Anyone help with this ?
Anyone help with this ?
I have just installed a new irf520 transistor. When i key up the power starts to drop as the transistor heats i mean like with in 20 seconds it goes from 15 watts to under 10 watts is that normal ?
- listner132
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Re: Anyone help with this ?
What radio have you fitted the 520 in too ?
Re: Anyone help with this ?
Hi it's in a amp rm 35listner132 wrote:What radio have you fitted the 520 in too ?
- 163TM847
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Re: Anyone help with this ?
How much power are you putting into the amp ?, It must be kept below 4w, Also the Mosfet will burn up quickly if the gate voltage is too high [over 4v].
Re: Anyone help with this ?
3 watts i've even tried 0.5 watts and it still does the same thing.Black Spirit wrote:How much power are you putting into the amp ?, It must be kept below 4w, Also the Mosfet will burn up quickly if the gate voltage is too high [over 4v].
Re: Anyone help with this ?
In transmit ?Black Spirit wrote: Also the Mosfet will burn up quickly if the gate voltage is too high [over 4v].
- 163TM847
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Re: Anyone help with this ?
YesClassic wrote:In transmit ?Black Spirit wrote: Also the Mosfet will burn up quickly if the gate voltage is too high [over 4v].
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Re: Anyone help with this ?
Nick's bang on.... gate voltage is critical on mosfets, as is keeping it stable....
Alan 26FB806
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27.385 LSB, 27.555 USB, 27.78125 FM
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27.385 LSB, 27.555 USB, 27.78125 FM
Use it or lose it!!!!
Re: Anyone help with this ?
Tested and the meter goes off the scale. Also when i tried the amp on a switch mode psu as soon asi keyed up it blow up. Now that has haqppened 2 times. It don't happen on the old psu which isn't a switch mode.Black Spirit wrote:YesClassic wrote:In transmit ?Black Spirit wrote: Also the Mosfet will burn up quickly if the gate voltage is too high [over 4v].
Re: Anyone help with this ?
Do you have a schematic for the amplifier?
What was the original transistor - is this a "mod"?
Why an IRF520? They are notoriously unstable for RF applications above 7MHz.
What was the original transistor - is this a "mod"?
Why an IRF520? They are notoriously unstable for RF applications above 7MHz.
Re: Anyone help with this ?
I was told i could use it in this amp no problem.2E1IIP wrote:Do you have a schematic for the amplifier?
What was the original transistor - is this a "mod"?
Why an IRF520? They are notoriously unstable for RF applications above 7MHz.
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Re: Anyone help with this ?
Ok thanks I will look over it, but at a glance the gate voltage should never exceed 20V as it clamped with a zenner.
Re: Anyone help with this ?
So from the diagram is there anything i can change to get the gate voltage to 4 volts as black spirit recommended ?2E1IIP wrote:Ok thanks I will look over it, but at a glance the gate voltage should never exceed 20V as it clamped with a zenner.
Re: Anyone help with this ?
The MOSFET Gate is tolerant to +/-20V, the gate is clamped to a maximum of 20V with the zenner diode - I am not sure why it is failing - I would try a different device - is it genuine or a Chinese import?Classic wrote:So from the diagram is there anything i can change to get the gate voltage to 4 volts as black spirit recommended ?2E1IIP wrote:Ok thanks I will look over it, but at a glance the gate voltage should never exceed 20V as it clamped with a zenner.
Re: Anyone help with this ?
Also check the gate voltage with a DVM and an FM carrier not exceeding 5W, check the diodes and the zenner diode to be sure.