An update.

The Avantek YTO requires a lot more current to tune to the required frequencies than the HP YTO it replaces.? I was running into trouble because I was actually measuring the 2nd harmonic, which explained why it showed weak on the bench 8566A.? I was seeing minus some odd dBm where I would expect the 1st LO output should be around +10 dBm.? This is why I was having difficulties. I needed to look lower in frequency than I thought for the strongest output.

Tho get the Avantek to run at the needed frequencies required some circuit modifications.

Bottom line, it required adding some extra resistors in parallel to the current sense resistors in the Q301 and Q302 circuits.? In each case, the two parallel 100 ohm resistors had to have added two each precision 76.8 ohm low TC resistors.? This moved the 50 ohm sense resistor to 21.72 ohms.? Once this was done, I was able to get the YTO tuning alignment completed successfully at 3.200 and 6.050 GHz per the manual.

The Avantek main coil is 10 ohms while the HP coil was 39 ohms. To limit dissipation in the drive transistors and sense resistors, I added a 20 ohm 5 watt resistor in series with the main coil, at the YTO.? At the 305 mA required at 6.050 GHz, it dissipates 1.8 watts. The power dissipation in components is calculated to be within limits.

The analyzer errors disappeared and I can work further on it.

I did notice that the drive transistor for the YTF is running VERY hot.? I will need to look into that.

Peter


On 3/18/2024 6:33 PM, Peter Gottlieb via groups.io wrote:

So my adventures in restoring this instrument continue.

The YTO I got from ebay had a definite intermittent short between one side of the FM coil and the -5 volt pin.

I cut it open and this was a manufacturing defect.

The ebay seller sent me another unit, which is fine.? He didn't give me a hard time at all, very honorable.

So I mounted it in the instrument with the adapter plate I had made, hooked up the -5 volt regulator and everything else, and tried the YTO adjustments.

I could set the low to the 3.200 GHz but I couldn't get the high to go to 6.010 GHz.? Not enough range in the adjustment pot.? In the circuit there are R44 and R126, each 100 ohm 0.1% resistors, in parallel, in the current sense part of the current source circuit. I found that an added 1K resistor in parallel would give me enough range so I added a high quality 1% 1K resistor there.

I was then able to go back and forth on the low and high adjustments until they were right.

However, that resistor might not be the right value even though I could get the adjustments to work, because I am getting an error 319, which is a warning that the coarse YTO tune DAC is near its limit.

I will have to look at the DAC output to see if this is for the lower or upper limit and go from there.

This is promising.? It looks like this substitute YTO might just end up working out.

Peter

Hello there!
I like to take advantage of everything the internet has to offer before asking questions here. But on this topic, every time I go online to look for information, I get more confused.
I have a collection of HP equipment, as some of you may know. I would like to command them by GP-IB through a USB adapter (I don't have a tower PC to use a PCI card). A sea of ??doubts assails me.

*Most important doubt: *what adapter to buy? eBay is full of counterfeits, and I don't know the consequences of not having an original adapter. I am not looking for professional use, but I would like to do automatic tests, program my own small tests and barely-complex measurements (for example phase noise measurements with my 8566B, register level flatness and frequency stability of an oscillator for several hours or scalar network analysis using coax switches and so).

There is a library of model programs for this kind of uses? Maybe a library of HP programs like they record on tapes to verify it's own test gear, like the show by CuriousMarc on YouTube with a 8662A and 8568B.

I have no idea how it is programmed or the possibilities of controlling the equipment in this way. My test gear was manufactured between 1979 and 1991, I understand that not all commands work. I also don't know if the disparity in manufacturing years would prevent them from being used together.

Apart from the manual on HP-IB published by Hewlett Packard (which I have not paid much attention to because I don't know if it is too outdated, given that I intend to control the system with a modern PC, with Windows 10)
I look forward to your recommendations, suggestions on bibliography and other advice.
Thank you very much in advance