PL 700 II Clair Bros Rising from the Ashes

[WOPL Sniffer]

HUH?

 

[Peter S]

Couldn't that screw short B+ or B- to the chassis?
We have to be pretty dedicated PL fans to forgive a "bone-head" mistake like that---and have it make it all the way into production! I see that the Clair Bros mods were three steps forward and maybe two back! I better not criticize too much, my biggest bone-head moves are probably still ahead of me.

 

[Gepetto]

Couldn't that screw short B+ or B- to the chassis?
We have to be pretty dedicated PL fans to forgive a "bone-head" mistake like that---and have it make it all the way into production! I see that the Clair Bros mods were three steps forward and maybe two back! I better not criticize too much, my biggest bone-head moves are probably still ahead of me.

Yes it is a B- short to ground waiting to happen.

 

[Peter S]

I have been "populating" my back planes and see that C1 and C2 are optional. The 'BOM' says "DO NOT POPULATE these components Optional not necessary"
Is there any reason not to install these caps? Isn't more filtering always better?
Also, regarding B+ and B- fuse size, what is the final word about size. I believe an original manual mentioned that 5 amp fuses are for home use, but 8 amp could be used for heavy service. I have had a couple of Flame Linear events and the DC fuses either held or did not blow quick enough to save the speaker.
Not to 'cheap-out' after all this, but I have an endless supply of 10 amp fuses, is this a foolish idea? (10 amps through 8 ohms is 800 Watts)

 

[Gepetto]

I have been "populating" my back planes and see that C1 and C2 are optional. The 'BOM' says "DO NOT POPULATE these components Optional not necessary"
Is there any reason not to install these caps? Isn't more filtering always better?
Also, regarding B+ and B- fuse size, what is the final word about size. I believe an original manual mentioned that 5 amp fuses are for home use, but 8 amp could be used for heavy service. I have had a couple of Flame Linear events and the DC fuses either held or did not blow quick enough to save the speaker.
Not to 'cheap-out' after all this, but I have an endless supply of 10 amp fuses, is this a foolish idea? (10 amps through 8 ohms is 800 Watts)

Hi Peter
DO NOT POPULATE means just what it says. Those 2 locations are vanishing in a future artwork.

I run 5A AGX

 

[Peter S]

Hi Folks;
Progress is slow, but there's no deadline! I have see a (possibly tantalum or some type of non-polarized) cap straddling the bridge. My Clair Bros amps don't have this and I see no mention of it in the WO literature. What are the merits of this seemingly optional feature. If it is a worthwhile addition, could anyone suggest a (range) of values for this cap, if it should be added.

 

[WOPL Sniffer]

I use .01uf 400 volt caps (across all 4 tabs of a new 50amp Bridge Rectifier which are less than 5 bucks).

 

[WOPL Sniffer]

I also get rid of the AGX fuse holders since you'll never find AGX fuses in my town. I switch to AGC's, 10 amp main, 5 amps for the other 4

AGC fuses are common.

 

[WOPL Sniffer]

Here is how some of us set up the BR for the snubbers. These are .01uf 630v

 

[Gepetto]

Hi Folks;
Progress is slow, but there's no deadline! I have see a (possibly tantalum or some type of non-polarized) cap straddling the bridge. My Clair Bros amps don't have this and I see no mention of it in the WO literature. What are the merits of this seemingly optional feature. If it is a worthwhile addition, could anyone suggest a (range) of values for this cap, if it should be added.

That is a film cap and is targeted at the same function that Perry has shown in his illustration. My 700B had the same treatment that your picture shows. One cap bridging the AC input terminals of the bridge.

 

[Peter S]

Hi Perry;
Bad coincidence regarding the fuse holders. I took the opportunity tighten the speaker terminals and......fuse holders. Well, the project lost some of it's thrill and the night went a little longer after I broke one of the fuse holders. I transplanted one from my scrap heap, after having rotating the side tab to join to it's neighbor. I guess I'm looking for a set of new fuse holders.

 

[Peter S]

Thanks for the snubber info.

 

[WOPL Sniffer]

Hi Perry;
Bad coincidence regarding the fuse holders. I took the opportunity tighten the speaker terminals and......fuse holders. Well, the project lost some of it's thrill and the night went a little longer after I broke one of the fuse holders. I transplanted one from my scrap heap, after having rotating the side tab to join to it's neighbor. I guess I'm looking for a set of new fuse holders.

I bought NOS fuse holders off of the Bay for cheap. I bought a couple boxes of 100 since I use 5 new ones per amp.

https://www.ebay.com/itm/10-NEW-BUS...413276?hash=item469a4c775c:g:6H8AAOSwZvldO4Q7

 

[MarkWComer]

What are the merits of this seemingly optional feature. If it is a worthwhile addition, could anyone suggest a (range) of values for this cap, if it should be added.

Those caps cut switching noise from the rectifier.

 

[WOPL Sniffer]

Noise and heat=the enemy

 

[oldphaser]

Here are some scans taken from the 6/81 revision of the Phase Linear 400 and 2/81 revision of the 700/700B service manuals:
"connect four .01/1000V ceramic or mylar capacitors across each terminal of the bridge rectifier..."

The purpose of these capacitors was to eliminate Radio Frequency Interference (RFI) "radiated by the bridge rectifier in the power supply".

To my knowledge, this information did not appear in any 400 or 700 series amplifier service bulletins or series II service manuals.

 

[Peter S]

Hi Folks; It's been a little while! I've taken Perry's advice and replaced all AGX fuse holders with new AGC holders. Yes, I could only find AGC 5 Amp fuses locally. I'm glad I did---found a second broken holder. I'm still far from bringing up even the back-planes but Joe mentions "bring up on DBT and Variac" several times...What is a DBT?
That was my daily dumb question.

 

[Peter S]

Here is the bridge with 'snubber' caps. I had .33 uf 630V metallized polypropylene caps handy, are they too big? (I may be exceeding my daily allowance of dumb questions)
The bridge was manufactured by 'Solid State', not the 'Sensitron' device mention in the service bulletin, thanks Ed.

 

[Peter S]

Driving the PL700 with a balanced signal source. Attached is a proposal for 1/4" TRS input jacks and input cable.

 

[Gepetto]

Driving the PL700 with a balanced signal source. Attached is a proposal for 1/4" TRS input jacks and input cable.

Do you have a 2 contact or 3 contact 1/4" plug?