[SignalOne] [signal-one] Transmit Level

jerry jerry at tr2.com
Tue Nov 19 17:31:28 EST 2024 

On 2024-11-19 11:06, K5OG wrote:

> If you want more power hook it up to an Alpha 77.  HI HI

*** Don't have an Alpha 77 :(.   However - I *do* have an Alpha 78.
It's sitting out in the (insulated, sheetrocked & waterproof ) shed.  I 
was thinking it
would be fun to put together an ultimate 70's station with the CX7A and 
the 78.

The 78 got obsoleted by a homebrew project; a 1-KW LDMOS.  Much smaller, 
lighter
and acoustically very quiet.  The switching power supply is in a box 
under the bed.
This little guy makes 1100W *output* running off a 15A 125V socket!  
It's got the biggest
heatsink I could fit - sticking out the back.  Almost the whole back 
panel is heatsink.
And two dead quiet Noctua fans fastened to the back of that heatsink.

                     - Jerry, KF6VB







> 73 de
> Fred
> K5OG
> www.signalone.org
> 
> On 11/19/2024 12:54 PM, Phil Patton via SignalOne wrote:
>> 
>> This list is for discussions regarding collecting, repair, use and 
>> sale of Signal/One radios and accessories.
>> 
>> Documentation on Signal/One radios can be found at 
>> http://www.hamanuals.com and several other sites on the Web.
>> 
>> .
>> The pots you mentioned are likely misadjusted. One of them is to be 
>> adjusted to zero volts. If it is off it can cause what you are seeing. 
>> The procedure is in the manual.
>> 73,
>> Phil
>> 
>> Sent from Proton Mail Android
>> 
>> 
>> -------- Original Message --------
>> On 11/19/24 10:59 AM, jerry-KF6VB <jerry at tr2.com> wrote:
>> 
>>>   Well,
>>>        The Plot Sickens, as my mother used to say.  It's the ALC.  I
>>>   disconnected it and all the gain was back.  Of course, without it
>>>   there is no protection for the tube grids, and you have to be very
>>>   careful.  But there's full output with the OUTPUT control at
>>>   nine-oclock,
>>>   and also full output on 10M.
>>>        I already found one severely drifted carbon comp resistor in 
>>> the ALC
>>>   system;  I wonder if there's more?
>>>        In the table of transmit voltages, the manual says:
>>>     5.  This measurement point is ALC voltage.  It must be within +/- 
>>> 100MV
>>>   P-P of the voltage present at IC1 Pin 1.
>>>     What does that even mean?  ALC is a *DC* voltage.  There are 
>>> multiple
>>>   bypasses - and a 10uF electrolytic to make
>>>   sure it's DC.
>>>     OK.  With the ALC disconnected and scoped, and the radio in TUNE 
>>> mode
>>>   and the output control full CCW ( no output ),
>>>   the ALC voltage is -400mV.  If I start gingerly turning the output
>>>   control CW, it suddenly jumps to -4V.  Keep turning,
>>>   and it jumps to -11.4V.  These jumps seem to occur in discrete 
>>> steps.
>>>   Turn the knob down, and the ALC lazily drifts back up to -400mV.
>>>     I'm guessing that the initial -4V is the "screen current" jump, 
>>> and the
>>>   second one is the "grid current" jump.  Or
>>>   I could be wrong.  What happens when a zener diode conducts into a 
>>> high
>>>   impedance?  Is the voltage of the zener subtracted?
>>>     It's possible that I have simply misadjusted R31, R34 and R19.  I 
>>> think
>>>   I'll review those settings.
>>>                     - Jerry, KF6VB
>>>               On 2024-11-19 08:01, jerry wrote:
>>>   > This list is for discussions regarding collecting, repair, use 
>>> and
>>>   > sale of Signal/One radios and accessories.
>>>   >
>>>   > Documentation on Signal/One radios can be found at
>>>   > http://www.hamanuals.com and several other sites on the Web.
>>>   >
>>>   > .
>>>   > Hello!
>>>   >
>>>   >    My CX7A is transmitting well on all bands except 10M.  
>>> However, the
>>>   > transmit chain seems to have low gain.  For decent output, I have 
>>> to
>>>   > turn the OUTPUT knob all the way CW.  According to the manual, I
>>>   > shouldn't have to turn it
>>>   > past 9 O'Clock!
>>>   >
>>>   >    The list of transmitter voltages in the manual is confusing to 
>>> me.
>>>   > The exact conditions of measurement.
>>>   >
>>>   >   SO:  Here I have the radio on 40M.  TUNE mode.  100W output.
>>>   > Probing at the input to the RF board ( Pin 267 ).
>>>   > The OUTPUT control is slightly past its midpoint.  Seeing 760mV
>>>   > peak-to-peak.
>>>   >
>>>   >   Can anybody tell me:  is the low gain BEFORE that input, or 
>>> AFTER it?
>>>   >
>>>   >   OK, I think I answered my own question.  Regardless of 
>>> conditions -
>>>   > the table says that when the voltage at the
>>>   > RF board output is 40V p-p ( see some clipping at that level ), 
>>> the
>>>   > input voltage at pin 267 should be 180mVp-p.
>>>   > Whereas it is ACTUALLY 940mV p-p.  So something ON THE RF BOARD 
>>> is not
>>>   > performing up to spec.   The board as a whole
>>>   > should have a voltage gain of 222 whereas it actually has a 
>>> voltage
>>>   > gain of 42.
>>>   >
>>>   >   Now to do the same exercise inside the board.  I really hope 
>>> it's
>>>   > the CA3028A;  I have two of those here.  The big
>>>   > transistors are pretty much unobtainium.  But it's not 
>>> necessarily a
>>>   > semiconductor;  this thing is full of carbon comp
>>>   > resistors, and I have already found two that have drifted up in 
>>> value.
>>>   >
>>>   >   For this work, I really love my Hantek 2D72 handheld 
>>> oscilloscope.
>>>   > It has measurement functions that let me just
>>>   > read voltages off a tiny numeric display, instead saying "Lemme 
>>> see:
>>>   > We're set at 100mV per division, and we have a 10x probe, and the
>>>   > signal starts HERE and ends THERE and...let's nudge it down just 
>>> a bit
>>>   > and look at the top..."
>>>   >
>>>   >                         - Jerry, KF6VB
>>>   >
>>>   >
>>>   >
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