Johnson Ranger modulator screen grid R35 modification.

[Knightt150]

Hello: Dose anyone know if the screen grid modification for the modulator (replacing R35 20K) in my ranger 2 is still available ? And did it work, If not where can I purchase a new 20k resistor  mine is partly open.

John W9BF

[DMOD]

I would suggest two 25 Watters such as NTE 10K 25WF310 in series and use this circuit as a screen regulator.

Phil - AC0OB

[Knightt150]

Hello: On ebay sometime back there was for sale a modification kit to replace R35  20K resistor in the ranger 2, that adjust the screen voltage on the modulation tubes. Dose anyone have one of those kits, willing to sell it. And dose it work? My R35 is partly open  and I don't want to put that hot resistor back in the transmitter.

John W9BFO

[Tim WA1HnyLR]

Hi John,
 The "heater ' resistor is a very poor way of obtaining screen voltage in the Ranger. Screen voltage regulation is very poor with this method along with more heat under the chassis  . I use the low voltage power supply as the screen voltage source. Modulator idle adjustment is accomplished by replacing the two 4.7 K 1/2 watt resistors that make up a bias voltage divider,  with a 10K pot,wiper arm to the CT of the driver transformer secondary.Modulator screen voltage is removed during standby. As part of a correct method of PTT, there MUST be 4 poles of relay, NOT 2 poles, as in the factory suggested implementation. It will be noticed that during standby there still is a significant amount of modulator current draw.The modulator MUST be disabled during standby.
One of the additional set of poles is in line with the outpoot of the LV supply. This kills the Mod screen voltage as well as the B+ feed to the top of the drive control pot.The B+ feed to the 12AU7 audio driver is also fed from this point. Therefore less heat generation.  also A 100 2 watt resistor is placed across the relay pole that is in line with the LV B+. This provides enough voltage at the top of the drive pot to obtain a usable spot signal
 level. This keyed LV source  also is used for the screen voltage feed to the 6AQ5 clamp"Goose"tube. In the stock Ranger PTT system the 6146 PA tube pulls about 50-60Ma. The 6146 is dissipating nearly it's maximum plate dissipation rating in standby. No wonder one can fry an egg on the top of the cabinet.The fourth relay pole is wired up in the following manner. Connection from screen dropping resistor to screen of 6146 is disconnected at tube socket screen pin. It is now connected to the N.O. contact pole. The arm of the pole is connected to the screen pin of the 6146. The N.O. pole tied to ground. The 6146 screen is grounded during stand by. The idle current will be in the order of 20Ma or so. The screen dropping resistor and the 6AQ5 goose tube will generate very little heat during stand by. The final move shall be solid stating the high and low voltage power supplies. This all may seem like too much work at first. The Ranger is considered to be a good low power transmitter,but has a number of issues that need to be corrected. Why bother replacing the 20K adjustable resistor.Just get rid of it.
Tim WA1HnyLR

[Knightt150]

Hello: Thanks to every one for the help, but due to my shakey hands and poor eye site anymore, I would have a hard time doing all the mods that you suggest Tim. I need a simpler way of doing the mod's I guess I will just replace the old resistor if I can find one, do they still make R35 a 20k open resistor anymore?

Thanks John
W9BFO

[Opcom]

https://www.digikey.com/products/en/potentiometers-variable-resistors/adjustable-power-resistor/83?k=&pkeyword=&sv=0&pv2085=u20+kOhms&sf=0&FV=ffe00053&quantity=&ColumnSort=0&page=1&pageSize=25

showing all wattages of 20K adjustable power resistors