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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders.

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Old 5th Jan 2020, 5:26 pm   #1
Shortcircuit
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Default TE-20D signal generator

I have one of these and looked at tge waveform on the output😕seems to be an awful sort of square wave with spikes!.
I was expecting a lovely sinewave😁,I have tried ECC82 valve for a replacement oscillator valve(same awful waveform),changed caps,checked resistors to no avail.
I am wondering if this waveform is correct in some way as to to get the harmonics for the higher frequencies?
I have read a closed thread on this signal generator about mods etc,seems othes have had the same problem,can someone give a definitive answer before I pull my hair out!😁
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Old 5th Jan 2020, 7:38 pm   #2
David G4EBT
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Default Re: TE-20D signal generator

Below are the waveforms to expect from a TE20D if working correctly.

First pic is the AF trace, which - on the ones that have passed through my hands over the years - has typically been around 500Hz. Second pic is what the modulated waveform should look like, which - in the picture - was at 465kHz. Third pic is unmodulated RF waveform at 2.5 KHz.

You probably already have the circuit, but there are some scruffy versions kicking around on the net. I've attached one that I cleaned up with voltages shown which might be useful in searching for any wide discrepancies. Unfortunately, given that the TE20D harks back to the 70s, most will have passed through several pairs of hands and may have been meddled with by those with delusions of adequacy. The circuit looks rather more simple than does relating it to the somewhat compact PCB, switchery and 'rats' nest' of wiring.

For reasons that I've never been able to get to the bottom of, the coil for band 'F', 36 - 130 MHz on the ones that I've had appeared not to have not been fitted at the factory. When you mention 'harmonic frequencies', all of the bands from A to F operate on fundamental frequencies - the only band that operates on harmonics is the highest frequency band - F' - 100 - 500 MHz. (Assuming that band F (36 - 130 MHz is working!).

You'll find several threads on the forum and elsewhere which outline any number of problems, but correspondingly fewer solutions. I guess you'll have checked that you have 120V AC going into the rectifier and 155 - 160V DC out of it, and about 115 - 120V HT after the 2K HT load resistor in the smoothing circuit. If all the voltages look more or less OK, apart from dry joints or wiring that's come adrift, maybe trace the waveforms around the circuit either side of coupling caps to see if any are suspect?

My approach would be as a first step, to get a good clean AF sine wave, then a clean sine wave on each RF range in turn, starting with the lowest, then check what the RF waveform looks like when modulated.

If working well, the TE20D - rather like the Heathkit RF-1U - is more than up to the task for hobbyists, albeit beneath the dignity of test-gear 'aficionados'.

Hope that might help a bit.


Good luck in your endeavours.
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Last edited by David G4EBT; 5th Jan 2020 at 7:48 pm.
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Old 5th Jan 2020, 8:48 pm   #3
Shortcircuit
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Default Re: TE-20D signal generator

Thank you for the quick reply and suggestions also the schematic and photos,yes I do have a somewhat scruffy diagram��
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Old 6th Jan 2020, 7:38 pm   #4
Shortcircuit
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Default Re: TE-20D signal generator

Looked at my Signal Generator today,made by Eagle and is model SG70, it looks exactly as the TE-20D.
Some info found in shed😀
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Old 7th Jan 2020, 2:25 pm   #5
David G4EBT
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Default Re: TE-20D signal generator

Yes, that's identical to the TE20D.

In case you don't have the other pages, they're attached below. (Pages 2,3, 4 and the front cover).

I attached a cleaned up version of the circuit in my earlier post.

Good luck in sorting it out.
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Old 8th Jan 2020, 7:47 pm   #6
Shortcircuit
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Default Re: TE-20D signal generator

Thank you for thinking that but I do have the other pages,thought the top frequency info would come in handy for others��
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Old 11th Jan 2020, 1:07 pm   #7
6AL5W-Martin
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Default Re: TE-20D signal generator

a TE20 with a accurate sinewave is defect
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