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Old 24th November 2010, 01:30 AM   #1
nige838 is offline nige838  United States
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Default Heater problem

Hello, I've been working on the following schematic. I subbed the 35w4 for the 35z5 and the 12at6 for the 21sq7. I replaced the dropping resistor in the heater chain and used a 6h6 (only the heater's wired) to take up the extra 6 volts, leaving me with 115v. Anyways, the heater chain is as follows: AC directly to 35w4....50l6....12sq7....12at6....6h6.

THE PROBLEM:
The 35z5 gets REALLY BRIGHT, and the rest of the tubes don't light at all, leading me to believe that the 35z5 is absorbing all of the voltage somehow. given, the amp doesn't work at all.

I've triple checked the heater chain, all is ok. even double checked the pinout with the datasheet. I'm really stumped on this one. This is my second build of this circuit, the first worked flawlessly...but was built EXACTLY to spec...

Please help,
Nick G.
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Old 24th November 2010, 01:36 AM   #2
nige838 is offline nige838  United States
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sorry, forgot to post schematic...
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Old 24th November 2010, 01:41 AM   #3
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One approach would be to measure all the heater impedances in circuit.
This would prove you have the heater wires wired up correctly.
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Old 24th November 2010, 01:48 AM   #4
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Hmmm you might want to use the correct resistor and get rid of the 6H6. It's heater draws 300ma while the rest are all 150ma.
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Old 24th November 2010, 01:54 AM   #5
nige838 is offline nige838  United States
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ok, so this just got weirder...

I switched the power cord to this around and everything EXCEPT the 35z4 lit...what the heck is going on? I've got to be missing something, but for the life of me, I don't know what...

next, I'm going to try to find a 35w4 to sub back in it's place...
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Old 24th November 2010, 01:57 AM   #6
nige838 is offline nige838  United States
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thanks for the quick replies...

I used the 6H6 because I built this from 100% scavenged parts, which was a goal. Why would the different heater currents matter? Wouldn't they just take what they wanted?

Also, I'm a poor college student and can't afford the shipping for parts...


Thanks for the replies,
Nick
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Old 24th November 2010, 01:57 AM   #7
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Quote:
Originally Posted by nige838 View Post
THE PROBLEM:
The 35z5 gets REALLY BRIGHT, and the rest of the tubes don't light at all, leading me to believe that the 35z5 is absorbing all of the voltage somehow. given, the amp doesn't work at all.

I've triple checked the heater chain, all is ok. even double checked the pinout with the datasheet. I'm really stumped on this one. This is my second build of this circuit, the first worked flawlessly...but was built EXACTLY to spec..
35Z5: 35V / 0.15A
12SQ7: 12.6V / 0.15A
50L6: 50V / 0.15A
12AT6: 12.6V / 0.15A
6H6: 6.3V / 0.3A

That, right there, is your problem. That 6H6 requires twice the heater current, and given that, you can't expect the other 0.15A VTs to split the voltage as they should. There is a reason why all those types that were designed to run with series connected heaters are almost universally designed to pull 0.15A of heater current. I'd ditch the 6H6, and install an appropriately sized ballast resistor.

It also looks a helluvalot like you're fooling around with a power transformerless design there. I would suggest getting a different design, as that's mega-dangerous Yeah, they used that a lot back in "the day" to save a few $$$$, but horror stories of electrocutions and near electrocutions also abound from those days. Besides, how many CD players, sound cards, iPods, etc can stand up to 120Vrms if you plug the durn thing in the wall socket the wrong way?

Better to get all 12V versions of the types listed here, a proper power xfmr, and a 12.6V xfmr to run the heaters.
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Old 24th November 2010, 01:59 AM   #8
nige838 is offline nige838  United States
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the only resistors that i have that are high wattage are two 10ohm resistors @ 5 watts...I don't think that they will help me...
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Old 24th November 2010, 02:01 AM   #9
nige838 is offline nige838  United States
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Quote:
Originally Posted by astouffer View Post
Hmmm you might want to use the correct resistor and get rid of the 6H6. It's heater draws 300ma while the rest are all 150ma.
Quote:
Originally Posted by Miles Prower View Post
35Z5: 35V / 0.15A
12SQ7: 12.6V / 0.15A
50L6: 50V / 0.15A
12AT6: 12.6V / 0.15A
6H6: 6.3V / 0.3A

That, right there, is your problem. That 6H6 requires twice the heater current, and given that, you can't expect the other 0.15A VTs to split the voltage as they should. There is a reason why all those types that were designed to run with series connected heaters are almost universally designed to pull 0.15A of heater current. I'd ditch the 6H6, and install an appropriately sized ballast resistor.

It also looks a helluvalot like you're fooling around with a power transformerless design there. I would suggest getting a different design, as that's mega-dangerous Yeah, they used that a lot back in "the day" to save a few $$$$, but horror stories of electrocutions and near electrocutions also abound from those days. Besides, how many CD players, sound cards, iPods, etc can stand up to 120Vrms if you plug the durn thing in the wall socket the wrong way?

Better to get all 12V versions of the types listed here, a proper power xfmr, and a 12.6V xfmr to run the heaters.
Thank you very much for your explaination. I see the error of my ways...
BTW i've got AC mains running into a 40v .5A transformer and then back into a twin transformer to isolate it from mains...but thanks for caring...

Thanks again,
Nick
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Old 24th November 2010, 02:16 AM   #10
nige838 is offline nige838  United States
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Quote:
Originally Posted by Miles Prower View Post
35Z5: 35V / 0.15A
12SQ7: 12.6V / 0.15A
50L6: 50V / 0.15A
12AT6: 12.6V / 0.15A
6H6: 6.3V / 0.3A

That, right there, is your problem. That 6H6 requires twice the heater current, and given that, you can't expect the other 0.15A VTs to split the voltage as they should. There is a reason why all those types that were designed to run with series connected heaters are almost universally designed to pull 0.15A of heater current. I'd ditch the 6H6, and install an appropriately sized ballast resistor.

It also looks a helluvalot like you're fooling around with a power transformerless design there. I would suggest getting a different design, as that's mega-dangerous Yeah, they used that a lot back in "the day" to save a few $$$$, but horror stories of electrocutions and near electrocutions also abound from those days. Besides, how many CD players, sound cards, iPods, etc can stand up to 120Vrms if you plug the durn thing in the wall socket the wrong way?

Better to get all 12V versions of the types listed here, a proper power xfmr, and a 12.6V xfmr to run the heaters.
Sorry to bother you again, but here is what I did....

I subbed the 6h6 for a 12sa7, 12.6v heater @.15A...
Same problem persisted...
the voltages add up to around 122 (I have 120 at the wall)
I still can't figure out what is going on, do you have any more ideas?

Thank you very much for your time,
Nick
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