On 1/24/2014 6:27 PM, tom armour wrote: > With the old amp should I have an AUX cable? or is the RCA cables Rig->KAT500->Amp enough? That's what you MUST use. I don't know anything about PTT for that particular amplifier, so you should investigate voltage and current to make sure it's OK with the K3. Most modern amps are. 73, Jim K9YC