I just picked up a pristine Phase Linear 400 and truly think I can hear a notable improvement over my Adcoms, at least the GFA-555s (haven't A/B'd it against the GFA-5500 yet). And damn, it's got HUGE VU meters on it! Yay for the vintage look! But no dedicated power switch?!?! What were they thinking?

Good catch.
Those units fall into the 'Love um or hate um' category.
I had 4 at one time and liked them.
I would not pass up another if I ran accross one.
They did have some problems in the past but if yours is still working you got lucky.
Do not leave it powered up unattended.

A powerfull sweet beast with a neat 70's looks. Luv the vu's. Enjoy.

http://www.phaselinearhistory.stereomanual...00seriesamp.htm

Congrats! Interesting that Carver would go in opposite directions with his heavy metal PL's and the lightweight Magnetic Field Amplifiers in his self-named stuff.

nice grab John. what speakers have you run with it? i wouldnt be surprised to find that its a sweet match with the DQ-20's.

Thanks guys!

I notice one bulb below the left VU meter is out, other than that it seems to look and play very sweetly. Barely even warm to the touch, takes quite a bit of twist on the volume to get the needles really swinging, brought my AR9LSs alive like the Adcom GFA-555 never did. Haven't tried it on the DQ's yet... waiting to run to ratshack after some better banana plugs this afternoon.

It also appears mine has upgraded cooling fins in the back? Look to be more like the series 2 with the VU meters of the original version.

As I said it takes quite a bit of volume on the preamp to make the meters move. Is that normal from your experience?

I can listen comfortably (with no background noise anyway) at around -20db on the preamp and needles barely move. Around 0 and they are bouncing maybe up to 30% of their full swing but damn that's loud! I can't imagine how loud it would be to get them really swinging.

The VU's sensitivity of a 200W power amp is different/slower than one with only 100W.

From rane.com:

"VU meter (volume unit) The term volume unit (originally called VI or volume indicator; now archaic usage) was adopted to refer to a special meter whose response closely related to the perceived loudness of the audio signal. It is a voltmeter with standardized dB calibration for measuring audio signal levels, and with attack and overshoot (needle ballistics) optimized for broadcast and sound recording. Jointly developed by Bell Labs, CBS and NBC, and put into use in May, 1939, VU meter characteristics are defined by ANSI specification "Volume Measurements of Electrical Speech and Program waves, " C16.5-1942 (which is know incorporated into IEC 60268-17). 0 VU is defined to be a level of +4 dBu for an applied sine wave. The VU meter has relatively slow response. It is driven from a full-wave averaging circuit defined to reach 99% full-scale deflection in 300 ms and overshoot not less than 1% and not more than 1.5%. Since a VU meter is optimized for perceived loudness it is not a good indicator of peak performance."


IMO, for a meter to be of practical use, 0dB would need to be calibrated to the maximum rated output power of the amp. Let's take the your amp as an example, 0dB would be around 200W into 8 ohms. On a conventional analog "VU" meter, the meter needle would hardly move when the amp is putting out 2,0W, and that's usually already a fair amount of sound pressure level on most speakers. If you crank up the sensitivity of the meters to show movement at low/mid volumes, then the meter would simply peg on the right hand stop when the amp is called upon to deliver more of its power.
Notice that the meter on the McIntosh MC1.2KW amp, has almost 60dB of range: They have an enormous dynamic range, much more so than the typical "VU" meters that could manage only about -20dB to +3dB.
http://www.mcintoshlabs.com/products/Power-Amplifiers.asp

I don't remember how much gain it took to push that amp.
I was using 4 of them running mono into 4 B*se 901's.
I believe I was using a SAE preamp at the time.

I have also pushed a set of AR 10 pi's with one.
They are one of my favorite amps.

On a tangent it was a pair of B*se 901s that this amp was demo'd on. The first pair of B*se speakers that I think I actually liked the sound of

Good read! Yeah, I'd like a Mac one day too...

Or Todd to get bored with his Yammy and sell it to me!

I was talking about Mac gear as an example, i'm certain the good Yamaha, Pioneer or Sony gear of that time have also very good VU meters aswell.
The thing about AC VU meters is that sometimes - depending of the models - they get in the way of the signal path and injecting distortion to it.

I went on a quest today to see if I couldn't find replacement lightbulbs. Finally ended up extending my search to directory assistance where I started with Hawthorne Stereo in Seattle, a place that is known to occasionally stock nice, vintage gear. They in turn referred me to NW Audio Repair in Seattle, the shop that does most of the work for them... who in turn gave me the name (and phone number) of a Mr. Dean Nissan, apparently one of the original technicians that worked on the design and construction of this particular branch of the Bob Carver family tree some 30 odd years ago!

Mr. Nissan was quite friendly and informative. While he works on Phase Linear (as well as other branches) as a spare time hobby these days he said he was quite backlogged at the moment. I'll be hoping to get my PL400 into him sometime in the next month just for an "annual checkup", replacement of those pesky bulbs and maybe a modest upgrade or two (power cord comes to mind).

He confirmed that the meters are calibrated to 50w/20v at zero and reassured me that if they only move a tiny bit during my usual listening sessions that that was a good thing as it wasn't being abused... nor was my hearing

On a tangent I just couldn't bring myself to drop the plastic on Monster brand banana clips at ratshack at just over $5 EACH so my DQ test with the PL400 will either have to wait or be done very gently. The Monster ones didn't look stout enough to contend with one twisted pair from Canare 4S11 wire anyway... Anyone recommend a really great (and affordable) banana clip? Maybe I should try spade connectors?

i almost always get my connectors from partsexpress or westlake, both offer wide selections and competitive prices. for budget brand banana's i look at neutrik first.