- low current circuit breaker or fuses? - 2 Updates
- Why was the circuit designed to use a Callins in C7? - 23 Updates
| Witherspoon <ws194@aol.com>: Dec 12 02:55PM -0500 Over the past week, I built a small nichrome based 50 watt heater that runs from 12 VDC power supply. It currently has 5 amp fast blow AGC fuses in both lines, but what's to stop me from using a small circuit breakers in each line instead? I see plenty of NOS or used ones on eBay at maybe double the price for fuses, but not always the case as I've seen fuse packs of similar price to the breakers. |
| "Peter W." <peterwieck33@gmail.com>: Dec 13 04:08AM -0800 a) Ever see a fuse jam? Breakers are a risk on purely resistive loads. Nothing to stop you, however. b) I would never purchase a critical part from eBay - no guarantee that it is as described, or even from a legitimate manufacturer. Peter Wieck Melrose Park, PA |
| "Don" <g@crcomp.net>: Dec 12 04:44PM > would show up on the schematic and BOM. > As it is, specifying a 6V electrolytic to filter a > 6.2V reference is probably a mistake. Excellent observation! There's actually a 25 V Callins on the board itself. So, there's definitely a mistake on the schematic. Danke, -- Don, KB7RPU There was a young lady named Bright Whose speed was far faster than light; She set out one day In a relative way And returned on the previous night. |
| "Don" <g@crcomp.net>: Dec 12 04:45PM > capacitors. There is absolutely nothing special about the electrical > characteristics needed of C6 and C7 in that unsavoury circuit and my > guess is that the assemblers just randomly picked that brand. Thank you for confirming my suspicions. It turns out there's a typo on the schematic. The actual Callins capacitor on the board is 25 V. As an aside, perhaps the circuit's relaxation oscillator looked a little less unsavory back in the hazy 1970s, back when Woz won Bushnell's bonus to minimize the chip count. :) Danke, -- Don, KB7RPU There was a young lady named Bright Whose speed was far faster than light; She set out one day In a relative way And returned on the previous night. |
| "Don" <g@crcomp.net>: Dec 12 04:46PM > AR and KLH seemed to use quite a few of them in some models. > Maybe they are charging so much because they are the only good ones > left on the planet? People get nostalgic about all sorts of things. And it's OK with me if they spend good money to make the object of their obsession a perfect replica in every way. Some people pay a lot more for questionable fine art. It turns out there's a typo on the schematic. The actual Callins part is rated at 25 V. Regardless, thank you for taking the time to confirm my suspicions about it. Danke, -- Don, KB7RPU There was a young lady named Bright Whose speed was far faster than light; She set out one day In a relative way And returned on the previous night. |
| jlarkin@highlandsniptechnology.com: Dec 12 09:23AM -0800 >(and another smaller value) though I couldn't locate it on the >schematis.. >RL The old bakelite Black Beauty film (or maybe paper?) caps are highly prized/priced because some people can hear the difference. If I paid $25 for a 0.022 uF cap, I bet I could hear the difference. I wonder how many of these sorts of things are Chinese fakes. -- John Larkin Highland Technology, Inc The best designs are necessarily accidental. |
| jlarkin@highlandsniptechnology.com: Dec 12 09:25AM -0800 On Sat, 12 Dec 2020 13:25:26 +0100, Arie de Muynck >> Is that a non-polar electrolytic? Looks like two regular caps potted. >> What use is a 300 uF non-polar 'lytic? >The second picture (un)clearly shows + + + marking. I think so. So it's one ordinary cap potted. -- John Larkin Highland Technology, Inc The best designs are necessarily accidental. |
| jlarkin@highlandsniptechnology.com: Dec 12 09:34AM -0800 >Interesting, but it doesn't answer my question: >Why was the circuit designed to use a Callins in C7? >Danke, Was it designed that way? That circuit was barely designed at all. What's it supposed to do? -- John Larkin Highland Technology, Inc The best designs are necessarily accidental. |
| jlarkin@highlandsniptechnology.com: Dec 12 09:37AM -0800 >As it is, specifying a 6V electrolytic to filter a >6.2V reference is probably a mistake. >RL Lytics usually have a pretty good overvoltage tolerance, and a little leakage wouldn't do any harm in a power supply filter. It may have failed by drying out over the years and been replaced by whatever was handy. -- John Larkin Highland Technology, Inc The best designs are necessarily accidental. |
| "Don" <g@crcomp.net>: Dec 12 05:54PM >>Why was the circuit designed to use a Callins in C7? > Was it designed that way? > That circuit was barely designed at all. What's it supposed to do? Your question restates the gist of this thread. How can you know the circuit was barely designed at all if you don't even know what's it supposed to do? Danke, -- Don, KB7RPU There was a young lady named Bright Whose speed was far faster than light; She set out one day In a relative way And returned on the previous night. |
| John Robertson <spam@flippers.com>: Dec 12 10:03AM -0800 On 2020/12/12 8:44 a.m., Don wrote: > Excellent observation! There's actually a 25 V Callins on the board > itself. So, there's definitely a mistake on the schematic. > Danke, Engineers make mistakes? Never! (ducking) John :-#)# |
| jlarkin@highlandsniptechnology.com: Dec 12 10:19AM -0800 >Your question restates the gist of this thread. >How can you know the circuit was barely designed at all if you don't >even know what's it supposed to do? Because it's full of trimpots and selected values. It was probably futzed until it worked. What's it supposed to do? -- John Larkin Highland Technology, Inc The best designs are necessarily accidental. |
| piglet <erichpwagner@hotmail.com>: Dec 12 06:41PM >> even know what's it supposed to do? > Because it's full of trimpots and selected values. It was probably > futzed until it worked. What's it supposed to do? My guess is it was some kind of analog synth VCO, inputs EFG are summed and make the ramp, square and triwave outputs at jacks HDJ. Dig the 3.6V D3 zener in the path, the 3.9Meg and 680R R19 R20 and the kooky voltage follower Q3 Q11 Q4 - the unijunction Q2 is probably the least nasty part of it all. Thats why I used the word unsavoury! piglet |
| legg <legg@nospam.magma.ca>: Dec 12 01:46PM -0500 On Sat, 12 Dec 2020 09:23:52 -0800, jlarkin@highlandsniptechnology.com wrote: >prized/priced because some people can hear the difference. >If I paid $25 for a 0.022 uF cap, I bet I could hear the difference. >I wonder how many of these sorts of things are Chinese fakes. I recall there being an oversupply of non-polarized electrolytics at one time, mainly because of their perceived mark-up value. The value was due to their predominant sale to low-volume hobbyists. The Callins part is polarized and of no special importance to the circuit in which it was employed. The Hafler circuit was the DH110, which used descrete transisators of both polarities in complimentary pairs. I still don't see the C109 part in the schematic. RL |
| Jeroen Belleman <jeroen@nospam.please>: Dec 12 07:53PM +0100 On 2020-12-12 19:46, legg wrote: > circuit in which it was employed. > The Hafler circuit was the DH110, which used descrete transisators of > both polarities in complimentary pairs. I still don't see the C109 [...] ^^^^^^^^^^^^^^^^^^^^ Every time I see that, a vision of them congratulating each other comes to mind. It's complementary. - Jeroen Belleman P.S. Oh, and 'discrete'. |
| "Don" <g@crcomp.net>: Dec 12 06:56PM >>even know what's it supposed to do? > Because it's full of trimpots and selected values. It was probably > futzed until it worked. What's it supposed to do? It's the VCO module from an old synthesizer. It has three triangles on its face-plate and it's right above the left hand side of the keyboard in the first image shown here: http://www.johnnypumphandle.com/johnny/Paia/paia.htm Danke, -- Don, KB7RPU There was a young lady named Bright Whose speed was far faster than light; She set out one day In a relative way And returned on the previous night. |
| legg <legg@nospam.magma.ca>: Dec 12 02:12PM -0500 On Sat, 12 Dec 2020 19:53:22 +0100, Jeroen Belleman > - >Jeroen Belleman >P.S. Oh, and 'discrete'. I flipped a coin with complementary. Discrete has no excuse. It was the DH100, not 110, using ICs, that had the C109 issue in it's docs. If I had a board, I'd make the schematic alteration. Looks like all pns 100+ were added post-design. Stuff like RF filtering on inputs, belt and braces decoupling, grounding leakage paths etc. Most show up. RL |
| Tauno Voipio <tauno.voipio@notused.fi.invalid>: Dec 12 09:19PM +0200 On 12.12.20 6.49, Don wrote: > For the time being, the Callins will be substituted with a new > electrolytic in a can. > Danke, There must be some audio magic inside the Callins, but I see it difficult to get any advantage in a power supply filter. If you're not happy with a garden-variety aluminum, get a tantalum one, and please, with a little more than 6V rating, as the power line is nominally 6V. -- -TV |
| legg <legg@nospam.magma.ca>: Dec 12 02:24PM -0500 On Sat, 12 Dec 2020 14:12:05 -0500, legg <legg@nospam.magma.ca> wrote: <snip> >Looks like all pns 100+ were added post-design. Stuff like RF >filtering on inputs, belt and braces decoupling, grounding leakage >paths etc. Most show up. I'm a dolt. C9, C109 set the LF gain corner of the first IC's gain stage. Part numbers above 100 are right channel, not repeated in schematic. . . . Q has hovered for some decades in rubbish area of skull. RL |
| Tauno Voipio <tauno.voipio@notused.fi.invalid>: Dec 12 09:24PM +0200 >> Danke, > Was it designed that way? > That circuit was barely designed at all. What's it supposed to do? Agreed. There is a voltage-controlled UJT sawtooth generator, with outputs sent to three places: - direct output, - a differential pair-rectifier to cut it at the middle for a (maybe) symmetric triangle, - a Schmitt-trigger to create a variable width pulse There is plenty of opportunity for improvement even when using the block diagram (and forgetting the UJT). -- -TV |
| "Don" <g@crcomp.net>: Dec 12 08:14PM > On 12.12.20 19.34, jlarkin@highlandsniptechnology.com wrote: <snip> > - a Schmitt-trigger to create a variable width pulse > There is plenty of opportunity for improvement even when > using the block diagram (and forgetting the UJT). You seem to know what you're talking about. :) Although its ramp and triangle outputs are now restored, the Schmitt trigger's still a work in progress. It's (manually transcribed from a PDF and as typo-free as possible) Design Analysis is shown below. The last paragraph in the analysis leads me to believe the Callins capacitor was plausibly used by design. DESIGN ANALYSIS The central feature of the 2720-2A VCO is the self-zeroing, summing voltage to current converter comprising of IC-1, Q1 and associated components. Unlike the more conventional inverting summer, the feed back voltage does not come directly from the output of the amplifier but rather from the emitter of the current source transistor Q1. In operation positive voltages applied to one or more of the summing resistors (R1 - R3) force the output of the amplifier to go to whatever negative voltage is necessary to make the same voltage appear at both the inverting and non-inverting inputs of the op amp. Feedback circuits are always a balancing act and the balanced point in any linear operational amplifier circuit is reached when the two inputs are at equal voltages. Since in this case the non-inverting input is grounded (0v.) the inverting input must also go to zero volts. Since the base emitter junction of Q1 is inside the feedback loop of the summing amplifier, both the natural non-linearities and constant voltage drop of the junction are eliminated from the response of the current source. Both sets of resistors that serve as emitter resistances for the current source (Range trimmer R7 in series with R6 both paralleled by R4) terminate at ground and a virtual ground so that for zero control volts input the source must generate zero current. The output of the current source charges capacitor C1 which in conjunction with Unijunction Transistor (UJT) Q2 forms a relaxation oscillator. As increasing voltages are applied to the control inputs, the current supplied by Q1 increases causing C1 to charge more rapidly thereby increasing the frequency of the oscillator. The ramp waveform that appears across C1 is applied to the input of the darlington emitter follower consisting of Q4 and Q11. The high input impedance of this emitter follower is important in presenting negligible load to the timing capacitor C1. A second emitter follower Q4 in conjunction with zener diode D3 performs a level shift so that the ramp is transposed to slightly above ground potential while a third emitter follower (Q5) provides a low output impedance buffer to couple the signal to the rest of the waveforming circuitry. The ramp waveform is used three ways. First, it is applied to the voltage divider string consisting of R11, R24, R23 and R22. Between R11 and R24 the string is capacitively coupled through C5 directly to the "RAMP" output jack J1 where it becomes available as a signal source. Secondly, the ramp is applied to the Schmitt trigger composed of Q9 and Q10. A Schmitt trigger has a low output or a high output depending on whether the input voltage is above or below a pre-set design level. As the ramp input to the trigger begins to rise the output remains low until the voltage exceeds this level and then abruptly changes to the high state. The output of the trigger, then, is a rectangular pulse at exactly the frequency of the ramp input. By varying the amplitude of the ramp you regulate the duration of the pulse by changing the relative point at which the trigger changes state. Finally, the ramp is applied to the input of the differential pair Q6 and Q7. In the differential configuration the voltage at the collector of Q7 is in phase with the input ramp and the voltage at the collector of Q6 is inverted. The diodes D1 and D2 "select the higher of the two collector voltages and apply it to the base of emitter follower Q8. During the lower half of the input ramp's excursion Q6's collector voltage is higher and that section of the ramp is presented in an inverted form to the base of Q8. There is a slight rounding at the bottom of the wave during the cross over between Q6 and Q7 and a slight pip at the top during the ramp "flyback" but neither of these imperfections are audibly noticeable. The most voltage sensitive portions of the circuit are powered from the simple series voltage regulator consisting of zener reference diode D4 and pass transistor Q12. Less critical parts of the circuit are powered by the decoupling networks R33/C6 in the positive supply line and R35/C8 in the negative supply. Danke, -- Don, KB7RPU There was a young lady named Bright Whose speed was far faster than light; She set out one day In a relative way And returned on the previous night. |
| jlarkin@highlandsniptechnology.com: Dec 12 12:18PM -0800 On Sat, 12 Dec 2020 21:19:50 +0200, Tauno Voipio >If you're not happy with a garden-variety aluminum, get a >tantalum one, and please, with a little more than 6V rating, >as the power line is nominally 6V. Derate tants about 3:1 on a supply rail. That seems to be reliable. -- John Larkin Highland Technology, Inc The best designs are necessarily accidental. |
| Steve Wilson <spam@me.com>: Dec 12 09:21PM > Derate tants about 3:1 on a supply rail. That seems to be reliable. If you have to derate, there goes the size advantage. If the tant is at the end of a long power supply lead, there could be a spike when the power is attached. See Williams for more info. With the risks of tantalum, why not use poly instead? -- The best designs occur in the theta state. - sw |
| Cydrome Leader <presence@MUNGEpanix.com>: Dec 12 09:49PM > characteristics needed of C6 and C7 in that unsavoury circuit and my > guess is that the assemblers just randomly picked that brand. > piglet "BULLSHIT". phil allison told me to let you know this. |
| "Don" <g@crcomp.net>: Dec 13 05:13AM > In sci.electronics.design legg <legg@nospam.magma.ca> wrote: <snip> >> 6.2V reference is probably a mistake. > Excellent observation! There's actually a 25 V Callins on the board > itself. So, there's definitely a mistake on the schematic. Whoops, it turns out the (loose) 25 V Callins belongs to another module. Although the VCO's original 6 V Callins is long gone from my PCB, Inet images show it present on other people's VCOs. It also turns out there's a typo with D4. Its correct value is 5.6 V. By inspection the emitter voltage of Q12 is then determined to be ~ -4.93 V, which jibes with the measured drop across C7 of 4.87 V. Danke, -- Don, KB7RPU There was a young lady named Bright Whose speed was far faster than light; She set out one day In a relative way And returned on the previous night. |
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