If the stock ZMA draws 150 watts of power from the wall allowing for a lagging power factor of 0.85 the current draw is about 1.5 amps from the wall.

The recommended fuse size for most electrical equipment can vary between 1.25 to 1.5 times the actual current draw of the equipment, some times higher depending of the type of load to prevent nuisance blows. Try putting in a fuse that is even a generous double the said above current which is based on 150W say a 3 amp fuse in this case and see if it blows. In my experience when mine was still stock specs., 6.3 amp fuses were blowing and so I had to go higher at that time. I believe in most other cases a 6.3 amp fuse is fine.

To measure the current draw I used a clamp current meter on a discarded power cable with live, neutral and ground cables separated from each other.

After 30 minutes of operation it probably draws about 7 or 8 amps. I have not checked it at this stage and do not intend to experiment further as it is not important from me what ever it is since I am using a solid wire in place of a fuse and it will be time wasted fabricating a wire again.

Sure additional heat is dissipated from KT150 compared to the KTs rated below it. But as you can see from the attached picture taken a few minutes ago after a couple of months with KT150s usage, the meters and the surroundings are as good as new, no heat related issues.

I too am conscious of its electricity consumption. No sooner I am done listening I turn it off.

Besides I have built it to a level with money and effort such that it is irreplaceable for me no matter what the price of another amp. The outcome is so good that I want it to last 25 years or more.

Heat multiplied by the duration of heat application is the worst and only enemy of capacitor and transformer life span. That is why as a small mitigating measure I made vent holes on the bottom board of the casing to somewhat at least induce natural ventilation from the bottom holes to the large cap circumferential gap. Small outcome but better than fully sealed I think.

Thanks for sharing all of this! This is very cool!
I would also be interested in a Decware amp that comes with KT150's and would offer 60-80W, in case you are listening (or reading this) Steve  ;)

I am so impressed with what excess power reserve provided by the amp can do for the same set of speakers that I have decide now to increase it further.

Having this power reserve to more easily drive the speaker drivers is analogous to driving a car weighing say 2 tons (about normal weight of a midsized car) with say a 500hp engine versus another similarly weighing 2 ton car driven by a 250hp engine. The latter will be sluggish, less responsive compared to the former. You do not need 500hp to propel the car all the time but if a change of speed (dynamism) is what the moment dictates the higher power car will respond better in that moment. Similarly for music as it is constantly varying. Conversely one could reduce the weight of the car to increase the power to weight ratio if engine power increase is not feasible.  

Since my ZMA has reached its limits in terms of power increase capability I decided to replace 4 of the drivers in my 5 way PSB T3 speakers with Lii audio's premium 7" full range high efficiency drivers. This will also enable me to remove four of the power guzzling, signal corrupting and more importantly signal coloring crossovers in addition to the 89db drivers. Multiple gains. Just 2 of these full range drivers will cover the work of 4 power hungry drivers and crossovers giving me in theory (at this point) more audio output and speed. I'll just leave the lone PSB driver (woofer) and it's crossover that covers the range from 24Hz to 60Hz as the Lii audio full range drivers specs show the need for help is needed in that area.

As always I try to do things that can be easily reversed if it does not work out. It's the same in this case.

I am excited about this. This is not my original idea. I must again give Steve credit for it. He has far more audio related experience and importantly shares it. Through his writings he unknowingly instilled this idea in my mind.

I second Stefan's request to Steve for a KT150 amp preferably in a single chassis to keep build cost down and the cost for the end user as well. Should cost about 20% more than a ZMA (because Steve will have more bargaining power with suppliers than me) and at that price it would be a steal for what you get from an audio uplift stand point compared to a ZMA.

Hi folks, have not been here for a while as other stuff in life is keeping me busy.

For those wondering, the modified ZMA is still regaling us driven by KT150's on full range speakers and solid high purity copper wires in place of the fuse.

I have not worked on it since my last post here as I have reached a point of substantially diminishing returns for this design of the amp and more importantly am very satisfied with the outcome. Besides all the lessons learned here is another one. If I were to do it again I would probably build one from scratch based on the ZMAs simple straight forward no nonsense design instead of modifying the stock one. As it turned out I needed a slightly larger enclosure and another enclosure dedicated to power supply filtering that plugs in to the main enclosure

Cheers,
BAndrade

New "fuse" installed.  Immediately awesome.  Fullness and clarity is my first description.  The link will expire eventually so if the photo doesn't work, the new fuse is 6n pure copper.
https://share.icloud.com/photos/0adOlhLWHkPvnbunTlmCq4V7w

after an hour listening to it, I can say that the fuse isn't going back in for listening.  I will want to put it in while swapping tubes--especailly to NOS tubes or used tubes that could be suspect.  

I'm toying with the idea of putting a toggle switch to bypass the fuse so I can switch back and forth quickly.

Thanks BAndrade.  I'll get them on order. --Jerry