rci2970n2 bias help

[AudioShockwav]

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

 

[radiofoxtrot]

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. ?

 

[The Mad Scientist]

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.

I find this very interesting. But not likely to find their way into a commercially built amplifier due to cost.

Perhaps a custom homwbrew amplifier? That's a design worth taking a look at.

 

[JASTECH]

Jeff, Thank you for the link to this thread. I have a 2950 with n2 bottom end that is a project along with a 2510. I have good and bad days so my projects take a while, but get done proper.

 

[Scania]

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

Hi!
I try this om my friends 2970N2, black display.
I can not get the voltage on the finals in ssb mode.
Should the "short circuit" PCB be in or out the holder?
PA BOARD is okey to make the alignment on.
Lars