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Author Topic: 2SC2290 versus MRF421C replacements?  (Read 9143 times)
W1BR
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Posts: 4189




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« on: April 07, 2012, 10:27:15 AM »

My NSD-515 JRC transmitter original used 2SC2290 transistors. It was used at the ERAG field days for several years before I picked it up a few decades ago. The 2SC2290 transistors failed almost immediately. A vendor suggested using MRF421C replacements, and that is what installed in the transmitter to this time. I did increase the bias to about 190 mA per device, in keeping with the minimum suggested by Motorola's apps notes.

The MRF-421C transistors have been very reliable, but I am wondering if the vendor gave
good advice about these being direct drop in replacements for the 2SC2290 devices? I'm tempted to grab some of the earlier 2SC2290 parts before they are totally obsolete. Can any RF engineers give some good guidance on this subject?

Pete
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ZS6BIM
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Posts: 67




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« Reply #1 on: April 08, 2012, 04:05:36 AM »

Hi Pete

I agree with your increasing the bias of the MRF421’s to +/-200mA each.

The only possible problem I can see is that the driver stage of the NSD-515 JRC might not be able to drive the MRF421’s to rated output on 10m with the desired linearity.

The two reasons this may occur are firstly the MRF421 has a typical gain 1,8dB lower than the 2SC2290 at 28MHz and the second because the MRF421 is a much larger device (100W vs. 60W) the input impedance at 28MHz is lower. (0,7, -j0,5 Ohms vs. 1,02, -j0,17 Ohms)

This will result in the driver stage “seeing” a less than optimal impedance at the higher frequencies.

However driver stages are normally conservatively designed so unless you notice significantly less output power on 10m or receive reports of splatter on that band I would definitely stay with the MRF421 – a hard to beat 12V linear bipolar of the last century that’s extremely rugged.

73
Mike
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KD8DEY
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Posts: 369




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« Reply #2 on: April 09, 2012, 01:05:16 PM »

In case you ever come across them at a ham fest
ECG/NTE-317 & SK 9603 are the direct subs for the 2290

http://www.hbfelectronics.com/index.php?action=disp_item&item_id=414187
« Last Edit: April 09, 2012, 01:09:34 PM by KD8DEY » Logged
W1BR
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Posts: 4189




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« Reply #3 on: April 09, 2012, 01:28:37 PM »

Tnx,  "original" 2SC2290 devices are still available from RF Parts.  I noticed the MRF-421C have become much,
much harder to find, however.

Pete
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