Altai 'TE20D' (solid state) Signal Generator

[David G4EBT]

I've come across two versions of the valved TE20D, usually branded 'TECH'. Each uses two valves - a 12BH7A and 6AR5. One version has an upright style - the other is oblong. There have been several threads on the forum about them, notably their inability to oscillate on the highest frequency range - Band 'F', 36 to 130MHz. However, until recently, I was unaware that there was a solid state signal generator called 'TE20D', branded Altai. I came across this one on the BVWS stand at the NVCF in a sorry state. It was shabby and the rusty case was hanging off, though not beyond redemption.

I assumed it was valved but when I got it home, I discovered it was solid state.

It felt a bit damp so I removed the case and popped the chassis in the greenhouse for a few days, given that the RF coils are wound on cardboard formers and if damp, would dobtless have had a bearing on their inductance. I guess it would be a non-worker, so no surprises there. There was a fuse on the PCB is a 20mm fuse-holder and in checking if it had blown I noticed that it was loose and wobbling about. The spring end caps of the holder had opened up and were no longer springy, so I fitted a new PCB fuse-holder and a 100mA fuse.

Tried in on my scope and frequency counter, and all was working fine. The 1kHz audio waveform for use in signal tracing and to modulate the RF output was nice and clean (nearer to 900Hz than 1 kHz but that's on no consequence). Likewise, the waveform of the unmodulated RF output on all bands was clean, and the modulated waveform looks good too.

The Frequency ranges are:

A: 100KHz ~ 320KHz.
B: 300KHz ~ 1,100KHz.
C: 1MHz ~ 3.3MHz.
D: 3.0MHz ~ 11MHz.
E: 10MHz ~ 35MHz.
F: 32MHz ~ 150MHz.( up to 450MHz on 3'th harmonics)

Spec:

RF output is 100mVrms, approx (up to 35MHz unloaded). Output control: High-low switch and fine adjuster. Modulation: INT. 1KHz (AM) 30% approx. EXT. 50Hz ~ 20KHz, at less than 1Vrms input. Audio output: 1KHz, Min. 2 Vrms. Crystal oscillator: For 1 ~ 15MHz crystal in type HC-6u holder. Power requirement: AC 230V, 50 / 60Hz Approx 3VA. Dimensions & weight: 150 (H) x 250 (W) x 130 (D) mm.

The stated frequency accuracy is ±5%.

It has a nice clear large dial and I checked the accuracy of the generator at various points on all bands with the following results, which fall comfortably in the claimed ±5% accuracy range. Just as well as there are no means of adjusting the coverage such as coil cores or trimmers:

Band A:

Dial 300kHz, readout is 310kHz (+ 3.3%)
200 kHz, is 195 kHz (-2.5%)
100kHz, is 103 kHz (+3%).

Band B:

1MHz, is 995kHz (- 0.5%)
600kHz is 585kHz -2.5%)
300kHz, is 306 (+2.6%)

Band C:
1 MHz, is 1 MHz (no error)
2 MHz, is 1.9 MHz (-0.5%)
3.5 MHz, is 3.44 MHz (1.7%)

Band D:
11Mhz, is 11 MHz (no error)
8 MHz, is 7.66 MHz (-4.25%)
5 MHz, is 4.86 MHz (-2.8%)
3 MHz, is 3 MHz (no error)

Band E:
35 MHz, is 34 MHz (-3%)
14 MHz, is 13.5 MHz (-3.6%)
10 MHz, is 9.85 MHz (1.5%)

Band F:
150 MHz, is 152 MHz (1.3%)
100 MHz, is 96 MHz (-4%)
50 MHz, is 47.6 MHz (-4.8%)
32 MHz, is 32 MHz, (no error)

There are several examples of this model having been sold on ebay in the last year or so and one currently for sale at Radioworld:

https://www.radioworld.co.uk/second-...00khz---150mhz

I couldn't find a manual or circuit for it on internet, but it looks very much like the Leader 'LSG-16' in appearance, though that only goes up to 100 MHz (300 MHz on harmonics), though that has a claimed accuracy of 1.5%. If a frequency counter is to hand, the accuracy of the generator dial settings ceases to be important.

The Leader LSG-16 manual is here:

https://www.kevinchant.com/uploads/7...16_sig_gen.pdf

I've cleaned it up and resprayed the cabinet and it looks quite bonny, leastways, I think so. Yes, it's a budget generator aimed at hobbyists, as was the Heathkit RF1U, and a hobbyist is what I am. I restore old radios - I'm not putting rockets into space, and simple test gear suits me fine.

Pic 1, the PCB with the duff fuse-holder.
Pic 2 the coil-pack on cardboard formers.
Pic 3, 900Hz audio waveform.
Pic 4, modulated 465 kHz waveform.
Pic 5 modulated 10 MHz waveform.

A few more pics to follow.

Hope that's on interest.

[David G4EBT]

A few more pics below.

Pic 1 shows the nice clear dial.
Pic 2, after the case has been re-sprayed and reassembled.
Pic 3, an internal view.
Pic 4, the AF output frequency.
Pic 5, the readout of the generator at its maximum frequency of 150 MHz.

All in all, a nice little "I'm not going to buy anything at the NVCF" project!

(And I bought yet another Heathkit RF1U in a similar state).

Oh well, simple things amuse simple minds.

'Use what talents you possess - the woods would be very silent if the only birds that sang were those that sang the best'.

[chriswood1900]

I hope people don't mind me adding some more info to this thread, a while ago I repaired one of the Rapid electronics versions 85-1200.
These signal generators appear under many names including Dick Smith SG4160B, Lodestar SG4160B, Maplin XG-94, Rapid 85-1200, Sun SG4160B, Tenma 72-585, Elenco SG9000 and there appears to be be 3 main versions the Leader LSG16 possibly the original and then SG4160A as with David's version above as a Tenma TE20 followed by many versions of the SG4160B mentioned earlier. As has been pointed out the most common circuit diagrams includes an error missing a link from the gate of Q1 to the wafer switch. I include a corrected circuit.
Whilst I was repairing mine I often take pictures of the boards and mark up the components where they are not marked to make tracing easier so to aid others I include them below.
There are 3 boards in the B versions the PSU and AF oscillator the RF board attached to the variable capacitor and on some but not all a board linking the front panel controls and sockets. I include the layouts of the first 2 plus a component BOM which is correct according to my version, but there may be some changes in some batches. The PSU board seems to have provision for a regulator which has been bypassed on mine with a resistor which is as per the circuit.
My guess is that all the common models we see come out a of the same Chinese factory perhaps even being a subcontractor for Leader and then branching out on their own, does anyone know more?
I hope there are no errors but if anyone spots one please let me know.
Chris

[ms660]

Originally Posted by chriswood1900

I hope there are no errors but if anyone spots one please let me know.
Chris

Drain ?

Lawrence.

[chriswood1900]

Sorry I mean't gate! Had a brain fade moment.
I also opened up my unit to double check the voltages, across C15 there is around 25V and across C16 19V which makes the feed to R7 19V. I fitted 470uf at 35V to replace C15 and 220uf at 35v for C16 and it worked fine.
Chris

[ms660]

Yes, the circuit as shown won't work, S1b's wiper should go to Q1's drain.

Lawrence.

[MrBungle]

That design was rather long lasting. I had one of the plastic fronted ones cross my workshop recently that had surface mount parts in it date coded 2004!

[chriswood1900]

Please find a corrected circuit diagram of the circuit for the SG4160B shown in Red.
If the MODS could remove/replace the circuit in my post no 3 it would help avoid confusion for others.
Thanks
Chris

[David G4EBT]

Thanks for reading the thread guys, and for your input.

There are similarities of that (corrected) circuit to the one in the full manual of the Leader LSG-16, the link to which I posted in post #1 above.

Interesting that it's popped up in all sorts of guises and brand names over the years.

Aesthetically pleasing to my eyes, with a clear un-cramped dial and smooth reduction drive.