Ham Radio Forum

HI. i have constructed this linear amplifier 500w rms (2kw pep) (50ohm) with 12 mosfet irfp360, http://tzitzikas.webs.com/linear500w.jpg for 160m band.

i sorted all connections.
When i gave 3watts of driving r.f power, it gave to output only 190w at 106VDC (6A current). Two radio amateurs who have construct this linear claim tha it gives 500w
r.f power at 110vdc.
But when i tried to give 4watts of driving r.f power the ferrite Cores (43 material)
of transformer T3 broken! Which do you think is the problem??

some pictures
http://tzitzikas.webs.com/linear20a.JPG
http://tzitzikas.webs.com/ferrite_broken1.JPG

the feerite cores that i use are:
http://uk.farnell.com/fair-rite/2643626 ... dp/1463423
from manufacter:
http://www.fair-rite.com/cgibin/catalog ... lect:freq1
Round Cable EMI Suppression Cores
Broadband Frequencies 25-300
MHz (43 material)
some radio amateur told me that maybe this cores are improper for these frequences. But the designer of this linear
claims that we must use 43 material cores for the transformers.
Thank you.

Type 43 core material should be ok. There are other possibilities:

1) Is it possible that the insulation on one or more of the windings around that core is nicked and that copper wire is in direct contact with the core? That could cause core overheating.

2) RF feedback of some kind might be causing the amplifier to break into oscillation at some point as you increase the RF input power. The input transformer core could overheat if enough power is being fed-back from the RF amplifier output. If you have an oscilloscope, hold its input probe near to the amplifier as you gradually increase the input driving power and watch for a sudden burst of RF voltage on the scope. The RF voltage picked up by the probe shouldn't increase suddenly. If it does, the amplifier is breaking into parasitic oscillation.

Gordon

Gordon wrote:Type 43 core material should be ok. There are other possibilities:

1) Is it possible that the insulation on one or more of the windings around that core is nicked and that copper wire is in direct contact with the core? That could cause core overheating.

2) RF feedback of some kind might be causing the amplifier to break into oscillation at some point as you increase the RF input power. The input transformer core could overheat if enough power is being fed-back from the RF amplifier output. If you have an oscilloscope, hold its input probe near to the amplifier as you gradually increase the input driving power and watch for a sudden burst of RF voltage on the scope. The RF voltage picked up by the probe shouldn't increase suddenly. If it does, the amplifier is breaking into parasitic oscillation.

Gordon

thank you. do you know the characteristics of 31 material? It is proper for 1-2mhz?

hi friends , if problem with ferrite core broke , impedance doesn't match .
or maybe self oscillation ,the ferrite with go to over heat