¿ªÔÆÌåÓý

ctrl + shift + ? for shortcuts
© 2025 Groups.io
  1. Ham-Amplifiers
  2. Messages
Single Messages Topics Expanded Polls

Re: High Temperature in Toroid of the PI-L network (Alpha 78)

 

FT8 is a 100% duty cycle mode and at some point depending on wire size and physical size of the toroid it will at some point overheat. ?It it overheats too much the permeability of the core itself will change and rewiring it will change the actual inductance. ?I had the toroid in a Commsnder 2500 catch on fire and totally destroyed for running 1500 watts RTTY. ?I a customers amp that is. ?It¡¯s the nature of the beast that it will eventually burn up at some point .




On Saturday, March 2, 2024, 11:55 PM, Arturo LU6ETB <lu6etb@...> wrote:

Hi,

Last week my Alpha 78 stopped working.
I found the windings of the L5 was burned.
I rewinded the toroid with new wires.
Now, it is working.
I checked the temperature after transmitting on 80 meters FT8 with approximately 1 KW output.
Plate current 0.85 Amper, HV 2000 V and Grid current 25 mA.
After 30 minutes the temperature readings with a digital multimeter were.
L5 119 C (246 F)
L4, 64 C ( 147 F)
L6, 49 C (120 F)

Are those temperatures right?
What maybe the cause of the high temperature?? ?
Should I have to replace also el toroid???
?
Thanks in advance for the comments.
73 de Arturo, LU6ETB
Join [email protected] to automatically receive all group messages.