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Adjust/setting heater voltage?

Kegger

Kegger

R.I.P. 1/12/1966 - 6/1/2017
What are some of the ways/best ways/easiest ways to set the propper heater voltage supply?

If your using say ac heaters and looking for 6.3 volts but your closer to 7 what would you do?

Just slap a couple resistors on each side of the ac supply to the heaters?
(Making sure there propper wattage rated of'course):D
 
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The first thing is to check the calibration of your AC meter, and find out if it is "average" or "true RMS" The 6.3v would be RMS.
If all this checks ok, then add a series resistor.
 
Yep, Series resistor. Indm showed me how to calculate it, but I can't find my notes.:thumbsdn: I had nearly the same scenario and ended up with a 5watt .33ohm on my SE amp. I like to have it exactly 6.3. I figure if the guys who designed the tubes went to the trouble to include the .3, why shouldn't I.:D
 
Thanks for the info guy's! Not sure if my meters are RMS or not, I'll check both.

I know what I usually read on heater circuits with the meter and this unit is higher.

Do you just put a series resistor on one leg of the 6.3 or on both halves to level it?
 
Mine is just on one side. BTW if your really fussy, be sure to re-check voltage after everything warms up to operating temp.
 
Hey!!!,
Just a point to consider...the heater voltage delivered by the winding is going to change as the TX gets warm. It should drop as the copper gets hotter. This drop may be significant, so see how big it is and that will give some insight on compensating for it.
cheers,
Douglas
 
Got yu, yah it doesn't take much resistance to affect that circuit I see.
When your drawing an amp or more of current the voltage changes quick.

This is on an EZ81 rectifier on a 2.5a 6.3volt source. (Only thing on the circuit)
 
Hmmm, I wouldn't have thought the 1amp draw of the EZ81 would give very much "sag" on a 2.5 rated winding.
 
yea i ended up dropping the voltage on my 2x6SN7 linestage with a 1-watt .47-ohm resistor. i didn't bother checking but i figure that it should drop around 1/2 a volt on the 1.2A from 6.9 to 6.4-ish, so i'm happy.
 
jaymanaa said:
Hmmm, I wouldn't have thought the 1amp draw of the EZ81 would give very much "sag" on a 2.5 rated winding.
Click to expand...

Yah I think that's the problem JAY, I'm not weighing down the trannie enough so the voltage is high.

--------------

Yes it looks like less then 1ohm is all I'll need.
 
Hey!!!,
If you're dropping less than a volt, 1R/1W metal film is a good way to build a proper resistor. Just put the right number in parallel to get your required resistance. they're quite cheap at Mouser.

The temperature induced loss is more of an issue with higher voltage TX's run closer to their limits. All this came to light with my DH amp running 12VAC to its heaters. I need better filament Iron, that is quite clear...:) Good thing the next amp has some really tough filament TX's. 96VA for each of the finals.
cheers,
Douglas
 
Allright about as close as I'm gunna get, 1 meter says 6.2, 1 meter says 6.3 and one says 6.5volts.

Here's some pic's, as we all love those pics of our funky contraptions. Using a 12k 12W load resistor.

It's a power supply for a preamp, (RC, LC, RC, LC) for 300 volts. (plenty of oil and poly)
(At the moment it will power a 76 based pre with some parts from a local buddy, Terry)
 

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Love the pics Kegman.:thmbsp: It's a good thing we don't live closer to each other. I'd be hangin out at your workshop ALL the time. I didn't know you were working on a 76 pre.:yikes: I've heard that tube can be very addictive. Let us know how it works out, Jay
 
Thanks for the props JAY! I didn't know I was working on a 76 pre either
until I met up with a friend and was handed some parts to play with. :D

Well not sure if it's the pre or the HKeg with the new EL86 "triode" drivers
but it is a soundin quite nice though!:music:

Here's another pic of it in the system.:thmbsp:
 

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Kegger said:
Thanks for the props JAY! I didn't know I was working on a 76 pre either
until I met up with a friend and was handed some parts to play with. :D


Here's another pic of it in the system.:thmbsp:
Click to expand...

Hey-Hey!!!,
I recognize some of those bits...:) I have some output TX's I want to use for a PP pre. They're ~6:1 step-down so I need some gain. A LTP-style will cut gain in half. Now something running 20-plus would be nice. There are a lot to choose from. ECC99 keeps comming to mind.
cheers,
Douglas
 
yes nice how some of our parts get recycled around the clan!

If your in need of any 20-40mu dual triode 9pinners to use I got's plenty!
I tried pretty much every one under the sun on the 70 then on the Hkeg.

Still feel the 12BH7 is one fine tube! Really like the 6829 as well.
 
For what it's worth, hearing the 76 in Terry's system and now mine, that tube
has all the clarity of the best I've heard. Real nice bass weight, smooth mids,
with a top end that seems to go on forever, these are not your fathers rolled
off highs, flabby bass tubes, no hint of the "overly tubey" sound of yesteryear.


Oh yah there ST shaped to boot!:banana: :thmbsp: :smoke: :yes: :music:
 
Have you noticed any problems with microphonics using the 76 Paul? I have a bunch of these and want to try them in a pre-amp and in a driver stage for a 300B.

Have you drawn up a schematic of your pre-amp? I'd like to see it and I tend to like your approach to power supplies - tube rectified, lots of iron and oil caps.
 
Neither Terry nor I have had microphonics problems, just decent vibration dampening.

And interesting you say use it as a driver as both Terry and I were talking the
same thing as this circuit comes from the tube cad journal and is suggested as
it's use being a driver for an amp and not really a pre but works very nice though.

I would think it would make a fine driver to a 300B based amp or so.

here's a link to the journal with a bit about the circuit.
http://www.tubecad.com/january2000/page5.html
(The Ultra-Linear Cascode)

We are using the circuit "basically" as is but I changed the cathode resistor to 470ohm
to up the grid voltage a touch (just so I feel better at -3 or more)

My power supply is just a little over 300 and the top 76 is running at 233 plate voltage and
8.5ma while the bottom is running at 120 plate voltage and 7.5ma (1ma lost with 100k to ground)
EDIT (Since the tubes are in series and the bottom tubes plate is connected to the cathode of
the top tube, the top tubes plate to cathode voltage is just about 110 with both tubes running
at 7.4ma as the other 1ma is going through the 100k to ground setup)

This circuit is still being tweaked and may have some other (I would think minor) changes. :D

I'm going to try running a second pair of rca outs from the cathode of the top tube (in between the tubes)
as a second output with about half the gain as the other, in case an amp with a lot of gain is to be used.
 
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