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When did they slack off? Among the many diversive systems I designed, oversaw testing, installation, etc., or as part of a design team, all electrical systems I'm aware of were hi-pot, megger tested regardless of its intended app.Quote:
Originally Posted by Elitopus1
GM
When I first started in aviation, we didn't have that many task cards requiring the wires to be meggered. Maybe this work was done at other checks. I work at an MRO doing mostly heavy checks.Quote:
Originally Posted by GM
Now we have quite a few cards requiring the megger. From testing wiring to fuel pumps. The older planes get a lot more of this. And the McDonald Douglas planes get a whole lot of it. Could just be because of the aging fleet and wire insulation breaking down.
I'm sure they do a lot of testing on the new systems. I have never been involved in the manufactering of aircraft, so I don't see this part.
My work gets my brain so screwed up, it takes me a while to digest the stuff in this thread.Quote:
Originally Posted by LowOhms
Yes- I see the separated black and white wires in the picture. Looks like could be the 2 x 12AWG-per-polarity (9AWG!) Mil-spec setup you described earlier in this thread.
I see what looks like a 604, rear mounted in center of baffle of "transmission line speaker". Gonna study this design- and MLTL as possible new future 604 enclosures.
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Megger Ohm meter. I've heard of them- but never saw or used one. Understand the concept well- a weak circuit may show no resistance without a load. We have electronic liquid sensing monitors on our petrol tanker equipment that are supplied thru a circuit that runs from battery then goes down a rabbit hole in the massive wire bundles in the truck cab area for its switching and CBs. Then heads back along the frame to the truck tank monitor- and splits to the 7-way plug and back to the trailer monitor. Many opportunities for weak link. The monitors use about 0.2 amperes. If a monitor fails while loading a load of gas at the refinery, the loading process terminates, and because of sequential blending, the partially loaded product cannot be sold. In fact, my company has to pay to have it disposed. I use a spotlamp bulb (3 amps) as load at the monitor end of the power supply circuit to make the circuit fail and get the intermittent weak link to come out of hiding.:)
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I think this open baffle setup is breaking in. Currently using Mac Mini computer streaming college FM radio stations thru iTunes (iTunes is my nemesis- but sound quality forces me to try to figure its interface out). Then USB out to tube DAC- then RCA cables direct into 300B monoblocs (no preamp- volume control in streaming program). Seems to have real good synergy.
I want to gather info, specs, and some pics of this OB build and make a small document for the forum. Am trying to learn how to use Layout program from Sketchup. Any recommendations for simple draw program? I think with some application, Sketchup layout is gonna work for me I hope.
I'm building my own crossovers for 604-8G based on the Markwart design. My current plan is to split off the speaker input to hf and lf using 20 awg silver plated solid for the hf and 12 awg stranded silver plated cu for the lf. These gauges will be used for the entire run, hf and lf, through the crossovers to the speakers. Please beat me up or approve.....
regards -- Roger
Sounds like a solid plan to me.Quote:
Originally Posted by rogerh113
I used 12 awg wire, Jantzen coils, Genteq oil caps, and Dayton resistors in my Markwart 604G xover build. I ended up using fixed resistors instead of an Lpad.
J Markwart did a great job designing those crossovers! I'm sure you will like them. Post some pics after you build yours
Thanks. I also plan on a fixed resistor once the crossovers settle in. For me it is all new - will have to tune the bass port and work through the entire process. I have time, so it is a lot of fun. I've de-constructed the Altec Magnificents and resized all of the parts so they are suitable for the 604s (9+ cu ft). Starting to fabricate the baffles and cut the dados in the cabinet walls to accommodate the baffle and horizontal structural support (ala Billfort cabs) . Will post xover pics once I have done them. They should be pretty straightforward, so I am tackling the cabs first....
regards -- Roger
Hi Roger !!Quote:
Originally Posted by rogerh113
Good idea using different gauges for the tweeter and woofer. You have READ what I do, in this thread, hope it helps you some.
I have a problem with fixed resistors.
EVERYONE "knows" and will prefer them over a potentiometer or a rheostat, but there is a problem in getting the EXACT Ohmic value I want, to pad the high frequency driver, so its playing at its absolute best level in a room.
I am not sure what the best answer will be, to resolve these conflicting needs ( the sonics of " no Pot " - a nice soldered-in resistor, vs: the VERY FINE adjustment capability of a really good wirewound pot. )
On a superbly well set up ALTEC system, I am sure we all can deduce and easily hear one tenth of an Ohm of tweeter padding, and, I further feel we can adjust things to MAYBE as low as 2 /100ths of an Ohm, .... JUST SUBJECTIVELY GUESSING.
Of course, there is NO way of nailing 2 or 3 /100ths of an Ohm, with fixed resistors, UNLESS you revert to paralleling UN-LIKE and high-value Rs, which is not an optimum technique.
Part of the degradation of a Pot is the small contact area between the resistive coil, and the wiper contacting that coil, diode effects, etc.. There are other negatives, associated with a Pot, differing materials, etc.
My present personal solution, perhaps its temporary, in 2017, is to parallel TWO Ohmite " J " series 50 Watt wirewound Pots, say, 30 Ohms each pot, so I have an effective 15 ohm / 100 Watt rated pot, with double the contact area, wiper to resistive coil. I use 16 AWG M22759/11 to do the paralleling, and Wonder Solder.
Ohmite MADE hardware, to parallel two 25 Watt ( H ) or 50 Watt ( J ) pots, although its fairly costly. One COULD make a DIY coupler by visting your local ACE Hardware store, and applying their imagination. I have, with " H" pots.
I spent a couple decades of my life adjusting Fulton Premiere speakers which have a five-way tweeter, and an " H " Ohmite for EACH driver's level control. I sometimes used a cotton cue tip, to " touch-gently " the screwdriver slotted control shaft", to get the final adjustment. Boy, that would freak-out some of my audiophile friends. One can hear - or perhaps sense - this stuff if they concentrate and have a decent set up-overall. I believe its a natural and G-d given capability, we all have.
Anyhow, I am pleased with the 2017 Paralleled " J " pots, in my A7-800 DIY crossover.
Wanted to share that idea with others. Feel free to try it, and listen to that, tell me what YOU hear .
Ohh, one other thing I like, I mass load my DIY crossovers. A plywood crossover base is suspended on three Golf balls - beneath the base, held in position by three small rolls of multi-colored Electrical Tape from WalMart. On TOP of the base, I have screwed in place a triplet of wooden dowels, maybe five incheshigh and one inch in diameter. I then put 48 pounds of Patio Stepping Stones ( 3 ) on top of each crossover...... sounds better that way, at least to me, at home.
Everything is important . Have fun.
Thanks,
Low Ohms....Jeff .
What's wrong with paralleling resistors to nail a specific value? It's done all the time. I need and want a real explanation to this. You can't keep making outlandish claims without backing them up.
BillWojo
Hi Bill,Quote:
Originally Posted by BillWojo
I'll explain it as best as I can. In the highest of high-end audio, the best builders will tell you, unequal valued paralleled resistors produce SKEWS to the signal, and the music.
I THINK the MFA Luminescense was built with paralleled plate resistors, equally matched value resistors. In its time, it was considered the best possible PHONO preamp on the market!! I have also seen EE Thorsten Loesch post schematics making extensive use of paralleled, equal resistors. Best to just use two Rs, less chance of skewing than with 3 or 4 !!
It is FINE to parallel resistors, IF the resistor values are the same value, but NEVER different values in parallel Bill.
When paralleling two Rs of the same value that MEASURE within 1 % of each other, you earn a "C+" . If you can parallel two that measure within one tenth of one percent of each other, you have earned an " A ".
In my SET implementations, I will parallel TWO resistors, matched, whenever possible.
In Greg's new Type 46 SET amp for his Valencias, I ordered ten Roderstein MK-8 ( 2 Watt ) resistors, which I believe are 1% parts, from Percy, 549 K Ohm as I recall. I was able to harvest two pairs, closely matched ( Fluke 8060A ) out of the ten pieces. But I GOT two - HIGH QUALITY - and great-sounding 274.5K Ohm plate resistors.... for Greg to ENJOY.
Two resistors, when paralleled properly, on a tube's plate and cathode, IS literally " State of the Art " in tube SET implementation.
The better, most experienced SET builders will know and always do this. But the Rs must be closely matched to avoid skews. Greg's amp is sounding NICE to my ears. Am having Johnnie Cash's 21 year plus touring sound man, come by tomorrow, for him to give a listen to my VOTTS. He'll critique me..... honestly. Larry..... aka..... L.J.
This implementation, as I am describing it to you, done for Greg, gives TWO equal paths for the signal to develop in the plate resistor, and since both Rs are CLOSELY MATCHED, there is NO adverse signal SKEWING when paralleling.
Its only dropping 170 VDC across the plate resistor, at 0.0007 A. for ONE section of a 12AX7. So Bill, its only dissipating 0.119 Watts, and it has a four Watt ( 2 Xs 2W. ) rating. That offers circuit stability and beneficially, has PLENTY of resistor lead wire in the path, to maintain SUPERB transfer function.
I routinely do the same procedure, on the cathode of the Driver tube. for maximum sound quality. Everything matters.
There... 'ya got it Bill.
Best wishes,
Jeff Medwin.....Low Ohms.
Jeff. What nonsense. You are making this forum a laughing-stock.