The PHILCO Phorum

Are there recommendations for a signal generator for a newbie? I have been looking on Amazon and eBay, there is a lot to choose from but I have no idea what is needed.

From experience.
Don't waste time buying old SG8 and such tube generators. Feels good but works bad.
Buy an inexpensive digital set.

Hello Vintagerocks,
I have a Few different ones but my Go To is my Stark LS-10A which is tube based it works very well when I use my digit freg counter .
If you want new there tons of Digit ones out there and even a good used one like from HP or Sencore .
Sincerely Richard

Koolertron Upgraded 15MHz DDS Signal Generator Counter,High Precision Dual-Channel Arbitrary Waveform Function Generator Frequency Meter 200MSa/s (15MHz)


https://www.amazon.com/dp/B07211YWMK/ref...Y2s9dHJ1ZQ==

This is from Amazon, would this be a good digital alternative?

Will cover up to 22M SW band.
Won't 19, 15, 13 and 11M.

Of course, you might not need them.
You could also use harmonics to go for higher frequencies.

Another problem with that generator is that it does not have an output attenuator and I don't believe it has audio AM modulation.

It has only a high level output with no means to reduce the signal to a point where it could be directly connected to the antenna for alignment.

The generator is really a high output function generator, not an RF signal generator for radio work.

The one plus it has is that it is synthesized, so it does deliver accurate frequency signals.

Mondial

It does. But the knob will wait until you pick a function. You can see the amplitude (this is attenuation) and "MOD" (which should be a modulation).

According to the answered questions on Amazon, minimum output is around 10 mV which is still a lot for alignment without using an external attenuator. So yes, the output is adjustable but you would still need some sort of switchable attenuator to get down to the microvolt output level.

As per this response, there is no AM or FM modulation:


What is the minimum sine wave output? can this unit do am of sine wave, say 1khz mod of a 5 mhz sine wave?

Answer:
I cranked mine down to 10 mV P-P at 10 MHz and the waveform display on my scope was a little smeared, that is not a real clean trace but still a sine wave. The question of modulation has come up before since there is a input connector, but that connector is for using the generator as a counter. So no, you cannot modulate the output. If you want an AM signal it should be easy to put the output thru a FET modulator circuit. There are all kinds of FET circuits online for doing just that. For FM no such luck. Yeah that made me unhappy too when I needed an FM signal. 

According to the answered questions, this model does have the AM capability:

https://www.amazon.com/dp/B08T9H9FBY/ref...RydWU&th=1

Maybe, but they look like the same model (with a different freq range) from two different chinese sellers, made in the same backyard.

Hmmm. I had one of those Koolertrons until I destroyed the output. It does AM and FM modulation using the channel 2 as the source, along with several other modulations. I currently use a FY6800. Very similar. Output amplitude goes down to .0001 and up to 20 volts at some frequencies. Not sure if the output is actually that low as I have no way to actually measure that low. However, it seemed to work as a direct connection to the antenna without activating AVC. I am now using morzh's circuit to protect the input from spikes. It's a 60mHz unit. I use the harmonic to work in the FM band.

Seems as this is another mystery to research, which is fine.

Thank you for all the input, I will gather up the details and see what I can find that is reasonably priced.

A word from my own point of view. I bought a modern sig gen off eBay, like this one... https://www.ebay.com/itm/114899896592?ha...SwkL1g01mH . It was never very accurate, and crapped out after less than a year of use. I have also bought several different vintage, tube type signal generators, from a Heathkit SG-8....


(not mine, but same model...) to an EICO model 324....



The EICO is what I currently use because it is a little more accurate. Both of these old tube type sig gens work fine and reliably once you replace any paper condensers in them, and any electrolytic condensers. The Heathkit is pretty fixed, and is a little less accurate frequency wise, so I had to constantly check it with a good, modern, digital readout radio. I dialed in the EICO which is more adjustable using that method. I find that it now is so accurate that for most alignment work I don't have to double check the frequency.

Neither of these sig gens cost me more than $70. They are perfectly adequate for 99% for the work we do restoring antique radios. About the only thing they lack is a frequency modulated FM frequency band output. There are work arounds for this which can be found in the literature for the Philco 48-482.

So, there you have it. I prefer these old tube type signal generators over the modern Chinese junk.

The output levels of any type of generator can be reduced using inductive coupling. No fancy attenuators are needed for hobbyist work.

Purists will complain that you can't "measure" the stage gains, etc, etc, but I have yet to meet an average hobbyist who wants to get to that level of alignment sophistication anyway.

Most people simply reduce the generator signal levels to the lowest that they can either hear in the speaker, or measure at the output and never bother to measure the actual output voltage at the generator. in most cases it's not only not necessary, but there are no spec's provided anyway, at least for most vintage AM/SW consumer tube radios. (amateur/commercial is a whole different game).

I have been using a BK4040 for many years now. It has done everything I have asked it to, because I understand it's limitations and make the necessary adaptations myself for the generator, said adapting mostly being the use of inductive coupling.

If I were buying again today I wold buy a Siglent type of function sweep generator, good for up to say 30-50MZ, from an Amazon vendor, knowing that most Amazon vendors have very permissive return policies, and if it didn't do what I wanted, as well as I wanted, I could return it.

YMMV

What I have done with my Heathkit SG-8 which was my dad’s, is I replaced all the old output jacks with BNCs which makes it more compatible with modern cables and my frequency counter. Since I’ve never need to modulate with an external source, Ive repurposed the audio input connector and rewired it to before the RF attenuator, that way I can connect my frequency counter and have a strong input to it regardless of my output settings that I use for alignment. Works great and gets the job done!

Ron