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Author Topic: Matched MRF-150's  (Read 4624 times)
N4EDI
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Posts: 15




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« on: April 17, 2012, 12:28:53 PM »

How closely do the MRF-150's need to be matched for the EB-104 amplifier? Is the same lot number close enough? What happens if they are not a matched set?
Thanks

Ed
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K8AXW
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« Reply #1 on: April 17, 2012, 08:32:18 PM »

When you first tune the 104 you set the bias for equal current for each FET.  They don't have to be a matched set.
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N4EDI
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« Reply #2 on: April 19, 2012, 01:51:47 PM »

Would the Chinese ones that are on Ebay work ok?
Thanks
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K9AQ
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Posts: 55




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« Reply #3 on: April 19, 2012, 02:15:03 PM »

I have had good luck with Chinese MRF150's in my EB104.  I got mine from Sharpseller2000.  I had one DOA and they replaced it at no charge.

Don
K9AQ
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N4EDI
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« Reply #4 on: April 19, 2012, 04:47:23 PM »

Do they need to be from the same lot?
Thanks
Ed
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K8AXW
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« Reply #5 on: April 19, 2012, 09:09:24 PM »

How much are the Chinese MRF150s ?

I have 6 MRF151s I'd like to sell..... same as the 150s but a little heavier.
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N4EDI
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« Reply #6 on: April 20, 2012, 04:24:31 AM »

They are $107.99 for 4 pieces with free shipping.

Ed
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N4FBW
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« Reply #7 on: April 24, 2012, 10:45:52 PM »

It is a good idea to use matched pairs of MRF-150's. Here's a quote from the EN-104 app note:

 "The bias for each device is independently adjustable, therefore no matching is required for the gate threshold voltages. Since the power gain of a FET is largely dependent on the drain bias current, only gm matching is required, and it can be only ± 10%."

gm is transconductance which is measured in mhos. The bias adjustment is only taking care of the differences in gate threshold voltages between devices, the bias adjustment does not compensate for variations in transconductance between devices. Since transconductance affects the gain of each device, it is good practice to match the gm specs closely when using pairs of FETS.

HTH!
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G3RZP
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« Reply #8 on: April 26, 2012, 03:27:30 AM »

gm should be measured in Siemens (or micro Siemens) these days. But I prefer mhos!
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K9FV
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Posts: 480




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« Reply #9 on: April 26, 2012, 02:18:41 PM »

Isn't that "EB-104" on page 1, top of right column?  What year was this written?  Have MOSFET specs improved any over the years?

Just how important is "matched quads" (or pairs) these days with MOSFET with separate bias adjustment for each device?

Just asking, seeking knowledge

73 de Ken H<>
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W9GB
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Posts: 2626




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« Reply #10 on: April 26, 2012, 04:19:57 PM »

CTR Surplus in Crestline, OH has TWO GA4204A 4kw RF Amplifiers listed on eBay.
ctrsurplus2 , 170829687547

These medical/industrial units use TWENTY-FOUR (24) MRF150 Transistors and includes the
Nemic Lambda Power Supply EWS1500 AC Input: 240V, 16A, 50/60Hz; Output:48V DC, 32A.

That is a lifetime supply of MRF-150 RF transistors.   Wink
« Last Edit: April 26, 2012, 04:28:06 PM by W9GB » Logged
G3RZP
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« Reply #11 on: April 27, 2012, 02:44:17 AM »

I would say that matching gm is important. A bad mismatch will lead to more 2nd harmonic if nothing else, but there will be one side trying to do more work than the other.
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K9FV
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Posts: 480




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« Reply #12 on: April 27, 2012, 06:39:24 AM »

Hmmmm, CTR Surplus in Crestline, OH has TWO GA4204A 4kw RF Amplifiers for $750...... and it does not work.  That is $31.25 each (plus shipping) each, and the item is listed as "not working" - of course you do get a 48 vdc power supply.....  "IF" it works.

OR: the Chinese MRF150 for $27 shipped?  Of course it is Chinese stuff - but it would be a lifetime supply.

Ken
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