Warning: Creating default object from empty value in /homepages/11/d132647312/htdocs/Amfone/mkportal/include/SMF/smf_out.php on line 47
Gonset G-50




 
The AM Forum
June 20, 2018, 03:22:23 AM *
Welcome, Guest. Please login or register.

Login with username, password and session length
 
   Home   Help Calendar Links Staff List Gallery Login Register  
Pages: 1 2 [3]   Go Down
  Print  
Author Topic: Gonset G-50  (Read 2084 times)
0 Members and 1 Guest are viewing this topic.
WB4YVO
Member

Offline Offline

Posts: 28


« Reply #50 on: June 07, 2018, 07:31:16 PM »

Well, I messed it up again.. I was trying to get more power out by adjusting L2 and L3 for Grid current.. got about 15 watts output  Then I turned it off put it right side up and powered it up again.. Now I get NOTHING.. NO RX and NO TX.. Have no clue what I did to make it stop Receiving..  Only thing I touched was L2 and L3 ..

Not happy with myself I should have left well enough alone..

Skip

   
Logged
PA0NVD
Member

Offline Offline

Posts: 224


Nico and Chappie (Chappie is the dog...)


« Reply #51 on: June 07, 2018, 07:42:49 PM »

Congratulations Skip, you for sure found the problem, bad solderings.
So the set has quite a few bad solderings. Perhaps it is good to just re-flow the solder joints. may be a metallurgical problem with a cleaning process or so. You may run in a few more bad solder joints. I think your new problem is just related to that. Take some time and reflow all solder joints till you see they solder is flowing well, perhaps add some flux.
I remember when I did work in a microwave lab, that the joints and flanges of 10 GHz waveguide were soldered. One day we had failures and we saw that the flanges just came off the waveguide, one by one, after a few years of use. The lab did investigate and did track back to an aggressive flux, that kept attacking the surface of the copper after soldering, somthing similar to S39. We had to clean and re-solder almost a hundred flanges.
When I don't have the means to measure power, I normally connect a small vacuum diode with the anode to the output and the cathode to 10.000- Pf to ground. The DC voltage over the cap is the peak-voltage of the RF. The RMS voltage is 0.707 x Vpeak. The power is RMS squared divided by 50 So easy to calculate the power (if the RF load is a good 50 Ohms). Is quite accurate.
73
Nico
Logged
WB4YVO
Member

Offline Offline

Posts: 28


« Reply #52 on: June 07, 2018, 08:52:28 PM »

Well, I hope its that.. We will see.. Will let you know if I get it  working again and what it was if I know..

Thanks for all your help.

Skip
Logged
PA0NVD
Member

Offline Offline

Posts: 224


Nico and Chappie (Chappie is the dog...)


« Reply #53 on: June 07, 2018, 08:57:32 PM »

I am sure you will fix the set Skip. Please take into account that these kind of failure are extremely difficult to find, they are not obvious. Re-flowing is the best option
Good luck and happy to help
Logged
WD5JKO
Member

Offline Offline

Posts: 1691


WD5JKO


« Reply #54 on: June 08, 2018, 11:47:40 AM »



I have been watching this thread evolve. Nice back and forth with good information, and good results forthcoming.

Concerning reflowing connections, I will add my 2 cents. If possible use solder wick or solder sucker to remove the old solder. Then remove residual flux with brush and solvent. I use 100% (IPA) alcohol at work, and the 80% stuff from a drug store at home. Then use new solder with some added flux to renew the connections.

The G50 modulator has serious design limitations that can be removed without too much trouble. The main issue is the Heising choke has too much current flowing through it, and the core is close to saturation. As a result audio below 500hz gets distorted, and full modulation is not possible. Gonset turned this into a Marketing "feature" describing this as a way to prevent over modulation!
See Reply 2 and 4 at this thread. I talk about my G50 modulation changes, and define design limitations:
http://amfone.net/Amforum/index.php?topic=34714.msg267903#msg267903

I look forward to more progress.

Jim
Wd5JKO
Logged
PA0NVD
Member

Offline Offline

Posts: 224


Nico and Chappie (Chappie is the dog...)


« Reply #55 on: June 08, 2018, 02:18:48 PM »

A good option for the choke saturation is finding a balanced AF output transformer. e.g. for two KT88 or EL 34 tubes or so.  The center tap to the HV, one side to the modulator tubes and the other side to the 6146. Than the DC currents will almost cancel and you can modulate with a substantial smaller iron without distortion. Because the iron can be smaller, should be easy to find a transformer that fits.
Logged
WB4YVO
Member

Offline Offline

Posts: 28


« Reply #56 on: June 08, 2018, 08:00:24 PM »

Ok, Re soldered a lot of connections.. Radio now receives and TX .. The only problem now is power output is lower than spec.. I get about 15 watts .. Spec says about 27 or 28 watts?  Could be my 6146B  tube  . I have a lot more I could sub along with some drivers 6AQ5..

So far so good..

Skip
Logged
PA0NVD
Member

Offline Offline

Posts: 224


Nico and Chappie (Chappie is the dog...)


« Reply #57 on: June 09, 2018, 10:08:42 AM »

That's a good message Skip, makes me Happy Smiley
If the grid current is normal and it tunes with a nice dip of approx -25%, indeed can be the 6146. If you are looking for a replacement, try to find the A version, is slightly more suited for VHF. It is the equivalent of the QE05/40
Logged
WB4YVO
Member

Offline Offline

Posts: 28


« Reply #58 on: June 09, 2018, 11:34:49 AM »

Yes, It tunes great..I do get grid current but didn't look at it for a value.. I put in a 6146W and get about 20 Watts out now.. I will look to see if I have a 6146A.. Not really concerned over 7 to 8 watts.. But would be nice to see what the differences are between tubes..

Thanks again for all your help.. Without it It would have taken me a lot more time to get this running..

Skip 
Logged
PA0NVD
Member

Offline Offline

Posts: 224


Nico and Chappie (Chappie is the dog...)


« Reply #59 on: June 09, 2018, 05:47:41 PM »

You  are more than welcome Skip. Whenever you plan a trip to Costa Rica, give me a PM
Logged
WB4YVO
Member

Offline Offline

Posts: 28


« Reply #60 on: June 12, 2018, 09:31:04 PM »

Ok , Found some more bad solder joints.. Mainly Ground connections..  so now all seems to be good..

Wired up a D-104 Microphone.. I now have modulation..

But its downward..Is that normal for this radio? or does it require special tuning?

I remember back in my CB days in early 60's..  had to do some special tuning to get upward Modulation..

Skip



 
Logged
PA0NVD
Member

Offline Offline

Posts: 224


Nico and Chappie (Chappie is the dog...)


« Reply #61 on: June 12, 2018, 10:45:47 PM »

No, should not be downward. Measure if the screen voltage is ok. See if the grid current is sufficient, low drive level may be a cause.  A too heavy load may be a reason as well, tune for a deeper dip until the power goes approx 10% down.
An other cause may be low emission of the tube. If you raise the filament to 7 - 7.5 Volts and the modulation improve (becomes positive), the tube doesn't have sufficient emission. Raising the filament should have just a minor improvement of both power and modulation. A substantial improvement indicates low emission, both for indirect and thoriated filaments.
Logged
WD5JKO
Member

Offline Offline

Posts: 1691


WD5JKO


« Reply #62 on: June 13, 2018, 01:49:47 PM »

  A scope looking at the modulated envelope would be most helpful. My last comment about the G50 modulator earlier shows that in my case, the Heising choke was saturating, and audio below 500 hz was progressively more and more distorted as the frequency goes down. Distortion worsened, and upward modulation was limited.

   Besides the good stuff already mentioned by PA0NVD, a simple test would be to load the D-104 cartridge with something like a 100K load. This will attenuate most of the lows, and if the audio Heising reactor were saturating, getting rid of the lows should improve things a lot. It would sound like a stock Apache though!

   Lightly loading the RF stage should also help with modulation capability.

   Funny discovery in my G-50. The modulators were original Genelax KT-77's instead of 6L6's. What a find!

Regards,
Jim
Wd5JKO



* KT77.png (477.62 KB, 1127x446 - viewed 17 times.)
Logged
PA0NVD
Member

Offline Offline

Posts: 224


Nico and Chappie (Chappie is the dog...)


« Reply #63 on: June 13, 2018, 02:16:59 PM »

Hi Jim
Indeed nice find. I love the KT77, in UL mode these tube perform excellent with very low distortion.
The choke saturation can be solved by finding a balanced output transformer e.g. for 2 x KT88 or EL 34. There are plenty. Center tap to HV, one side to the modulator and the other side to the PA. Than the DC magnetization is almost canceled and you can modulate the transmitter with less iron and less distortion. Simple to try temporarily with the iron externally wired with clip leads.
Logged
WD5JKO
Member

Offline Offline

Posts: 1691


WD5JKO


« Reply #64 on: June 13, 2018, 03:35:03 PM »


  A picture of the output/modulation transformer, and two scope plots. The tone modulation is nice up to 80%, but from there the negative peak shows a little "tilt" toward the center. There is little difference at 80hz versus 1 Khz. For voice modulation, with a properly phased D-104 element, 100% positive peaks are obtainable.

  The schematic I posted earlier shows some changes to the 6146 screen modulation. I added a negative peak clipper to the screen only, and compensated the screen dropping resistor for less phase shift. With a plate modulated 6146, "hard" limiting the screen voltage to something like +10v minimum (diode clamp) seems to provide a "soft" downward limit to the plate side envelope pattern. Full modulation with voice, and NO "white Lines" on the scope.

Jim
Wd5JKO



* New_Mod_XFMR.JPG (88.59 KB, 800x600 - viewed 14 times.)

* 75_mod.jpg (60.83 KB, 800x600 - viewed 11 times.)

* YEA_AM.JPG (61.76 KB, 800x600 - viewed 10 times.)
Logged
WD5JKO
Member

Offline Offline

Posts: 1691


WD5JKO


« Reply #65 on: June 13, 2018, 10:47:07 PM »


    Skip,  I am not stealing your thread, but while waiting for your next report, I am adding a little info pertaining to my G50 modulator experiences. I attach three schematics for you and Nico to mull around. Perhaps there is a better way, or a simpler way to get good modulation with low distortion. The D-104 trick I mentioned to roll off the lows is as simple as it gets. That is a big bang for less than a buck.  Wink

Jim
Wd5JKO


* Schematic_P1.jpg (136.86 KB, 1043x800 - viewed 30 times.)

* Schematic_P2.jpg (154.29 KB, 1052x800 - viewed 32 times.)

* G50_SCH.jpg (35.03 KB, 726x656 - viewed 28 times.)
Logged
PA0NVD
Member

Offline Offline

Posts: 224


Nico and Chappie (Chappie is the dog...)


« Reply #66 on: June 14, 2018, 09:27:53 AM »

Hi Jim
Thanks for the diagrams. As you may remember, I once made a small AM transmitter using the trick with the balanced output transformer instead of the straight Heising coil. We did discuss  that before. I indeed had some white lines with negative modulation peaks, I like your trick with the negative peak limiter at G2  Cheesy  When my house is ready and I have my shack again, I will try that for sure.
I think the balanced output transformer instead of the Heising choke will give most of the improvement and allows more lows in your modulation.
Logged
WB4YVO
Member

Offline Offline

Posts: 28


« Reply #67 on: June 14, 2018, 07:10:03 PM »

Well, Here we go again.. While running radio everything was working perfect  Good RX and TX.. But then I heard a small popping sound and the Receiver went dead.. The audio level dropped a lot . So tried to inject signal from SG  and got Nothing.. So back to square one.. This is getting to be a project from Hell..

Underside showed no burnt or discolored parts all looks like it did.. No smell as in overheated parts ETC..  So Not sure where to start again..But I will start to look to see  if I can find any parts that my have opened or shorted..

PS The TX still works fine..  But no spotting as RX is dead..

Skip

 
Logged
PA0NVD
Member

Offline Offline

Posts: 224


Nico and Chappie (Chappie is the dog...)


« Reply #68 on: June 14, 2018, 08:47:20 PM »

Hi Skip
A small popping sound does point a lot of times to a shorted cap. Measure at all receiving tubes the anode voltage and the G2 voltage. Go from there.
I don't know if you did recap, but that can happen. Please don't get de-animated, you came a long way successfully!!!
Logged
WB4YVO
Member

Offline Offline

Posts: 28


« Reply #69 on: June 14, 2018, 09:25:05 PM »

My thoughts also.. I tested the tubes again and found my RF tube a 6BZ6 now shows a short between the plate and  screen.. Thats where I will start looking..

Skip..
Logged
PA0NVD
Member

Offline Offline

Posts: 224


Nico and Chappie (Chappie is the dog...)


« Reply #70 on: June 14, 2018, 10:41:23 PM »

That's weird, never saw that before.
Logged
Pages: 1 2 [3]   Go Up
  Print  
 
Jump to:  

AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
 AMfone 2001-2015
Powered by SMF 1.1.21 | SMF © 2015, Simple Machines
Page created in 0.064 seconds with 19 queries.