70v speakers and low output

I'm in the process of replacing all of our dressing rooms speakers. Most are original to the building and are just rotted. Also replacing the volume controls and taking the system from a non working 5 channel to a 1 channel system that actually works.

Years ago, we bought a Speco PL-260A amp/mixer. That was terminated to the channel one of the system and left there. None of the rooms ever sounded good... most speaker sounded crackly and over driven.

I'm now going through and replacing all the speakers with Atlas HD72W's. I am replacing the volume controls with Speco WAT10 volume controllers. I'm wiring all the speakers (17 total) to the 4W tap on all the speakers. Half the the speakers are running off the 1st zone on the Speco amp and the other half are running off the second zone. All wiring is 14 gauge.

Here is my issue... these things are not loud enough. The second I really gain up the input and show some meters moving on the amp the speakers sound like they are going to blow. The sound really over driving and like they are clipping. At this level they are barely above a standard conversation in volume. I can get them stable at a slightly lower volume. Even when connected directly to the amp the speakers sound like this. Is there a setting on the PL-260 that I am setting wrong? The amp is set to 70v mode. Should I take the amp into the shop because it could have an issue? Any help would be great... I have not spent too much time with these type of systems.

My initial thought is if everything else is correct, the input level is off.

CV systems are always a bit of a pain. I am sure I am covering things you already know, but here goes:
1) The total wattage taps of all speakers should equal the power rating of the amp: In this case 17*4 = 68 watts If the power amp is rated at more than 68 watts, the balance of the power rating is being lost due to the mismatch. Same goes in the other direction as well.
2) The output of the power amp should be matched to the 70 volt CV line either through it's own transformer of through a matching transformer at the power amp. If not, most of the output will be lost. (There are some amps that produce a direct-couple 70v CV output)
3) Make sure there are no hidden speakers on the system that may have had their transformers bypassed. Did a call to a school once and found that over the years, EVERY transformer had been bypassed! (0 ohm load on amp!)
4) Beware of any of those transformer-tap volume controls. They always seam to develop setting shorts! No idea why, but you move the controls around a bit and they start working.

in the case of the Speco PL-260A, it is rated at 260 watts , and therefore developed 70v at full output. (Internal CV transformer) In other words, 75% of it's output is going nowhere if you have 17 speakers wired at the 4 watt tap. (Still should be loud enough.) Pull the lines of the amp and meter them to make sure something isn't shorting one of them. Of course, this model also has a 25v CV output, but I assume you are tied to the 70v output. (25 would only drop the loading down to below 20 watts in the current configuration.)

Any suggestions on the cause of hiss in a 70volt system? In order to get enough volume output, I've got quite a lot of hiss, and I can't figure out what to do to eliminate it!

You are over driving the input stage of the amp. Inputs on amps like that don't tolerate much level. You will need to build an attenuator. What source are you driving it with, and which input is being used? I can calculate the resistor values for the pad once I have a bit more info.

Just an FYI on this, turned out I still have a bad speaker in the system that was causing a short and dropping the whole system down. At the same time I had to really drop down the input on the amp. With a 0db line level signal I put a direct box in line and that brought it down to a manageable level.

I'm glad you got it resolved. A DI box gets the job done, but it is kind of overkill when $1 worth of resistors and some soldering will work fine.