[hpsdr] Munin lll

[rwfish]

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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