[Pithicus999]

Tone..? What if my Sig Gen has no tone or sound at all. The light comes on. Other than that, I don't notice any thing happening.

[Walston]

I bet there is a Radio Club or Ham Radio Club near by that one of those guys would have signal generator you could use if your doesnt work.

[jerryhawthorne]

Pith, time to post a nice picture of the front of your sig gen or at worse a manufacture and model number. Most have the ability to add a "tone" to the frequency you select on the generator. The generator is like a little radio station in which you can select the frequency you wish to "transmit" on. If you don't have a tone on it, you will not be able to hear it at your speaker or measure it on your meter. It is usually around 400 cycles (annoying). This is often referred to as internal modulation.
As I recall the one you bought had an external modulation feature but that is of little use and requires you to apply a "tone" from another source. I'm hoping it also has an internal "tone" source function.
Picture please.

Jerry

[Pithicus999]

Hey Jerry, here is a video I took. It's much crappier video than I thought, you may need to adjust the settings down on your monitor to a lower speed or bit-rate to see it. Let me know if you have any issues viewing.

Also, I joined 'snapfish' or whatever the name of the online picture uploading deals, and I'll try to post some pics from there maybe this weekend.

Going over dad's Saturday and I'll try to get some good voltage readings...more to come! Here's the vid link:

http://www.youtube.com/watch?v=lDJQUpCkjV0

Thanks.

[jerryhawthorne]

Went back to post 46 I believe and you indicated you adjusted the IF coils and received a peak and tone correct? So it sounds like your generator is working with an internal tone nice.
Now if your saying that you set you generator up to say 1000KC center of the AM band and hook it to your antenna and ground on the back you can't get any tone out of the speaker while tuning around 1000 KC with the radio dial? Make certain your band selector on the radio is in the broadcast band mode.

Jerry

[Walston]

Here are a couple links to information on your SG-7 and instructions on the SG-8. The operating instructions are missing in the SG-7 link but they are the same. The way I tested out my old signal generator is with using a modern digital receiver. That way I was able to confirm the signal it was putting out was in line. I took the signal output and coupled it to the antenna input on my receiver, set the AM in an are where there was no station and adjusted the generator to a low value of output and tuned it until I hear the maximum output on the modern receiver. In my area 800 KC is pretty empty so I started there. This worked very well. Turned out that my generator was quite accurate. I did several in AM and FM to confirm the generator was accurate. I suggest doing this first to ensure when you use it to align the 18 you know it is working properly. It is actually quite easy to do. If this is not clear, let me know.

http://pdf.textfiles.com/manuals/SCANNER...t-SG-8.pdf
http://tubularelectronics.com/Heath_Manu...7/SG-7.pdf

[Pithicus999]

Cool, thanks Walston.

Got voltages, they were not spot on. Will try to post them tomorrow.

[Pithicus999]

Here are the voltages I took on Saturday 5/4.

Circuit I.F. Det. Osc. R.F. 2nd Det & 1st A.F.
Tube Type 78 RESULTS 6A7 RESULTS 78 RESULTS 75 RESULTS

Filament Volts: F to F 6.3 [5.9] | 6.3 [5.9] | 6.3 [5.9] | 6.3 [5.9]
Plate Volts: P to K 210 [272] | 210 [246] | 210 [272] | 120 [192]
Screen Grid Volts: SG to K 80 [85.3] | 80 [88.7] | 80 [88.7] | N/A [N/A]
Control Grid Volts: CG to K 0.3 [0.0] | 0.15 [3.18] | 5.3 [0.0] | 0.3 [1.42]
Cathode Volts: K to F 2.8 [9.3] | 2.8 [5.9] | 5.3 [12] | 0 [2.8]
G1 to K N/A [N/A] | 35 [12.4] | N/A [N/A] | N/A [N/A]
G2 to K N/A [N/A] | 130 [109.7] | N/A [N/A] | N/A [N/A]



Circuit Driver 2nd A.F. Output (Class "A") Rectifier
Tube Type 42 RESULTS 42 RESULTS 42 RESULTS 80 RESULTS

Filament Volts: F to F 6.3 [5.9] | 6.3 [6.0] | 6.3 [6.0] | 5.0 [ 4.7]
Plate Volts: P to K 205 [258] | 280 [292] | 280 [272] | 350 [365]
Screen Grid Volts: SG to K 200 [257] | 300 [292] | 300 [272] | N/A [N/A]
Control Grid Volts: CG to K 0.35 [15] | 28 [27] | 28 [27] | N/A [N/A]
Cathode Volts: K to F 0 [0.0] | 0 [0.0] | 0 [0.0] | N/A [N/A]
G1 to K N/A [N/A] | N/A [N/A] | N/A [N/A] | N/A [N/A]
G2 to K N/A [N/A] | N/A [N/A] | N/A [N/A] | N/A [N/A]

[jerryhawthorne]

Pith, please look at post 140 and respond so we know where your at. When you try it, have the radio volume at max. If you indeed peaked the IF section with success at 260KC via a tone, we can assume that all is working well from the IF (78 tube) back through the speaker. Can you lay out the voltages on the RF and Det./Osc voltages in a more readable mode? Sorry, I get a headache trying to figure them out. Problem appears to be in the area of those two tubes and associated circuits.
Jerry

[Pithicus999]

Hi Jerry,

Sorry about that, I tried to put the expected voltages next to my voltage readings.
I can redo them. I'll check post 140 and get back to you.

[Pithicus999]

Formatting sucks on these posts...I'm goin to need to get creative...one minute

[Pithicus999]

Jerry, here are the results

EXPECTED RESULTS ARE FIRST, AND MY RESULTS ARE INSIDE THE [BRACKETS]


...................................78-I.F...............6A7-Det._Osc............78-R.F...............75-2nd Det

Filament Volts F to F:............6.3 [5.9]................6.3 [5.9]...........6.3 [5.9].............6.3 [5.9]
Plate Volts P to K:...............210 [272]................210 [246]...........210 [272].............120 [192]
Screen Grid Volts SG to K:........80 [85.3]................80 [88.7]...........80 [88.7].............N/A [N/A]
Control Grid Volts CG to K:.......0.3 [0.0]..............0.15 [3.18]...........5.3 [0.0]............0.3 [1.42]
Cathode Volts K to F:.............2.8 [9.3]................2.8 [5.9]............5.3 [12]...............0 [2.8]
G1 to K:..........................N/A [N/A]................35 [12.4]
G2 to K:..........................N/A [N/A]..............130 [109.7]



EXPECTED RESULTS ARE FIRST, AND MY RESULTS ARE INSIDE THE [BRACKETS]

.................................42-2nd A.F.........42-Output..........42-Output............80-Tube

Filament Volts F to F:............6.3 [5.9]..........6.3 [6.0]..........6.3 [6.0]...........5.0 [ 4.7]
Plate Volts P to K:...............205 [258]..........280 [292]..........280 [272]............350 [365]
Screen Grid Volts SG to K:........200 [257]..........300 [292]..........300 [272]
Control Grid Volts CG to K:.......0.35 [15]............28 [27]............28 [27]
Cathode Volts K to F:...............0 [0.0]............0 [0.0]............0 [0.0]

[Pithicus999]

Also, I didn't have a chance to copy post 140 in practice, I'll need to take the generator over my dad's and hook it back up.

[jerryhawthorne]

Pith, much more readable. I know it is tough to get data formated nicely on these boards. They seem to have a mind of their own. I will leave the interpretations of your voltages to someone sharper than me. That would include most everyone. It will be interesting to hear from you on trying again to run a RF modulated signal from the antenna input as suggested. Remember, radio volume max, generator output mid range and radio on BC band to see if you can hear that tone on the radio somewhere about the frequency the generator is set at.
Jerry

[Mondial]

The cathode to filament voltages of the 78 RF and 6A7 tubes are a bit puzzling. According to the schematic, the cathodes of both of these tubes are connected together, so their voltages should be the same. They are also higher than they should be. There should be a 200 ohm resistor from the cathodes to ground which should develop the 2.8V bias. Your voltages are much higher which is producing more negative bias, reducing the gain of these tubes and therefore the sensitivity of the set. You might check the cathode circuit wiring of these tubes for any errors if you did any work in this area.

The cathode voltage of the 78 IF tube is also high which also reduces your sensitivity. Check the value of the 2500 ohm resistor from cathode to ground. If it has increased in value, it will cause the cathode voltage to be higher than normal.

You might try measuring the cathode voltage of these tubes with the negative probe of the voltmeter connected to the chassis instead of the filament (cathode to chassis ground). The superimposed AC filament voltage may be distorting the DC voltage readings.