Need Wiring Help - Key-up Voltage Question

[Riverman]

Hooking a noise toy (Yeah, I know).
The toy replicates the Browning Golden Eagle key-up sound. Am wiring it to a Browning Brownie.
Anyway, most of it is simple. Red wire to 12+ volts. Black wire to chassis ground. White wire to audio.
It's the orange wire that's got me. It says it goes to 8-volt key-up voltage (not mic transmit voltage).
I have no idea what that is.

Would appreciate any help.

Thank you!

 

[TM86]

I'm looking at the schematic in Sam's CB-80, so if it's wrong then so am I. This radio does not appear to have an 8 Volt source that is switched on in transmit. It does have an 8 volt and a 12 volt source that are switched off when the the PTT button on the mic is pressed.

There is a constant 8V source at the junction of R31 and C32. If the TX/RX relay has enough spare contacts you could route it through there so that it only shows up on one of the previously unused normally open contacts. Or you could use another relay or a transistor that gets switched on when the TX/RX relay is turned on. The TX/RX relay is on when the junction of C50, CD8, and R58 goes to 0 volts. Or tap into pin 3 on the mic connector, since it goes to that same junction.

You could also put together an 8 volt regulator circuit using an LM7808 that only gets turned on when grounded, but that might be overkill.

Sorry I can't give you any more than that. I don't have one of these to play with.

 

[Riverman]

I'm looking at the schematic in Sam's CB-80, so if it's wrong then so am I. This radio does not appear to have an 8 Volt source that is switched on in transmit. It does have an 8 volt and a 12 volt source that are switched off when the the PTT button on the mic is pressed.

There is a constant 8V source at the junction of R31 and C32. If the TX/RX relay has enough spare contacts you could route it through there so that it only shows up on one of the previously unused normally open contacts. Or you could use another relay or a transistor that gets switched on when the TX/RX relay is turned on. The TX/RX relay is on when the junction of C50, CD8, and R58 goes to 0 volts. Or tap into pin 3 on the mic connector, since it goes to that same junction.

You could also put together an 8 volt regulator circuit using an LM7808 that only gets turned on when grounded, but that might be overkill.

Sorry I can't give you any more than that. I don't have one of these to play with.

Thanks for your help. Most of that is above my pay scale of knowledge. Didn’t expect the orange wire. The others I could handle. Thanks again.

 

[Riverman]

I'm looking at the schematic in Sam's CB-80, so if it's wrong then so am I. This radio does not appear to have an 8 Volt source that is switched on in transmit. It does have an 8 volt and a 12 volt source that are switched off when the the PTT button on the mic is pressed.

There is a constant 8V source at the junction of R31 and C32. If the TX/RX relay has enough spare contacts you could route it through there so that it only shows up on one of the previously unused normally open contacts. Or you could use another relay or a transistor that gets switched on when the TX/RX relay is turned on. The TX/RX relay is on when the junction of C50, CD8, and R58 goes to 0 volts. Or tap into pin 3 on the mic connector, since it goes to that same junction.

You could also put together an 8 volt regulator circuit using an LM7808 that only gets turned on when grounded, but that might be overkill.

Sorry I can't give you any more than that. I don't have one of these to play with.

If you find the time, could you check and see if the Royce 619 has an 8 volt source that switches on when transmitting?

 

[brandon7861]

Thanks for your help. Most of that is above my pay scale of knowledge. Didn’t expect the orange wire. The others I could handle. Thanks again.

The transistor method TM86 mentioned is pretty easy, all you need is a PNP transistor. Doesn't really matter what one A 2N3906, 2SA1282, 2SA473, just find a parts radio and yank out the first PNP transistor you see.

 

[Riverman]

The transistor method TM86 mentioned is pretty easy, all you need is a PNP transistor. Doesn't really matter what one A 2N3906, 2SA1282, 2SA473, just find a parts radio and yank out the first PNP transistor you see.View attachment 70400

Don’t laugh. How will I know a PNP when I see it?

 

[brandon7861]

Find a junk radio you can use for parts, then find the schematic for that radio, then find a transistor that is PNP (see attached), then using that component number (Q34, TR21, whatever it may be), find that part in the radio using the silkscreened labels on the board. Verify by looking at the number on the transistor. For example, on the Galaxy 959, part Q30 (a 2SA1282) would work.

 

[brandon7861]

I don't have the schematic of the Brownie that TM86 was looking at, but I will use the royce 619 as an example to illustrate a potential problem and solution to using the mic pin as a source of TX low for the PNP transistor.

In the 619, there is a constant 9v source (Q401's emitter). The PTT signal on mic pin 3 is held high when PTT is not pressed by that same regulator via R109 and D103. Because of the voltage drop across D103, the voltage floating on mic pin 3 may be around 8.6v which could be low enough to start turning on the added PNP transistor. To remedy this, add a diode between that 9v source and the PNP emitter. This will drop the emitter of the PNP to about the same so the high level signal on the PNP's base is not low enough to turn it on prematurely.

 

[brandon7861]

In the case of the royce 619, you would want to do this

 

[Riverman]

Okay, I think I’m in over my head. Getting dizzy.
I need a radio with an intermittent 8 volt source clearly marked with a miniature red flag.

 

[TM86]

If you find the time, could you check and see if the Royce 619 has an 8 volt source that switches on when transmitting?

I would recommend what brandon7861 drew up. There's an 8 volt source that switches off in transmit, but that doesn't really help.

Don’t laugh. How will I know a PNP when I see it?

As far as how you can tell a PNP from and NPN, the PNP Points In Proudly, while the NPN is Not Pointing iN. Corny, but if you can remember that you'll know which is which every time you see a transistor on a schematic.

How can you tell by looking at the transistor in an open radio? No idea, I can't unless I can read the part number and already know what it is.

 

[brandon7861]

How can you tell by looking at the transistor in an open radio? No idea, I can't unless I can read the part number and already know what it is.

Some transistors used a standard format, and I think there was a thread here about it. For example, 2SA1282, the 2 is the number of leads on the part minus 1, so transistors are 2, diodes are 1 etc. The SA part refers to the type of semiconductor, S for silicon, and the A (choices are A, B, C and D) is the polarity and frequency range. A and B are general use/audio, C and D are RF. A and D are PNP, B and C are NPN. I would have to find that thread for more details. the 2Nxxxx is a different naming scheme. There is some rhyme and reason to the numbers, but not always.