Personally, I would use dropper resistors to pull down the heater voltage if it needed it, and I wouldn't bother with the thermistor(s).
Douk Audio Tube Amplifier Kit Assembly Advice Needed!
- Thread starter mfenberg
- Start date
Lavane
Lunatic Member
I mentioned that in post #17. I've gone that route with a couple Ch-Fi products using 110v primaries. Even with the higher voltage on the secondaries, the B+ wasn't too high, but the heater voltage was, and dropping resistors did the trick.
buickguy62
Active Member
Maybe you could work with the OP to decide on the value of the resistor, type, wattage, maybe a quick sketch for installation, I'm sure he would appreciate that.
looks like heater current for a 6N2 is 340ma, and a 6P1 is 800ma (times two) for a total of 1.94 amps. If we're starting at 6.9 volts and want to be at 6.3 volts, 0.6 / 1.94 = 0.31 ohm drop resistor, or 0.33 is close enough. 0.6 V * 1.94 A = 1.2 watts, so a minimum of a 3 watt resistor would be appropriate here. Its going to get warm so keep wires away from it.
I found this good YouTube video...
If you use dropper resistors on the heaters they will act as in-rush current limiters too.
What I don't much like about thermistors is that they're dissipating power all the time and dropping voltage. Ok, in your case you want to drop the voltage anyway.
Well, I'm only telling you what I would do, not telling you what you should do. Just be aware that my choice is an informed one.
Thanks for this information! I was not aware that the dropping resistors would also act as in-rush current limiters as well. This amplifier "kit" is built on a fairly small chassis and I can see how using a thermistor might heat things up underneath! Definitely something to keep in mind!
Lavane! Thanks for the information and sketch! I'm waiting for some parts to arrive by the end of the week before I can continue the build.
g73! Thanks for doing the math for the dropping resistors and for letting me know that a 3 watt resistor will be sufficient. I'll order a pair today. Thanks again!
Will these work? https://www.ebay.com/itm/252977511552?hash=item3ae6a27c80:g:RmAAAOSwYlRZNuou
Lavane
Lunatic Member
That was kind my thinking on going with 5 watt dropping resistors instead of a 3 watt like gadget suggested. The 5 watt may not generate as much heat. But they probably will be physically larger than a 3 watt resistor.
I'm seeing quite a few 5 watt ceramic resistors on eBay. In the attached picture, there would probably be sufficient room to mount them between the transformer and tube socket.
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Lavane
Lunatic Member
Looking at the picture there is plenty of room. The 3 watt should work fine. There is plenty of space for heat to disapate.
Thanks! I'll go ahead and order the resistors from the link I provided in post #70
3 watt would be the minimum, 5 watt would also be perfectly fine.
something I probably should have been clear about, thats 0.33 ohms total. If you want the heater string to be balanced, one 0.15 ohm per side would get it done. Those would need to be at least 2 watts each.
something I probably should have been clear about, thats 0.33 ohms total. If you want the heater string to be balanced, one 0.15 ohm per side would get it done. Those would need to be at least 2 watts each.
Thanks for clarifying this! I've already purchased two of the .33 ohm resistors, so will just add them to my parts box! I'll go look for .15 ohm resistors now!
I just ordered 0.15 ohm, 5W resistors as seen here.... https://www.ebay.com/itm/265233770929 I trust these will work?
Hi all! Here's an update as of 8-6-21.
I took some time and drew out a pictorial of the hardware mounted in the chassis. I can use it to draw where the parts should go, based on the schematic. I can print out this pictorial as needed, if I make mistakes with wiring!!
I took some time and drew out a pictorial of the hardware mounted in the chassis. I can use it to draw where the parts should go, based on the schematic. I can print out this pictorial as needed, if I make mistakes with wiring!!
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Thanks for pointing that out concerning the (-) speaker terminals. I believe I did notice this in both the pictorial and schematic. Concerning the shielded cable, yes, there is a small length included and I've already soldered it to the inputs of the volume control. From what I can see from the picture of the chassis, it appears that the shielded cable is only used from the input jacks to the volume control. From the control to the tube, it appears to be using only the included hookup wire.
