You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.

Reply to thread

Message

Using ohms law I came up with about 120 milliamps of collector current and 84 milliwatts dissipation on the PNP transistor. That indicates even the smallest PNP from Radio Shack should work fine here. Nothing wrong with using a bigger one here. Just be sure if it's a TO220 case that you insulate the metal tab. It need not be attached to a heat sink since it won't get hot. Heat shrink tubing works good for insulating here.

This transistor will be activated by the amplifiers original keying transistor. The transistor is connected to the keying relay coil mounted on the board. This relay coil will have a diode soldered directly across it. You can feed the 1000 ohm resistor directly from the anode side (without stripe) of this diode. Check with your volt meter first to be sure this point changes from about 12 volts with the amp on but not keyed, to around 0.6 volts keyed.

<blockquote data-quote="Shockwave" data-source="post: 265232" data-attributes="member: 10882">Using ohms law I came up with about 120 milliamps of collector current and 84 milliwatts dissipation on the PNP transistor. That indicates even the smallest PNP from Radio Shack should work fine here. Nothing wrong with using a bigger one here. Just be sure if it&#039;s a TO220 case that you insulate the metal tab. It need not be attached to a heat sink since it won&#039;t get hot. Heat shrink tubing works good for insulating here.This transistor will be activated by the amplifiers original keying transistor. The transistor is connected to the keying relay coil mounted on the board. This relay coil will have a diode soldered directly across it. You can feed the 1000 ohm resistor directly from the anode side (without stripe) of this diode. Check with your volt meter first to be sure this point changes from about 12 volts with the amp on but not keyed, to around 0.6 volts keyed.</blockquote>

[QUOTE="Shockwave, post: 265232, member: 10882"] Using ohms law I came up with about 120 milliamps of collector current and 84 milliwatts dissipation on the PNP transistor. That indicates even the smallest PNP from Radio Shack should work fine here. Nothing wrong with using a bigger one here. Just be sure if it's a TO220 case that you insulate the metal tab. It need not be attached to a heat sink since it won't get hot. Heat shrink tubing works good for insulating here. This transistor will be activated by the amplifiers original keying transistor. The transistor is connected to the keying relay coil mounted on the board. This relay coil will have a diode soldered directly across it. You can feed the 1000 ohm resistor directly from the anode side (without stripe) of this diode. Check with your volt meter first to be sure this point changes from about 12 volts with the amp on but not keyed, to around 0.6 volts keyed. [/QUOTE]

Top Bottom