SP44 pan adapter with SX28

[ke7trp]

I got an Sp44 to go with my SX28.  I read the manual for the SP44 several times.  Under the install, it says, Remove the converter tube, put the spring on the plate pin and the ground to the chassis, Put the tube back in.  Ok.  What tube is this in the SX28? 

On my other radios with pan adapters, they hook to the First IF tube or the IF output jack. 

Any help would be great. I would like to get it installed tomorrow as I have the time. I just cant find much info on the web.

C

[ke7trp]

I found instructions to hook a military Pan adapter up. They tell you to use the plate of the Mixer tube V3 and to use a 10PF or smaller Cap as to not load the reciever down. 

The Sp44 says to hook to the convertor tube directly to the plate. No cap.  On the SP44 schematic, they show a .01 inline from that wire into the rest of the schematic.

Any help would be great. I dont want to damage anything.

C

[Pete, WA2CWA]

Mixer (sometimes called Converter tube or 1st Detector tube depending on the receiver) is 6SA7. Connect one end of a 56K (approx.) resistor to pin 3 of the 6SA7 mixer. Keep the lead short. Other side of resistor connects to center conductor of coax. Ground the shield of the coax at this point to ground. Connect other end to SP-44. Keep the coax length as short as possible between receiver and SP-44. Panadaptors are always connected before the IF amplifiers not after them.

[The Slab Bacon]

Mixer (sometimes called Converter tube or 1st Detector tube depending on the receiver) is 6SA7. Connect one end of a 56K (approx.) resistor to pin 3 of the 6SA7 mixer. Keep the lead short. Other side of resistor connects to center conductor of coax. Ground the shield of the coax at this point to ground. Connect other end to SP-44. Keep the coax length as short as possible between receiver and SP-44. Panadaptors are always connected before the IF amplifiers not after them.

The first mixer / converter plate is also the point where you would jump in a Q-Multiplier.

You want the panadapter connected in BEFORE the IF amp so as not to influence its range / display with the receiver's IF bandwidth.

[KM1H]

AND in the SX-28 that 1st IF is part of the NB circuit so you will see all the static crashes at the 6SA7 plate. The SP-44 will be jumping but the speaker noise will be muted. For that reason I dont care for using it below 20M.

I have a pair of SP-44's and the other will be going on the HRO-60 once its overhauled.

Carl
KM1H

[ke7trp]

Ok.. So V3. Its in the box on the 28. Second tube back.    Thanks so much for the info Pete.  Why the 56K resistor? 


C

[ke7trp]

Ok..  Here is a pic of the scope. Its wonderfull.  It has a nice screen and line on it. The case is just great. There is a dent on the case on the back. I am going to eventualy knock that out.  Sitting on the table, It wont show.

Making up the cable now.. Going to take petes advice and try the resistor to the Coax cable.. I will post pics of it working later!

C

[ke7trp]

Well that was easy.. Thanks to the directions posted in this thread!

I found an old BNC cable. Cut the end off, Stripped the wire back.  I soldered a 70K resistor inline. I did not have a 56K.  I used heat shrink over the resistor. Then made a loop to go around the tube pin number 3 on the plate of the Mixer tube.  I put a second piece of heat shrink on so just the loop is exposed. 

I then soldered a clip lead onto the shield wire and heatshrinked that connection. 

Install is simple.. Open cover, Remove tube. Place the Ring around the tube pin 3.  Clip the ground to the case, Feed the wire out the back.  This way the reciever is not modified in any way.  I can use it any reciver I have.

It sure works and looks just great!

Thanks for the help once again!  Now for the pictures!

clark

[ke7trp]

More pics

[Pete, WA2CWA]

Nice, but, can it do this:

[ke7trp]

Pete. I got a problem. The thing works FB on BC band.  But on 75, I cant see anything.  I through a 25 watt carrier on the icom and I can see that.. But nothing on the actual band. Even when the S meter is at 40 DB over from AM stations.

Also.. The RF gain does not effect the PIP.  On my Heath pan adapter and the SP600, It does. IS that the nature of the Receiver?

Cable to long? Its about 3 to 4 ft.  I used a 70K Resistor.

C

[Opcom]

Pete, it can't do that unless you hook it to a computer and build an elephantine adapter, which would totally defeat the purpose of the instrument itself. Why downgrade?

[K9ACT]

Pete, it can't do that unless you hook it to a computer and build an elephantine adapter, which would totally defeat the purpose of the instrument itself. Why downgrade?

Never ceases to amaze me what excuses people use to rationalize stone age technology.

That tiny scope makes a nice mood light and a fun project to get going but it no longer has any real purpose.

You could build a Soft Rock in less time and have a real man's panadapter.

Having said that, I would really like to see a picture of what it actually displays when you get it working.
I almost bought one before I discovered Softrock and would like to see what I "missed".



js

[Opcom]

Looking at the way the SX-28 is made, the RF gain and the two AVC's are operated separately.

The RF gain knob controls the resistance from all the cathodes in the RF and IF stages except the mixer V3.

The AVC circuit #1 is V8 the 6B8 amplifier and AVC detector which is fed by the mixer output and is controlling (making) the grid bias on RF amps V1 and V2 and the mixer V3.

AGC #2 is taken from V7 the detector's diode and is used to control the 1st IF V5's bias only (and the same tube drives the S meter).

The point of this is that there is a lot going on, if something is wrong, the S-meter could show strong and yet the signal there be attenuated.

Have you used a scope to look at the signal on the plate pin 3 of the mixer?
For the same S-meter reading, what difference is there between it on the BC band and on the 3 to 5.8 MC band?
Is the difference according to the microvolts expected?

Bands 1 and 2 have that extra RF amp. Band 3 where 75m is, does not have it. Could there be an RF amp or mixer problem?

Could C1 the input blocking cap in the panadapter be leaky?

Just throwing some things on the table that are pretty easy to revisit.

[ke7trp]

We tested all bands on this 28.  All where 1 except 10 meters which was 1 5.   Its super hot on all bands.  Hotter then the SP600.  I actualy run the Gain down in the 7 or 8 range and not full out.  I was comparing it to the Sp600 the other day on 75 and 40 am.  Its showing higher S meter and louder audio.. But ALOT less noise between band conditions.  This receiver has had ALL caps and resistors changed. ITs rebuilt.

This being said, I dont think there is an issue with the 28.  Its possible.. But it sure seems FB.

I put 455 into the pan adapter. It had a huge pip. It seems to be working. It works FB on the BC band.  Nice signals. I can see the width of different stations ect..

I think my trouble is in the coupling of the pan adapter to Pin 3.  I used a 70K resistor as I did not have the 56K that pete suggested.  Tomorrow I am going to try a few different resistors and maybe none at all.  I might try a coupling cap like 10 puff. 

The other thing is that the Cable I am using now is LONG. Its possible that there is just not enough signal to reach the scope.. After I play around with the new cable and hook up, I will report back.

Thanks alot for the help.

As for why some people use old gear, We like it.  ITs just that simple.  I like the 28 and I like the Pan adapter.They look great to me in the shack and they are a real conversation piece.

 I agree. the pan adapter is not very usefull.   Its a neat thing to have with the receiver and thats about it We talked about this on 40 AM today.  These old pan adapters are a novelty.

Clark

[Opcom]

aww Pete is just jealous and stirring the pot.. I didn't see any excuses in the post.

Maybe it is the connection method, but it's odd that the mixer output should have the same spectrum at its plate on any setting yet once the setup goes above the first two bands the signal is difficult. It will be interesting to see if redoing the cable and connetion fixes it. I too have an SX28 and would like to do something similar.

Something that occurs to me is that the RF cable might very well be part of the tuning circut for the input transformer of the panadapter. It is so for some other models like the Panoramic SA-1 about which Chuck McGregor (master of panoramic adapters) has said to me: "Originally, there would have been a grommetted hole in the chassis with a shielded cable about 3 feet long coming out. Cable type at that time was apparently low-capacitance microphone cable with rubber dielectric. Polyethelylene dielectric coax cables were currently under development. The capacitance of the cable from this connector on to the receiver is part of the capacitance tuning the input transformer, and must be present for alignment." the online SA-1 manual also says this same thing and its schematic is almost exactly the same as the Halicrafters because it was made for Halicrafters by Panoramic. About the resistors, the SA-1 uses a 250K. just an interesting point, might have to do with bandwidth of +/- 50KC instead of +/-100KC.

[ke7trp]

I will let you guys know what I find.  I am going to try a handfull of resistors and caps today.

C

[ke7trp]

I got it to work FB!   

Sorry for all questions. In the end it was my fault.  When I looked at the schematic and found pin 3, I flipped it. I simply had the cable on the wrong pin. 

The sockets are not labled. I got a tube adapter from my TV7 and found Pin 3.Then confirmed that was to the right of the Notch.  It now works 100% on all bands. 

The RF gain controls the Pan adapter and now I have a decent pattern.  I calibrated it. I can see 200KC. 

Thanks for all the help! 

Clark

[w1vtp]

Pete, it can't do that unless you hook it to a computer and build an elephantine adapter, which would totally defeat the purpose of the instrument itself. Why downgrade?

Never ceases to amaze me what excuses people use to rationalize stone age technology.

That tiny scope makes a nice mood light and a fun project to get going but it no longer has any real purpose.

You could build a Soft Rock in less time and have a real man's panadapter.

Having said that, I would really like to see a picture of what it actually displays when you get it working.
I almost bought one before I discovered Softrock and would like to see what I "missed".



js

Agree.  But having said that.  I have one of those old panadapters that worked 25 years ago.  Problem is the CRT is burnt where the trace is most of the time.  I'd like to hook it up to my Hammarlund SP-400 when I get it going mostly to see the thing work.  I'll probably use the SDR display if I get serious with using it in my station.  Who knows? It might be useful.  It's a slick thing to look at. It does need some sort of trace gigit to keep it from burning the CRT

Al

[ke7trp]

I took a few short videos of the pan adapter in action.  They are 300K each.  I cant upload them. The site wont let me.  If anyone wants to see them, Just email me.  Clark at clarkturner dot com  I wills end you the videos.



You will need to download these and play with quicktime.

[KM1H]

Nice, but, can it do this:

I'd rather have the old Halicrafters stuff

The last thing I want in a vintage shack recreation is a bunch of noisy computer crap. 

Carl
KM1H

[ke7trp]

Yeah. I have one laptop computer on the table   I sold all that flex and SDR crap off.  Its great for monitoring.  But why would I concern myself with how someone is operating his or her station?  Thats just smug

C

[Pete, WA2CWA]

Connected it initially to Pin 6 
Keep the resistor at around 50K or more. You don't want to load down the SX-28 IF transformer connection. Cable length should be 24 inches or less.

[Pete, WA2CWA]

You can see typical displays in the SP-44 manual or the Panoramic PCA2 manual

[ke7trp]

Yeah..  Let me ask a stupid question.. When you see a tube diagram in a manual. Are you looking at the tube from the top or bottom?

I works GREAT now Pete. No loading down at all with 70K resistor.  I am on 40 AM now at 7293.  There was a Sidebander on 7290. I could really see him on the scope. I narrowed down and slid over and he is about gone. Pretty neat.

C