rci2970n2 bias help

[AudioShockwav]

If the factory didn't set up the radios correctly before they shipped them out; then they would be deluged with returns and warranty repairs.

It is my understanding that when this model first came out, this is what was happening, guys were seeing huge numbers out of the radios, they were drawing excessive amperage and running hot as a firecracker.....and a lot of them dropped like fly`s.
I think that problem was addressed by Ranger and it got solved.
If Larry ( DX Man ) see`s this I think when he got one of the new ones he was seeing large current draw, and If I remember right, Dave (DTB Radio) helped him sort it out.
Maybe he will jump in here and correct me if I am wrong.

73
Jeff

 

[AudioShockwav]

Posted By DXMan:

Many of the N2 were coming out doing 300 watts (I also heard of one that was doing close to 400)- but this does mean that they were rated at 300.

Have you tested any of the 2nd version's yet? I have heard of several now that are coming out of box doing around 215/225 - which is what they should be doing.

I had mine retuned from the factory 300 watts down to 215, I am now running it on a 36 amp P.S. - draws 18 amps on SSB (which is what the manual states it should draw).

73
Jeff

 

[cbkidd1]

Thank you jeff for taking the time to help me. Maybe someone with more knowledge will step in and give me the right voltage for the irf520. You know i can not find the service manual for the ept-695015a board.Maybe rci just have not put it out yet sure would be a big help.

 

[AudioShockwav]

Have you e mailed Ranger to see if they can advise?


73
Jeff

 

[DXman]

From what I've found out was; the first production N2's were coming out with the "gate voltage" to high, this was causing the failure of the Mosfits. Guys were seeing 300 watts with a 50-60amp draw.

So after I found this out, I then sent mine into DTB radio for his complete alignment/tune. I explained what I had found out and to check the "gate voltage" and set to radio to do no more than 225 watts with roughly 18 amp draw.

Well the radio came back doing the 215-225 watts and 18 amp draw which was prefect for me. Now the radio is running cool and I am using just a 35 amp P.S..

The 2nd version is now working better than the first. From what I have been hearing, Ranger has gotten the wattage down lower (around the 200 watt mark) now and they seem to be doing better.

One more thing - I have heard of (2) of first series N2's blow up and sent back to Radio Active Radio for repair (which is where they were first bought and tuned), repair bill on one was around $200. This came right from the owner! So.......as we all know.......................................!!!

PS - I have no idea what the gate voltage is.

 

[cbkidd1]

I really appreciate all of you taking your time out to help me with the irf520 mosfet gate settings. I sure have learned a lot about mosfets in the last few days lol. Would i be right in saying rci should have used a power mosfet like a erf7530 or something close to it?

 

[Robb]

Hey, its what we do forums for.
No problemmo . . .

The ERF-7530 is mfd by the owner of Magnum radios, Sam Lewis/EKL components. In fact, all of the ERF-series MOSFET's are made by EKL. RCI/Ranger USA isn't going to buy EKL parts. That would be like Chevy buying their motors from Ford!

The EKL brand makes their devices specifically for RF applications. Most of the IRF-520 'x' MOSFET's are not built for RF signals and only one or two of them will work for RF apps. If you are going to replace a MOSFET device; I would stick to the EKL brand - IMO . . .

 

[cbkidd1]

I emailed ranger tech support last week. And chip sent me all the info that they had right now regarding the rci2970n2. I hope this info will help others. I will let Jeff put this were he thinks it should go.

Sorry for the delay. They are still working on a service manual for this model.



The 2970DX manual can be used for alignment as it is the same with exception of the driver and final transistor alignment which is as follows.



Turn carrier and mic gain control on front to minimum.



Turn mode switch to SSB



Key transmitter and set the following voltages measured on the gate of each transistor



MAIN BOARD



Driver gate voltage 3.6VDC +-.1VDC

Final gate voltage 3.4VDC +- .1VDC



PA BOARD



Bank 1 VR-2 gate voltage 3.5VDC +-.1VDC

Bank 2 VR-3 gate voltage 3.5VDC +-.1VDC





Please note also same alignment as in service manual except higher wattage listed below.



Carrier should be set to no more than 100 watts at max power AM/FM

SSB should be set to no more than 200 watts PEP at max power SSB





Regards,



Chip



RADIO SHOP SUPPLY

RANGER USA PARTS & SERVICE

1672 Main Street Suite E #228

Ramona, CA 92065

(760) 440-0125



Hours 9am - 5pm PST Mon-Fri

 

[AudioShockwav]

Thank you for posting the reply, I am sure it will help others that are looking for the same info.

73
Jeff

 

[GnG8d]

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?

 

[ElectronTubesRule]

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.

 

[eagle1911]

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.

 

[kc8adu]

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/datasheets/data/irf520n.pdf

 

[Robb]

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/datasheets/data/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.

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.

 

[Gizzmo]

2970 dx 150

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!