UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - TE-20D signal generator

David G4EBT · 5th Jan 2020, 7:38 pm

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.

5th Jan 2020, 7:38 pm	#2
David G4EBT Dekatron Join Date: Feb 2003 Location: Cottingham, East Yorkshire, UK. Posts: 5,763	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. Attached Thumbnails __________________ David. BVWS Member. G-QRP Club member 1339. Last edited by David G4EBT; 5th Jan 2020 at 7:48 pm.