I called into a bric a brac shop where the guy has baskets of old style wall warts ,
I grabbed myself a unregulated transformer based 15V dc 800mA adapter ,
Unloaded volts were 18.8 ,
on load with the EQP I measured 15.8v ,
we know the pair of tube heaters want around 150ma each at 12.6V , so the transformer is at around 50% load ,
Its around a volt higher than what the SMPS puts out , but the regulated heater still measured 12.64 V and no problem with the extra heat , never the less attaching a small heatsink to the 317 regulator might be a good idea in the long run .
Just be aware the KT2A runs a hefty 12BH7 , so requires a lot more heater current than the EQP , Id suggest at least double the capacity of what Im using in the EQP .
So I had a closer look at the main PCB on the EQP and I have to say Im impressed .
theres not an SMD component in sight , which really is great news for the Diy'er
The components that are there look like good quality metal film resistors and foil caps ,
electrolytics are the typical Chinese made stuff , but they do at least bear 105c temp ratings .
I found a local source for the dual voltage shaver socket , 11.50 euros in white plastic
The metal clad pattress or back box costs around 5 euros ,
the blanking plate is around 10 euros
Then I added a couple of metal cable glands , with 20mm thread adapters to fit the knock outs in the enclosures ,
mains plug and cable I cut off an old electrical appliance at the recycling centre ,
I have bags of unused 330v/100uF caps from disposable flash cameras , although I think for safety a 450V component is better for first filter ,
A high voltage bridge rectifier and 450v cap can be found in any SMPS
Theres no need for a PCB , a couple of tag strips and hard wire will do ,
I was thinking of using lever terminal blocks to mount the dropper resistors , along with 110/230V secondary selection it makes for a very versatile passive tube pre HT supply .
The two back boxes, one for HT ,one for LT , two blanking plates ,transformers ,other hardware/components and cables this thing amounts to a very tough 2kg all metal lump ,
with excellent magnetic screening , both between the two internal transformers and external equipment .
I checked the spec of the Pultec EQP 1a , noise -89db
The EQP KT claims a noise of -101db ,
Cleaning up the out of band noise might not make a huge difference to the numbers ,as far as 20hz-20khz S/N goes , but it can reduce whats now a sea of modulating fuzz tones , to noise of an entirely random nature which doesnt intermodulate with the audio in anywhere near as destructive a way as cylical noise .
I also found neat touch proof stainless vents for the 20mm knock outs ,
That should allow adequate ventillation so the internal temp in the box doesnt rise and rise over the course of hours ,days, weeks , instead it just comes upto opperating range in under 30 minutes and stays where it is ,just warm to the touch .
The EQP-KT totally neglects air ventillation in the vicinity of the tubes ,
again ,in my opinion thats a mistake under any circumstances as it pushes the time it takes the units internal temperature to stabilise out to hours and hours ,
directing heat from the tubes away from electrolytics is also likely to extend the units life .
I grabbed myself a unregulated transformer based 15V dc 800mA adapter ,
Unloaded volts were 18.8 ,
on load with the EQP I measured 15.8v ,
we know the pair of tube heaters want around 150ma each at 12.6V , so the transformer is at around 50% load ,
Its around a volt higher than what the SMPS puts out , but the regulated heater still measured 12.64 V and no problem with the extra heat , never the less attaching a small heatsink to the 317 regulator might be a good idea in the long run .
Just be aware the KT2A runs a hefty 12BH7 , so requires a lot more heater current than the EQP , Id suggest at least double the capacity of what Im using in the EQP .
So I had a closer look at the main PCB on the EQP and I have to say Im impressed .
theres not an SMD component in sight , which really is great news for the Diy'er
The components that are there look like good quality metal film resistors and foil caps ,
electrolytics are the typical Chinese made stuff , but they do at least bear 105c temp ratings .
I found a local source for the dual voltage shaver socket , 11.50 euros in white plastic
The metal clad pattress or back box costs around 5 euros ,
the blanking plate is around 10 euros
Then I added a couple of metal cable glands , with 20mm thread adapters to fit the knock outs in the enclosures ,
mains plug and cable I cut off an old electrical appliance at the recycling centre ,
I have bags of unused 330v/100uF caps from disposable flash cameras , although I think for safety a 450V component is better for first filter ,
A high voltage bridge rectifier and 450v cap can be found in any SMPS
Theres no need for a PCB , a couple of tag strips and hard wire will do ,
I was thinking of using lever terminal blocks to mount the dropper resistors , along with 110/230V secondary selection it makes for a very versatile passive tube pre HT supply .
The two back boxes, one for HT ,one for LT , two blanking plates ,transformers ,other hardware/components and cables this thing amounts to a very tough 2kg all metal lump ,
with excellent magnetic screening , both between the two internal transformers and external equipment .
I checked the spec of the Pultec EQP 1a , noise -89db
The EQP KT claims a noise of -101db ,
Cleaning up the out of band noise might not make a huge difference to the numbers ,as far as 20hz-20khz S/N goes , but it can reduce whats now a sea of modulating fuzz tones , to noise of an entirely random nature which doesnt intermodulate with the audio in anywhere near as destructive a way as cylical noise .
I also found neat touch proof stainless vents for the 20mm knock outs ,
That should allow adequate ventillation so the internal temp in the box doesnt rise and rise over the course of hours ,days, weeks , instead it just comes upto opperating range in under 30 minutes and stays where it is ,just warm to the touch .
The EQP-KT totally neglects air ventillation in the vicinity of the tubes ,
again ,in my opinion thats a mistake under any circumstances as it pushes the time it takes the units internal temperature to stabilise out to hours and hours ,
directing heat from the tubes away from electrolytics is also likely to extend the units life .
