1963ish Western Auto Truetone DC-1454

[quaddriver]

Im starting in on the target radio: 1963ish Truetone (Western Auto) DC-1454 - AMFM, wood case, 6 tube, SE rect blah blah blah

Its booked as a 50W radio. Why?

Welllllll, It draws the expected 35-ish watts for the heaters and whatever is needed across some plates. But it has a pilot light. (not the gas kind, the electric kind ;-) )

The light is a 6v-ish bulb connected right across the mains/switch

But but but, you say, you cannot run a 6v bulb on 117 or so volts. Well not for long. so, it has what measures out as an 870ish ohm 20W resistor. So this dang thing consumes 15w to light a dial, and boy does it get hot. Nu-cu-lah hot.

Unacceptable. 'Specially seeing as I am about to s&%tcan the SE rect for a diode and a new inrush thingy.

So....which way would yinz proceed?

My thoughts are to a) rectify the leads to this bulb and either zener it or LM317 it to 6v (gotta look up the specs to make sure that they can handle 150ish volts of supply voltage)

b) Tap the already rectified voltage at the first section of the can and do the same (the diodes I use can supply 2.5amp and typically the plates take a quarter amp)

and perhaps drop all this to 3.2v and use one of my super LEDs instead

c) I dont really wanna use a 60hz transformer inside this thing and deal with hum

d) there are 2 other voltage sections after the diode, one after a 56ohm and then the third after a 750ohm, however... the current limitation inherent due to being behind a 56 ohm and later 750 ohm resistor might make the 15-20ma the LED needs or eighth amp the bulb needs....well, taxing.

What say ye?

And while we are at it - is there a source for the schematic around somewhere?

thanks in advance and merry stuff with happy things

[Electronic M]

A neon bulb across the cord will not draw much current (with a proper limiting resistor).

I'd personally use a incandescent and a small transformer (I have one from a BT TV ant amp PS that is smaller than any AA5 speaker transformer that would be great for this application).

Another option is to lookup the series heater current of the tubes in it, and get a 1-8V bulb that matches that current*, and put it in series with the heaters. You can often get away with adding as much as a 12V drop to a series string of tubes....ESPECIALLY if your line voltage is 125V or more...Many sets were designed to run ideally at 109-117V, and could stand an additional 10-20% change in line voltage about the ideal design point...

*If you can't find one, get a bulb with less current and calculate the bulb's hot resistance using Ohm's law and the current/voltage specs of the bulb, then grind the same equation substituting the bulb current for the heater string series current (that gives you the resistance you need), then calculate the parallel resistance you need (ask google if you don't know the formulas).

[maxhifi]

You could also take voltage from the cathode bias resistor of the output tube, to power an LED through a series limiting resistor. You may have to increase the value of the cathode bias resistor to make up for the current going through the LED, but it's already DC and will only cost you two resistors and an LED.

I like the neon idea a bit better though.

[quaddriver]

All good suggestions, great initiative. I have not found a schematic for this yet, so I am winging it decoding the PCB myself. It would appear that the pecking order for the tri voltage power supply (standard AMFM tube fare) is that the 50C5 sucks on the teat last, so I can derive the line currents by measuring the voltage drop across the 56ohm and the 750 ohm, but I fear that the cathode votage is going to be around 70+.

The LEDs like Vf at 3-3.2 (I tend to aim for 3) and the run current is 20-25ma with max at 50ma. Aiming low,a 70volts-3volts = 67 volts times say 20ma gives me a watt and a half resistor (yea, they make those...so 3W) and I need a 3.3K-ish - that might be doable, I think I saw a lot of O-O-R in the parts bin.

The reason I dont wanna do a 10 or 20:1 xformer is unlike the speaker transformer which sees ALL audio frequencies, this one will be 60hz only....AM radios just *love* to amplify this - I'd have to install chokes everywhere.

I do have a lot of neon bulbs hanging around, but I got these high intensity LEDs and droppers for a song from parts express. I have been doing some cool stuff in the vintage SS units (just got a scott LCD to light up nice - the owners threw it out because it was dark...)

As to the suggestion about the heater string, I think I am in fact 125ish here. I have 3 12's, a 14, a 17 and a 50 - 117 on the knoggin. that gives me 8v to futz with and I have a crapload of old mazda bulbs. Mebbe tomorrow I'll go picking around and take some readings...

i could always allow more volts and amps inside when I change the SE rect for Si...I add a minimum of 100ohm to the inrush limiter (generally 22ohm) to make up for the voltage drop inherent in being a SE rect.....

[maxhifi]

The cathode of the 50C5 will be at around 7.5V, and idle current around 50mA... I would put the LED in series with the cathode and adjust the series resistor until the cathode voltage gets back to around 7 or 8 volts.

[quaddriver]

Ahh you are right, the grid is 70+. I have to measure the current because 50ma is the max LEd current but I may have misread what you said, I would need a limiting resistor for the LED, I think the bias resistor is about 150ohms as is.

I would need about 220ohm in series with the LED to keep it at .020 Ma and increase the bias resistor to about 250 to get that current to .030 no?

[old_coot88]

If you put it in the cathode leg, it won't light until the tube starts conducting, around 20-30 seconds.

[dieseljeep]

The set probably had a 28 volt, 100 ma lamp, IIRC
The drop would be about 8 watts dissapation on a 20 watt resistor.
Does the label show an EIA number 742. Esquire or Channel Master?

[maxhifi]

If this is the case, that's a 2.8W bulb.... Substituting a 3W 120V bulb would seem to be the most obvious solution.

[quaddriver]

Originally Posted by dieseljeep

The set probably had a 28 volt, 100 ma lamp, IIRC
The drop would be about 8 watts dissapation on a 20 watt resistor.
Does the label show an EIA number 742. Esquire or Channel Master?

no sir, the backs' fiber board is printed/painted with western auto DC-1454

[quaddriver]

Originally Posted by maxhifi

If this is the case, that's a 2.8W bulb.... Substituting a 3W 120V bulb would seem to be the most obvious solution.

well the bulb I have is not burned out....works fine. I just wanna lower power consumption and heat. heat is our enemy. . global warming yanno.

the prez gave us half day off so I will have some voltages soon. I generally replace all the carbon comps anyways...

[quaddriver]

well the caps are replaced, the SE rect is gone and I went with 200ohms for the inrush...Im getting voltages much in line with this running on 117 instead of 125, I would have rather went 180ohm, but I aint got any in the 10W cement variety.

I did some math adding up the consumers - the dropping resistor for what turned out to be in fact a 6v bulb is about 1/3 the set consumption of 50W - I might have 180 in 3w size....we keep looking.

[Username1]

A neon light will most likely make noise on AM at least.....

QD - ""But but but, you say, you cannot run a 6v bulb on 117 or so volts. Well
not for long. so, it has what measures out as an 870ish ohm 20W resistor. So
this dang thing consumes 15w to light a dial, and boy does it get hot.
Nu-cu-lah hot.""

Pretty dam funny....

If'n yer after saving the cost of operation, natural gas is getting cheaper all
the time, you should convert that pilot light to gas, with some flint striker/
gas valve attached to the volume control..... Maybe even attache it to one of
those outdoor gas tanks for home gas grills. One tank may last 30 years....
Please post pictures.....


.

[quaddriver]

About to start back in on this. Oddly, Im also the STEM coordinator for the cub scout pack, so they are getting a peek at the guts. Next week they get a comparo between a 1963 tube AMFM and a modern battery powered AMFM...

pics soon.

[init4fun]

Originally Posted by Username1

A neon light will most likely make noise on AM at least.....

Hey Squirrel guy ,

Just for future reference , all those Zenith "propeller dial" mid 1950s AM FM 7 tube radios used a neon pilot light and they made no noise on AM . The example I have is a "T-825" which of course is 8 tubes , it's basically the same as the 7 tube but with a 6AB4 as a separate local oscillator . I'll enclose a couple of "action shots" of the neon in operation .