 50c5 in there. Doubt if it will get much use, more of a curiosity piece than anything. Bill
 
wlgrant6 said:
Thanks for the offer, but guess I'll just leave the 50c5 in there. Doubt if it will get much use, more of a curiosity piece than anything. Bill
Click to expand...
It's retro cool to listen to a ball game on an old radio with a legacy brand beer in hand. Think Blatz, PBR, Schlitz, Iron City, Falstaff, Budweiser etc... here's a couple of mine. Battery/ line powered "portables". Zenith, Westinghouse, RCA in that order.
 

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Catmanboo said:
It's retro cool to listen to a ball game on an old radio with a legacy brand beer in hand. Think Blatz, PBR, Schlitz, Iron City, Falstaff, Budweiser etc... here's a couple of mine. Battery/ line powered "portables". Zenith, Westinghouse, RCA in that order.
Click to expand...

I was working nights back in the 1990's, and would usually get home after midnight. I would fire up my Philco 19 Cathedral and go trolling for long distance using a long-wire antenna strung the length of the house, everybody else in bed asleep.

Got home one night just in time to catch a re-broadcast of the 1938 Orson Welles War of the Worlds coming in from the States.
Sitting in the dark, listening to this by myself, with just the glow of the tubes for company, was really quite spooky. And I loved every second of it!
 
arts said:
I was working nights back in the 1990's, and would usually get home after midnight. I would fire up my Philco 19 Cathedral and go trolling for long distance using a long-wire antenna strung the length of the house, everybody else in bed asleep.

Got home one night just in time to catch a re-broadcast of the 1938 Orson Welles War of the Worlds coming in from the States.
Sitting in the dark, listening to this by myself, with just the glow of the tubes for company, was really quite spooky. And I loved every second of it!
Click to expand...
That is beyond cool! That's right place, right time. You were privileged to step back in time like that, & feel that which the people at that time were freaked out on. Sweet!
 
Apologies to wlgrant6, it seems we've hijacked your thread with our ancient radios:cool:
Very nice Zenith, looks to be in fine shape. Glad to hear it's still in service.

Here's my Ma and Pa Kettle radio. Gotta find a speaker for it some day...

DSCF2322.JPG DSCF2323.JPG
 
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