Signal generators

[Herald1360]

FM I would have thought.....

[Andrewausfa]

Originally Posted by G0HZU_JMR

Note that I don't think the TF995 covers the LW and MW bands. I think it starts at 1.5MHz? Are there different variants of this sig gen that go lower?

Yes, the B/2M starts at 200KHz (to 220MHz) though it's a bit of a guess where you might be down there as at that end the dial is a bit sparsely marked.

Andrew

[Spencervs]

Wow so much info on here! Thanks so much for discussing these generators! I decided to go with the All-wave one that I linked in post #4 which someone here identified for me. I know it's probably not a good one but probably easy to recap and get running. Also thinking of checking it with the following:

https://www.ebay.co.uk/itm/8-bit-0-1....m46890.l49286

Would something like that be ok? What leads do I use for this and how do I test with the small cheap device? I don't want to buy a huge counter machine... I only live in a flat 😂

Thanks,

Spencer

[Andrewausfa]

That TestGear Acton one will do for now, bit of a spiky output but you're not expecting perfection. First check is to make sure it's been wired to mains correctly and not dangerously bodged like mine was.

Can't comment on your little eBay thing but by the time you've bought a box for it, BNC and power supply connectors etc you could probably pick up one of the smaller form factor counters like the Black Star Meteor or a Thandar/Thurlby for £20-30 or possibly one of the RACAL 9XXX series if you're lucky.

Andrew

[David G4EBT]

That digital frequency counter could be connected to a signal generator with an analogue dial, to give a more accurate indication of the frequency to which the generator is tuned.

As to a generator, something like this would be the sort of thing to look out for. Solid state, and covers from 250kHz - 100 MHz:

https://www.ebay.co.uk/itm/274832288...53.m1438.l2649

Hobbyist signal generators such as the Heathkit 'RF1-U' often crop up, and the 'TECH TE20D' but they're valved, and now 50 years old. Hence, unless you are very lucky, or find one that has been competently restored, they become a restoration project in their own right and may have safety issues which need attention.

Good luck in your quest - it sounds as though you might be sorted for now.

[Spencervs]

Amazing! Do you guys know what sort of leads I will need for the Acton machine I bought? Also I have an oscilloscope that I was given by work (quite old and says calibrated in 1992) but pat tested only last month. Would this tell me the frequency of the generator? Like I say this is all new to me!

[chriswood1900]

An oscilloscope is not the easiest thing to measure frequencies with but an approximate reading is possible.
A useful guide I often point new users of scopes to is this one by Tektronix which is great for learning to use one.
https://download.tek.com/manual/070869001.pdf
Frequency measurement is covered on Page 17 and 45.

The best way to learn is hook up your equipment and practice whilst trying the suggestion in the guide and you will find it great fun.

[Andrewausfa]

That Acton one looks as if it has a Belling Lee connector like the old TV aerial connector. You can still buy them, easy to strip off the connector from one end and make a lead with a couple of alligator clips. Might be easier option to convert it to BNC so you have a commonality with all your test equipment.

I'm not 100% about your scope, it does do a readout evidently but I'm not sure if that's concurrent with your input or if it only does it after it's stored a waveform. If it doesn't you can work the frequency out by maths but no-one really wants to do that nowadays do they?

Andrew

[chriswood1900]

In addition to my earlier post you may find the videos by Alan Wolke w2aew on Youtube useful. A former Tektronix employee and trainer he will take you through in a clear fashion a lot of the uses of your scope.
For example measuring frequency https://www.youtube.com/watch?v=OQMnjaMSKn8

[Spencervs]

Amazing video!! That's exactly what I wanted to see and will help me gauge whether the generator is roughly ok I suppose. My other question (sorry, I'm very needy!) Is how do I know if my oscilloscope is calibrated ok? And can I do this myself with no extra equipment/limited knowledge? Or is this unimportant? I have no idea on its history other than it was thrown out by the Museum I work for, is a bit dusty and has a faded sticker saying it was calibrated in 1992 but it has been regularly pat tested (this year actually)...

[chriswood1900]

It will be hard to check the calibration of your scope without extra equipment, but I would not worry at this stage my experience with Tek scopes is they are usually OK I would concentrate on getting to know your equipment.
Probably the easiest way to start is keep your eye open for a frequency counter to use with the signal generator as they usually have a crystal oscillator in which is another level of accuracy up from the either the scope or sig gen.
Most of all have fun playing with it all and Alan's videos cover a wide range of topics to help you learn as you go.

[Spencervs]

Hello all so I have an update and some fresh questions! I have bought and received the All-Wave generator and I have found online a circuit diagram which is missing values and I am not so sure that I am looking at the exact piece. Could someone confirm?

I decided seeing that there has been work done prior (and a label assuring me it works dated 2017) to plug it in and it works. Still waiting on the frequency counter to tell if its ok however. I have a few questions below:

1. 1 Why is there a seemingly random potentiometer in this set? I tried to turn it and valve voltages seemed to not move...
2. So clearly someone has been fiddling with the trimmer capacitors and I fear that an alignment will be inevitable... is there a procedure? and do I turn the lugs in the coils as well as the trimmers?
3. What does the metre on the front measure and how can I connect it? It seems to be there just for fun at the moment.
4. The valves are loose around their Bakelite shells. What glue will set them in place? will superglue or gorilla do?

[Cruisin Marine]

Don't glue the valve's in! They sit snugly in the socket, normally that should be fine.
If the sockets are loose fitting, you could (carefully nip up the valve base sockets and clean them if needed)
Do you know the make/model number so you can locate a manual and give a link here if possible?
Then answers will be far easier for us all.
PS: that looks like a brown 2 core mains supply lead?
That will not be safe, a three core earthed mains lead making an earthed chassis would be much safer for you.

[Bazz4CQJ]

I'm sure you're eager to get going with this, but it would be best if you wait for some advice, before doing anything.

Pic 1 shows brown twin flex but Pic 2 shows white 3 core with an earth. It's really most important that you run it with an earth connection and a 3amp fuse in the plug. Do explain what goes on with the cables. Don't mess with the valves just yet until someone gives advice. I would be inclined to use good PVC tape rather than glue, but see what others have to say.

The meter is important, it is used to correct for different levels of RF being generated across the different bands.

I'm attaching a sig gen operating manual for a comparable model which gives you some background.

B

[Spencervs]

Hi yes so I should clarify, I don't mean glue the valve into the socket, but rather the heat over the years has caused the glass to come loose from the male bakelite plug portion which I have read that people have re-secured with glue.

Also it's not a branded item but a member who has been posting on here said it originates from Test Equipment (Acton) LTD. I have seen the odd radio magazine advert for them but this is all.

Regarding the plug, don't worry I changed this already! I could sense a bang afoot if I just wired it up, so I used a three core and earthed to chassis via the negative terminal for the power caps as shown in the circuit diagram attached to the previous post and as advised, a 3 amp fuse was used. I figured it needn't be higher and it's an added bit of safety!

[Spencervs]

Originally Posted by Bazz4CQJ

I'm sure you're eager to get going with this, but it would be best if you wait for some advice, before doing anything.

Pic 1 shows brown twin flex but Pic 2 shows white 3 core with an earth. It's really most important that you run it with an earth connection and a 3amp fuse in the plug. Do explain what goes on with the cables. Don't mess with the valves just yet until someone gives advice. I would be inclined to use good PVC tape rather than glue, but see what others have to say.

The meter is important, it is used to correct for different levels of RF being generated across the different bands.

I'm attaching a sig gen operating manual for a comparable model which gives you some background.

B

Fantastic! So helpful on the manual there! And yes the metre actually has no wires going to it at all so it's plain dead when in use. Also when I say potentiometer in the machine, there is literally a concealed pot within the chassis next to the valves..seems to connect to the anode of the large grey one but I may be wrong... Some kind of fine tuning?

[Bazz4CQJ]

Ok, yes, understand the valve issue; I would use tape - others may suggest other options.

It would be a good idea if you search this Forum and Google and think about building a "lamp limiter" - a really simple device to give you some safety when working on mains equipment of unknown provenance! Essentially, it wires an old filament bulb in series with your sig gen; if the sig gen draws only normal power, the lamp will drop hardly any voltage, but if your unit is faulty, the lamp will drop lots of volts and offer protection. However, you may wish to consider switching on without that.

Glad you recognised the need for an earth. Clearly someone has done some maintenance on it, and you will now be finding out what they did both good and bad .

Seems like he started re-doing the meter circuit, using the potentiometer, but did not complete it.
B

[Bazz4CQJ]

Here's a circuit which will be comparable to yours, and shows how the meter may have been wired and may have been set (using VR2 to adjust the HT on the oscillator).

B

[Radio Wrangler]

Your fourth photo shows that some parts are missing from one of the trimmer capacitors. Were they rattling around loose inside the case, or are they lost?

Both the coil slugs and the trimmer capacitors are used to set the output frequency to match the reading on the dial scale. One slug and one of those compression trimmers per band.

It is usual to adjust the inductor to get the low frequency end accurate, then adjust the capacitor to get the high frequency end accurate. Adjusting each one will affect the other, but done this way round the effect on the opposite end will be reduced, and repeating the process several times will allow you to converge on the optimum setting. Do it the other way round and the alignment process diverges into getting things maximally wrong.

This is a common adjustment technique and you'll also find it used to adjust tuning in receivers.

David

[Cruisin Marine]

1 Why is there a seemingly random potentiometer in this set? I tried to turn it and valve voltages seemed to not move...

As a pure guess (with no manual) it could be setting the valve bias or a pre-set to set a level for something, it may even be a meter calibrate- truth is,I don't know and it needs some tracing to pin it down.

So clearly someone has been fiddling with the trimmer capacitors and I fear that an alignment will be inevitable... is there a procedure? and do I turn the lugs in the coils as well as the trimmers?

I notice the nut has fallen off one of the trimmer capacitors, that will have to be replaced if it isn't lurking trapped inside the genny.
The alignment procedure has been referred to by another poster.

You adjust the inductors to set the lower frequency and the trimmers to set the higher frequency on the read out scale- you will have to go back and forth a few times to get it near accurate. One capacitor and one inductor for each waveband.

What does the metre on the front measure and how can I connect it? It seems to be there just for fun at the moment.

That would be an RF level meter, or possibly AF level, or even both, as I am not familiar with these units, hard to be definite.

The valves are loose around their Bakelite shells. What glue will set them in place? will superglue or gorilla do?

I have used Araldite in the past with no problems, just use it sparingly and press in a small amount to look like a seal, that will stop the glass moving from the base.

A manual sure would make your job a LOT easier.

Here is some info. on your unit http://vintageradio.me.uk/workshop/testeq.htm