Thank you, Tim.

That's certainly a better answer than assuming I want to overdrive it, or telling me what I already knew, that I needed to regulate it. I'll check RV1.

I'm still a bit confused about what kind of power to put INTO the thing, though. 12v at how many amps? My bench supply can put out 3a easily, but I've been running it at 1.5. I got one suggestion to regulate the input power...isn't that what I was doing, with the bench supply? Maybe I need a link to a reference or something, because the docs aren't very explicit and so far I've gotten 3 wildly different opinions on it.

Another that more closely resembles the V4 circuit with improvements.

The two NPN can be 2n3904 and the pnp is 2n3906.

I've used this flavor from 5V though 20V.? At 12V it will put 250mW in to a 8ohm speaker.

Allison

Tim no.

The problem is if the first transistor Q71 is not biased to the half power supply
point the output are both unbalanced and the bias is wrong.? IF Q71 collector
is not at about 6V (for 12V supply) full stop.? Adjust R72 until it is.? Then adjust
the bias if needed to the complementary pair.??

The most common variation is to derive the bias from the common point of both
emitters as then it tries to self center at 6V or half the supply.? The cost of of doing
that is lower gain but higher fidelity.

See the design from this site (attached) and explanation.


Do not let their published 3V power scare you it works well at 12V too.
The key is how Q1 is biased and the resulting bias to the output string (3904 and 3906).

Allison

It should be possible to change the V4 circuit to that.

I've build SS amps for radios up to 350W and never had RF get into a power supply.

I could understand if the antenna was poor and you had high shield currents but?
a dummy load?? No.

I'd suspect the wiring of the antenna connection from the board to the load
has the ground and RF hot reversed.? If you did that you would have RF all
over the place and possible ill effects.

I have two Astrons and they are not particularly RF sensitive.

Allison

Understanding the circuit...

Both the pre-driver and driver the pairs have their own (per transistor emitter resistors) and?
the idea is to have the device operating at a reasonable point that being 20ma per device.
If there are two its still 20 ma per deives and you get that by measuring across the emitter
resistor and applying ohms law V/R=I? so .22V arcoss a 11ohm resistor is .02A (20mA).

If too high changing the various bias resistors is called for.

Running too high a current is a waste of power and does not enhance performance.

Allison

As did I, David. Thanks for the reply. The popularity of the uBitX continues I see.

Hal
AC0AX

开云体育

Bo,

开云体育

Thanks, Iz.

This sure sounds like a good arrangement.

tim ab0wr

On Fri, 29 Jun 2018 14:41:50 -0400
"Bill Cromwell" <wrcromwell@...> wrote:

Hi Mark,

I laid out and folded a case of steel for my ubitx. Looking from the
front, my antenna connector is at the far right rear corner and the
internal connector wire is less than two inches long to reach from
the board with just a little slack. The DC power connector is over at
the far left back. The volume control is way over on the lower right
corner of the front panel along with the on-off switch. I routed the
power wires under the ubitx board to take advantage of the mostly
ground plane board to help shield it from RF at the finals, output
filters, and antenna connector. The power line runs much closer to
the front of the radio until it gets to the left side and then back.
It only comes out from under the circuit board *AT* the back corner.
There is no problem with RF. I hope this is helpful to you and others
when they layout and assemble theirs.

On 06/29/2018 01:17 PM, Mark M wrote:

The issue discussed in the 'RFI from uBitx TX after AGC and other
mods installed' thread appears to be caused by RF getting into the
12v supply and from there into the 5v supply that feeds the AGC
board (the ND6T/K5BCQ kit). At least that appears to be the issue
on mine. I thought I'd start another thread to talk about that.

I have the ubitx in a case from amateurradiokits.in. The power
comes in thru a plug in the rear panel at the right of the panel
(looking at it from the front), thru a fuse and then thru three
wires twisted together along the rear panel to the connector on the
board at the far left. There's also a polarity protect diode across
the supply. The power connector is right next to the antenna
connector and the supply wires run past the final transistors and .

I'm running the ubitx on 13.8v from an Astron 20A power supply, The
testing was done feeding a Heathkit Cantenna dummy load.

So, any suggestions on how to fix this would be appreciated. Don
mentioned heavier supply wires and capacitor at the input. I
thought I'd try re-routing the supply wires inside case to get them
away from the RF section. Moving the power connector to the other
end of the rear panel would make the run much shorter. Other than
that, I don't know. RF hardware is not my forte (I'm mostly a
software guy).

Thanks.... Mark AA7TA

Gwen,

Anytime you control the amperage to a linear amplifier, such as with a
current limiter, you make it non-linear. This will cause all kinds of
inter-modulation products. It is similar to "flat-topping" a linear
amplifier where you no longer have a linear relationship between the
input and the output.

The only way to control the maximum output of a linear amplifier is to
control the maximum input levels to it. That keeps the amplifier
linear.

The method for doing this in the ubitx is the RV1 control. If you want
less output then turn RV1 down.

tim ab0wr

On Fri, 29 Jun 2018 10:50:40 -0700
"Gwen Patton" <ardrhi@...> wrote:

You misunderstand me, Ralph. I don't WANT it to act the same. If I
wanted that, I'd just run it directly from the jump box. But I don't
want it to run away in RF, as at that level it can damage my tuner. I
want it to run at 5-10 watts, not 18-20! I can control it with the
amperage, and since the fuse is a 2A inline, I don't want it to run
more than that. So I'm certainly not going to set it to 3A unless I
want to toast marshmallows on my tuner.

sorry for bw..... finally found it.

开云体育

Got it, Ralph.

Good morning, Bill and all.

Thanks for your words.

Well, I could sleep well. :)

This is my first time to build up a transceiver in my life.

uBITX really gives me a exciting opportunity that I haven’t had in my life.

OK, time to go to AKIHABARA.

Have a good day, Bill.

// hiro, JJ1FXF


2018/06/30 3:46、Bill Cromwell <wrcromwell@...&驳迟;のメール:

Three diodes won't fix the problem that the bias on the base of Q73 is
highly dependent on Q71 collector voltage.

If you ever redesign this circuit I would use capacitor coupling from
the collector of Q71 to the bases of Q72 and Q73. The base bias
of Q73 would then be set with a resistor to ground. Then everything is
symmetric and distortion should be minimized.

tim ab0wr



On Fri, 29 Jun 2018 15:45:51 +0530
"Ashhar Farhan" <farhanbox@...> wrote:

What if we use three diodes instead?

On Fri, 29 Jun 2018, 13:35 Raj vu2zap, <rajendrakumargg@...>
wrote:

Got back to town and plugged in the uBitxr4 and found the audio
distorted.

Poking around the finals I found that the two diodes D15 and D16
gave only a drop of 1.2V total
but the final transistors needed more like 1.5V. i.e. 0.75v each.

I simply cut the track between D5 and D16 and soldered a 100 ohms
multiturn preset as shown
in picture below. (Preset leads used is center and one side)

Start with the two soldered connections of the preset set to ZERO
ohms.

Power on and tune to a station at low volume and slowly increase the
preset till the audio
becomes clear. In my board the RX power consumption increased by
25mA at the best sound.
Just check and see that the output transistors are not getting hot.

My board sounded great with 47 Ohms between D15 D16 and I run at
13.6V. If you run at the
same supply voltage then you can try a fixed resistor. For 12V
supply you could try a higher value
like 56/62 or even 68 Ohms.

Cheers

--
Raj, vu2zap
Bengaluru, South India.

[image: Emacs!]

ian or anybody, I am trying to locate the actual source of Ian's files for the NEXTION displays to download.

I have looked over Ian's web pages but just cannot find? a link to the files. Any ideas?

glenn
vk3pe

Thanks John,
glad to hear you like the software.

73 Allard PE1NWL

“DId you parallel the emitter resistors too?“
A: R87&R88? No, I was not going to, have not done anything yet but order the 2N5109.

“my 5109s wanted to sit there at 70ma and get very warm
That is way to high even 20mA (each) is more than enough.”
Q: for the predriver I was only going to use one, will 20 to 30 ma emitter current be good if only using one? (For the driver I ordered metal 2N2222A’s)

thanks

Hal
I ordered mine (6/21) and this morning (6/29) received notice it departed on DHL, estimated delivery (7/6)

David
KG7WFM