Heaters to high

[Tone Junkie]

So my heaters on my tubes are at 6.8 . I’m not good with the math any idea what ohm to stick in there to lower. And what wattage z if math example is put in the answer I can put this on my wall of knowledge for later use. I’m forgetful so I post it in my computer room wall. So I can quickly get the answer next time . Lol Bill

[Willabe]

Tubes can run their heaters +/- 10%. So your still good.

6.3 x .1 = .63 

6.3 + .63 = 6.93 

6.3 - .63 = 5.67

What's your wall acv? What amp? Is it old, schematic show 117acv wall voltage or lower? What PT? Does your PT have an over rated current heater supply for what tubes your running in the amp? Did you change power tubes that draw less heater current? Like going from EL34's to 6L6GB/GC's?

You could build a bucking transformer box. From Sluckey's web site, 2nd page, Buckaroo; 

http://sluckeyamps.com/misc/Amp_Scrapbook.pdf

[Latole]

Tubes can run their heaters +/- 10%. So your still good.

 What's your wall acv?
What amp?
 Is it old, schematic show 117acv wall voltage or lower?
What PT?
Does your PT have an over rated current heater supply for what tubes your running in the amp? Did you change power tubes that draw less heater current? Like going from EL34's to 6L6GB/GC's?

 

Right !

[PRR]

> what ohm to stick in

That question needs Current. Which means looking-up and adding-up the tubes in your unspecified amp.

[acheld]

But, why?

[Tone Junkie]

2x6l6 and 3 12ax7s  the transformer is new but could be 20 years old. New as in hasn’t been inside anything.

[Tone Junkie]

Could be an over rated supply.

[Willabe]

Could be an over rated supply.

What PT?

Brad/name, model #?

[Tone Junkie]

Ok I’m at work right now. Will put up when I get home. Thanks

[PRR]

You want to drop 6.8V-6.3V= 0.5V at 0.9A+0.9A+0.3A+0.3A+0.3A= 2.7A

0.5V/2.7A is 0.1852 Ohms.

0.5V*2.7A is 1.35 Watts. (Round up at least double.)

While maybe not essential, it is prettier if split to both sides. Two of 0.09Ω@2W

DigiKey:
53JR10E RES 0.1 OHM 5% 3W AXIAL $0.25     4,407 - Immediate
13FR080E-B RES 0.08 OHM 1% 3W AXIAL   $1.26   800 - Immediate
12FR090E RES 0.09 OHM 1% 2W AXIAL $1.83     14 - Immediate

The 25 cent parts will drop 2*(0.1Ω*2.7A)= 0.54 Volts, from 6.8V makes 6.26V, which is close enough for Maine contra-dancing.

[glass54]

I've done exactly the same. Marshall JCM2000 series was running heaters at 7.4V!! (Someone in the Transformer factory must have put in a couple extra turns in Heater winding for Good Luck  )
I did a little trial and error (based on common sense and using Fluke multimeter), finding a suitable resistor, halved that and used 3W wirewounds in each Heater leg (because I had the correct values) and ended up with 6.38V. Amp was happy.
Regards
Mirek

[Tone Junkie]

Thanks you guys . Bill