I'm learning here, never knew that a push-pull configuration for MMIC's was a thing.
But plenty of google hits, figure 2 on page 4 here shows one:
    https://www.modelithics.com/models/Vendor/MiniCircuits/PHA-22plus.pdf

Even configured for push-pull, there aren't many MMIC's that can deliver
the nearly 1W of power needed to drive those IRF510 gates at 30mhz.
There are MMIC's that could deliver the 100mW needed to replace Q911,912
when configured as a single.

I'm really curious how well that ADA4895-2 works for driving the the IRF510's.

Still not sure about the 2v.
The MMIC's are designed for a specific operating voltage, if designed for 4.0v and
you drop it to 2.0v, it won't draw any current from the supply and won't work.
My guess is that the 4.0v (4.5v absolute max) spec on the cheap BGA616 MMIC is the "supply voltage",
used in calculating how many ohms for the dropping resistor from your particular supply rail
to get the desired 60ma quiescent current into the MMIC.  Signal rides on top of that, so it's fair to 
have instantaneous voltages in excess of 4.5v on the output pin of the MMIC.

Jerry, KE7ER


On Sat, Jun 9, 2018 at 12:25 pm, Howard Fidel wrote:

Jerry:
When you use a transformer with the push pull configuration like Q93, Q97. the collector sits quiescent at the supply voltage. Then you add the + signal swing on to that to get the maximum voltage the device sees. So with a +2 V supply, you can't go lower then 0 volts, so you can't go higher then 2+2= 4 volts. That leaves a 1/2 volt margin for derating the device.

Howard

Jerry:
When you use a transformer with the push pull configuration like Q93, Q97. the collector sits quiescent at the supply voltage. Then you add the + signal swing on to that to get the maximum voltage the device sees. So with a +2 V supply, you can't go lower then 0 volts, so you can't go higher then 2+2= 4 volts. That leaves a 1/2 volt margin for derating the device.

Howard

Howard,

Thanks for posting that!
I find it interesting that you got away without a transformer at T10.
You say flat to 30mhz, have you breadboarded it, or is that a result from simulation?

Those parts are likely a bit too expensive for hfsignals, but way more cost effective for most of us
than spending weeks trying to get some $0.15 parts to do the job.

>  The MMIC has a absolute maximum voltage of 4.5 VDC.
>  Assuming you use a transformer (actually you must to get the drive level  you need for the output stage)
>  you an only use a +2 volt supply for the device for a 4 v p-p swing.

Mouser summary for the BGA616 mmic says a 6v supply, but turns out that's the rail
feeding the resistor, the device sees 4.5v max.
Most of the new devices are shooting for very low power supply voltages. 
I can't quite follow the logic regarding the statement  "you can only use a +2 volt supply".
With a transformer between the mmic and the load it would seem the mmic supply could be most anything.
Data sheet suggests it would typically be a 33 ohm resistor from 6v, device drawing 60ma,
so 6v - 33*0.060 = 4.0v at the device if trying to use the BGA616 mmic.

At 18dBm, that mmic might just barely replace Q911,912.
But not drive the IRF510's.
Not a good choice for inclusion in the uBitx.
But still, an interesting and very cheap mmic.

Jerry


On Sat, Jun 9, 2018 at 06:00 am, Howard Fidel wrote:

Attached is my driver it goes between VR1 and the outputs of T10 you need to remove C84 and T10 and insert this circuit. I am using the AMP signal to reduce the overall power output when driving a linear amp which needs 5W not 10W. U7 is a current driver, I chose it because I have a number of them, I probably could select something better, or use an emitter follower but it should do the job at 0 cost for me. The same with the T13-1 transformer, I have them. The opamp was selected for its speed slew rate voltage and current drive capability. C45 is there because U7 needs a minimum load capacitance for stability. I will see if I need to add something there later. TX is the switched 12 volts that is there in transmit only.
I am working on a PCB with this being one part of a daughter board for the uBitx. I would be interested in any feedback. I am not suggesting that this is a cost effective way of improving the uBitx for production. I will post the entire schematic in a few days.

Those parts are likely a bit too expensive for hfsignals, but way more cost effective for most of us
than spending weeks trying to get some $0.15 parts to do the job.

Il giorno 09 giu 2018, alle ore 18:15, Bill Cromwell <wrcromwell@gmail.com> ha scritto:

Hi Allison,

This played a big part in my choice if the ubitx. I don't foresee any effort on my part to increase the power output at 10, 12, or 15 meters. I have used rigs on SSB with two watts and less on 10 and 15 meters to work the world. Of course, solar activity cycles influences that but I have worked a lot stations with power levels low enough that no meters were moving! Another way to express your point is - if we really wanted a radically different radio maybe that is what we should have bought.

Like you, I already have higher powered radios. Some of them weigh a pound per watt <evil grin>. Some are more reasonable. But 100 watt radios (even solid state rigs) on a park bench quickly burn through the batteries!

I do expect to make some minor mods involving CW keying, thumps, and a front panel "drive" control to manage the power levels. Ten watts is not *always* needed. One watt is not *always* enough. Sometimes one hundred watts is not enough. Change bands. The ubitx has all of the HF bands.

73,

Bill KU8H

On 06/08/2018 10:35 PM, ajparent1/KB1GMX wrote:
---snip------
As a QRP rig it is what it is for a good price. If I want 100W radio I
have it already.
Where the uBitx fits is the QRP replacement for a monoband only radio, its
multiband.

Allison
_._,_._,_

--
bark less - wag more

---snip------
As a QRP rig it is what it is for a good price. If I want 100W radio I
have it already.
Where the uBitx fits is the QRP replacement for a monoband only radio, its
multiband.

Allison
_._,_._,_

Attached is my driver it goes between VR1 and the outputs of T10 you need to remove C84 and T10 and insert this circuit. I am using the AMP signal to reduce the overall power output when driving a linear amp which needs 5W not 10W. U7 is a current driver, I chose it because I have a number of them, I probably could select something better, or use an emitter follower but it should do the job at 0 cost for me. The same with the T13-1 transformer, I have them. The opamp was selected for its speed slew rate voltage and current drive capability. C45 is there because U7 needs a minimum load capacitance for stability. I will see if I need to add something there later. TX is the switched 12 volts that is there in transmit only.
I am working on a PCB with this being one part of a daughter board for the uBitx. I would be interested in any feedback. I am not suggesting that this is a cost effective way of improving the uBitx for production. I will post the entire schematic in a few days.

Very nice.  I wood use a radio like that.
--
Lee - N9LO  "I Void Warranties"