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12b4, 6ca4 build questions....

bricktop said:
Douglas, do you know if DC heaters were necessary with this linestage?
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I've been assuming DC requirements for a while now. It is a bit of a pain, but I suspect it will be needed given the heater-cathode leakage this type is prone to. fire it with AC first...:) if DC is needed, a 12V regulator will be fine, no need to go and find 12.6 as that usually needs an adjustable regulator.
cheers,
Douglas
 
Once you get it together saltwater, give it a listen. If you notice some hum (that we can be sure is just from the heaters), I'll send some parts for a DC regulator.:thmbsp:
 
hey brick what are those lil black things that look like the 3545. solid black up top, 4 legs on it, and they say:

you sent them to me.... just dont know what for?

RS103
A 30
+ AC -
 
Those are bridge rectifiers..I forgot I sent some to you...You'll be able to use them for the DC heater supply if you need it:thmbsp:
 
Did I toss in any regulators:scratch2: LM317s or the like? I can't remember. Did you ever find any wood, I didn't have anything tall enough in my pile.:thumbsdn:
 
no regulators, i posted everything you sent me on the very first post, even i had to go back and check..... im taking apart this organ, and gonna use some of that wire. and possibly some of the wood! :thmbsp:
 
saltwater said:
no regulators, i posted everything you sent me on the very first post, even i had to go back and check..... im taking apart this organ, and gonna use some of that wire. and possibly some of the wood! :thmbsp:
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I started out by scrapping organs myself.:thmbsp: My 12B4 circuit was completely different than the one you're doing, but it even hummed with DC on the fils untill I referenced one side of the string to ground with a resistor. Hopefully you won't have that problem, but if you do, I have some small regs.
 
Damn organ is solid state though! i thought i had a gold mine, then reading about organ amps not good for hi-fi, that was like a punch in the face... anywho its going.....
 
Ive been looking at alot of tube preamps, and amps. Alot of them dont have heatsinks for the 2540's. or they look like 2540's. do i need it? its just so big of a heat sink, also bolting it to the chassie would render fixing if something burned up... am i ranting? sorry if im being stupid...
 
Well, there is an easy way to figure this out...:thmbsp:

Let's say worst case you have a 300VDC supply in your amp, it's probably not that high, but it never hurts too much to overestimate your safety margins. Also consider you have each CCS set for 15mA, which corresponds to a 12B4 plate voltage of about 90V. This means you have P = V*I = (300-90)*0.015 = 3.15 Watts per DN2540N5.

This is where it kinda goes from electrical engineering to mechanical engineering (Douglas' forte). Say we have no heatsink, which indicated by the datasheet means a junction-to-ambient thermal resistance (theta_ja) of 70celsius/watt, which means that for every watt dissipated, the junction temperature goes up by 70 degrees Celsius. At our 3.15 watts at an ambient temperature of 25C, the junction would operate at 25+3.15*70 = 245.5C (Ouch!). It would burn up rather quickly since max operating junction temp is 150C.

If we use a heat sink, we use the junction-to-case thermal resistance of the DN2540 (theta_jc = 8.3C/Watt) plus the thermal resistance of the heatsink (mount-to-ambient). For the one I gave you (Wakefield P/N 637-20ABP), it mentions no natural convection thermal resistance, but claims a temperature of 55C@6W, which is about what you will be doing with it with two DN2540s on it. Assuming that the case is 25C+55C (which is most definitely will not be, but assumptions make life easier), that means that the junction temperature is 8.3*3.15 + 25 + 55 = 106C. That's pretty hot, but within operational limits of the device.

Personally, that temperature would make me want to bolt them to the chassis, but it should work ok with the heatsink too. Keeping the high voltage power supply low will be the easiest way to reduce power dissipation in the devices A good number to shoot for would be about 200V, but 250V is fine too.

Bottom Line: The heatsink should be fine. It would definitely not work without at least the heatsink. The best option is to bolt to the chassis.
 
Ok brick! heatsink is staying, Im still dumbfounded on the wood as everything is not wide enough! It sucks, i did get a 3 prong cord, and some organ wire(thanks organ), i got the power wired up, i also am having probs figuring out if i did it right, im gonna take the chance and instead of the three position switch i got from jay, get the one out of the organ, its just an on/off.

Thanks for going in depth like that, i keep underestimating you but i can clearly see you know your shite! :thmbsp:
 
Ok heres where im at,

I got it Finished, 1 problem, I fried the resistor going from pin 3 of the 6ca4 (3w 470 ohm) to the 47 uf and 10h 150ohm choke, i dont understand why it burned up, everything is the way it is in the schematic, minus the ugly underside! But it all lit up and tubes glowed! :thmbsp: Only prob is that resistor burned up. dont understand it! any ides fellas.... :tears: thats the only smoke i let loose! Still have no base, and i got shocked by touching that switch, old wall outlet will get ya! ill try to get some pics up but im having issues right now. thanks...
 
Also my led's did not light up... any ideas there. I do have that 3 w 470 ohm grounded to the same terminal as the led's, also the 3 w 470 ohm resistor has cooled down and returned to its same color, when it got hot it turned black... but now its back to orig color, think it's ok?
 
saltwater said:
Ok heres where im at,

I got it Finished, 1 problem, I fried the resistor going from pin 3 of the 6ca4 (3w 470 ohm) to the 47 uf and 10h 150ohm choke, i dont understand why it burned up, everything is the way it is in the schematic, minus the ugly underside! But it all lit up and tubes glowed! :thmbsp: Only prob is that resistor burned up. dont understand it! any ides fellas.... :tears: thats the only smoke i let loose! Still have no base, and i got shocked by touching that switch, old wall outlet will get ya! ill try to get some pics up but im having issues right now. thanks...
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hmmm, that probably blew up because of a short elsewhere, which might be a good thing since resistors are cheaper than tubes and mosfets. How long did it take after power was applied until the resistor smoked? Are both the CCSs hooked up correctly? If one was backwards, it could easily look like close to a short-circuit. Post a picture if you can so we can get some more sets of eyes on it.

saltwater said:
Also my led's did not light up... any ideas there.
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They won't light up unless the 12B4s are warmed up and drawing current. If drawing too much current, they may open up, acting as sort of a fuse. You can test them with your meter on the diode setting, they should read about a 1.7 volt forward drop if they are ok.
 
saltwater said:
Also my led's did not light up... any ideas there. I do have that 3 w 470 ohm grounded to the same terminal as the led's, also the 3 w 470 ohm resistor has cooled down and returned to its same color, when it got hot it turned black... but now its back to orig color, think it's ok?
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If the resistor measures about 470 ohms, it should be ok. That resistor shouldn't be grounded anywhere, are you sure you meant that it's grounded?
 
bricktop said:
hmmm, that probably blew up because of a short elsewhere, which might be a good thing since resistors are cheaper than tubes and mosfets. How long did it take after power was applied until the resistor smoked? Are both the CCSs hooked up correctly? If one was backwards, it could easily look like close to a short-circuit. Post a picture if you can so we can get some more sets of eyes on it.

It was only about 30 seconds, then i started smelling something warm ,flipped it over and seen where it was coming from.. unplugged it. I powered it up at first w/ no tubes in it, that went goo, i shut her down put the tubes in it and 30 sec later smoke!


They won't light up unless the 12B4s are warmed up and drawing current. If drawing too much current, they may open up, acting as sort of a fuse. You can test them with your meter on the diode setting, they should read about a 1.7 volt forward drop if they are ok.
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diode setting, whats that, ohm? :thmbsp:
 
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