Another matchless hotbox question

[numpty]

Does the power consumption for the above require more than 6VA?

[bancika]

two 0.3A 6.3V heaters give ~3.8VA
four triodes at ~250V drawing about 1mA each give 0.25VA
so no, it won't need more than 6VA, that's for sure

[Rafa]

What about the transformers Im gonig to use two, Can I use a 220v/9v -1A- and then a 9V/220-100ma- as the biggest consumption is at the heaters. For the triodes is only 1ma each needed so?
Thanks
Rafa
PD: Bancika Im going to order the tubes probably in this week to banzaieffects.com, what tube sockets do you recommend me?

[Aharon]

RAfa,unless you are going with regulated DC for the heaters you need two 220V/6V or 220V/12.6V back to back , depending on how you want to run your heaters.
That's how I built mine ,albeit with two 110V/6.3V and then a voltage doubler,worked like a charm.
Aharon

[JimRayden]

PD: Bancika Im going to order the tubes probably in this week to banzaieffects.com, what tube sockets do you recommend me?

The cheap ceramic Fenders they have work splendid! Pretty good for the price.

----------
Jimbo

[Rafa]

Aharon thanks for the tip.
I also would like to know if both transformers should be 900ma for example. I thought of using a bigger one first where the 6,3V is taken for the heaters and where more current is needed (300ma each heater) and then a smaller one for the second, because tubes need little current 1ma each -12ax7.
Both transormers will be 220V/12v and will be wired back to back
Cheers
Rafa

[bancika]

yeah, you can use smaller second transformer. But if you plan to make separate enclosure and run 4 conductor cable to effect unit I don't recommend using AC heaters since it could induce ripple in DC. If you use 6V heaters than 12VAC will be too much to start because after rectification you'll get around 16VDC which is 10V higher so regulator will get very very hot. I don't think there's enough voltage to go with 12V regulator (then you need 150mA for heaters instead of 300), if you can get 220/15V transformers you could do that without a problem.
As for sockets I usually use ceramic chassis mount sockets.
Cheers

[Rafa]

So 220V/6V  transformers would be the best? So I could get 6,3V
What does it change if  I supply the heaters withr 6,3 or 12,6 V? Does the sound change?
Rafa

[swt]

sound won't change. maybe hum will. series have less current consumption. 150ma, against 300ma in parallel. my advice is: use a 9v back to back pair. rectify the heaters, and use a 7806 regulator, with heatsink.use the parallel method, pins 4,5 to +, 9 to -, this is important.  the second transformer can be 100ma. if this is your first tube project, be carefull with high voltages, and lead dress...as you can have oscillations, and also hiss/hum induce by messy dressing. good luck, and ask for help if you need/want. or pm me.
PD: i live in argentina and design/custom build tube amps...so i have lots of experience.

[numpty]

How much above the recommended 250 vdc HT can you go could you run it as hot as 300vdc, the reason I ask is that I have 230v mains voltage and already have two spare transformers which are, one 230 to 6v wired to a 12 v to 230 ( back to back transformers) which gives me 150v ( too low). Using voltage doubler diodes I could increase this to 300vdc. Do i need to reduce it by regulating it down or by resistors, or could i get away with it as it is, with the benefit of high headroom or will it take it beyond the designed operating condition from a loadline point of view which may mean altering the anode load resistor or cathode resistor or both (I'm not confident about doing that).

[Aharon]

So 220V/6V  transformers would be the best? So I could get 6,3V
What does it change if  I supply the heaters withr 6,3 or 12,6 V? Does the sound change?
Rafa

Hey RAfa:
Here's a link to a project similar to the HotBox,has a lot of documentation and step by step instructions.
http://www.hoffmanamps.com/projects/tube_box.htm

Good luck
Aharon

[Aharon]

How much above the recommended 250 vdc HT can you go could you run it as hot as 300vdc, the reason I ask is that I have 230v mains voltage and already have two spare transformers which are, one 230 to 6v wired to a 12 v to 230 ( back to back transformers) which gives me 150v ( too low). Using voltage doubler diodes I could increase this to 300vdc. Do i need to reduce it by regulating it down or by resistors, or could i get away with it as it is, with the benefit of high headroom or will it take it beyond the designed operating condition from a loadline point of view which may mean altering the anode load resistor or cathode resistor or both (I'm not confident about doing that).

I think I had 275V coming out of my power supply.............
Anyways....here's a link to a power supply calculator,you can actually see the voltages and other parameters change as you cahnge the resistor values etc.
http://www.duncanamps.com/software.html
Great tool and it's freeware.There's other useful programs too.
Hope it helps.
Aharon

[fikri]

You will get different result by using lower/higher plate supply, Make sure you dont exceed more than 270V when you are reading  pin one

[bancika]

as swt said, it's best to use 9VAC and regulate it. That's exactly what I did in my build and it works great.
numpty, no problem with 300V, it will only sound a bit cleaner maybe. Mesa runs tubes with over 400V, so don't worry.

[numpty]

I tested the six volt transformer it read 8.56 vac with one 12ax7 6.3 volt wiring (so thats under load).I was told by the suppliers that is normal - so regulation is important (the 12 volt transformer read over 18vac).
I don't know why they are much higher than spec. Filaments rated at 6.3v should not be supplied below 5v or above 6.9v or they will be damaged. As they were not meant to be filament transformers, but built for PSU applications I suppose they don't need to be accurate with regulation and they may have a reduced output under higher loads anyway.I think its worth testing though.

[bancika]

yeah, voltage depends on load. If transformer is rated at 2.5 A for example and you have only 300mA load voltage will be higher than expected. Regulation rules