[Johnson] Ranger 1 Turbo Modulator Instability

[Kenneth Goodwin]

Thanks for the response Ashley.   My answers below:

 

Hello,

   Is the MOD Idle IP set to Johnson spec ? 

** Yes, I’ve checked both the screen bias at 300 VDC and set the idle mod plate current to 80 mA.

   

 

Does this spike happen with different 6550's ?

** Haven’t tried but a good suggestion.

 

   We suggest looking at the +300V rail to see if there is an instability. If the original Ranger screen adjustment ( adjustable tap on HV bleeder) is present, try lowering the ES on the modulator tubes and see if the instability changes or disappears.

** The modulator screen bias is one of the standard mods which is set at 300 VDC fixed using solid state devices.

 

   Try, also, lowering the MOD Idle IP from Johnson spec and see if the instability changes or disappears.

** I will try this also.  The suggested IP is 70 – 90 mA so I’ve set it at 80 mA but will try some different settings to see what changes.

 

73, Ken Goodwin K5RG

 

From: ashley40 at aol.com <ashley40 at aol.com> 
Sent: Tuesday, July 17, 2018 5:20 PM
To: krgoodwin at comcast.net
Subject: Re: [Johnson] Ranger 1 Turbo Modulator Instability

 

Hello,

   Is the MOD Idle IP set to Johnson spec ? 

   Does this spike happen with different 6550's ?

   We suggest looking at the +300V rail to see if there is an instability. If the original Ranger screen adjustment ( adjustable tap on HV bleeder) is present, try lowering the ES on the modulator tubes and see if the instability changes or disappears. 

   Try, also, lowering the MOD Idle IP from Johnson spec and see if the instability changes or disappears.

 

 

Ms Ashley Hall, W7DUZ