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  #1  
Old 05-23-2014, 03:57 PM
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Speco Portable Signal Tracer

Hi guys;

I'm looking for a schematic to a signal tracer I've had tucked away in a shed for 20 years. It's a Speco Signal Tracer. The only reference to a model I can find is "Signal Tracer". It's a portable battery operated unit though.

front: https://flic.kr/p/nFuMNm
inside: https://flic.kr/p/nHvxUd

I probably won't need a schematic; as the thing looks relatively simple. However, I don't know what kind of battery this thing was supposed to run off of. Still not an issue; but it'd be nice to know the expected B+ voltages. I know I had one; I just haven't gone back in to the shed to dig for it.

Does anyone have a schematic; or know what kind of B+ I should run it on? The tubes are 1S5 and 3S4.

-Jay
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Old 05-23-2014, 04:53 PM
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Odd, if the tube data here is correct, these tubes have different heater
voltages, and different current ratings, so I would guess they are not
used as a series string in your amp. So first check out to see if they are in
series of not.... Then it looks like the plate voltage is no more than 90v.


http://www.radiomuseum.org/tubes/tube_3s4.html


http://www.radiomuseum.org/tubes/tube_1s5.html
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Old 05-23-2014, 07:01 PM
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The 3S4 has a center-tapped filament so it can be connected to work at *either* 1.4V at 0.100 amp *or* 2.8V at 0.050 amp.
jr
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Old 05-23-2014, 08:06 PM
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I really didn't want to go digging through that dusty, snake infested, spider infested, cobwebbed mess of a shed looking for the book. Still, after I looked more at the thing to see how the filaments are connected; I was confused. I googled for a while; could find nothing about this tracer.

So, back up the shed I went; and on the floor under a recently placed bin; I found the book; which was lucky because I expected to be up there a while and get bitten by something.

It's a Speco Model STAB. It actually used two batteries. "2-#2 flash light cells"; and any number of 67.5V batteries. There is also apparently a 1S5 tube in the probe; so I'll have to pull that apart.

I think I might actually have a transformer that puts out in the neighborhood of 60V; so I may be able convert it to AC.

schematic: https://flic.kr/p/nHDKWV
tech details: https://flic.kr/p/nFB9ih
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Old 05-24-2014, 10:20 AM
dieseljeep dieseljeep is offline
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Quote:
Originally Posted by dewdude View Post
I really didn't want to go digging through that dusty, snake infested, spider infested, cobwebbed mess of a shed looking for the book. Still, after I looked more at the thing to see how the filaments are connected; I was confused. I googled for a while; could find nothing about this tracer.

So, back up the shed I went; and on the floor under a recently placed bin; I found the book; which was lucky because I expected to be up there a while and get bitten by something.

It's a Speco Model STAB. It actually used two batteries. "2-#2 flash light cells"; and any number of 67.5V batteries. There is also apparently a 1S5 tube in the probe; so I'll have to pull that apart.

I think I might actually have a transformer that puts out in the neighborhood of 60V; so I may be able convert it to AC.

schematic: https://flic.kr/p/nHDKWV
tech details: https://flic.kr/p/nFB9ih
The B+ source is relatively easy to build, the 1.5 volt, high current supply is a little more difficult. The schematic shows that the filaments are wired in parallel.
BTW, the 3S4 is only rated for around 67.5 volts, plate and screen, so I would try to stay around those parameters.
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Old 05-24-2014, 10:59 AM
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Quote:
Originally Posted by dieseljeep View Post
The B+ source is relatively easy to build, the 1.5 volt, high current supply is a little more difficult. The schematic shows that the filaments are wired in parallel.
BTW, the 3S4 is only rated for around 67.5 volts, plate and screen, so I would try to stay around those parameters.
I was planning on building this:

http://www.antiqueradio.org/art/Powe...ySchematic.jpg


My filament draw is only .2 amps; and quite frankly; I'd those off batteries if I had to. But that has a 300ma 1.5V filament supply and 20ma b+ supply; the b+ draw is about 9ma. I think that transformer is only around $11; and the parts are small enough I could build where the batteries would reside.
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Old 05-24-2014, 11:35 AM
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Given how often a signal tracer is actually on, I would use a strong of 9v batteries from a dollar store in series for B and some D cells in parallel for A. After all
Big advantage of a battery powered signal tracer is it's not referenced to ground, you will lose this advantage building a power supply. You would
Have to do a whole lot of signal
Tracing to run down the batteries fast, it's a piece of test
Gear not a radio which will be on for hours.
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Old 05-24-2014, 01:11 PM
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Part of the reason I don't want to do that is because even though it's not on often; the batteries could still die without warning; leaving me to have to change batteries. We had one at work that ran off a 9V; I got tired of having to put off projects because we didn't keep 9V in the shop. I stuck a basic 9V wall-wart on it; never had an issue with it again.

I'll work around the reference to ground stuff when it comes around; but I'd like to have a piece of test equipment I can just plug in and work; not have to check batteries and then rig some up just to use it for five minutes. I have had cases where I've run the signal tracer for 2 or 3 hours a day; simply because I was moving amps on and off the bench and wanted to be able to grab the probe and start testing.
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Old 05-24-2014, 06:39 PM
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Fair enough that's a pretty good argument for a power supply!
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Old 05-25-2014, 10:38 AM
dieseljeep dieseljeep is offline
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Quote:
Originally Posted by dewdude View Post
I was planning on building this:

http://www.antiqueradio.org/art/Powe...ySchematic.jpg


My filament draw is only .2 amps; and quite frankly; I'd those off batteries if I had to. But that has a 300ma 1.5V filament supply and 20ma b+ supply; the b+ draw is about 9ma. I think that transformer is only around $11; and the parts are small enough I could build where the batteries would reside.
That's an interesting looking power supply. I already have some of the parts for it.
I'll use a power transformer from a scrap VTVM, that wasn't worth repairing.
I can always use an extra power supply for a battery tube radio.
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Old 05-27-2014, 10:47 AM
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Quote:
Originally Posted by dieseljeep View Post
That's an interesting looking power supply. I already have some of the parts for it.
I'll use a power transformer from a scrap VTVM, that wasn't worth repairing.
I can always use an extra power supply for a battery tube radio.
That power supply looked much safer than some of the transformerless ones I saw. There was another one on that page that basically rectified line voltage; which would have required all sorts of isolation.

The transformer I think is about $11; which doesn't seem too bad. We had a very similar supply at work that came as a kit (I had to assemble). It was different than this circuit; provided more voltages, but fundamentally the same.

It worked rather well. Never had a ground problem; so I'm pretty confident this design will work well.

Quote:
Fair enough that's a pretty good argument for a power supply!
Well, this is what I told my boss. If he wanted me to get amp's fixed and off the bench in under an hour (because god forbid he pay me more than $12 to fix an amp); I don't have time to remember to turn the signal tracer on when I have to worry about high b+ and other issues. I can work safely and efficiently; but I have to do things like leave test equipment on during the duration of the day.
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