5f11 dropping B+ voltage

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Mike52
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Re: 5f11 dropping B+ voltage

Post by Mike52 »

sluckey wrote: Tue Feb 20, 2018 12:08 am
(btw, pin 8 is also the OT Center tap)
Well, you simply move the OT lead to the original 16µF cap. This may be a factor for why you did not get the desired voltage drop to begin with. There must be sufficient current flowing through the zener for predictable results.
Yep. Done
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Re: 5f11 dropping B+ voltage

Post by sluckey »

Did you get the desired results? Or did you just quit?
Mike52
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Re: 5f11 dropping B+ voltage

Post by Mike52 »

sluckey wrote: Tue Feb 20, 2018 1:11 am Did you get the desired results? Or did you just quit?
My 5y3 is dead. I suspect it was something I did being careless with the multimeter.

But voltages through the current limiter with no tubes in tells me the OT CT swap will be fine.
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Re: 5f11 dropping B+ voltage

Post by Mike52 »

-
Mike52
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Re: 5f11 dropping B+ voltage

Post by Mike52 »

Hmm. Not what I was expecting, but interesting. And the voltage drop looks pretty consistent, so that's something to work with. I didn't take current readings across the diodes.


JJ 5Y3-S. Here's some data:

B+ 382v
1x15v...............374v...........8v drop..........53.3% of zener voltage
1x20v...............369v.........13v drop..........65%
3x12v...............363v.........19v drop..........52.8%
3x15v...............358v..........24v drop.........53.3%
1x43v...............352v..........30v drop.........69.8%
2x20v...............349v..........33v drop.........82.5%
1x15&1x43v.......344v..........38v drop.........65.5%

I think this is going to need filtering when its finally in place.
Mike52
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Re: 5f11 dropping B+ voltage

Post by Mike52 »

Fixed.

I gotta say, the level of support here was pretty underwhelming. I would have thought more people were familiar with a fixed bias circuit. But that's ok, no one is obligated to help anyone.
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Re: 5f11 dropping B+ voltage

Post by pompeiisneaks »

as with any forum, they tend to go through cycles. Some days I see people on it all day and responding in seconds other times it may go a few days without responses.

What did you do to get it fixed?

~Phil
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Mike52
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Re: 5f11 dropping B+ voltage

Post by Mike52 »

Thanks mate,
I got help on another forum. And ultimately it was a process problem.

I needed to get my initial cathode bias, add zeners to get expected B+ drop, then rebias back to the original cathode bias to get the actual B+ drop.
I was missing the last step and at a dead end. I needed to essentially suck the current through the zeners and out the cath-to-ground to make the zener perform.
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Re: 5f11 dropping B+ voltage

Post by pompeiisneaks »

Oh cool great to know, for me as well!

~Phil
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Re: 5f11 dropping B+ voltage

Post by sluckey »

sluckey wrote: Tue Feb 20, 2018 12:08 am ...There must be sufficient current flowing through the zener for predictable results.
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pompeiisneaks
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Re: 5f11 dropping B+ voltage

Post by pompeiisneaks »

sluckey wrote: Tue Feb 27, 2018 5:54 pm
sluckey wrote: Tue Feb 20, 2018 12:08 am ...There must be sufficient current flowing through the zener for predictable results.
ooo bam sluckey for the win again :)

So yeah you did have your answer here.

Thanks again for rocking sluckey!

~Phil
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martin manning
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Re: 5f11 dropping B+ voltage

Post by martin manning »

Mike52 wrote: Tue Feb 27, 2018 3:31 amI gotta say, the level of support here was pretty underwhelming. I would have thought more people were familiar with a fixed bias circuit. But that's ok, no one is obligated to help anyone.
Steve went above and beyond trying to help you out. I think everybody here knows their way around a fixed-bias amp. That is probably why it just didn't occur to anyone that you would be trying to measure the idle voltage without resetting the idle operating point ;^)
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didit
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Re: 5f11 dropping B+ voltage

Post by didit »

Aaron also deserves more than honourable mention for providing a less problematic option than a careless string of Zeners. Wise horses drink when led to something truly refreshing.
xtian wrote: Mon Feb 19, 2018 3:57 pm You can drop up to 80 volts by using a MOSFET B+ reducer on the HT CT: http://ampgarage.com/forum/viewtopic.php?t=27035
Best .. Ian
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Re: 5f11 dropping B+ voltage

Post by sluckey »

didit wrote: Wed Feb 28, 2018 1:01 am Aaron also deserves more than honourable mention for providing a less problematic option than a careless string of Zeners. Wise horses drink when led to something truly refreshing.
xtian wrote: Mon Feb 19, 2018 3:57 pm You can drop up to 80 volts by using a MOSFET B+ reducer on the HT CT: http://ampgarage.com/forum/viewtopic.php?t=27035
Best .. Ian
That's true. You can even put a big dropping resistor in the CT. But in the case of a fixed bias amp such as the 5F11 that develops it's negative bias from a tap on the HT winding, you will be jacking the bias voltage also. IMO it would be better to put any B+ reducer in the B+ line, not the CT.
Mike52
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Re: 5f11 dropping B+ voltage

Post by Mike52 »

pompeiisneaks wrote: Tue Feb 27, 2018 7:59 pm
sluckey wrote: Tue Feb 27, 2018 5:54 pm
sluckey wrote: Tue Feb 20, 2018 12:08 am ...There must be sufficient current flowing through the zener for predictable results.
ooo bam sluckey for the win again :)

So yeah you did have your answer here.

Thanks again for rocking sluckey!

~Phil
Well I'm not interested in getting in a bickering match here about who was the most helpful and who wasn't in a forum that I don't use often, and where no one has to be helpful at all if they don't want.

And, yes i could have gotten a mosfet, which I understand is a thing. Can't argue with that.

I could have also completely changed course and bought a new transformer. And then used the old transformer to build an official copy of a John Mayer thingamajig. That appeared to be the crowd favorite. Although it may have been a more intriguing idea if it had the word "Dumble" in it, which I understand is also a thing.

I appreciate the input I got from Sluckey early on, I enjoy his posts over at Hoffman's forum and have enjoyed his build page. Love the Leslie speaker. And I appreciate that he wasnt suggesting that I scrap my dumb idea mid-stream and buy something else.

His comment in passing about current was good information in that in retrospect it was factual. However, these zeners were getting current through them and they were dropping voltage, but not as much as I expected. So the mystery for me was defining what "sufficient" actually means. Should I put a filter cap on pin 8 of the 5y3, will that make it sufficient? Dunno. In any case, i got it licked (no Sluckey, I didn't quit) and I'm smarter for the experience. Enjoy.
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