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Cliff Jones
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PostSubject: Signal Generators   2011-02-15, 12:50 pm

First topic message reminder :

Signal generators can be used for more than alignment of radios. You can test inductive and capacitive components.

The Idea is when an AC signal is connected to a capacitor and a resistor in series, a voltmeter is first put on one component, then the voltage is read, then the other component is read for its voltage. When the voltages are equal you can determine the Impedance. I haven't tried this yet so I'll have to read up on it again.

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PostSubject: Re: Signal Generators   2013-10-17, 5:22 pm

Frank, That Capacitor Wizard looks like a nice tool. A bit out of my league for very part time hobby stuff, but I'll keep an eye out for one. I did see a vid on YouTube using a scope to check caps and such. Needing them out of circuit is not very convenient though.

Well, with much perseverance I finally have the overload circuit working in a manner I suspected it should. This required some slight modifications to the circuit a bit. I redrew it in cad to better reflect the intent of the design.

The principle of this circuit is primarily to flash the LED only. This is enabled when the transistor turns on hard in saturation pulling the ground side low. The LED was always on giving a false indication of an overload condition. As connected the transistor never did go into cutoff and the LED was tied to emitter not the chips common reference ground at the collector. Both issues were causing current flow through the LED although the 555 timer was not fully on. Now it works like I thought it should. I may add in green power on LED just cause I can....

With that part out of the way I can concentrate on the lack of RF output. I'll post back with those details as I progress.

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FrankB
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PostSubject: Re: Signal Generators   2013-10-18, 12:05 am

I think I paid $189.00 for mine and $25.00 for the protection kit.
There are cheaper ones out there, but this one came with full schematics and troubleshooting info too. the others I looked at did not.

I paid for this one in the first 2 TV repairs I did after I got it.
It saved mass time, especially with vertical circuit problems.
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PostSubject: Re: Signal Generators   2013-11-03, 5:53 pm

Found some bad transistors in the front end of this Generator. Finally have a Modulated output, although not quite as stable as I would have expected. It's not like this is a lab grade generator. Probably good enough for educational purposes as intended.

Seems to jump around on the scope +/- 5-6Khz with it centered at roughly 455Khz. About half that much deviation without modulation. Scope could be triggering on some harmonics? Scope is a Tektronix TDS2022C. Not that the measuring capability of these digital scopes is accurate on an analog signal either.

Can anyone comment if this is stable enough for troubleshooting and tuning AM radio circuits?
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Cliff Jones
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PostSubject: Re: Signal Generators   2013-11-05, 12:08 pm

FrankB mentioned caps so as old as they are you might check the ripple across them and cleaning of all connectors and switches. Possibly look at the regulation and stability of the power supply. I will be doing that on my units, that's for sure.

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PostSubject: Re: Signal Generators   2013-11-05, 6:06 pm

I see about 200-300mv ripple and the voltages are +13.4 & -14.8vdc. The positive rail does have greater ripple.

Even with the scope ac coupled, I see the signal jump around similar to the AM ouput. I little better with a 470pF cap blocking DC. Probably need to drop 4 new 1000uf caps and 1 2200uF in it.

Intersting side note is the RF section is very similar in components and layout to the Sine/Square section. That gave me some comparable voltages and signals expected since the sine wave side was working.
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Cliff Jones
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PostSubject: Re: Signal Generators   2014-05-14, 2:29 pm

I now have an HP 606A signal Generator (I picked it up after the Ham Fair MIKE and Key Club in Puyallup) that I am starting to tear into. There is a problem with the Modulation meter setting at 40%. So I started to test the tubes first. ARRRRGH First three tubes I tested were all reading LOW so I suspected My B&K 747 tube tester of being in need of alignment. Started the alignment and ran into Murphy's Law again. So now I have two repair projects.

Getting back to the signal Generator, I am trying to remove the chassis Box where most of the tubes are hidden. I have run into a problem with the hardware. Around the box are a number of screws, easy to remove, they are all regular slot heads. But on the side between two of the boxes are Socket Head screws. It takes a special wrench that has a couple of Fahnestock clips to store it inside the Generator. Of course the wrench is gone.

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I found the description of the wrench in the manual :
According to the HP-606A manual I have, the wrench in question was part number 1470-0010. The manual defines this wrench as Hex socket 0.1087 inches across the flats.
-------------------------
The closest SAE size is 7/64 inch (0.1094 inch). I was actually able to insert that size in the socket screw and had a nice tight fit.
The shaft length should be 12" for the handle to clear the end of the chassis.

The chassis from the screw to the end of the chassis is 10" (+) so I would consider the extra (2") = (12"total) for clearance for the "T" handle.
-------------------------------
So my friend is going to braise the tip to a long extension to get at those pesky socket head screws.

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NT9K

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PostSubject: Re: Signal Generators   2014-05-16, 3:53 am

HI Cliff, nice catches on the signal generators! If I'm not mistaken that URM-25 is the source of the "Holy Grail" of crystal radio air variable capacitors. That one air variable cap could bring more than the $60 you paid. Seems like the URM-25D had the single gang silver with ceramic insulators and the URM-25E had the dual gang silver with ceramic insulators. Have you checked inside that one yet? Can you confirm the air variable cap in the B model please?

By the way, I did find the schematic for my old RCA signal generator kit. Should anyone else need a copy, I have posted it on my website!
Thank you! Bill NT9K..

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Cliff Jones
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PostSubject: Re: Signal Generators   2014-08-11, 7:41 pm

I also obtained about a Month ago a Navy Signal Generator TS/413/U
It has two Meters which is extra nice, one is R.F. Modulation -Audio Volts, and the other Meter is R.F. Volts rms.
OH Boy more knobs to twiddle with Muh Ha Ha!!!!!



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frank1956

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PostSubject: Eico 324 re-capping   2014-09-14, 8:02 pm

Since I finished my RCA X551 the other day I decided to re-cap my eico 324 signal generator. I changed all the resistor and the two (2) electrolytic. I found a you tube video on how the electrolytic were done and followed that process since it was straightforward and seemed fairly simple. The processed called for a 5 prong terminal strip,  two (2) 20 mf @ 150 v electrolytic, one (1) silicon rectifier, 1000 PRV 2.5A, and to replace the original 2.2 K resistor with a 2.4 K resistor.

I doubled check the video after I was done and notice that between the 2.8 K resistor and the positive side of the second electrolytic there was what looked like as I call a solder bridge between the pos side of the electrolytic and the hot lead going to the 12AU7 tube. After all was said and done and I turned it on the 2.4 k resistor started smoking What a Face . Needless to say I turn it of and removed the solder bridge, problem solved wrong. Since I have removed the solder bridge between the two the signal generator does not work. Do not want to proceed any further without some advice, any idea!!  Not sure if this make a lot of sense, so I have attached so pic's of what I have done so far. If you would like to see the video [You must be registered and logged in to see this link.]

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Cliff Jones
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PostSubject: Re: Signal Generators   2014-09-15, 9:08 am

From the video there looked like a solder bridge also. I can't find the schematic right away, but that looks like the B+ as its a red wire. Either your polarity with the caps is an issue which I doubt, if you were careful. Or a short in a tube. Also did you replace the caps across the ac line?
If that was taken are of, remove the tubes and check the power transformer voltages. Disconnect the diode first.
If they are correct voltages then you will need to check for miss-wiring. Remember this was a kit and builders do not always know what they are doing. Let us know what you find.

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frank1956

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PostSubject: Re: Signal Generators   2014-09-15, 10:01 am

Cliff, here a copy of the schematic. I did replace the cap's across the AC line. When I first finished all replacement ie. cap's, resistor and the solder bridge I turned it on and took my voltage reading per the schematic the voltage coming from the diode to the 2.4 k resistor R1 should be 125 V I was getting 150 V. That when the 2.4 K resistor started smoking. Since I have removed the solder bridge I get about 108-109 V. I literally removed everything and started over, ensuring the diode was installed correctly, electrolytic were correct pos,neg, neg, pos , and replaced and checked the 2.4 K resistor to ensure it was good. Everything was ok. Prior to doing the re-capping the generator was working 100%. The only reason for the work was a couple of nasty looking cap's.


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frank1956

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PostSubject: Re: Signal Generators   2014-09-25, 8:34 am

Project completed. Signal generator is back up and working.
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MEZLAW

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PostSubject: Re: Signal Generators   2014-09-25, 12:02 pm

[You must be registered and logged in to see this link.] wrote:
Project completed. Signal generator is back up and working.

what did you find to be the problem?
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CHUCKSUE



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PostSubject: heathkit 1g-102   2015-01-07, 10:25 am

I bought this off of Ebay. It turns on and the scope sees a signal. I watched the Utube video on a generator like mine and he has a clean waveform. Whoever built this did a nice job. I found a resistor R6 that is wrong according to the schematic. He had a 4.7k and it calls out for a 10K. This resistor goes to the plate of the 6AN8. I tested all the resistors with my meter and they are good. Any suggestions?
One of the plates of the variable capacitor was shorted and I fixed that.
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FrankB
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PostSubject: Re: Signal Generators   2015-01-07, 1:03 pm

If the generator is working fine, I'd suggest leaving it alone.
They did make errors in parts lists and schematics. More often than one would like.( And mismarked parts too. Cathode bands on diodes at wrong end, resistor color codes marked wrong on resistors, to name a few problems I have run across.)
often they would include an update or errata page with the manuals too. That may have gotten lost over the years too.
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Cliff Jones
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PostSubject: Re: Signal Generators   2015-01-07, 4:16 pm

So what your saying is, your not getting a clean signal?

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CHUCKSUE



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PostSubject: Re: Signal Generators   2015-01-10, 2:52 pm

Yes the signal looks like the signal you would see in a radio in the IF stages.
What is a demodulation probe?
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Cliff Jones
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PostSubject: Re: Signal Generators   2015-01-11, 10:34 pm

Simply, A demodulation probe usually consists of a Diode that rectifies a modulated RF signal, it strips off the RF portion and leaves only the audio portion intact. This type of probe can be used with VTVMs and O'scopes to measure audio voltage.

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PostSubject: Re: Signal Generators   2015-01-26, 6:53 am

I read up on how to read freq. on the scope. With the scope set at 1micro sec. ch1 , 20 mil. Volts

RF generator set at band A , Coarse attenuator at high, FR attenuator at high.

Pointer at 10, I see one cycle

Pointer at 20, I see two cycles

Pointer at 30, I see three cycles.

When I turn the variable attenuator down at one point I lose the signal.
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