Rebuilding extremely early 700, would love input and assistance.

George S.

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#23
Mark C., My 400 S2 WOPL drives 2 Dayton Audio subs that are 4 ohms ( dual 2 ohm voice coils wired in series). No issues with heat at all, but then I'm feeding them a 20-80 MHz "slice" of spectrum through a MiniDSP 2x4.
Maybe Joe can comment about stock amps and WOPLs driving a 4 ohm or lower load.
 

George S.

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#27
Wow, I had no idea. Don't speakers generally have varying resistance depending on the frequencies given them? Wonder how one could graph this? I'm starting to like Marks idea of adding resistance.
 

MarkWComer

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#29
Remember Lee, this early PL700 is deficient of the full output count. It is a PL400 with the transformer power supply voltage of a PL700

I would tread very carefully even at 8 ohms. PL went back and added output stages after they discovered what SOA meant. :)
And that is why I said to stay away from low impedance speakers!
 

MarkWComer

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#30
Wow, I had no idea. Don't speakers generally have varying resistance depending on the frequencies given them? Wonder how one could graph this? I'm starting to like Marks idea of adding resistance.
I think it has to do with the crossover points of the crossover networks of the speakers, but as I recall, impedance does vary.
 

Gepetto

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#31
I think it has to do with the crossover points of the crossover networks of the speakers, but as I recall, impedance does vary.
Basic voice coil equipped speaker impedance varies with frequency, true. By nature they are inductive but resonance plays a big role in the impedance response as well. Speakers have an electrical and mechanical time constant, like any DC motor does. The mechanical time constant is generally lower in frequency than the electrical time constant.

Crossovers certainly play a part. Many crossovers, including the one Lee uses in his K horns dump undesired frequency content into power dissipating load resistors. This definitely impacts impedance.

Electrostatics are a whole other kettle of fish since the ES drivers are fronted by electronics that also come into play on the apparent impedance.
 

laatsch55

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#32
Remember Lee, this early PL700 is deficient of the full output count. It is a PL400 with the transformer power supply voltage of a PL700

I would tread very carefully even at 8 ohms. PL went back and added output stages after they discovered what SOA meant. :)
Ohhh....only 4 per column eh?
 

Saabracer23

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#37
Wow! A lot of action I didn’t know about. Okay, no 4 ohm speakers. I had to step away from electronics for a bit, my wife just gave birth to twin girls and I had to spend quite a bit of time before hand prepping a nursery and just overall preparing. Of course after they were born I didn’t have time for much else. My wife has now gone back to work and I’ve become accustomed to being a stay at home dad and can get back into my groove. Anyways, it was perfect timing as I was waiting on arrival of the filter caps.

Alright, got the new filter caps in place along with the RCA 410s and 2N3439s that were sent by Iaatsch55. I am ready to bring it up on the isolation transformer/variac/DBT supply. Do I just follow procedures from the 700 manual since it has a 700 power supply? It appears there is no method of bias adjustment, it’s just set by transistors. Only trimmers being for input and output offset which I assume would be adjusted according to the waveform on the oscilloscope? I just want to make sure I bring this up correctly, so any pointers would be great. I’ll obviously go through the testing procedure, but are there any specific areas I should check?

Also, even with an 8 ohm load I’ll suggest a fan. We did discuss adding a protection circuit like the one from watts abundant, but he isn’t too keen on putting too much money into this amp since he can’t white oak it. So we discussed series fusing on the outputs to protect the speakers.


Thank you,
Dan
 
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wattsabundant

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#38
Use a 100 watt incandescent bulb. No load. It will not come up with a load while using bulb. variac not needed. Light bulb does the work. DC offset will be lots of volts until at least 50 VAC input probably higher.

Offset is adjusted after several minutes of operation with no signal and normal line voltage.
 

VSAT88

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#39
Klipsch Palladium P-38 around 6000.00 used. Dons board around 150 bucks new. I dont't get it. He does not want to spend around 150.00 to protect 6000.00. and you are going to put in used parts too ? Lordy, not trying to be an asshole but damn.
 

FredR

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#40
Wow! A lot of action I didn’t know about. Okay, no 4 ohm speakers. I had to step away from electronics for a bit, my wife just gave birth to twin girls and I had to spend quite a bit of time before hand prepping a nursery and just overall preparing. Of course after they were born I didn’t have time for much else. My wife has now gone back to work and I’ve become accustomed to being a stay at home dad and can get back into my groove. Anyways, it was perfect timing as I was waiting on arrival of the filter caps.

Alright, got the new filter caps in place along with the RCA 410s and 2N3439s that were sent by Iaatsch55. I am ready to bring it up on the isolation transformer/variac/DBT supply. Do I just follow procedures from the 700 manual since it has a 700 power supply? It appears there is no method of bias adjustment, it’s just set by transistors. Only trimmers being for input and output offset which I assume would be adjusted according to the waveform on the oscilloscope? I just want to make sure I bring this up correctly, so any pointers would be great. I’ll obviously go through the testing procedure, but are there any specific areas I should check?

Also, even with an 8 ohm load I’ll suggest a fan. We did discuss adding a protection circuit like the one from watts abundant, but he isn’t too keen on putting too much money into this amp since he can’t white oak it. So we discussed series fusing on the outputs to protect the speakers.


Thank you,
Dan
Congrats! Girls are the best. Sugar and spice and everything nice! My girls.
 

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