Fw: [JMS] 90800/p.s. progress

Sun, 22 Feb 2004 19:10:44 GMT

Hi Jim:
Thanks for the info. I'll probably save that up for James Milen 90800 #2. That one will receive a retrofit in order to use some of the more common Bud/B&W/Johnson/Decker tank coils. Unfortunately, the Millen stock seems to be made of "impossitanium" ("unobtainium" has been recently discovered so I won't use that term here).

Back to the JM transmitter: I decided to make a similar unit without the 90881 transmitter. It will be more or less in a class with the Ranger type transmitters. I'll use another outbard 90831 modulator and power supply setup but instead of being "QRP" to drive an amp, the output on such a transmitter should be a dedicated 40-60 watts barefoot. 
Cal N6KYR. 

----- Original Message ----- 
From: JAMES HANLON 
To: [email protected] ; [email protected] 
Sent: Sunday, February 22, 2004 11:24 AM
Subject: Re: [JMS] 90800/p.s. progress

Cal,

Sounds very good!  If you want the ability to run greater input to the 90800 at this power supply voltage, check the screen voltage on the 807.  The ARRL Handbook rates the 807 screen for 250 volts in normal class-C service with a maximum of 300 volts.  If your screen voltage is a bit low, as it is likely to be because of your 450 volt power supply, you could put in a shunt pot around the existing 3500 ohm screen resistor in the voltage divider from the B+ line.  That would allow you to adjust the screen voltage and also the output from the 807 - essentially it would be an electronic, variable drive control for your final amplifier.  You might even want to put a fixed resistor in series with the shunt pot to prevent you from inadvertently setting the 807 screen above 300 volts.  

One extra hint, if you want to measure the control grid drive to the 807, just put a milliamp meter in series with the bias battery.  3.5 ma is about right for the 807 grid drive current.  If that's too high or too low you can always adjust the variable coupling capacitor from the 6L6 plate to the 807 grid.  

73,

Jim, W8KGI

________________________________________________________________
The best thing to hit the Internet in years - NetZero HiSpeed!
Surf the Web up to FIVE TIMES FASTER!
Only $14.95/ month -visit www.netzero.com to sign up today!