Videokarma.org

Go Back   Videokarma.org TV - Video - Vintage Television & Radio Forums > Diagnostic & Test Equipment

We appreciate your help

in keeping this site going.
Reply
 
Thread Tools Display Modes
  #1  
Old 11-25-2014, 07:16 AM
VTVM VTVM is offline
VideoKarma Member
 
Join Date: Jan 2014
Posts: 35
Built myself a retro signal tracer for tube radios

Here is the homebrew signal tracer project I made. I tried to keep it retro in styling and electronically. It is 100% "hollow state" --there are nothing but tubes in the circuits right down to the 6AL5 small signal rectifier to drive the meter.

The speaker is a 5 watt, 4" unit. Fidelity is good, as it must be to find sources of distortion or excessive hum in an amplifier or radio. There is an output for an external meter or scope if specific (relative) signal voltages are needed or if the audio waveform or RF modulation envelope (demodulated) is to be observed visually. I also put in a noise test circuit with a momentary push button that puts out B+, through a high value resistor, to the audio input probe. Any roughness in this current flow caused by a cold solder joint or suspected "noisy" component is amplified by the audio amplifier. That test works similar to the old Eico 147 signal tracers.

I prefer a meter to an eye tube, so this meter was salvaged from the junk box. It is an old HP 400 series meter. The RF input probe uses a subminiature 5603WB triode as a grid leak detector to demodulate AM radio signals and amplify the corresponding audio signal, which is then sent to the audio-taper gain control potentiometer in the grid circuit of the 1st 12AX7 dual triode amplifier. The other half of this tube gives another stage of gain and feeds the grid of a 50C5 power pentode to drive the speaker though an audio output transformer. The secondary of the audio output transformer also feeds a signal to a 6AL5 dual diode tube to rectify the signal to the meter. The meter gives a relative signal level, and is responsive enough to bounce along with audio of a radio station or give a steady reading from a tone injected into the device being tested. The speaker can be muted by a single pole double throw switch that cuts out the speaker and replaces it with a 5 watt, 10 ohm load resistor. The power supply is a 35W4 half wave rectifier tube filtered by an RC pi filter.

The unit is sensitive enough to give a clear signal right from the antenna lug on an AM radio that is tuned into any reasonably local radio station, or can be turned down enough to get a signal right off the plate of a typical radio's output tube. It should be handy for audio amplifiers and phonos as well as radio work.

The faceplate and chassis are made from 6061 sheet aluminum. The cabinet is 1/4" red oak with poplar framework. The probe housing is made from 3/4" brass tubing, insulated with heatshrink.
I am still waiting for a 4 pin jack to arrive for the final hookup to plug in the active RF probe, and also have a black hinged handle ordered for the top of the cabinet.

(Note: I do not claim that this tracer meets UL or any other safety standards, but it is only for my use, and I know where and how I'm using it.)





















Reply With Quote
  #2  
Old 11-25-2014, 10:04 AM
JBL GUY JBL GUY is offline
VideoKarma Member
 
Join Date: May 2009
Posts: 138
Very nice!

Thanks for the pictures.
Reply With Quote
  #3  
Old 11-25-2014, 10:40 PM
VTVM VTVM is offline
VideoKarma Member
 
Join Date: Jan 2014
Posts: 35
Thanks. It was fun. I need new pics of the proper jack installed for the RF probe and the handle on top where I can wind up all the cords.
Reply With Quote
  #4  
Old 11-26-2014, 06:38 AM
Sandy G's Avatar
Sandy G Sandy G is offline
Spiteful Old Cuss
 
Join Date: May 2003
Location: Rogersville, Tennessee
Posts: 9,571
Ya done GOOD ! (grin)
__________________
Benevolent Despot
Reply With Quote
  #5  
Old 11-26-2014, 07:43 AM
hi_volt's Avatar
hi_volt hi_volt is offline
Vintage TV and Radio Nut
 
Join Date: Dec 2011
Location: Tucson, AZ
Posts: 1,142
Outstanding job!

I'm convinced that solid state electronics and overhead valves for automobile engines are passing fads.
Reply With Quote
Audiokarma
  #6  
Old 11-26-2014, 08:54 AM
VTVM VTVM is offline
VideoKarma Member
 
Join Date: Jan 2014
Posts: 35
LOL. Thanks guys.
I used it to test a phono pickup and a weak IF stage in a radio so far. It works great. I have a factory built Eico 147 Tracer that has been restored and works well, but I kind of prefer this one.
Reply With Quote
  #7  
Old 11-26-2014, 07:57 PM
dieseljeep dieseljeep is offline
VideoKarma Member
 
Join Date: Jul 2010
Posts: 7,562
Quote:
Originally Posted by VTVM View Post
Thanks. It was fun. I need new pics of the proper jack installed for the RF probe and the handle on top where I can wind up all the cords.
A great deal of craftsmanship is evident. I would use a microphone connector from a scrap CB rig, for the probe connector. They usually have several pins for the PTT function.
Reply With Quote
  #8  
Old 11-26-2014, 08:38 PM
VTVM VTVM is offline
VideoKarma Member
 
Join Date: Jan 2014
Posts: 35
Quote:
Originally Posted by dieseljeep View Post
A great deal of craftsmanship is evident. I would use a microphone connector from a scrap CB rig, for the probe connector. They usually have several pins for the PTT function.
That's exactly what I ended up using!
Reply With Quote
  #9  
Old 12-01-2014, 09:12 AM
dieseljeep dieseljeep is offline
VideoKarma Member
 
Join Date: Jul 2010
Posts: 7,562
Quote:
Originally Posted by VTVM View Post
That's exactly what I ended up using!
What did you use for punching the holes in the aluminum chassis. They look a lot cleaner than a drilled hole.
BTW, I never saw a 6AL5 of that style. It must be foreign make.
I would've liked to have seen the inside of the probe.
I have a fairly new Hickok, signal tracer, set tester. There's a tube in the probe, as well.
Reply With Quote
  #10  
Old 12-06-2014, 02:48 AM
transmaster transmaster is offline
VideoKarma Member
 
Join Date: Jun 2013
Posts: 87
The is nicest bit of home-brewing I have seen in years.
Reply With Quote
Audiokarma
  #11  
Old 12-12-2014, 12:53 AM
Tubejunke's Avatar
Tubejunke Tubejunke is offline
VideoKarma Member
 
Join Date: Apr 2003
Location: Martinsville, VA
Posts: 1,823
VERY NICE! I want one!
__________________
"Face piles of trials with smiles, for it riles them to believe that you perceive the web they weave, and keep on thinking free"
Reply With Quote
  #12  
Old 12-12-2014, 08:52 AM
dieseljeep dieseljeep is offline
VideoKarma Member
 
Join Date: Jul 2010
Posts: 7,562
Quote:
Originally Posted by Tubejunke View Post
VERY NICE! I want one!
With a cabinet like that, It belongs in the living room, instead of the work shop.
Reply With Quote
  #13  
Old 12-22-2014, 10:20 PM
VTVM VTVM is offline
VideoKarma Member
 
Join Date: Jan 2014
Posts: 35
Thanks guys.
dieseljeep: i used a step drill bit. I will take pictures of the probe insides and the finished unit with the mic jack...I forgot.
Reply With Quote
  #14  
Old 12-22-2014, 10:23 PM
VTVM VTVM is offline
VideoKarma Member
 
Join Date: Jan 2014
Posts: 35
The 6al5 is in fact a european four numbered equivalent drop in for an American 6al5. I can't remember the number. The insides are the same but the bulb is taller.
Reply With Quote
  #15  
Old 12-23-2014, 08:45 AM
dieseljeep dieseljeep is offline
VideoKarma Member
 
Join Date: Jul 2010
Posts: 7,562
Quote:
Originally Posted by VTVM View Post
The 6al5 is in fact a european four numbered equivalent drop in for an American 6al5. I can't remember the number. The insides are the same but the bulb is taller.
I was thinking about a EAA91, but you said four numbered.
BTW, I'll keep the step bit idea in mind.
Reply With Quote
Audiokarma
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 01:39 AM.



Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
©Copyright 2012 VideoKarma.org, All rights reserved.