diyAudio

diyAudio (http://www.diyaudio.com/forums/)
-   Tubes / Valves (http://www.diyaudio.com/forums/tubes-valves/)
-   -   Wiring up 3 6.3 Volt Heaters to a 12V supply (http://www.diyaudio.com/forums/tubes-valves/228076-wiring-up-3-6-3-volt-heaters-12v-supply.html)

supersonik319 18th January 2013 05:56 AM

Wiring up 3 6.3 Volt Heaters to a 12V supply
 
Hi there,

My tube amp project involves 3 6BQ7A tubes, and I will use a 12VDC supply for the heaters. I'm wondering if the best choice would be to:

A) Use a voltage divider with high Wattage resistors to drop the voltage down to 6.3 and wire the tubes in parallel from that supply.

B) Wire two tubes' heaters in series, and have one tube's heaters in parallel with one of those two tubes. I am unsure of the consequences this approach, and it seems unconventional.

Thanks for your advice in advance!

Richard Ellis 18th January 2013 06:55 AM

Just use a 12BQ7A, same tube but uses a 12.6 Volt heater..........

__________________________________________________ _Rick...

Vinylsavor 18th January 2013 07:03 AM

Hi!

If you want to use option B, do it like this: wire two tubes heaters in parllel.
Wire a resistor in parallel to the single tube which is left, which draws the same current.
Then put these two proups in series

Thomas

supersonik319 18th January 2013 07:46 AM

Quote:

Originally Posted by Richard Ellis (Post 3331021)
Just use a 12BQ7A, same tube but uses a 12.6 Volt heater..........

__________________________________________________ _Rick...

I tried searching eBay, but there don't seem to be any for sale... These I also have in my hand, so I'd like to use them if possible :)

http://www.r-type.org/pdfs/6bq7a.pdf

Each heater takes 0.4 amps, so at 12 volts, I should use a 30Ohm, 5Watt resistor, just to confirm:

+12V ---^--^--- GND
+12V ---R--^-- GND

Where ^ = 6.3V heater, R = 30Ohm, 5Watt resistor.

or

+12V ---^--\/--^--- GND
+12V ---R--/\--^-- GND

Where ^ = 6.3V heater, R = 30Ohm, 5Watt resistor., and the wires cross at \/ and /\

Elvee 18th January 2013 07:55 AM

If your 12V is strong and healthy (comfortably sized transformer), you could try to rectify and filter, and feed the three tubes in series.
You should use schottky diodes in the bridge to minimize the losses.

Vincent77 18th January 2013 10:35 AM

The filaments are not strictly identical between tubes. If you wire them in series, one tube may end up at 5.7v and the other at 6.3...
The right voltage if you want the maximum performance is 6.3V, not 6 or less. Yes, it's only a 5% difference, but it does have an influence on the tube's parameters and lifespan.
It didn't matter in the 60's because there were millions of spare tubes around and they didn't have good and cheap voltage regulation... But today we should do better!

Why not doing it the right way??
Buy an adjustable DC-DC LM2596 converter module ($3 on ebay), it's good for 2 Amperes and wire the heaters in parallel.

DF96 18th January 2013 11:45 AM

Use the first connection in post 4: one leg with two heaters in series, the other leg with heater plus resistor, and no cross-connection. Omitting the cross-connection will reduce the warm-up stress on the heater which would otherwise be placed in parallel with R, and will avoid any similar stress created if R goes open circuit.

Although (unlike 4BQ7A and 5BQ7A) the 6BQ7A does not have a controlled warmup heater it should be OK in short series heater strings.

supersonik319 18th January 2013 03:10 PM

Quote:

Originally Posted by Vincent77 (Post 3331209)
The filaments are not strictly identical between tubes. If you wire them in series, one tube may end up at 5.7v and the other at 6.3...
The right voltage if you want the maximum performance is 6.3V, not 6 or less. Yes, it's only a 5% difference, but it does have an influence on the tube's parameters and lifespan.
It didn't matter in the 60's because there were millions of spare tubes around and they didn't have good and cheap voltage regulation... But today we should do better!

Why not doing it the right way??
Buy an adjustable DC-DC LM2596 converter module ($3 on ebay), it's good for 2 Amperes and wire the heaters in parallel.

That's....actually a good point. LM317s could also go up to 1.5Amp..... I think I'll go with this method as I have voltage regulator chips lying around, and no 30 Ohm 5Watt resistors (I was planning on using 3 10 Ohm sandbars I already had). Thanks for the help!

I'll do some more research into heater power specifics to understand DF96's proposal to keep the knowledge for when I run out of chips :)

KatieandDad 18th January 2013 03:23 PM

Just be careful of relative voltages.

Don't put yourself in a position where one heater could be grossly positive with respect to the cathode, you might end up with conduction between the cathode and the heater.

supersonik319 18th January 2013 03:52 PM

Would that be possible if I wire the three heaters in parallel with the output of the LM317 chip? How would I go about minimizing this risk?


All times are GMT. The time now is 11:03 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio


Content Relevant URLs by vBSEO 3.3.2