In my early days I worked with Telco stuff. I suspect the back to back Zener diodes on the amp output were there to protect the amp from external applied signals. Like 90V 20Hz ringer voltage or step transients from connecting to -48V T/R pair. When testing faulty telco circuits you never know what kind of garbage is on the line. Always loved HP manuals with circuit descriptions with schematics
Great presentation of quality circuit design. Brings back memories of working on HP medical equipment vs the other brands. With HP it was like we were working with the masters. The other brands, well we felt that D- sophomore students were at play.
Excellent, I really like explanations of circuits, when explained it seems so obvious and yet when I first look at the circuit one wonders what on earth is going on. Totally agree, learn from the masters
Again great advice. I recognised some solutions and they really make sense. Getting understanding for solutions takes a lot of experience and knowledge though, often you comment casually but that is very informative. Thank you for taking the effort to pass your knowledge.
I like the tiny "scope" diagrams of the signal in that one part of the circuit. Like they knew someone was going to look at the schematic and wonder "WTF is going on in here?!" and left them some hints.
I agree. I have learned much by studying circuits designed by others. I think it is shortsighted of modern companies to keep this education from the public.
The back to back Electrolytic is a trick used buy "old timers" to get to a non-polarized electrolytics. There was limited selection of those for a long time. Now you could replace them with non-polarized these days. At least that is what I remember from school.
@@sanjikaneki6226yes, they do seem a bit pricey, their use seems to have gravitated to crossover networks etc, in an emergency for testing i stick two back to back.
I've got a question on the power supply. The upper secondary winding on the power transformer has a half-bridge rectifier but doesn't appear to have a return path. What's going on there - did they just neglect to draw the connection to GND for that winding?
I have the same question. I mean it looks like a full-wave rectifier using a center tap, and it looks like it provides some biasing for a protection circuit, but what the heck?
It appears that part of the transformer is connected as a ground to what they are referring to as the ground plane. You can see that the center tab of the other winding is connected to this as well and you can see the shielding or core of the transformer is connected as well. I think it's just a two-tap winding. Somebody has more useful information or if I'm wildly wrong please correct me
Schematic must be missing the R/R center tap return connection. Check the actual transformer. Either it has another wire or the return is internal to the transformer with the G connection.
In this scheme, either an error is made, or the central point of the upper secondary winding, or part of the rectifier bridge, was not printed. upd In this scheme there is an error with the drawing of a supplying transformer. Here is only one secondary winding with several taps. Y-R-G-R-Y upd Oops, I should have read all the comments above )))
@@IMSAIGuy 🙂I didn't forget. NIST has a really good set of web pages and documents related to the SI and its use. SP 330 and SP 811 in particular are really helpful. In SP 811 they say: "When spelled out in full, unit names are treated like ordinary English nouns. Thus the names of all units start with a lower-case letter, except at the beginning of a sentence or in capitalized material such as a title." BIPM, the international body that maintains the SI, to which the US is a signatory also has the SI Brochure (9th edition) which provides the same guidance - see Section 5.3, Unit Names. I can provide links to the above if desired.
@@IMSAIGuy Perhaps, but as NIST has noted, deaths have occurred. www.nist.gov/pml/owm/metrication-errors-and-mishaps Medical dosing errors are a really scary topic WRT units.
Question about the power supply that you haven’t covered. The top section only has 2 diodes followed by a TRIAC. The schematic labels that as "crowbar overvolatge protect". Sorry, my brain is a bit damaged, so I need somebody to explain that part of the circuit to me as though I am 5…😢.
In this scheme there is an error with the drawing of a supplying transformer. Here is only one secondary winding with several taps Y-R-G-R-Y. And the protection scheme works quite simply, in case of over-voltage any of the power rails, the secondary winding is shorts to the ground through the diode bridge with a TRIAC. The over-voltage sensors are CR18 CR25 CR23 and CR7
In my early days I worked with Telco stuff. I suspect the back to back Zener diodes on the amp output were there to protect the amp from external applied signals. Like 90V 20Hz ringer voltage or step transients from connecting to -48V T/R pair. When testing faulty telco circuits you never know what kind of garbage is on the line. Always loved HP manuals with circuit descriptions with schematics
Great presentation of quality circuit design. Brings back memories of working on HP medical equipment vs the other brands. With HP it was like we were working with the masters. The other brands, well we felt that D- sophomore students were at play.
this is a beautifully drawn schematic. very clear to understand what is with each block.
Excellent, I really like explanations of circuits, when explained it seems so obvious and yet when I first look at the circuit one wonders what on earth is going on. Totally agree, learn from the masters
Again great advice. I recognised some solutions and they really make sense. Getting understanding for solutions takes a lot of experience and knowledge though, often you comment casually but that is very informative. Thank you for taking the effort to pass your knowledge.
I like the tiny "scope" diagrams of the signal in that one part of the circuit. Like they knew someone was going to look at the schematic and wonder "WTF is going on in here?!" and left them some hints.
I agree. I have learned much by studying circuits designed by others. I think it is shortsighted of modern companies to keep this education from the public.
The back to back Electrolytic is a trick used buy "old timers" to get to a non-polarized electrolytics. There was limited selection of those for a long time. Now you could replace them with non-polarized these days. At least that is what I remember from school.
i have problem finding good replacements that are not super expensive
@@sanjikaneki6226yes, they do seem a bit pricey, their use seems to have gravitated to crossover networks etc, in an emergency for testing i stick two back to back.
@@sanjikaneki6226 , I have noticed that air conditioning compressor capacitors are not polarized. This might be back to back electrolytics!
thanks really useful 💯
I've got a question on the power supply. The upper secondary winding on the power transformer has a half-bridge rectifier but doesn't appear to have a return path. What's going on there - did they just neglect to draw the connection to GND for that winding?
I was wondering the same thing. I even paused the video and expanded the screen to look around and didn't see a return?
does look like there is a missing center tap on the schematic
I have the same question. I mean it looks like a full-wave rectifier using a center tap, and it looks like it provides some biasing for a protection circuit, but what the heck?
yep. Someone drafting, went for coffee. Probably when that really attractive young lady happened by. 73 de W3IHM
It appears that part of the transformer is connected as a ground to what they are referring to as the ground plane. You can see that the center tab of the other winding is connected to this as well and you can see the shielding or core of the transformer is connected as well. I think it's just a two-tap winding. Somebody has more useful information or if I'm wildly wrong please correct me
😁 when analog was analog,... great stuff
Schematic must be missing the R/R center tap return connection. Check the actual transformer. Either it has another wire or the return is internal to the transformer with the G connection.
Today's circuit designs get lost in the bit bucket. Great recap
CR17 and 18 I don't see a ground on the secondary winding. Centre tap left out??
Yeah, that top part of the circuit before the regulator confuses me, together with the TRIAC part.
wont the back to back capacitors degrade over time if configured like that?
At 4 minutes, CR17 and CR18 both rectify positive going to R30. What is that doing?
In this scheme, either an error is made, or the central point of the upper secondary winding, or part of the rectifier bridge, was not printed.
upd In this scheme there is an error with the drawing of a supplying transformer. Here is only one secondary winding with several taps. Y-R-G-R-Y
upd Oops, I should have read all the comments above )))
Kelvin ohms and kelvin hertz used in the schematic. HP usually does better . . .
you forgot to capitalize kelvin and hertz
@@IMSAIGuy 🙂I didn't forget. NIST has a really good set of web pages and documents related to the SI and its use. SP 330 and SP 811 in particular are really helpful. In SP 811 they say: "When spelled out in full, unit names are treated like ordinary English nouns. Thus the names of all units start with a lower-case letter, except at the beginning of a sentence or in capitalized material such as a title."
BIPM, the international body that maintains the SI, to which the US is a signatory also has the SI Brochure (9th edition) which provides the same guidance - see Section 5.3, Unit Names. I can provide links to the above if desired.
@@RideGasGas This is a topic that I find trite.
@@IMSAIGuy Perhaps, but as NIST has noted, deaths have occurred.
www.nist.gov/pml/owm/metrication-errors-and-mishaps
Medical dosing errors are a really scary topic WRT units.
Question about the power supply that you haven’t covered. The top section only has 2 diodes followed by a TRIAC. The schematic labels that as "crowbar overvolatge protect". Sorry, my brain is a bit damaged, so I need somebody to explain that part of the circuit to me as though I am 5…😢.
In this scheme there is an error with the drawing of a supplying transformer. Here is only one secondary winding with several taps Y-R-G-R-Y. And the protection scheme works quite simply, in case of over-voltage any of the power rails, the secondary winding is shorts to the ground through the diode bridge with a TRIAC. The over-voltage sensors are CR18 CR25 CR23 and CR7