[Central-Electronics] 20A restoration: Tuning a PS-1

George W1LSB GeorgeW1LSB at verizon.net
Sun Feb 28 23:27:58 EST 2021 

Hi Jim & all: 
Sorry for the lag in responding! Great to hear from you as well. Thanks for the QRP 
labs info; quite interesting.  

A few years ago, I acquired a Juma TRX2A, which is an SDR based transceiver kit from Finland.  Long story short, it also uses polyphase networks and got me to thinking along those lines.  There are some photos of the networks on their web site: http://www.jumaradio.com/juma-trx2/

The radio itself is really sweet and gets excellent reports on the air.  Truth be told, I also have their PA-100D 100W linear which is nearly a perfect match for getting CE 10A/B and 20A exciters up to an RF level that will drive a hefty amplifier.  Thinking about my Henry 3KA here!  

Hope all is well!

73, George - W1LSB
Sent from my iPad Pro

> On Feb 20, 2021, at 3:12 PM, Jim Candela <jcandela at prodigy.net> wrote:
> 
> 
> Hi George,
> 
>    Long time no hear....Hope you are doing well. You stated, "One of these days, I’m going to get focused on building a modern day polyphase network into a PS-1 sized can.  From everything I’ve read on the subject, it should not be that difficult."
> 
> Take a look at these links, and rearrange the circuit from a receiver to a transmitter:
> 
> 
> https://qrp-labs.com/polyphase.html
> https://qrp-labs.com/receiver.html
> 
> 
> Quite doable idea I think. 
> 
> 73,
> 
> Jim
> Wd5JKO
> 
> On Saturday, February 20, 2021, 11:52:51 AM CST, George W1LSB via Central-Electronics <central-electronics at mailman.qth.net> wrote:
> 
> 
> One of these days, I’m going to get focused on building a modern day polyphase network into a PS-1 sized can.  From everything I’ve read on the subject, it should not be that difficult.  
> 
> Keep ‘em going guys!  Love those 20A’s.
> 
> 73, George - W1LSB
> Sent from my iPad Pro
> 
> > On Feb 20, 2021, at 10:15 AM, Jim Candela <jcandela at prodigy.net> wrote:
> > 
> >  Another good reference, see Reply 17:
> > http://amfone.net/Amforum/index.php?topic=27305.0
> > 
> > JimWd5JKO
> >    On Saturday, February 20, 2021, 9:07:43 AM CST, Jim Candela <jcandela at prodigy.net> wrote:  
> > 
> >  Somehow I hit send while typing...see below:
> >    On Saturday, February 20, 2021, 9:01:53 AM CST, Jim Candela <jcandela at prodigy.net> wrote:  
> > 
> >  Bill, etc, all;
> > Since your PS1 is likely broken, I'd try to isolate which section is miss-behaving. As I recall, one side has a 45 degree "lead", and the other has a 45 degree "lag". Therefore I would check each side individually to narrow the problem in half.
> > The link below has a lot of good info, particularily Reply 6 from me:
> > http://amfone.net/Amforum/index.php?topic=37143.0
> > 
> > Many easy to implement enhancements...
> > 73,JimWd5JKO
> >    On Friday, February 19, 2021, 10:32:38 PM CST, Bill Blackwell <bblackwell2009 at gmail.com> wrote:  
> > 
> > A couple of folks wanted more info so I am copying the group.
> > 
> > First, the issue of GE Ham News describing PS-1 alignment is here: http://n4trb.com/AmateurRadio/GE_HamNews/ge_ham_news.htm
> > Scroll down to Volume 5, Number 6 for Nov-Dec 1950, and download the PDF. It's the article on Page 1, "SSB Jr."
> > 
> > To those who know the 20A, the schematic will be familiar in the modulator stages and the PS-1, which is identical, including labeling and values of caps and resistors. PS-1 alignment begins on Page 6 for those who built it from components. The Designer's Corner following the article is by the same author and designer, Don Norgaard, W2KUJ. We are very grateful to Brian Page N4TRB, for providing these wonderful issues of GE Ham News from the past.
> > 
> > Dave: Yes, I measured the phase shift by using a dual trace scope and wave generator. I applied an audio signal from the WG to the mic input of 10 mV peak (7.1 mV RMS) to stay below distortion level. The probes were connected to pins 2 and 7 (grids) of the 12AT7(b) which are the PS-1 output. Starting at 300 Hz I could see both signals in quadrature (90 deg). Changing to 1 kHz and beyond, I watched the traces go farther apart as I went up in frequency. They shouldn't do that. At 1.5 kHz they were actually 180 degrees shifted.
> > 
> > If you switch the scope to XY mode you should see a perfect circle when the phase shift is 90 and amplitudes are equal. If unequal, an ellipse. If not 90, the ellipse or circle will be slanted. Voltages of input pins to PS-1 should be in a 2:7 ratio so adjust R15A to get that. I tested all audio frequencies with speech level pot at 50% and 100% (fully clockwise) and results were unchanged.
> > 
> > One effect of the signals not being at 90 degrees is that one sideband will not be suppressed enough. For the 20A, 40 dB suppression is the goal.
> > 
> > I am new to the list and haven't searched the archive to see if this material is anywhere else, so please excuse if it is!
> > 
> > 73,
> > Bill
> > AB1XB
> > 
> > -----Original Message-----
> > From: David Olean <k1whs at metrocast.net> 
> > Sent: Friday, February 19, 2021 5:44 PM
> > To: bblackwell2009 at gmail.com
> > Subject: Re: [Central-Electronics] 20A restoration: Tuning a PS-1
> > 
> > Bill
> > 
> > I would be interested in what you find. I have a 20A that I restored, but I did not check the phase shift network. The SSB sounds good and I did not investigate further. How did you measure the phase shift?  Did you use a dual trace scope and an audio oscillator?  I will drag mine back out and check it.  Any details?
> > 
> > Dave K1WHS
> > 
> >> On 2/19/2021 4:51 PM, Bill Blackwell wrote:
> >> Good afternoon.
> >> 
> >> Has anyone tried to tune a PS-1 phase shift network?
> >> 
> >> The 20A that I am restoring has about a 150-degree audio phase shift 
> >> measured at the PS-1 output pins, at 1000 Hz. At higher frequencies it 
> >> gets worse. At lower frequencies (around 390 Hz), it's a perfect 90 degrees.
> >> 
> >> The PS-1 input voltage divider is correct at very near a 2:7 voltage ratio.
> >> Phase shift is constant over any speech level input. So I suspect one 
> >> or more of the capacitors in the PS-1 has drifted out of tune or gone 
> >> bad in the 50+ years it has sat on the shelf.
> >> 
> >> I found, thanks to N4TRB, the issue of GE Ham News where Don Norgaard, 
> >> designer of the "SSB Jr" (precursor of the CE exciters), describes how 
> >> to tune the PS-1 in some detail. Is this the best way to go about it? 
> >> I hesitate to start clipping component leads in this little box to 
> >> start testing and tuning. The fact that lower frequencies are OK while 
> >> higher ones are not, could indicate which RC pairs I should start with first.
> >> 
> >> Is there a better way? Any help or insights appreciated.
> >> 
> >> Thanks, 73!
> >> 
> >> Bill
> >> AB1XB
> >> 
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