1. Home
  2. Electronics Design
  3. Using a small portable solid state amplifier to trace an audio circuit???

Using a small portable solid state amplifier to trace an audio circuit???

I have a small portable solid state amplifier that can run off batteries or a wall wart. (12V).

I want to trace the circuits in a solid state Hammond Organ. (To listen for audio signals).

So, this amp is ready to go. Has a speaker and a wall wart connected.

I could also use some powered computer speakers too.....

My question is this:

To trace this organ (or any other audio signal), do all I need to do is isolate the input of this amp, using a capacitor? Then connecting a test lead and probe to the cap? (I assume shielded wire should be used from amp to the probe).

What size cap?

Since I work on a lot of tube stuff....

Could this also be used to trace tube amplifiers, assuming I use a cap that is rated at 600V or more?

I know, the main thing is to make sure that the high voltage DC (B+) dont get into the amplifier and ruin it.....

I was looking on ebay for "Signal Tracers", and could not believe the high prices. An old Micronta (Radio Shack), tester that tests both AF and RF, sold AS-IS for $50 and did not even include the test leads. I know the RF test lead is more complicated and has a circuit inside the probe. No, I wont pay that much..... I'll wait till I find one that is priced reasonably....

I dont really need to test RF at the moment anyhow.

Reply to
oldschool
Loading thread data ...

Something in the order of 0.1ufd will work fine.

Yes. Look up the old Heathkit Audio/RF Signal Tracer or the far more recent Dick Smith Signal Tracer.

formatting link

I have both and they work just fine. The DS version is the size of a smallish, fat, remote control. I need to scan those and host them someday.

Hence the isolation capacitor.

The RF test is a trivial change - you simply need a diode. See the Heathkit schematics.

John :-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup) 
John's  Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9 
(604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games) 
                      www.flippers.com 
        "Old pinballers never die, they just flip out."
Reply to
John Robertson

I'd use back-to-back diodes from the amplifier input to ground and a big series resistor and series cap in the probe.

I don't know anything about the equipment you're testing, but I think it would be risky (possibly fatal) to assume that there's a ground point in the system that isn't somehow connected to the AC line.

Reply to
mike

You also need a pot on the input, or large swings will produce severe distortion. I'd add a fixed resistor too, who knows what the amp input can handle.

if it's not low impedance and you care about hum

size it to pass 20Hz

A spike of 600v into an unknown solid state amp is likely to kill it very dead. Your input cap won't prevent that. Add a resistor & diodes to protect it.

You can always use your audio to test the rf envelope. Just needs diode & capacitor.

NT

Reply to
tabbypurr

Yes, some tube kit is live chassis.

NT

Reply to
tabbypurr

What do you mean by back to back? Woundnt a diode short the audio signal to ground? Maybe I'm not picturing this right....

I dont work on any of them AC-DC sets (live chassis) without an isolation transformer. In fact I dont usually evne get that stuff with live chassis. It's not worth salvaging.... That was a poor design right from the start.

Reply to
oldschool

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.