Question for Joe or builders with appropriate test equipment.

Gepetto

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Old 'Arn Enthusiast
#21
If need be, I'll agree to disagree.

I think we all agree the P/L power supply is a conventional unregulated power supply. If line voltage drops, the +/- DC drops and so does maximum output power. Therefore, I contend that if output power is being stated, line voltage is relevant.

Ed B. is noted for being a stickler for specs, sometimes to the dismay of others. I applaud him for acquiring and paying attention to standards. If line voltage is 117 VAC for 400/700B etc (which I do not dispute, I just couldn't find it stated in the manual) and 120 VAC for series II amps so be it.

Legit car stereos do have switching power supplies that step up the +/- DC voltage. Yes they have large heatsinks. A kilowatt of audio power at 12 volts DC requires something like 100 amps from the alternator/battery. There is this thing called efficiency. That's why headlights flash on bass transients when the amplifiers demand more than the alternator can supply. Some people go to the extreme of adding farads of stiffening capacitors or a trunk full of batteries to stabilize the DC voltage. The typical car stereo enthusiast seems more concerned about sound pressure level than fidelity. Otherwise the car wouldn't sound like a bad case of intestinal gas as it passes by.

In 1978 I got my first real job at a transformer shop. I hated it. BORING! 40 years later I still find my self educating people on line stabilizing transformers such as tap changers, mag amps (not the Carver audio amps) and ferroresonant transformers. If there is an interest in these I can supply supporting documents. Be careful for what you ask.
Damn Don, I haven't used a mag amp in 2 decades... :)
 

Skywavebe

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Work too much
#22
You can be picky all you want but a sagging supply voltage of a short time should not be noticed unless you are running your amp at near maximum power where it would be noticed. If you run a amp near it maximum then it is too small and you need a larger one. There are so many people that pay big attention to the tiny things while they neglect the big things that tells me they have mental problems. If you want more reserve in your amp then put in larger filter caps- it is ridiculous but space will be a problem. If you get a larger amp then that will be taken care of for you. Why is this country void of any common sense anymore?
 

mlucitt

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#23
Sam, I'm with you. How many people run their WOPL 700 at max volume, besides me and Lee? We have the speakers to do it - Lee picked Klipsch and I went with JBL Pro. First, you house wiring has to be up to snuff, including a 20 Amp dedicated breaker in the box and a 20 Amp receptacle with a good ground to Earth. Then, you need an upgraded power cord, because the original PL power cord was 18 or 16 gauge wire rated at 10 or 12 Amps. We use 600 Volt 12 gauge wire in our power cables rated for 20 Amps, and even then the power cables get warm at max volume...
This is all for nothing unless the amps are cooled with forced air (2 fans at a minimum of 100 CFM each). And we have no sagging supply voltage because we run the amps through a Variac to maintain 120V even at Mach 10 volume levels.
I swear this is all true.
 
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#25
Damn Don, I haven't used a mag amp in 2 decades... :)
For anyone that cares, magnetic amplifiers were used in a variety of applications through the 1950s. Carver's magamp did not fit the standard definition. Although they could be used for audio amplifiers the typical application was control for power generation, gun stabilizers, guidance systems etc. Known for reliability, they act like a variable inductor in series with the load. Since a small change of control current results in a large change in load current it fits the definition of an amplifier.

The application I am familiar with, that is still in use, is as a voltage regulating transformer for industrial applications such as power plants, refineries and chemical plants..
 
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#26
Sam, I'm with you. How many people run their WOPL 700 at max volume, besides me and Lee? We have the speakers to do it - Lee picked Klipsch and I went with JBL Pro. First, you house wiring has to be up to snuff, including a 20 Amp dedicated breaker in the box and a 20 Amp receptacle with a good ground to Earth. Then, you need an upgraded power cord, because the original PL power cord was 18 or 16 gauge wire rated at 10 or 12 Amps. We use 600 Volt 12 gauge wire in our power cables rated for 20 Amps, and even then the power cables get warm at max volume...
This is all for nothing unless the amps are cooled with forced air (2 fans at a minimum of 100 CFM each). And we have no sagging supply voltage because we run the amps through a Variac to maintain 120V even at Mach 10 volume levels.
I swear this is all true.
Yup, next upgrade on my two 400s is going to be power cords. I used largest flat two conducter extension cords I could find at the time in order to use the original Heyco grommets. I'm thinking they are 18 gauge at best, something I would normally use to rewire a table lamp with, but hey heyco, they matched the originals. Now they've got to go. I have some round 2 conducter 14 gauge cords coming, but have no idea about the diameter. Plan on using some of those cord grip cable glands as a strain relief, just have to get everything measured and scoped out to see if it'll work as there is very little room in that corner of the chassis.
 
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#30
That computer power supply type power socket is way too big for a 400, already scoped that out. Was thinking the 14 gauge cords I ordered were also going to be too big, but being 2 wire, not 3 wire, maybe, anyhow, I'll be able to measure them and have a better handle if maybe 16 gauge will work. My old 1960s Rockwell drill press and table saw could use new cords if the the 14 gauge are too big for the amps. Also have what I think is a 1959 Yuba SawSmith with a ratty power cord. Reminds of of a Ford Edsel Edsel every time I look at it. If a 1/2"grip nut isn't going to fit, I did see smaller, I'll have to look. Just not much room up in that chassis corner and I want to do it right. Thanks guys!
 
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#33
Looks like my old Rockwells are getting new cords and I need to place a order with Mouser.
For shop equipment like a table saw, planer etc, I think type SJ cable, which is widely available at Home Depot is the preferred choice. Also I would want a 3 conductor cable. I saw a person get a bad shock due to a ground fault in a table saw that used a 2 conductor cable. You definitely want the tool itself grounded so it trips a breaker if there is an insulation failure.
 
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#34
Good point, was just going to replace the old 2 wire cables with same, but modern cable with ground to match my outlets makes sense on the shop equipment. For the amps 2 wire only and no 3rd wire ground per the posts I've read. Thanks.
 

mlucitt

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#35
Good point, was just going to replace the old 2 wire cables with same, but modern cable with ground to match my outlets makes sense on the shop equipment. For the amps 2 wire only and no 3rd wire ground per the posts I've read. Thanks.
Here is a link to the WOPL power cords I use. I buy 5-6 at a time. they are brand name, very high quality cords. These don't get too warm when you crank up the volume to Mach 10.

https://tinyurl.com/y552fyvt
 
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#37
According to Joe, there should be only one three prong power cable ground in the system to the homes electrical system ground, this is at the outlet provided the home is wired correctly. This is how my PL2000 preamp is factory wired, a three wire cord with the ground wire connected to the chassis. Now, if I put a three wire cord on the amp and connect the ground wire to the amp chassis, the system will most likely suffer hum from ground loops. This is most likely why the preamps came with three wire ground cords, and the amps did not. https://forums.phxaudiotape.com/threads/this-grounding-thing.1568/page-2#post-86786 So, when I upgrade my amps to that great power socket and three wire cords, I will not connect the socket ground to the chassis.
 
Joined
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#38
Here is a link to the WOPL power cords I use. I buy 5-6 at a time. they are brand name, very high quality cords. These don't get too warm when you crank up the volume to Mach 10.

https://tinyurl.com/y552fyvt
Ordered 2 cords and 3 outlets from Mouser last night. Probably going to take some time off after Christmas and install them along with a pair of Joe's Cylon meters Thanks for the invaluable help!
 

mlucitt

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#39
According to Joe, there should be only one three prong power cable ground in the system to the homes electrical system ground, this is at the outlet provided the home is wired correctly. This is how my PL2000 preamp is factory wired, a three wire cord with the ground wire connected to the chassis. Now, if I put a three wire cord on the amp and connect the ground wire to the amp chassis, the system will most likely suffer hum from ground loops. This is most likely why the preamps came with three wire ground cords, and the amps did not. https://forums.phxaudiotape.com/threads/this-grounding-thing.1568/page-2#post-86786 So, when I upgrade my amps to that great power socket and three wire cords, I will not connect the socket ground to the chassis.
Could we see a picture of your three-prong cord PL2000? I have attached a Service Manual for the PL2000/2000 II and page 9 has a schematic of the power supply. I do not see a three wire power cord, but yours could have been a special order. Further, the 117VAC in the PL2000 immediately becomes the primary of a 24VAC center-tapped transformer; that means the rest of the unit is below fatal shock threshold and lightning continuity. I would much rather have the three-prong cord and safety ground connected to the amplifier, where there are fatal shock thresholds throughout the entire chassis.

Now, if you plug your amplifier power plug into the preamp accessory outlet, you will still not be grounding your amplifier because the accessory jacks are two-prong. However, the designer warned us not to exceed the wattage allocated for the accessory jacks and that is typically around 400 Watts maximum per outlet. Any WOPL 700 is going to consume greater than 400 Watts, so the power cord should go to a wall outlet or a dedicated power strip where it can be properly grounded/earthed.

The subject of safety grounding the chassis of a rebuilt PL400/700 (WOPL) has been a debate here for quite a while. Because I run a business and make a profit from my customers, I have contacted a lawyer regarding my liabilities. He stated that as long as I am following 'generally accepted practices' in my construction, I am fairly safe. That includes a three-wire safety cord and a safety ground on the chassis of all the amplifiers I rebuild. You are welcome to do as you wish, of course. I inform all my customers that the amplifier is safety grounded and if there is hum it is due to their house wiring, not the amplifier. I refer them to Section 250.4 of the National Electrical Code (NEC) and Standard 467 of the Underwriters Laboratory (UL).

With regards to signal hum, I do not ground or connect my signal coax input shields to chassis ground or each other. I allow the shields to enter into the WOA Dual Mono Control Board, and the separate shield/common connections flow to the separate WOA Backplane boards and then to the STAR ground that ultimately connects to single point ground on the chassis. For the two chassis ground points, I scrape the paint on the chassis, use sharp star washers, and crimp/solder the insulated terminal connector onto 16 gauge wire. I also add an AC-rated 275V X2 (self-healing in case of arc-over) .1uF safety capacitor (mouser P/N 667-ECQ-UAAF104M) across the line and neutral legs, and two 300V Y2 (never fail short) .01uF safety capacitors (Mouser P/N 72-VY2103M63Y5US63V0) between neutral and ground/line and ground of the power input connections to reduce AC-related noise. This is by design and none of the amps I have built display any 60Hz hum, most often as a result of cable problems or poor shielding; or any 120Hz buzz most often caused by ground loops.
 

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