The AM Forum

I own a very nice, unmolested Ameco VFO 621 that is paired with my Ameco TX2 Transmitter.  I have yet to test the VFO with the transmitter as the latter is on the bench undergoing a recap.  I was checking over the VFO and noticed I could not obtain an accurate reading on my handheld frequency counter at the FT-243 plug of the VFO.  To quote the manual, the VFO is "hetrodyned to 24-26 Mc.".  The frequency counter is all over the place and I cannot ascertain a stable figure anywhere close to 24-26 Mhz.

Am I missing something?  Resistors, tubes, and electrolytic are fine--all wiring appears original with no apparent signs of modification.

I appreciate the guidance.  

Chris, N4JOY  

Have you grounded the necessary terminals to make the VFO put out a signal?

The VFO output may not be sinusoidal, which will make the counter go nuts. A spectrum analyzer, or wideband SDR is helpful in situations like this.

Jim
Wd5JKO

Although the output is via a broadband tune amplifier it is likely some of the 4-7 Mhz. VFO output along with the 19.9 hetrodyne oscillator output is appearing along with the desired output and this will also confuse the counter.  I expect this VFO still depends upon the associated transmitter to provide additional filtering for acceptable spectral purity.

As others have noted you can use a receiver to determine whether it is truly producing a 24-26 Mhz. output and a receiver is called for  in the manual for alignment of the 4 to 7 Mhz. VFO section.  I used a receiver rather than frequency counter when I aligned mine a couple of years ago.

Silly me! Duh!  Yes, I checked the VFO with my Christmas present (SDR) and am indeed seeing a signal at the expect frequency.  I literally forgot I had the SDR.  Anyway, I do not have a functioning, general coverage receiver on HF at the moment so I ruled that out.  Well, problem solved.  I appreciate the very quick responses.  The manual's method of calibration is somewhat clunky so I wanted to use an easier method.

Thanks,

Chris, N4JOY

Well, after a warm-up I was very surprised to see that the VFO is nearly spot on.  Here is a screenshot from the SDR--the vertical red line is 25 Mhz.  The VFO is set to 50 MHz and is very close.