HP 211A

[MED6753]

Finally got some time to change out the remaining capacitors. It was a real chore to get to them on the range switch but I was ultimately successful. Changed out C6, C7, C8, C12, C13, C14.



The vanquished.



Test set up: 2465 set to 50 ohm input. 75 ohm output on the generator. Why hp chose 75 ohm is a mystery to me.

The results. Drum roll.....

X1 (Trust me, it's OK)


X10


X100


X1k


X10k


X100k


So the symmetry issue is finally fixed. All that's left to do is calibrate the frequency dial. There are adjustments for each range so it should fall into place easily. Stay tuned.

Oh and the 6BQ7A vacuum tube finally showed up today. USPS had it in their possession on 28 April. Took until today to come from California. I swear they must still use Pony Express.

[vk6zgo]

The delayed delivery is reminiscent of trying to obtain replacement parts from the EU or UK in the 1980s & '90s.
We could have sworn that a fast 1800s style "windjammer" service would have got them to Western Australia faster!

EU & UK manufacturers complained that "nobody in Australia bought their equipment", & Japanese companies were "eating their lunch".
Meanwhile, if you needed parts from Sony, they either had them in Australia, "First Airfreight", or somewhere else, available in a couple of days!

Unfortunately, nowadays,everybody seems to have returned to pre-windjammer days!

[MED6753]

FedEx and UPS at least 90% of the time meet or beat their own projected delivery date. USPS is at best 50% and I've even had them lose items.

[tggzzz]

We could have sworn that a fast 1800s style "windjammer" service would have got them to Western Australia faster!
...
Unfortunately, nowadays,everybody seems to have returned to pre-windjammer days!

My pension company office occasionally sends me letters. According to google maps and based on a 40 hour walking week 20 miles/day, they would reach me quicker if someone walked.

The HMRC tax letters typically give you 14 days to reply from the date of the letter, but they take a week to arrive.

That kind of issue has become a serious problem for people with medical appointments sent by post.

Deteriorata. Apparently around the time I was born it was normal for someone working in their London office to send their wives a letter saying they wold be "back at 6pm tonight".

[MED6753]

Today is frequency calibration.



The manual recommends something like this monster to set the frequency ranges. hp 523 or 524 series. We'll use something a little more modern.



Pulled the 2465 no option scope and substituted 2465 DMS which has frequency readout. So I can monitor the symmetry and frequency simultaneously.



Calibration completed.



Must pass a required burn-in of at least 2 hours. Once that's done this project is complete. If there's no additional posts from me you can assume it passed and it's a done deal.

[Cubdriver]

Mike, IIRC my 523D was working when last I powered it up - want to borrow it?





-Pat

[MED6753]

I think shipping would be a tad expensive.

[25 CPS]

Mike, IIRC my 523D was working when last I powered it up - want to borrow it?





-Pat

Oh yeah, I second that. 523D is definitely the way to go on this.

[MED6753]

The oldest counter I have is this bad boy. Twas a present from nixiefreqq. And it works perfectly too.

[Cubdriver]

The first 5245L was my gateway drug and what really began this slide into test equipment collecting insanity...


-Pat

[Zenith]

Finally got some time to change out the remaining capacitors. It was a real chore to get to them on the range switch but I was ultimately successful. Changed out C6, C7, C8, C12, C13, C14.

So this was nothing to do with silver mica capacitors. It was other capacitors setting the ranges. Were they paper capacitors or early film capacitors?

Anyway, a right result.

[MED6753]

Finally got some time to change out the remaining capacitors. It was a real chore to get to them on the range switch but I was ultimately successful. Changed out C6, C7, C8, C12, C13, C14.

So this was nothing to do with silver mica capacitors. It was other capacitors setting the ranges. Were they paper capacitors or early film capacitors?

Anyway, a right result.

You can't easily tell if the black beauties are paper or film unless you cut them open which I did not do and are already gone. I also changed the supposed .01uf mica capacitor because I suspect it's high value for a mica cap required possible paper content.

[Cubdriver]

The ones you can usually tell on are the old black tubular Sprague caps with the yellow or red lettering (can't recall the series off the top of my head). Yellow print means paper, they'll have become resistors. Red print means difilm; those are normally ok. The way I remember it is think like traffic lights - red = stop, don't change; yellow = caution, likely bad.

Striped ones just get replaced on sight.

-Pat

[Cubdriver]

Hey Mike - if you want to get the correct counter to calibrate your square wave generator, there's one on The Bay of Evil now!
https://www.ebay.com/itm/306299652398?_ ... BMwPmoq9ll

HP 524C.JPG

<ducks and runs>

-Pat

[mansaxel]

The 5245L is a wonderful machine, and it is certainly a rite of passage for TEA people. Of course I have one, here in very good company:



I did however get bitten earlier, by this little one:



Counters need nixies, or at least very good company:



That's a standard crystal in the 5316A, and it manages to count the 10MHz from the GNSS steered Rb in the MT1000A to the limit of its resolution.

[AVGresponding]

Nixies? What are those?

IMG_20250514_174741361.jpg

[25 CPS]

Hey Mike - if you want to get the correct counter to calibrate your square wave generator, there's one on The Bay of Evil now!
https://www.ebay.com/itm/306299652398?_ ... BMwPmoq9ll

HP 524C.JPG



<ducks and runs>

-Pat

I just looked at the listing and it shows up as sold on May 13th. Someone bought it yesterday.

[tggzzz]

Nixies? What are those?

I haven't got any device with numitron/minitron displays.

No, I don't want cockpit instruments nor petrol pumps, thank you very much.

[Cubdriver]

Nixies? What are those?

IMG_20250514_174741361.jpg

Contemporaries/successors of these:


I have a timer lurking about here somewhere with Numitrons, but can't find any handy pics of it.

-Pat

[25 CPS]

Test set up: 2465 set to 50 ohm input. 75 ohm output on the generator. Why hp chose 75 ohm is a mystery to me.

The results. Drum roll.....

So the symmetry issue is finally fixed. All that's left to do is calibrate the frequency dial. There are adjustments for each range so it should fall into place easily. Stay tuned.

Oh and the 6BQ7A vacuum tube finally showed up today. USPS had it in their possession on 28 April. Took until today to come from California. I swear they must still use Pony Express.

Cool! I'm glad the range capacitor changeout fixed up the symmetry issue. As for the 75 ohm, I was wondering the same thing. The only other thing I can think of off the top of my head that HP built with 75 ohm characteristic impedance are spectrum analyzers optioned for that for video system work like cable TV. I wonder if maybe HP designed the 211A with 75 ohm characteristic impedance so it could be used to do square wave frequency response tests on video systems back in the day? It's a possibility but there are other better way of testing analog video systems with purpose built equipment for that* but all of that might have come along after these were designed.

On the subject of video, I did get a couple of 75 ohm terminators to go with the 211AR but they're going to be used with the existing RG-58 BNC cables I have so there's still going to be some mismatch with that but it's going to have to do.

* I pulled out a nasty old video measurement book from 1983 and nothing was said about basic square wave tests so if that was something that was done in analog video systems, it was superseded long ago.

[vk6zgo]

Test set up: 2465 set to 50 ohm input. 75 ohm output on the generator. Why hp chose 75 ohm is a mystery to me.

The results. Drum roll.....

So the symmetry issue is finally fixed. All that's left to do is calibrate the frequency dial. There are adjustments for each range so it should fall into place easily. Stay tuned.

Oh and the 6BQ7A vacuum tube finally showed up today. USPS had it in their possession on 28 April. Took until today to come from California. I swear they must still use Pony Express.

Cool! I'm glad the range capacitor changeout fixed up the symmetry issue. As for the 75 ohm, I was wondering the same thing. The only other thing I can think of off the top of my head that HP built with 75 ohm characteristic impedance are spectrum analyzers optioned for that for video system work like cable TV. I wonder if maybe HP designed the 211A with 75 ohm characteristic impedance so it could be used to do square wave frequency response tests on video systems back in the day? It's a possibility but there are other better way of testing analog video systems with purpose built equipment for that* but all of that might have come along after these were designed.

On the subject of video, I did get a couple of 75 ohm terminators to go with the 211AR but they're going to be used with the existing RG-58 BNC cables I have so there's still going to be some mismatch with that but it's going to have to do.

* I pulled out a nasty old video measurement book from 1983 and nothing was said about basic square wave tests so if that was something that was done in analog video systems, it was superseded long ago.

Longline carrier telephone systems were standardised on 75 ohm back in the day, as were the baseband & IF stages of microwave systems. Not so sure about after the last up converter, but in a lot of cases that was direct to waveguide, so that may not have been an important distinction.

As to analog TV use, amplitude/ frequency tests were often performed on the video circuitry, back in the day, some adding the composite sync, others without.
We used Fernseh PGM 75s to sweep any video equipment which used keyed clampers, etc, as it had provision to insert syncs & blanking.

For sweeping the whole transmitter, from the (75 ohm) "video in" to the RF output, we used a device known as a "sideband analyser", which included a sweep with syncs, with the sweep synchronised to the vertical syncs & a built in RF demodulator.

[AVGresponding]

Nixies? What are those?

I haven't got any device with numitron/minitron displays.

No, I don't want cockpit instruments nor petrol pumps, thank you very much.

They do seem quite difficult to find. This thing is a real oddball, no manufacturers mark, probably an internal special or something. The trigger level setting is very odd; it's a window rather than a threshold.

[mansaxel]

We used Fernseh PGM 75s to sweep any video equipment which used keyed clampers, etc, as it had provision to insert syncs & blanking.

Caught at the German Technology Museum this summer: