PL 700 II Clair Bros Rising from the Ashes

We've seen what the ground bus became later, i'd be surprised if the hum shield started as that...
 
Gepetto said:
Hi Ed
Aluminum will not do much of anything for leakage magnetic flux, it will handily contain electrostatic fields however. In order to have aluminum be effective it has to be a canceling loop around the transformer leakage flux in which case it will generate an eddy current to cancel out the impinging magnetic field. But as an open plate, that circuit is not completed. Steel or MuMetal will contain magnetic flux fields by shunting those stray fields through the ferromagnetic material and then back to the source to complete the magnetic flux line.

Aluminum has a relative permeability of slightly over 1 (nearly the same as air), steel up to ~4000 and MuMetal in the ~18K range, Permalloy even higher. The more permeable, the better magnetic shield it is.

Would be interesting to see if the original PL700 hum shield makes any measurable difference, it would show how much electrostatic field is present. I often wondered if that aluminum plate was intended to be a ground bus or shield in the original 700.

Hope this makes sense.

Joe
Click to expand...

Joe,

It all makes sense.

I am not sure how effective the aluminum "hum shield" was as a ground bus. There was also a small jumper wife between the ground terminals.

I will take some measurements once my wife gets off my back on selling the other mechanical/physical measurement and test equipment I brought to Connecticut.

Thanks!
Ed
 
oldphaser said:
Joe,

It all makes sense.

I am not sure how effective the aluminum "hum shield" was as a ground bus. There was also a small jumper wife between the ground terminals.

I will take some measurements once my wife gets off my back on selling the other mechanical/physical measurement and test equipment I brought to Connecticut.

Thanks!
Ed
Click to expand...

Sure Ed, sometimes higher priorities get in the way :-) I understand.
 
Ed,
My PL400 meter bezels say "KEN COX" on them next to "PHASE LINEAR" and "PART NO. 030-0235-0". Do you know who he was?

Mark
 
mlucitt said:
Ed,
My PL400 meter bezels say "KEN COX" on them next to "PHASE LINEAR" and "PART NO. 030-0235-0". Do you know who he was?

Mark
Click to expand...

Mark,

Ken Cox was the purchasing agent at Phase Linear. In the earlier days at Phase Linear Ken ran the stores.

With perhaps the exception of some early 400 series 1 amplifiers that used Midland meters (I will have to double-check on this), the bezels used on the Phase Linear 400 and 700B series 1 amplifiers are the same and all have Ken's name on them. Most likely they were made at a local foundry in the Seattle area.

The founders of Spectro Acoustics were Robin Gudgel (Phase Linear Production Line Manager), Ken Cox (Phase Linear Purchasing Agent) and Bryan Morrison (Phase Linear Design Engineer) in 1973/4. Their first product was the RobKen 2123 preamp. NOTE: The model number 2123 came from Rob and Ken's ages at the time. Ken was 21 and Robin was 23.

Ken and Robin got tired of waiting for Phase Linear to come out with their Phase Linear pre-amplifier, so they built a simple pre-amp themselves. Ken and Robin built 23 of them because lots of their friends wanted a pre-amp so they could really use the Phase 700 watt amp, just like Ken and Robin.

Fast forward to a few year later:
Steve Johnston (Bob Carver's partner at Phase Linear) started Heart Interface......

"Heart Interface was the first company to attempt to build a reliable inverter for off-grid and mobile/marine applications. Their own personal experience told them that there was a huge market just waiting for the right product. Steve had the mechanical engineering skills and Heart had the electrical engineering skills. Steve rounded up a few of the old Phase Linear employees to help build the Heart inverters in Kent WA. Ken Cox was out of the Hi-Fi business by then so he elected to join Steve. Clyde Yamamoto, an ex-Phase Linear electronics technician, was available as well as Greg Johnston, (Steve's brother). All of these guys had experience at electronics manufacturing. Things went very well at first, but as time went on, it was evident that the inverters were not living up to Steve's reliability standards. This issue led to a breakup of the Steve/Heart relationship. In 1984, Steve, along with Ken, Greg and Clyde left Heart and moved into a three story building at the Arlington airport. They asked another Phase employee, Mike Frost, to join a newly forming company. Mike was a very good technician and became the chief design engineer for this company, Trace Engineering. Their goal was to build an inverter that wouldn't break. Ken Cox (Robin's old partner from Spectro) had the most experience at running a company, so he took the title of president. Everyone except Mike actually lived at the company up on the third floor."

Forward to 1998: The main owners of Trace decided it was time to sell the company.

NOTE: I am not sure what Ken Cox is up to these days. Most likely retired.

Ed
 
Ed, your embellishments to the basic story always make the answers interesting and often historical. Thank you for taking the time to answer our silly questions.

Mark
 
Thank you Ed for posting, I'm always read your posts to learn.
 
Hi Jim and All;
Thanks so much for your time and effort in contacting your transformer rewinding expert. The costs involved are understandably high and this is compounded by 2 way shipping costs. I have 4 PL700's of various vintages. They all have some degree of 'leakage'. I have not had this hum/buzz issue with the other amps. I have some further investigating to do regarding errors I may have made in rebuilding this latest PL700 II.
Also, I have some investigating to do regarding a standard for leakage tests. As mentioned, Joe found 32 VAC on his PL400 ( IIRC, chassis to line neutral with nothing else connected to the amp). If this leakage is from capacitance, rather than a resistance leak that might be the result of insulation break-down, I am concerned that rewinding may not resolve the issue. As Lee mentioned, the 700 II has a 12 VAC winding for the meters rather than the previous generations ( 6 V ) winding. Could this additional cramming of more winding into the same space result in more capacitance?

This is a test suggested on another forum;
"One way to simplify this would be to short the main primary wires together, short the secondary wires together, and then apply mains across the two with a 1 k resistor in series and connect your meter across the 1k resistor. Use your variac to gradually turn up the voltage. You should then get a decent leakage reading."

IMHO, having the windings shorted wound eliminate any induction influences and reveal only leakage from inter-winding capacitance and insulation breakdown issues. This test would require opening the amp and jumper-wives on the windings.

I have just rechecked my perfectly quiet WOPL'ed PL700B without shorting the windings but using a 1k ohm shunt to measure leakage: 43 VAC chassis to neutral---no inputs connected, no shunt
40 milli Volts with 1k shunt.

Strangely, there is 77 Volts on the chassis when the amp is switched off, dropping to 76 mVAC with 1k shunt.....and this is the quiet amp! If anyone could be persuaded, I would be very curious to see what voltage is measured on your PL700 amp, from chassis to neutral, with no inputs connected, with and without a 1k ohm shunt.
Thanks, all Peter in Canada
 
Just to clairify;
If anyone has the time and access to their PL700, it would be of great interest to me ( and possibly others) to measure the amplifier; chassis to line neutral without opening the amplifier, simply disconnecting the inputs.
 
Peter S said:
Hi Jim and All;
Thanks so much for your time and effort in contacting your transformer rewinding expert. The costs involved are understandably high and this is compounded by 2 way shipping costs. I have 4 PL700's of various vintages. They all have some degree of 'leakage'. I have not had this hum/buzz issue with the other amps. I have some further investigating to do regarding errors I may have made in rebuilding this latest PL700 II.
Also, I have some investigating to do regarding a standard for leakage tests. As mentioned, Joe found 32 VAC on his PL400 ( IIRC, chassis to line neutral with nothing else connected to the amp). If this leakage is from capacitance, rather than a resistance leak that might be the result of insulation break-down, I am concerned that rewinding may not resolve the issue. As Lee mentioned, the 700 II has a 12 VAC winding for the meters rather than the previous generations ( 6 V ) winding. Could this additional cramming of more winding into the same space result in more capacitance?

This is a test suggested on another forum;
"One way to simplify this would be to short the main primary wires together, short the secondary wires together, and then apply mains across the two with a 1 k resistor in series and connect your meter across the 1k resistor. Use your variac to gradually turn up the voltage. You should then get a decent leakage reading."

IMHO, having the windings shorted wound eliminate any induction influences and reveal only leakage from inter-winding capacitance and insulation breakdown issues. This test would require opening the amp and jumper-wives on the windings.

I have just rechecked my perfectly quiet WOPL'ed PL700B without shorting the windings but using a 1k ohm shunt to measure leakage: 43 VAC chassis to neutral---no inputs connected, no shunt
40 milli Volts with 1k shunt.

Strangely, there is 77 Volts on the chassis when the amp is switched off, dropping to 76 mVAC with 1k shunt.....and this is the quiet amp! If anyone could be persuaded, I would be very curious to see what voltage is measured on your PL700 amp, from chassis to neutral, with no inputs connected, with and without a 1k ohm shunt.
Thanks, all Peter in Canada
Click to expand...

Hi Peter
Have you started to test the steel plate shield yet that I mentioned back a few posts ago? When you mentioned that you experienced the buzz when you put a 10K ohm resistor across the input and removed the cabling to the input points, that got me thinking that your 2 amps may have excessive leakage flux escaping the transformer windings. That alternating magnetic field will couple into any loop that exists anywhere in that magnetic field (in essence it becomes a transformer winding, coupled to the transformer) and produce a voltage/current in that loop.

It is very likely that if you had these transformers rewound using the same prescription as the original, you would end up in the same place. It is more likely that the dual primary windings are the possible cause than the 12VAC winding (that is a very small wire gauge winding). Those dual primary windings use large gauge wire and it is more difficult to build transformers this way than the simple 120V only winding in your 700B.

Try it and see if you notice any differences. Also the leakage flux generally speaking in any PL amp causes the left channel closest the transformer to have more residual noise than the right channel. Distance from the source matters with leakage flux, like most things that are radiated.
 
I'm not much help with this one.
When I test my 700B for voltage from line neutral to chassis I get 0.125VAC because my 700B chassis has a third wire ground.
Perry understands why this is so...
 
Hi Joe, thanks again. My old offset meters PL700 has a plate mounted on the capacitor terminals but this plate is aluminum. My issue is more of a buzz mixed with hum. I think I have quoted this before;

"Another source is a signal lead running parallel to a mains power lead. Although the conductors of mains leads are twisted, the twist is usually fairly basic, so balancing of the magnetic field is rather poor compared to the tight twist of Cat-5 communications cable for example. The magnetic coupling is poor, and the greatest problems are likely to be caused by capacitive coupling. Since this favours high frequency noise, the sound is completely different from an earth loop, and it's a good idea to try to familiarise yourself with the different sounds made by the various issues that may plague hi-fi setups. If signal cables and mains wiring must cross each other, ensure they cross at right angles, and if possible separate the two as far as practicable. Capacitive coupling can also be an issue with transformer windings, where mains noise is coupled through to the secondary by inter-winding capacitance, or from Y-Class caps from mains to chassis"

As my approach seems to trial and error, what are your thoughts on creating a new, much heavier ground buss between the caps and make all connections by way of lugs soldered to the wires and held together on a centre mounted 1/4-20 copper stud. This would allow temporary removal of the transformer, extending the secondary leads to eliminate/determine the stray flux issue.
I will double check asap, but I believe I had a buzz even with the inputs shorted on the control board.
 
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