[JMS] power supply success

[Don Buska]

Hey Ronnie,

Actually a HB modulator would be a very good idea and as you state not to difficult to 
build.  Even another 60-100 watt rig modulator should work very well with the 
90801/90800 rigs.  Such as the Eico modulator or similar.

The early versions of the 90831 modulator used just as you suggested a pair of 6L6's.  
There are tons of 1950's articles describing such designs that you could copy.  
Including the original 6L6 modulator handbook design that the 90831 is based upon.  
Duplicating the 90831 would be very easy.  My 90831 uses a modulation transformer from 
a Johnson Ranger as it was one of the missing items from the chassis I bought from 
Ralph.  If you HB yours any of the 100 watts class modulation multi-tap transformers 
would work just great.

Sounds like a fun project and also a wonderful idea to write up your final design for 
the JMS webpage, hint.. hint.. ;)

Looks like you should be able to get that transmitter running tonite.  I wouldn't 
worry about the 450V under-load plate current.  You'll still see around 25 watts out 
of the transmitter at that voltage and the 6146 will love you for it, hi.  Mine is 
only at around 500VDC key down.

73

Don



On Thu, 8 Jan 2004 09:31:29 -0500, w5sum wrote:

>Don
>
>thanks for your prompt reply
>
>I have only powered this rig up, have not tuned her up or put her on the air. 
>I will do that tonight, and make all the appropriate measurements. It would 
>be real easy to adjust the screen voltage to 230-250 volts, via the sliding 
>tap on the bleeder.
>
>I have not looked at the screen current but will tonight. 
>
>hey have any of you fellows homebrewed a modulator for this rig? I would 
>never hope to find a millen modulator. A pair of 6L6's should do it. Just 
>curious.. that would be fun to do.
>
>Ultimatley, this rig will be used as the exciter in the homebrew 8/13/805 rig 
>I have been working on.
>
>thanks again
>
>Ronnie
>
>On Thu, 08 Jan 2004 08:10:58 -0600 (CST), Don Buska wrote
>> Hi Ronnie,
>> 
>> Per the spec sheet in Plate-Modulated RF PA (Class C) operation 
>> (See http://www.qsl.net/n2ckh/6146.pdf) with a plate voltage between
>> 480 and 600 VDC the screen voltage should be 250VDC max.  Normally 
>> in the Millen transmitter the screen voltage is derived through a 
>> 4.7K 1W resistor from the LV supply (mine is set for +250VDC).  This 
>> is for CW operation.  During AM it is via a voltage divider off the 
>> HV supply (They modulate both plate and screen).
>> 
>> With your 81 volt drop across the screen resistor it sounds like you 
>> have way to much screen current.  With a 250VDC screen voltage there 
>> should be around 50VDC drop across the 4.7K screen resistor assuming 
>> about 10mA of screen current.  
>> 
>> Question are your conditions measured under transmitter operation, 
>> i.e. oscillator is running and you are properly loaded into the 
>> antenna?  What grid bias are you using on the 6146?  Should be 
>> around -65VDC.  Be careful with such a large screen current.  You'll 
>> distroy the tube, plus you will exceed the screen resistor power 
>> rating also.  What does the 90801 meter indicate for screen current? 
>>  Manual states not to exceed 15mA.
>> 
>> 73
>> 
>> Don N9OO
>> 
>> On Thu, 08 Jan 2004 08:33:38 -0500, w5sum wrote:
>> 
>> >well I have completed the power supply for me 90801. It only delivers about
>> >450 volts under load on the B+, and I am taking the screen voltage off of 
>a 
>> >25K 100 watt tapped resisitor that is the bleeder in the power supply. I 
>> >powered her up this morning with a variac on the power supply. After 
>perhaps 
>> >an hour of burn in, I had the power supply at full line voltage and the 
>> >little rig sat there fine, with no smoke and no bad smells LOL
>> >
>> >WHAT is the proper screen voltage? I have about 100 volts going to the rig 
>> >and on the other side of the screen dropping resistor there is 19 volts. 
>> >
>> >Does all of this sound in line?
>> >
>> >If I get a positive response to that question, I'll power her up tonight 
>and 
>> >put her on the air on cw
>> >
>> >thanks for the help y'all
>> >
>> >Ronnie
>> >
>> >The "AM" voice of Shreveport, Louisiana USA
>> >formerly WN5AIA and WB5AIA
>> >I got my Extra Class the old fashioned way... I earned it!
>> >______________________________________________________________
>> >James_Millen_Society mailing list
>> >Home: http://mailman.qth.net/mailman/listinfo/james_millen_society
>> >Help: http://mailman.qth.net/faq.htm
>> >Post: mailto:James_Millen_Society@mailman.qth.net
>
>
>
>The "AM" voice of Shreveport, Louisiana USA
>formerly WN5AIA and WB5AIA
>I got my Extra Class the old fashioned way... I earned it!