- (seemingly) OT: KLH 4" full-range driver - 2 Updates
- Ampex F4460 reel to reel. - 3 Updates
- Speaker relay protection - 1 Update
| "William Sommerwerck" <grizzledgeezer@comcast.net>: Dec 20 04:13AM -0800 When I was a lad, I read "Popular Electronics" and "Electronics World". I distinctly remember an article about "full-range" driver KLH used in many products (8, 11, 14, 15, 19, 21). I need to find the article. So far, all I've found is a picture of the driver in an article about integrated amplifier/speaker systems. * The American Radio History site has a complete set of "Electronics World", but the only article that pops up when I search for KLH is the one just mentioned. I've started going through I'm pretty certain the article was not in R-E, as R-E rarely published articles of that sort. As there are lots of old farts in this group -- does anyone remember that article? Thanks in advance. PS: The January, 1963 issue has an article I well-remember -- building a vacuum-tube stereo FM signal generator! * Which is appropriate, but not exactly what I was looking for. |
| "William Sommerwerck" <grizzledgeezer@comcast.net>: Dec 20 05:06AM -0800 Error! Error! Error! My fault. The article about integrated amp/speaker systems //was// the article I was looking for. I had conflated it with photographs in KLH user manuals. Looking at old magazines sure brings back memories -- and provokes a lot of laughs -- and I'm not talking about John Frye's short stories. |
| Jon Elson <elson@pico-systems.com>: Dec 19 01:29PM -0600 > So I next got out the Strobeotac and put it on the motor capstan. The > motor is rated for 1850 RPM at 115V, and it's running rock solid at 1795. 1850?? How can the motor do 1850 on 60 Hz power? Many tape decks used hysteresis-synchronous motors, so they were designed to spin up as induction motors and then lock to the mains as synchronous. A 4-pole motor would run at exactly 1800.0 RPM. 1795 with a strobotac is probably 1800, and your strobotac is just a hair off calibration. You might just use a nean lamp in series with a resistor and diode to make an exact 60 Hz strobe, and see if a mark on the motor shaft stands still. Jon |
| Phil Allison <pallison49@gmail.com>: Dec 19 01:58PM -0800 Mike wrote: > > the needed matt one. > But why does it matter? The pinch roller does not need friction to the > tape. ** It absolutely does. The simple explanation is in the words you snipped. > It is the capstan that needs that. ** The capstan has no grip to the tape - since polished steel and smooth tape have no mutual friction. > I can see you might need some > resilience so that the tape is not nipped too tightly and thus reduce the > contact pressure, but that's not really a surface attribute. ** A shiny surfaced roller has no grip to the capstan. Why the heck do you think pinch rollers ( along with idler tyres and drive belts) are made from soft rubber in the first place ? You ever serviced a tape recorder in your life ? .... Phil |
| Mike <news@mjcoon.plus.com>: Dec 20 06:27AM -0600 On Fri, 19 Dec 2014 13:58:10 -0800, Phil Allison wrote: > Why the heck do you think pinch rollers ( along with idler tyres and > drive belts) are made from soft rubber in the first place ? > You ever serviced a tape recorder in your life ? No need to be rude! Actually I have only serviced special purpose players, for a decade or three until they were discarded in favour of CD drives. The media are all pre-recorded. I said why I thought the pinch roller needed to be resilient; just a matter of physics and pinch pressure. But now I see that you are relying on an unstated but reasonable assumption: that the pinch roller is wider than the tape so gets driven by the capstan on its margins and drives the tape between those margins. You could, of course, have explained that instead of ranting... Mike. |
| Phil Allison <pallison49@gmail.com>: Dec 19 06:25PM -0800 > >Relay shorted from amp to speaker. " > Incidentally I suggested a cure for that welded relay problem. Just throw a good crossover cap across the contacts. So what if the amp still produces sound when the protection kicks in, you are blocking the DC which is the object. > I think like a 22 uF/200 volt cap designed for speaker crossovers would do it. Two hundred volts is ALOT of power into a speaker so it should be fairly immune to shorting out, which would defeat the prupose. ** I have just been experimenting with a PCB mount, 240VAC/12amp relay made by "Schrack" and a variable PSU - consisting of a 300VA tranny, bridge rectifier and 10,000uf cap. The tranny was fed from a Variac. The relay, when energised, connected a 4ohm high power load to the PSU and tried to disconnect it when de-energised. With no cap across the contacts, serious flash arcing occurred at 30VDC. With 50VDC, you can normally expect the arc to become continuous, first shot. The maker's rating for DC switching is 24V at 10 amps max. However, with a 20uF film cap across the contacts, all signs of arcing at switch off disappeared. Amazingly, this was still the case when tried with 6, 3 & 1uF instead. When I tried 0.22uF, flash arcs appeared on about 1 out of 3 tries. To simulate a *bad* inductive speaker load, I added a 5mH air core choke in series with the 4 ohm load and saw slight flash arcing with a 1uF cap but none with 3uF. With a 8 ohm load and 100VDC, 6uF was enough to reduce arcing to minor flashes. So, a film cap across the relay contacts made a huge difference when breaking DC current at voltages well above the relay's ratings. FYI: the film cap delays the voltage rise across the relay's contacts for the first 10 to 50 *microseconds* after opening - which is when the arc forms. Delay that rise enough and there is no arc. .... Phil |
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