PL700B's...White Oak or Pine Box

[Peter S]

Hi Folks; Just wanted to say Hi to everyone that helped me restore my pair of Clair Bros 700 II's. I found these 3 (almost 3) 700B's and could not resist! As you can see, one is missing VU meters and I'm concerned that this may be a death sentence, for "parting out" only. Would VU meters be available that don't require a second mortgage?
Thanks again, all. I will post more of the nightmares inside, asap. Stay well, Peter in Canada.

 

[mlucitt]

I am working on finding some meter solutions for PL700B's. Stay tuned but don't hold your breath.

 

[Peter S]

No rush! I was even thinking about something LED, series II'ish...or maybe that's that sacrilege.

 

[mlucitt]

The other option is to part it out, now that is sacrilege.

 

[Gepetto]

The other option is to part it out, now that is sacrilege.

I don't know Mark, this makes me guilty of committing sacrilege with you involved...

 

[WOPL Sniffer]

How much you want for the meter-less 700B? I have been saving a couple sets for this occasion. Having a blind 700B sux.

 

[Peter S]

Hi Perry; I sent you a PM

 

[mlucitt]

I don't know Mark, this makes me guilty of committing sacrilege with you involved...

The previously deceased amplifier will live again!

 

[Peter S]

Hi Folks;
Still only just looking at my latest acquisitions. It turns out, one of the three 700B's is working! Outputs are all PL909's and mixed batch numbers so I assume it has had a troubled past. I was talking to Glen a little while back and he is bridging some PL's. I have always been dead set against bridging for various reasons, real or imagined. Walking past my home for wayward Phases (pictured), an idea came to me; why not bridge two PL700B's and use them to drive my 18" power hungry LF's?
A Crest CA-18 is currently serving this purpose. The Crest delivers 1000 Wpc into 8 ohms, but there have been occasions when I have actually seen the clip lights come on. If the math is correct, a wopl'd PL at 450 Watts, produces 60 Volts. So Bridged; 120 Volts into 8 ohms is....Voltage squared divided by R---1800 Watts ! Could this be??!! My next sofa will need seat belts.

 

[grapplesaw]

Peter why go to all that when you can buy these carvers pretty cheap. A new old stock one sold on eBay last month for $500

sell you 700b’s

Carver PT-2400
Professional Stereo Power Amplifier (1991)

Specifications
Power output: 750 watts per channel into 8Ω (stereo), 2400 watts into 8Ω (mono)
Frequency response: 20Hz to 20kHz
Total harmonic distortion: 0.5%
Damping factor: 200
Gain: 34 dB
Input sensitivity: 1.5V
Signal to noise ratio: 100dB
Speaker load impedance: 2Ω (minimum)
Dimensions: 133 x 483 x 324mm
Weight: 21.8kg

 

[Peter S]

Yikes! I went to extremes to get the torroid buzz and fan noise reduced in the Crest. It is a two tier class H. That Carver has 3 tier power supply. Looks like a service nightmare!
Crest specs;

• Model: CA 18
• 8 Ohms Stereo Power: 1000W 1kHz, 0.03% THD+N; 950W 20Hz-20kHz, 0.1% THD+N
• 4 Ohms Stereo Power: 1800W 1kHz, 0.03% THD+N; 1700W 20Hz-20kHz, 0.1% THD+N
• 2 Ohms Stereo Power: 2500W 1kHz, 0.03% THD+N; 2400W 20Hz-20kHz, 0.1% THD+N
• 8 Ohms Bridged Mono Power: 3600W 1kHz, 0.03% THD+N; 3400 W 20Hz-20kHz, 0.1% THD+N
• 84Ohms Bridged Mono Power: 5000W 1kHz, 0.03% THD+N; 4800W W 20Hz-20kHz, 0.1% THD+N
• Max RMS Output Voltage (each channel): 99V
• Peak Output Voltage (each channel): 140V
• Frequency Response (+0 / -0.3dB, 1W/8 Ohms): 20Hz-20kHz, -3dB@150kHz
• Power Bandwidth (rated power at 4 Ohms, 1% THD+N): 20Hz-20kHz, -.2dB/+.2dB

Besides a little more power, the Crest has damping factor 800 and S/N ratio -115 db.

 

[Peter S]

And a rack with four PL's might be nice to look at! These two Clair Bros Series II's have been completely "WOPL'ed" and have no audible turn-on thump. I was thinking of replacing the Yamaha P2200 with a Clair Bros, to drive the Planar tweeters. The Crest could be replaced by two 700B's.
My concerns with bridging would be that at there are two banks of output transistors in series with the output rather than one. Would this not mean twice the distortion, etc?

 

[mlucitt]

Model: CA 18

Someone should measure the output of that amplifier. I can find no reference that the power output is in Watts RMS. For example, from the brochure:
"Power figures are watts per channel, both channels driven."

Not that I doubt the marketing of power amplifier manufacturers, OK, I do, but you should know what's real. It is very likely that they are using "Peak music power" or "Peak continuous power" or some other designation dreamed up in the accounting department and not issued by the engineers.
Just sayin'.

 

[Peter S]

I have actually tested the Crest. I have a dummy load made from 30 kW electric furnace elements, reconfigured for 8 ohms. I got 92 Volts (RMS measured on a Fluke meter) before visible clipping. Seems pretty darn close to 1000 Watts. I used the same setup to test the WOPLed Clair Bros 700 II's and got 450 ish Watts . Admittedly, I'm only driving one channel, so I imagine there could be power supply limitations with both amps..

 

[grapplesaw]

Someone should measure the output of that amplifier. I can find no reference that the power output is in Watts RMS. For example, from the brochure:
"Power figures are watts per channel, both channels driven."

Not that I doubt the marketing of power amplifier manufacturers, OK, I do, but you should know what's real. It is very likely that they are using "Peak music power" or "Peak continuous power" or some other designation dreamed up in the accounting department and not issued by the engineers.
Just sayin'.

Here is the service manual spec

I had a pt1800 that worked quite well

From what I see Peter is looking for low frequency driver amp. This would work . I suggested he bridge his two 700b amps to mono. It’s going to cost to do up these.
this is just an idea for his low budget

 

[grapplesaw]

My Bad
Peter has now told me he wants the PL option

 

[Peter S]

Yes, anything PL seems to be a hole in the rack that you pour money into!

 

[laatsch55]

Glen , have you successfully bridged a 700 and tested it?

 

[MarkWComer]

Yes, anything PL seems to be a hole in the rack that you pour money into!

This ENTIRE hobby is a black hole that seems to suck every buck I get!
I won’t mention the antique phonos, but that’s another hole!

 

[grapplesaw]

Glen , have you successfully bridged a 700 and tested it?

Yes I have Lee. I have not tested both channels driven to max due to not havin finished my oil cooled load resistor setup. I also did a couple of 400 ‘S as well. Need lots of fans for long play. I use two 400’s for some base bins. They punch when asked to.