Date   
Re: The issues of the TDA2822

Jerry Gaffke
 

My impression is that the WX failure mode is one of too high a supply voltage
suddenly puncturing a barrier somewhere.  
There may be no noticeable heating prior to the failure.
Perhaps those cut from the periphery of the silicon wafer are more likely to fail.

Raj reports that with very loud audio coming through while running at 12v,
he can short the output of his FCI TDA2822 and have it get hot but not fail. 
There are likely other poor quality clones beyond the WX,
but TDA2822's from reputable vendors don't seem to fail even when abused a bit.

Jerry


On Mon, Mar 26, 2018 at 12:39 pm, Arvo KD9HLC wrote:
On Mon, Mar 26, 2018 at 12:00 pm, Tim Gorman wrote:
I have run the tda2822wx for 24/7 over the past week. No problem. The
chip never even gets warm on the strongest signals. This is with 12v
applied to the 2822.
Hi, Tim.

This is consistent with what''s been reported, that some WX chips seem fine while a few suffer early failure.

Re: #bitx40 #ubitx #bitx40 #ubitx

Don, ND6T
 

Thanks Jerry! I'll check it out. Shouldn't be any problem going the other way with control voltages. Guess I had better hold off and try that one. Great catch! Or was that a "save"? -Don

FS:Ubitx and Bitx40 ++

 

I have a Ubitx with CEC firmware and a bitx40.

 

Bitx40 Has the following:

USB/LSB

CW (using a qrpguys v1 keyer)

CW Zero beat LED

Nescaf cw filter

AGC with on/off

Mic is a new element JLI-52B

Silver case built like a tank. I have modded the power in to the raduino with the RC filter, as well as the LPF mod. The bpf is still the stock version with a little tweaking.

The radio is working 100% used CW/SSB/Digi no issues.

Ubitx Has the following:

Stock setup with CEC firmware has usb case mount and room for mods. TDA WX version has been replaced with IC socket as well as a 2073 works top notch.

 

I also have a QRPguys multi Z tuner unbuilt and a digital interface (will work with either radio) for sale as well.

Price:

Ubitx 120$ shipped with Stock Mic

Bitx40 100$ shipped With New mic element

Multi Z tuner 35$ shipped

Digital interface for either one is a easydigi with a FTDI232 board 25$

Will sell all as a package for 270$

If anyone has questions please send me a private mail/msg

 

 


--
David

 N8DAH
Kit-Projects.com

Re: #bitx40 #ubitx #bitx40 #ubitx

Jerry Gaffke
 

A BAP64Q pin diode attenuator gives 60dB of dynamic range:  https://groups.io/g/BITX20/message/32066
Attenuating back in RF gets around the limited dynamic range that Henning points out in the first post of that thread.
Note that the control voltage is inverted with respect to the 2n7002 FET, higher voltages give less attenuation.
Could get a slightly lower noise figure for the receiver if the attenuator is inserted at a later stage of the RF chain.

The BAP64Q is relatively expensive at $0.50 single piece,
the frugal among us will note it's down at $0.20 if you buy a few thousand. 
Mouser and Digikey both stock it, Mouser points you to the wrong BAP64* datasheet.
There are other similar small signal pin diode attenuators out there from other manufacturers.

Jerry, KE7ER


On Mon, Mar 26, 2018 at 01:18 pm, Don, ND6T wrote:
The "problem" isn't the detection, rather the range of a single control element (the MOSFET in this instance). 20 dB is pretty good but I shall always crave more.

Re: #bitx40 #ubitx #bitx40 #ubitx

Don, ND6T
 

As you can see, I am using a single BJT to amplify the sample from the hot side of the volume control. The "problem" isn't the detection, rather the range of a single control element (the MOSFET in this instance). 20 dB is pretty good but I shall always crave more. Probably another MOSFET up the receive chain is my next experiment. First, though, I want to tame the uBITX by installing the board there (providing an S meter there, too) and keep moving onward. No, I don't believe that AGC action is necessary below S8 or S9. My background noise level is usually S5 to S7. Instead, I am adverse to those loud excursions described in the article. I tried more amplification (quite simple to do) and it does not help things. I usually run the RF gain a bit low. All of the BITX series have very good gain and there is no reason to go flat out unless one enjoys listening to hiss.
More gain is easily accomplished by adding another BJT in cascade (another 2 cents). A wider control voltage range is available by adding 2 diodes and 2 capacitors for a voltage doubler (10 cents). Neither increases the dynamic attenuation range. Without an RF pre-amp stage we need to either improve the control element or add more of them up the receive chain. VVAs at this frequency either have excessive insertion loss or cost just too darn much. A single 2N7002 (2 cents) as a shunt shows no insertion loss at idle. Simple is good.
I'm just saying that there is always room for improvement.

Re: The issues of the TDA2822

Arvo W0VRA
 

On Mon, Mar 26, 2018 at 12:00 pm, Tim Gorman wrote:
I have run the tda2822wx for 24/7 over the past week. No problem. The
chip never even gets warm on the strongest signals. This is with 12v
applied to the 2822.
Hi, Tim.

This is consistent with what''s been reported, that some WX chips seem fine while a few suffer early failure.

Re: #bitx40 #ubitx #bitx40 #ubitx

Tim Gorman
 

Don,

What circuit are you using to obtain the agc voltage?

Even a simple 741 op amp would give more dynamic range than this (I
assume the use of a noisy op amp isn't a problem in an agc loop like
this).

Is the problem the dynamic range of the input signal?

tim ab0wr

On Mon, 26 Mar 2018 11:45:52 -0700
"Don, ND6T via Groups.Io" <nd6t_6=yahoo.com@groups.io> wrote:

Oh, it works. Been using it for more than a week. I would like more
dynamic AGC range (20 dB isn't quite enough for me) but it is the
best I have tried so far. -Don

Re: The issues of the TDA2822

w7hd.rh <w7hd.rh@...>
 

That is correct - either should work.  I chose to put it on the input side (pin 3) for simplicity.

Ron W7HD


On 03/26/2018 10:38 AM, Daniel Conklin wrote:
Ron, In your description you say put the capacitor between pin 1 and ground, but the photos shows between pin 3 and ground.  From the circuits I've seen it could be one or the other or both, so it's not going to cause a problem.  The capacitors are to filter off anything that's not DC current on either side of the regulator.
Dan,
W2DLC

-- 
Ron W7HD - NAQCC#7587 OMISS#9898 KX3#6966 LinuxUser#415320
Editor OVARC newsletter

Re: The issues of the TDA2822

Tim Gorman
 

Kevin,

I have run the tda2822wx for 24/7 over the past week. No problem. The
chip never even gets warm on the strongest signals. This is with 12v
applied to the 2822.

My cautions are *never* operate the 2822 with no load and never plug a
mono plug into the stereo jack if it is wired per the wireup
instructions.

The stereo jack has a switched connection that is closed when no plug
is inserted. Wire a small resistor to ground from that connection,
eight to 20 ohms. That way the 2822 will always have a termination and
will allow the series capacitor from the 2822 to charge slowly so you
don't get a big current spike when you plug in a speaker or headset.

I used a mono jack and wired an internal speaker to the switched
connection on it. The 2822 always has a load to work into. And the mono
jack doesn't risk shorting the 2822 output to ground like the stereo
jack can do. My internal speaker is an 8ohm speaker.

Most of the 2822 failures I've read about on here seem to be a thermal
failure, i.e. the case cracks. Voltage failures typically cause open
circuits instead of short circuits thus limiting thermal failure
symptoms. Thermal failures typically happen from high currents, caused
by the 2822 being hit with high current while charging the series
output capacitor or from operating the 2822 into a short caused by
using a mono plug in the stereo jack.

Limiting the voltage to the 2822 will, of course, also limit possible
current flows but it will also limit the possible output levels from
the 2822. That may not be a problem with most high efficiency
communications speakers.

Let us know what you decide to do.

tim ab0wr





On Mon, 26 Mar 2018 02:50:35 -0700
"Kevin Luxford" <kbgluxford@...> wrote:

Hi Raj
I am trying to implement your fixes for the audio problem.  I have a
16 ohm speaker on the way to me.  I am just trying to install a 78M09
voltage regulator.  I have removed the green masking over the track
as indicated in your picture.  However, with the board in the same
orientation as in your photo, the left end of the track is connected
to pin 2 of the TDA2822.  If I install the 78M09 in the same
orientation as shown in your photo, it appears to me that the input
of the regulator would be connected to pin 2 while the output would
be connected to the supply voltage.  To my inexperienced eye, the
regulator should perhaps be installed turned through 180 degrees,
i.e. with the tab facing the board edge opposite that of the
heatsinks.

Could you please enlighten this old ham before he ruins his lovely
uBITX?

Many thanks and vy 73

Kevin VK3DAP / ZL2DAP

Re: #bitx40 #ubitx #bitx40 #ubitx

Don, ND6T
 

Oh, it works. Been using it for more than a week. I would like more dynamic AGC range (20 dB isn't quite enough for me) but it is the best I have tried so far. -Don

 

Re: #bitx40 #ubitx #bitx40 #ubitx

Tim Gorman
 

Don,

Good idea!

I expect the mosfet will withstand any reasonable RF signal. Let the
group know how it works out!

tim ab0wr

On Mon, 26 Mar 2018 07:48:47 -0700
"Don, ND6T via Groups.Io" <nd6t_6=yahoo.com@groups.io> wrote:

Tim,
I opened the receive trace between K1 and K3
here ( http://www.nd6t.com/uBITX/RF%20Gain ) for the RF gain control.
This board is mounted on, and connected to, that pot. That way it has
no problems with the mixers and amplifiers. I've been using that mod
on BITX units for more than a year now without issues so I feel safe
in doing it. 73, Don

Re: The issues of the TDA2822

Arvo W0VRA
 

On Mon, Mar 26, 2018 at 02:50 am, Kevin Luxford wrote:
Could you please enlighten this old ham before he ruins his lovely uBITX?
The simplest fix is to replace the WX branded TDA2822 with one from a reputable manufacturer.

There is no evidence that further mods are necessary.

Re: The issues of the TDA2822

Daniel Conklin <danconklin2@...>
 

Ron, In your description you say put the capacitor between pin 1 and ground, but the photos shows between pin 3 and ground.  From the circuits I've seen it could be one or the other or both, so it's not going to cause a problem.  The capacitors are to filter off anything that's not DC current on either side of the regulator.
Dan,
W2DLC

Dual Display?

Dexter N Muir
 

A suggestion for those afflicted by FFS (Fat Finger Syndrome) but wishing for both fine granularity of frequency determination *and* rapid transition between bottom and top of band (CW to DX):
How about a dual display: keep your digital readout with 10 or 100Hz fine resolution and
For the BITX40 put Shuttle Tuning in play, changing the step size/speed and direction according to how far you're twisting the knob, or
For uBITX use the standard Dynamic tuning that varies the step size per speed of rotation of the tuning knob, then:
There's little chance of being able to display a position within up to 500kHz of band spread (on HF) both quickly and accurately on a rapidly-changing digital display, so convert your frequency readout to a digital span from zero to (say)1023 or 4095 -  10 or 12-bits (even the 1-byte 8-bit 255 might be enough), feed that into a D-to-A to give 0-5V out and measure that with an analog meter. You're far more able to follow a needle pointer to a reasonable approximation of your intended frequency while the knob's in a fast spin, and you'll develop a 'feel' for when best to stop the spin, then turn (more) slowly and get there while watching the Digital. It'll be a bit like the old dial-cord and pointer days, particularly if you use a soft detent (or none) in the encoder and a bit of flywheel mass on the shaft.
Comment/flames welcome, 73 ...
Dex, ZL2DEX

Re: Bitx20 I have completed the RF section and now doing the current test on transmit and recieve. #bitx20help

kc0wox Leeper
 

That confused the issue again. Is it a 2 board set?

Is this the pa board you are working on?
http://golddredgervideo.com/kc0wox/bitxver3new/linear.htm
Leonard

Re: Junkyard uBITX #ubitx

kc1at
 

Yup love radio surgery....its more rewarding than most QSO's I've had....and I've been a ham for over 40 years.

Got an AGC and mic audio compressor on the bench now...going to finish those up and duct tape them onto the board...
I do that cuz I know they're not going work the way I want them to. More surgery needed....

don

Re: #bitx40 #ubitx #bitx40 #ubitx

Don, ND6T
 

Tim,
I opened the receive trace between K1 and K3 here for the RF gain control. This board is mounted on, and connected to, that pot. That way it has no problems with the mixers and amplifiers. I've been using that mod on BITX units for more than a year now without issues so I feel safe in doing it. 73, Don

Re: #bitx40 #ubitx #bitx40 #ubitx

Tim Gorman
 

Don,

Where in the ubitx do you plan to tap into the RF part of the receiver?

There doesn't appear to be a good point to introduce an attenuator
without upsetting the termination insensitive amplifiers which are
critical to the double-balanced mixers terminations.

tim ab0wr

On Mon, 26 Mar 2018 06:52:48 -0700
"Don, ND6T via Groups.Io" <nd6t_6=yahoo.com@groups.io> wrote:

I just installed a 20 dB RF AGC modification in the BITX40. I have
not installed it in the uBITX yet but intend to soon. I have posted
the project on nd6t.com. ( http://www.nd6t.com/bitx/AGC.htm ) It's a
simple circuit and replaces the S meter circuitry, too. 73, Don

Don, ND6T
 

Sorry, forgot to title it!
I just installed a 20 dB RF AGC modification in the BITX40. I have not installed it in the uBITX yet but intend to soon. I have posted the project on nd6t.com.
It's a simple circuit and replaces the S meter circuitry, too. 73, Don

#bitx40 #ubitx #bitx40 #ubitx

Don, ND6T
 

I just installed a 20 dB RF AGC modification in the BITX40. I have not installed it in the uBITX yet but intend to soon. I have posted the project on nd6t.com.
It's a simple circuit and replaces the S meter circuitry, too. 73, Don