Can RF finals be "partially" shot?
I have an NTE342 RF final in a transmitter that is not putting out
full rated power (only 3 watts but should be more like 6 watts) -
Testing the transistor with a diode setting on my meter shows that its
okay, but I am wondering if it could still be partially damaged. I am
wanting to rule out the possibility thats its been damaged by heat in
my clumnsy attempt to install it!

"Mike" wrote in message
news:1113324846.cd06bd2ce55defd30b441770978debec@t eranews...
Can RF finals be "partially" shot?
I have an NTE342 RF final in a transmitter that is not putting out
full rated power (only 3 watts but should be more like 6 watts) -
Testing the transistor with a diode setting on my meter shows that its
okay, but I am wondering if it could still be partially damaged. I am
wanting to rule out the possibility thats its been damaged by heat in
my clumnsy attempt to install it!

Possible but remote and your symptoms indicate a different fault.
--
N

It sure is possible, and is known as 'low gain' or 'low beta'. Diode check
wont tell you a transistors gain. You need to put it on a curve tracer and
compare the curves for a range of given base current to a known good NEW
identical transistor to see the difference.

If I were you I would not use the NTE , and get the original number
transistor that was in there. The NTE replacements dont always match the
characteristics of the original 100% in detail, and certain differences can
cause it to run hotter than normal, and in the long run, reduce its gain.
Its also possible not enough heat sink compound was used, and other
possibilities too.


"Mike" wrote in message
news:1113324846.cd06bd2ce55defd30b441770978debec@t eranews...
| Can RF finals be "partially" shot?
| I have an NTE342 RF final in a transmitter that is not putting out
| full rated power (only 3 watts but should be more like 6 watts) -
| Testing the transistor with a diode setting on my meter shows that its
| okay, but I am wondering if it could still be partially damaged. I am
| wanting to rule out the possibility thats its been damaged by heat in
| my clumnsy attempt to install it!

what was the original transistor part number

what frequency are you operating at

are the leads all very short, especially the emitter lead

Mark

It was actually an modification, replacing a 2SC3553 with the NTE342
part for an increase in power in a QRP HF transceiver (other minor
changes to the circuit as well) - freq range from 3.5 to 30 mHz.
Leads are short. The NTE part definately runs hot even at 3 watts
output. Heatsink is bolted to the back using thermal compound.

On 12 Apr 2005 12:43:59 -0700, "Mark" wrote:

what was the original transistor part number

what frequency are you operating at

are the leads all very short, especially the emitter lead

Mark

"Mike" wrote in message
news:1113324846.cd06bd2ce55defd30b441770978debec@t eranews...
Can RF finals be "partially" shot?
I have an NTE342 RF final in a transmitter that is not putting out
full rated power (only 3 watts but should be more like 6 watts) -
Testing the transistor with a diode setting on my meter shows that its
okay, but I am wondering if it could still be partially damaged. I am
wanting to rule out the possibility thats its been damaged by heat in
my clumnsy attempt to install it!

1/ Substitutions are often "iffy" with RF devices.
2/ Some RF power transistors have multiple emitters and it's possible to
lose some of them which degrades performance.

Den Tue, 12 Apr 2005 13:52:42 -0700. skrev Mike:

It was actually an modification, replacing a 2SC3553 with the NTE342
part for an increase in power in a QRP HF transceiver (other minor
changes to the circuit as well) - freq range from 3.5 to 30 mHz.
Leads are short. The NTE part definately runs hot even at 3 watts
output. Heatsink is bolted to the back using thermal compound.

Try to tune the coil in output circuit. The replacement has possibly not
the same capacitance , as the original one.

P.S. I don't know the circuit, just my 0.5$



--
Med venlig hilsen

Christian Treldal

Mike wrote:
Can RF finals be "partially" shot?
I have an NTE342 RF final in a transmitter that is not putting out
full rated power (only 3 watts but should be more like 6 watts) -
Testing the transistor with a diode setting on my meter shows that its
okay, but I am wondering if it could still be partially damaged. I am
wanting to rule out the possibility thats its been damaged by heat in
my clumnsy attempt to install it!

Sure, happens all the time.
I've seen a bunch of 450 MHz finals that look just fine on a curve
tracer, but fail to output at 450 MHz.

I've given up trying to test RF transistors at DC or thereabouts.
mike

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