[hpsdr] Munin lll

[rwfish]

Hi Dan,
I have been meaning to get back here and update the post, thanks for the reminder. Yes, the resistor change did the trick. The bias adjustments fell right in. I am driving the Munin lll to over 100 watts on all bands with my Orion ll board. The exception is  6 meters (about 80 watts). I suspect that if I did a better job on L4 I could get the power on 6 up to par. I have some 50 ohm formable cable, the kind that looks like it has a soldered shield for the outer layer. It is small enough to fit four of them in the binocular core. I may try building a new L4 with the four coax method and throw it on the VNA to see if it performs any better up to 50MHZ. I am in no hurry as I have no 6 meter antenna at the moment. I am very pleased with the Munin lll amp. My thanks to all involved. If any other builders need me to make measurements or whatever to assist troubleshooting, just holler.

73,

Bob. K6GGO

> On Mar 9, 2018, at 9:48 AM, Dan Mitchell <danmitchell387 at gmail.com> wrote:
> 
> Bob;
> Were you able to get the idle current where you wanted it after changing the resistors?
> 73,
> Dan, W0IQ
> 
>> On Fri, Mar 2, 2018 at 9:22 AM, rwfish <rwfish56 at gmail.com> wrote:
>> ***** High Performance Software Defined Radio Discussion List *****
>> 
>> Hi Kjell,
>> Ah, the world makes sense again. I will change out the resistors and soldier on. I almost always emerge on the other side of these obstacles a little wiser. I will update when I get this thing working.
>> 
>> Thanks & 73,
>> 
>> Bob. K6GGO
>> 
>> > On Mar 2, 2018, at 12:48 AM, Kjell Karlsen <la2ni at online.no> wrote:
>> >
>> > ***** High Performance Software Defined Radio Discussion List *****
>> >
>> > Hi Bob.
>> >
>> > The problem is that when I built the first prototype of Munin III, I used a pair of RD100HHF1 from an old batch of transistors that have a low Vth (Gate treshold voltage) This voltage can be from 1,5-4,5V (see the date sheet page 1). If the Vth is in the upper part of the voltage range, R9 and R10 (1,5K) must be replaced with 2,2K resistors.
>> >
>> > I have received reports from 2 Hams that have had this problem. It seems as the transistors delivered today have higher Vth than before.
>> >
>> > Sorry for the problem but there has not been any issues before as far as I know.
>> >
>> > 73, Kjell, LA2NI
>> >
>> >
>> >
>> >
>> > På Fri, 02 Mar 2018 06:33:26 +0100, skrev rwfish <rwfish56 at gmail.com>:
>> >
>> >> ***** High Performance Software Defined Radio Discussion List *****
>> >>
>> >> Hello,
>> >> I recently finished building a Munin lll amplifier. I am having trouble setting up the bias for T1 and T2. I assume that the devices should be biased at 1A each as they are in the Munin 2. I can’t seem to get the the current to 1A on either device with the associated pot. I am measuring the total current to the board with a DMM in series with the +13.8 line. I thought perhaps the 10K thermistor circuit was loading down the bias circuit so I lifted one leg of the thermistor. This did raise the current somewhat however still not enough. I also have a bit of an imbalance between the devices (ie different gate voltage to get same source/drain current). The current maxes out at 800ma on one device and 400ma on the other. I then lifted the gate connection on each device and measured the range of the bias voltage. Both bias channels are identical at 2.5 to 4.3vdc. I then used an external dc power supply to bias the Mosfets. I was able to swing both mosfets all the way up to 5 or 6 amps or higher independantly with an external bias supply, but I do have to go slightly higher in voltage than 4.3v. Maybe 5v or so. I am stumped, any ideas?
>> >>
>> >> Sorry for the long winded post but I wanted to include most of the details.
>> >>
>> >> Thanks & 73,
>> >>
>> >> Bob. K6GGO
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