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Gonset G-50




 
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WB4YVO
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« on: May 29, 2018, 12:09:06 AM »

Ok new problem.. Radio motorboats.. Any Gonset Experts out there??

When squelch is off turned fully CW and I turn up volume at about 1/2 way its motorboats.. Then if I keep turning the volume up it gets loader and faster.. Have checked tubes and replaced as necessary.. Checked the resistors around the squelch circuit.. replaced 2 .. But still same .. Checked the 6AL5 voltages

Pin 2 Plate 99.3 volts no squelch 49.6 volts squelched
Pin 5 Cathode 108.9 volts no squelch 98.4 volts squelched

Other side ( other diode )

Pin 7 0 volts both ways
Pin 1 0 volts both ways

My B+ voltage is 259 Volts

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w4bfs
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« Reply #1 on: May 29, 2018, 12:22:08 AM »

have you recapped?
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Beefus

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It would from many blunders free us.         Robert Burns
WB4YVO
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« Reply #2 on: May 29, 2018, 12:25:22 AM »

Yes.. There were only about 2 or 3 besides the electrolytic and the bypass caps..

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w4bfs
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« Reply #3 on: May 29, 2018, 07:47:06 AM »

this is not specific to a G50 ...motorboating audio stages usualy happen when one of the power suppy decoupling electrolytics or other large value dry out ... you might try bridging an additional 10 uF or so to see if there is any improvement ...

other things are resistor value changes and corroded ground connections ...
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Beefus

O would some power the gift give us
to see ourselves as others see us.
It would from many blunders free us.         Robert Burns
WB4YVO
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« Reply #4 on: May 29, 2018, 05:12:02 PM »

Ok will give it a try..

Thanks
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WD5JKO
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WD5JKO


« Reply #5 on: May 29, 2018, 07:09:56 PM »



I also have a G50. Some years ago, I redid the RF and modulator, and a power supply recap. The receiver worked OK so I kept that stock. Some years later I noticed the same described motorboating around the squelch threshold. later on I could never break the squelch. The last few times I used the G50, I used it with an external receiver.

I have not spent any time researching the circuitry. Anyone looking for my G50? If so, email me.

Jim
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WB4YVO
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« Reply #6 on: May 30, 2018, 12:20:33 AM »

Ok, Well I did bridge an additional 10 uF or so to see if there is any improvement.. There was no improvement..

Still motorboats.. I can get volume about 1/4 way up ( very low volume) and no motorboating.. But as I go farther it starts..

When I inject a signal via Signal Generator.. I can get it up to around 1/2 way then can hear motorboating thru the signal..

I have replaced the tubes 6AV6,6AL5,6U8,6BE6,12AX7 Etc..  with no change..

Skip


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PA0NVD
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Nico and Chappie (Chappie is the dog...)


« Reply #7 on: May 30, 2018, 09:35:43 AM »

Can you post the schematic diagram?
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PA0NVD
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Nico and Chappie (Chappie is the dog...)


« Reply #8 on: May 30, 2018, 09:57:17 AM »

I found the schematic diagram, so no problem. It seems to me that the second cap in the PS (voltage CC) is not sufficient and critical, Can't read the value nor the number. This because the problem is frequent, so a design flaw.  I should add an other RC to the anode resistor R34 of the 6AV6 (V2) Coming from the HV cc  10 - 47 kOhm than  10 uF to ground and  to R34, the 470 k. anode resistor
You can try add an other cap to the VCC across the second electrolytic cap, but that should be a big one, not 10 uF
I use a lot the small caps out of the trow-away camaras con flash, they are in general approx 100 uF, 330VDC and are very small.
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WD4DMZ
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« Reply #9 on: May 30, 2018, 10:52:58 AM »

My HQ170 has a similar issue. It motorboats when the band width is in the 2 KHZ position but is OK otherwise.

Any ideas?

Thanks, Rich
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KB2WIG
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« Reply #10 on: May 30, 2018, 01:59:09 PM »

Try unsodering the 10 uF cap and tacking something bigger in its place....

KLC
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WB4YVO
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« Reply #11 on: May 30, 2018, 03:18:25 PM »

Here is my schematic.. PA0NVD The parts you list are not on my schematic.. Attached is one close to mine.. Only difference is mine uses a 6BE6 tube instead of a 6BH6 tube for V9.. This schematic is much clearer..

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* Gonset_G-50_Schematic (1).pdf (239.32 KB - downloaded 28 times.)
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PA0NVD
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Nico and Chappie (Chappie is the dog...)


« Reply #12 on: May 30, 2018, 04:27:43 PM »

Thanks for the diagram
I did look into it, and to my opinion the cap C! of 80 uF in the HV filter is quite marginal in relation to the load. Especially because there is no filtering additional at all for the HV to the AF pre-amp and the IF amps
I stick to that advice to add an extra AF filter in the power line to the V2 6AV6 anode, so in series with R34 of 470 K
Add e.g 47 k coming from EE and add 10 uF to ground between this resistor and R34 of 470 k
If this does not help, the feedback is entering to the HV variation of the IF power, BB or AA
As said before, you can also try to make C1 bigger, but substantial bigger, e.g. a few hundred uF But I consider that not a sound solution, adding extra filtering should have been done in the design phase, like a R in series with the HV feeding AA, BB and EE and after this resistor an Electrolytic to ground.
succes
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WB4YVO
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« Reply #13 on: May 31, 2018, 07:01:37 PM »

Ok, I feel stupid.. Motorboating gone.. This is what I did.. When I was recapping I got the 80uf and the 30 UF Electrolytic swapped.. Meaning the output of T2 ( B+) was a 30 UF instead of the 80 it should have been..

When I changed it to way it should be motorboating stopped..

Next I will see if I can see a signal..

Skip..



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PA0NVD
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Nico and Chappie (Chappie is the dog...)


« Reply #14 on: May 31, 2018, 08:35:26 PM »

That's a good message Skip
Glad to hear it's gone. But that means that indeed the value of the cap is critical. Should be better to add an other 100uF or so to prevent feedback in more extreme situations..
Nico
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KA2DZT
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« Reply #15 on: May 31, 2018, 10:58:31 PM »

Ok, I feel stupid.. Motorboating gone.. This is what I did.. When I was recapping I got the 80uf and the 30 UF Electrolytic swapped.. Meaning the output of T2 ( B+) was a 30 UF instead of the 80 it should have been..

When I changed it to way it should be motorboating stopped..

Next I will see if I can see a signal..

Skip..



Skip

No need to feel stupid,  at least you didn't wire them in backwards.  In fact, folks who have wired their electrolytics in backwards have been banned from the Forum.

So. you're still in good standing.

Fred




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PA0NVD
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Nico and Chappie (Chappie is the dog...)


« Reply #16 on: June 01, 2018, 10:01:42 AM »

 In fact, folks who have wired their electrolytics in backwards have been banned from the Forum.

 Cry Cry
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WB4YVO
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« Reply #17 on: June 01, 2018, 01:23:40 PM »

Well, I haven't done that yet...

But I took your advise and increased the 80uf cal.. I had 100 uf and put that in..

Now on to RX issues.. Started alignment the 455 Khz went fine as did the 2.3 mhz IF's.

injected a 51 mhz signal from generator was able to hear it. Then after about 5 minutes signal disappeared..

So now I will have to see whats going on.. Something heating up??

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PA0NVD
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Nico and Chappie (Chappie is the dog...)


« Reply #18 on: June 01, 2018, 02:28:06 PM »

Do you do hear noise? The same as before? The IF at 2.3 MHz still works ok?
Try first to change the 6U8 osc mixer. I saw various oscillators that did cease after a number of years.
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WB4YVO
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« Reply #19 on: June 01, 2018, 04:35:05 PM »

Yup Both IF frequencies are OK.. RX noise even when signal quits.. Has developed a new problem..  When signal generator is modulated I cannot hear tone.. The Signal is there but no tone.. Both the IF 2.3 and 455 I can hear the tone..

I will try the 6u8

thanks
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PA0NVD
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Nico and Chappie (Chappie is the dog...)


« Reply #20 on: June 01, 2018, 05:37:16 PM »

In the diagram I only see 1 IF at 2.3 MHz, no 455 kHz
If you hear a tone when you drive at the IF, the IF strip is ok. I think that you are not at the correct frequency when you hear no modulation. The signal generator does give a signal that does diminish the IF or RF gain, reason why you hear something, but the mixed signal is not at 2.3 MHz. Sweep your RF generator over a wider range, the oscillator of the receiver may be set wrong. I suppose that the receiver oscillator is below the RF frequency, don't have info about that. If so, try to measure the oscillator frequency, add 2.3 MHz and try again. If the oscillator is above the RF frequency subtract 2.3 MHz and try again.
A counter may be not sufficiently sensitive to pickup the oscillator frequency without excessive coupling which may pull the oscillator frequency, so checking the oscillator with a receiver may be better (if you have a receiver covering that frequency range)
Nico
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WB4YVO
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« Reply #21 on: June 01, 2018, 07:24:35 PM »

Ok there are 2 schematics floating around  One uses 2.3 mhz as both and 2nd uses 2.3 mhz and 455 Khz.. Thats the one my radio is.. The other difference is mine uses a 6BE6 as the RX 455kc IF.. The other schematic uses a 6BH6 for the 2.3 mhz IF..

I will post mine  its a little hard to read values..

Skip


* p0025.png (117.83 KB, 2464x3280 - viewed 21 times.)

* p0026.png (104.83 KB, 2464x3280 - viewed 21 times.)
* g50layout-and-adjustments.pdf (110.5 KB - downloaded 6 times.)
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PA0NVD
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Nico and Chappie (Chappie is the dog...)


« Reply #22 on: June 01, 2018, 07:39:42 PM »

Ok, I see. Except a second mixer and IF, the rest is the same. I still think hat you are at the wrong frequency. Especially when the RF generator signal is a little strong and with the RF amp, it is quite easy to get signals that do limit the RF amp or the first mixer or first IF without passing the second IF. Than the noise goes down like you receive a signal, but it is out of band for the second IF.
Can you measure the first oscillator frequency?
If not, a shortcut may be to tune the receiver at e.g. 51 MHz, put the signal generator at 51 MHz, approx 100 uV and turn the core of the first oscillator coil until you hear the modulated signal.
Nico
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WB4YVO
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« Reply #23 on: June 01, 2018, 08:36:44 PM »

I think the Osc is OK well maybe.. Here is what I found when a wiggle either or both of the tubes 6BE6 and 6u8 I can get good signal and tone if in right position..so I think either both sockets or maybe solder joints.. tubes are not making good contact.. once I find the spots on the tubes it works for a little bit then I have to try to find spots again..

PS I did clean sockets..  Also tried different 6u8 and 6be6.. with same results  wiggle right and it works..

Maybe I will try to tighten the pins a little?

Skip.. 
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PA0NVD
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Nico and Chappie (Chappie is the dog...)


« Reply #24 on: June 01, 2018, 11:19:55 PM »

So you found it! congrats.
Indeed check if the sockets are tight and not bend open.
When I have that problem, I normally scratch the tube pins a little, put some contact cleaner and insert and retract the tube a number of times to clean the sockets. Scratch pins are a little rough and do the job.
I like that set Skip, when aligned good, should be a fine set for 6 meters AM Unfortunately I don't have an AM set for 6 meters other than a Alinco DX70. But that doesn't glow in the dark like yours does Undecided
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