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rci2970n2 bias help

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  #25  
Old 09-11-2011, 09:00 PM
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My n2 came with the ept695015b board, must be a later revision. It also came with the final PA feedback added (there is another thread here about that HERE).

But my question is whether the bias on the driver and finals should be set by voltage, or set by current? It seems that since fets are voltage controlled, that would be the preferred method, but I have seen some bickering about that on other forums.

Also, I take it the test points are the same as the dx, only the voltages are being used?
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Old 09-20-2011, 10:10 AM
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It is too bad they went to Mosfet's for the driver and finals baring the linear amp I am guessing it is still using a single 2SC2879????? Please tell me they are not using mosfet's to replace the 2SC2879 bipolar transistor????? IF so I will not own one of those! I am not a fan of Mosfet's in high power RF circuits they seem to fail freq. Look at all those cheap RM and Zagoti RF amps that had Mosfet's in them.....Sure they where cheap but they had a lot of failures for a long time. I do not know if it has gotten better but why fix what is not broken????

That is terrible if they are shipping these with the bias set too high!!! We never had a 2950 or 2970 come into the shop the 2 years I worked their with any failed finals. It was always cold solder joint, crystal filter, a cap failure or voltage regulator failure if it was a warranty fix. Hooking them up backwards or using them on a faulty antenna system caused issues. On top of that I was in that area for 4 years and used to hang out with the guys that worked their after the shop would close. We sold the heck out the RCI 2950 and 2970 back when HRO was the only game in town for a while that sold them. The 2950 was $496 at first through them and if you ordered 5 you got the 6th one for $396 so $100 off and that is how I got mine. I waited until we had 5 customers ordered before I put in mine so I got it for $100 off list.I owned mine for 10 years before it was stolen. Never had a final go. So I think this is a terrible situation to have. Proper bias setting is rather fundamental thing to have set properly by the OEM to prevent warranty issues!!!

Please let us know what you find!! I am thinking about getting my boy a 2950DX for 10 and 12 meter work so I want to know if their is anything like a known issue I need to check or watch out for. It will not be modified for 11m at all it will stay 10/12m.

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  #27  
Old 09-20-2011, 10:30 AM
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Quote:
Originally Posted by ElectronTubesRule View Post
It is too bad they went to Mosfet's for the driver and finals baring the linear amp I am guessing it is still using a single 2SC2879????? Please tell me they are not using mosfet's to replace the 2SC2879 bipolar transistor????? IF so I will not own one of those! I am not a fan of Mosfet's in high power RF circuits they seem to fail freq. Look at all those cheap RM and Zagoti RF amps that had Mosfet's in them.....Sure they where cheap but they had a lot of failures for a long time. I do not know if it has gotten better but why fix what is not broken????

Actually those RM and Zetagi amps are not very good designs, and thus don't really represent the current state-of-the-art. Today's MOSFET technology is nothing short of incredible really.

You'd be pretty hard-pressed to find any modern commercial high-power RF amplifiers that are still using BJTs, due to the fact that FETs have some very nice endearing qualities such as higher input impedance (this just means that FETs don't require built-in impedance matching) and the fact that they are voltage-controlled devices instead of current-controlled like BJTs. This is a huge benefit when it comes to biasing. A bias circuit for a FET doesn't need to provide any significant current as opposed to a bias circuit for a BJT which must source a good deal of current, so a simple variable resistor in a voltage divider is sufficient. Also, FETs are less prone to thermal runaway so thermal tracking of the bias voltage is not always required which simplifies things even more.

The very latest high-powered RF FETs produce over 1.2kW across HF VHF and much of UHF (1.8-600MHZ). Freescale's latest offerings withstand up to a 65:1 SWR mismatch conditions at full output. NXP is claiming over 100:1 SWR ruggedness from their comparable devices. This is unheard of from BJTs.

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  #28  
Old 02-15-2012, 06:17 AM
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its no surprise these things are blowing up.
irf520 was never meant for rf use.and the erf parts are just irf520 bin sorted and remarked.
http://www.irf.com/product-info/data...ta/irf520n.pdf

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  #29  
Old 02-15-2012, 12:06 PM
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Quote:
Originally Posted by kc8adu View Post
its no surprise these things are blowing up.
irf520 was never meant for rf use.and the erf parts are just irf520 bin sorted and remarked.
http://www.irf.com/product-info/data...ta/irf520n.pdf
No, the 'ERF' marked devices are mfd exclusively by RF Limited in the Far East. They are specifically engineered for RF use. They also make the ERF-7530 that is used in the RFX-75 add-on unit.

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In past versions of this radio, they have gone from the dual 2SC1969 output transistors to the dual ERF 2030 MOSFET units made by EKL. Which - is a division of RF Limited - by the way. With the addition of the PowerBand RFX-75 and the elimination of the 2030 finals to the ERF-7530 MOSFET, the power on AM is a conservative 90 watts. On SSB mode, it will put out 70 watts. And on FM mode, it will do 20 watts.
You are quite right about the 'IRF' in one respect.
It is true that the 'IRF' devices can either work or not for RF applications and some were not intended to work at all.
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Last edited by Robb; 02-15-2012 at 03:11 PM.

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  #30  
Old 03-16-2012, 12:11 PM
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Hi Guys,
Brand new to the site but would like some help please. I am a radio ham but still have a keen interest in cb. I restore / tinker with old cb sets one of which is the ranger I picked up at a radio rally. I also have on the bench a pristine Lincoln President which I am looking for a reasonabley priced ChipSwich. I have a RCI-2970-DX-150 and would like to know if it can be put on 11 meters. I have been led to belive that there are two models, one can and the other can't, can anybody help. Secondly has the Radio Supply Shop got and email address so as I can talk to Chip. Many thanks in advance.

Regards,

Peter. G0ELC. Stockton-on-Tees. UK. Birth place of the railways!

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  #31  
Old 03-16-2012, 12:42 PM
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Hello, The ChipSwitch Is now out of production, so unless you can find a parts radio with one in it I doubt that you can get one.
I do not know of anyone that has stock left.
The Radio Shop can be reached at By clicking here.
This will take you to there contact Info.
Here is some Info that may be helpful with the conversion for the 2950 / 2970 Radios.


73
Jeff
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  #32  
Old 12-22-2012, 11:15 AM
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Can someone give me more info on how exactly to adjust these gate voltages for the driver and final. Where do you connect the volt meter to and what trimmer (VR) adjusts each voltage. ?

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