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September 23, 2020, 11:43:51 PM

Author Topic: Adjusting 300B filament voltage  (Read 2004 times)

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Offline Deke609

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Re: Adjusting 300B filament voltage
« Reply #30 on: August 21, 2019, 03:48:55 AM »
You could also get a 115:120 autoformer or power transformer to sit ahead of your BeePre.


Excellent idea! Thanks PB. And I can install a cheap analog panel mount voltmeter to monitor voltage.

Quote
Dropout occurs when input voltage and output voltage get too close together.  That's why low line voltage is an issue.  The regulator will not overheat with some other major problems going on.


OK, so I think I understand this part, b/c you've explained it to me before and I've read up a bit about regulators.  But then why/how does a draw of 1.3A cause dropout?  And why couldn't the heater circuit handle the 1.4A draw of an EML 300B Mesh? The LM1085 is good for at least 3A output - so I don't think the 1085 is the limiting factor. Just throwing out guesses here: Are the transistors current limited? Or does voltage output of the secondaries sag as the Volt-Amps demand approaches the VA rating of the secondaries? Is the power demand of 13.5V (after rectification) @1.3A just too much for the PT to handle? Or does something else explain this?


If the issue is limited VA output of the secondaries, then a relatively simple solution would be to get a separate heater transformer with higher VA rating. Does that make sense?


cheers and many thanks, Derek
Derek
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Roon Intel NUC ->  Yggdrasil DAC -> BeePre (w/ BeeQuiet and EML 300B)  -> Kaiju (w/ DCFil and EML 300B) or Stereomour II (2A3 [EML Mesh] and 45 Conversion [EML 45B])  -> Audeze LCD4

Offline Paul Birkeland

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Re: Adjusting 300B filament voltage
« Reply #31 on: August 21, 2019, 04:52:37 AM »
But then why/how does a draw of 1.3A cause dropout?
The voltage available from the raw DC supply drops, not necessarily only because of the 1.3A, but also because of low line voltage. 

  And why couldn't the heater circuit handle the 1.4A draw of an EML 300B Mesh?
The noise elimination circuit also has some series resistance, and drawing extra current through this will reduce regulated voltage.

If the issue is limited VA output of the secondaries, then a relatively simple solution would be to get a separate heater transformer with higher VA rating. Does that make sense?
The 6.3V secondaries have some extra current to give.  If you bought a power transformer that had two 7V/4A windings, that would bring up the raw voltage a bit as well.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Deke609

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Re: Adjusting 300B filament voltage
« Reply #32 on: August 21, 2019, 04:56:33 AM »
Awesome. Thanks PB. 7V/4A windings maybe hard to find. But I figure I can go with 10V/4A and use dropping resistors to dial in the voltage.


cheers and thanks, Derek
Derek
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Roon Intel NUC ->  Yggdrasil DAC -> BeePre (w/ BeeQuiet and EML 300B)  -> Kaiju (w/ DCFil and EML 300B) or Stereomour II (2A3 [EML Mesh] and 45 Conversion [EML 45B])  -> Audeze LCD4

Offline Paul Birkeland

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Re: Adjusting 300B filament voltage
« Reply #33 on: August 21, 2019, 05:09:53 AM »
10V/4A with a bridge instead of a doubler might also work.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Deke609

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Re: Adjusting 300B filament voltage
« Reply #34 on: August 21, 2019, 05:31:00 AM »
Cool. Thanks PB.

Along these lines, I might also be able to go with 12.6V/3A with full wave and skip the doubler. I can play around with PSUD to see what works.

Is there a rectification advantage to using a 4-diode bridge instead of two-diode full wave other than not needing a center tapped secondary? I.e., does a bridge produce less ripple?

For modelling the heater circuit in PSUD, do you have a recommended load resistor value? Or can I just use PSUD's default value (I forget what it is)? Guessing that the answer is: add up all the resistance in the heater circuit and plug that in - but just want to be sure.

Edit: one more question - I plan to install switches on the transformer to allow for nominal +5V, 0V, -5V changes to the mains voltage. Shorting or non-shorting? I have no idea which is best for changing between windings.

Apologies for all the questions - I'll try to stay quiet for a while after this ;D

cheers and thanks, Derek
« Last Edit: August 21, 2019, 08:21:29 AM by Deke609 »
Derek
______

Roon Intel NUC ->  Yggdrasil DAC -> BeePre (w/ BeeQuiet and EML 300B)  -> Kaiju (w/ DCFil and EML 300B) or Stereomour II (2A3 [EML Mesh] and 45 Conversion [EML 45B])  -> Audeze LCD4

Offline Paul Birkeland

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Re: Adjusting 300B filament voltage
« Reply #35 on: August 21, 2019, 09:34:18 AM »
In PSUD, you can change the resistive load to constant current. Most of the questions you're asking can actually be pretty well answered by doing some modeling in PSUD and looking at the power transformer current, ripple, output voltage, etc. 

If you're asking about +5, 0, and -5V switches for a step-up before the BeePre, I would just leave it at +5, there isn't much penalty for having a little extra AC voltage.  Otherwise I would recommend non-shorting switches.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Deke609

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Re: Adjusting 300B filament voltage
« Reply #36 on: August 21, 2019, 09:41:51 AM »
Cool. Many thanks PB.  that constant current feature will sure make things easier.


cheers, Derek
Derek
______

Roon Intel NUC ->  Yggdrasil DAC -> BeePre (w/ BeeQuiet and EML 300B)  -> Kaiju (w/ DCFil and EML 300B) or Stereomour II (2A3 [EML Mesh] and 45 Conversion [EML 45B])  -> Audeze LCD4

Offline Deke609

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Re: Adjusting 300B filament voltage
« Reply #37 on: September 04, 2019, 09:49:42 AM »
I'm going to try using an autotransformer to adjust mains volatge going to my BH amps. Since it's an autotransformer, it offers no isioation from mains power - but I figure this is ok since all BH amps have their own isolating transformers.


I'm going with the Hammond 168J - rated 2000VA and weighing 23lbs!  I plan to use a 10A fuse on the incoming mains power - so run it at a max of 1200-1250VA (depending on mains voltage variations).


And so here's my question: Am I correct that running the 168J well below its max VA rating gives me some latitude on how to wire it? Specifically, the Hammond schematic shows incoming hot wired to 115V with options to take 85, 95, 105, 110, 115, and 125V out. I want to take power from the 115 tap and use switches to connect mains incoming power to either 105, 110 or 115 for nominal +0V, +5V and +10V output options.  I figure I can  use  2 X SPDT switches (high voltage/current rated) - please see attached wiring scheme.


Does anyone see a problem with this?


many thanks, Derek
« Last Edit: September 04, 2019, 09:55:58 AM by Deke609 »
Derek
______

Roon Intel NUC ->  Yggdrasil DAC -> BeePre (w/ BeeQuiet and EML 300B)  -> Kaiju (w/ DCFil and EML 300B) or Stereomour II (2A3 [EML Mesh] and 45 Conversion [EML 45B])  -> Audeze LCD4

Offline Paul Birkeland

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Re: Adjusting 300B filament voltage
« Reply #38 on: September 04, 2019, 10:14:43 AM »
I'm going with the Hammond 168J - rated 2000VA and weighing 23lbs!  I plan to use a 10A fuse on the incoming mains power - so run it at a max of 1200-1250VA (depending on mains voltage variations).
Is this just for the BeePre?


And so here's my question: Am I correct that running the 168J well below its max VA rating gives me some latitude on how to wire it?
You may find that the listed input/output voltages are not at all accurate with that transformer lightly loaded.
I figure I can  use  2 X SPDT switches (high voltage/current rated) - please see attached wiring scheme.
What you're doing would work, but something like this will be a lot simpler:
https://www.mouser.com/ProductDetail/CK/R10307RN02Q?qs=sGAEpiMZZMvNbjZ2WlReYgfl1vEqXQaLTI2c32B8PEc%3D


The Hammond 168B is a far better choice to use with the BeePre.  This is an instance where spending 5x the money will net you far worse performance.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Deke609

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Re: Adjusting 300B filament voltage
« Reply #39 on: September 04, 2019, 10:17:22 AM »
It's for all BH amps - so, at minimum the Beepre and either Kaiju or an SII. And down the road, it might be running the Beepre, Kaiju and both SII's off of it at the same time.
Derek
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Roon Intel NUC ->  Yggdrasil DAC -> BeePre (w/ BeeQuiet and EML 300B)  -> Kaiju (w/ DCFil and EML 300B) or Stereomour II (2A3 [EML Mesh] and 45 Conversion [EML 45B])  -> Audeze LCD4

Offline Paul Birkeland

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Re: Adjusting 300B filament voltage
« Reply #40 on: September 04, 2019, 10:24:51 AM »
So 168C, or maybe D.  The Kaiju and SII are quite a bit more tolerant to line voltage fluctuations and have the universal power transformers that allow you to wire for lower line voltage if that comes up, so you may want to consider making this a BeePre only effort, as you could really dial things in if you only used the BeePre on the autoformer.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Deke609

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Re: Adjusting 300B filament voltage
« Reply #41 on: September 04, 2019, 11:44:28 AM »
Many thanks PB. Good to know that it should at least work in principle. I will weigh my options. I do like the idea of having everything plug into one unit. Maybe even my dac as well. The bigger plan is to incorporate 3-4 combo common/differential mode filters (already built), each rated 3A, and have 3-4 pairs of outlets - with switches for bypassing filtering and possibly even the autotransformer. I'm even contemplating using some high current/voltage schottky's with 1.5V forward voltage drop on switches to better calibrate the voltage. Plus an analog voltmeter dial to monitor what's going on.


cheers and thanks, Derek
Derek
______

Roon Intel NUC ->  Yggdrasil DAC -> BeePre (w/ BeeQuiet and EML 300B)  -> Kaiju (w/ DCFil and EML 300B) or Stereomour II (2A3 [EML Mesh] and 45 Conversion [EML 45B])  -> Audeze LCD4

Offline Deke609

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Re: Adjusting 300B filament voltage
« Reply #42 on: September 04, 2019, 12:04:20 PM »
I'll add that much of fun for me is being able to think something up myself, build it, and have it work reasonably close to as planned. I 'm ok with the prospect that years from now (or perhaps much sooner) I'll look at the thing and realize that I could have achieved the same or better results for 1/5 the price and 1/4 the effort. And if I later choose to dismantle it, I'm pretty confident that the parts will get used in other projects. 


cheers, Derek
Derek
______

Roon Intel NUC ->  Yggdrasil DAC -> BeePre (w/ BeeQuiet and EML 300B)  -> Kaiju (w/ DCFil and EML 300B) or Stereomour II (2A3 [EML Mesh] and 45 Conversion [EML 45B])  -> Audeze LCD4

Offline Deke609

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Re: Adjusting 300B filament voltage
« Reply #43 on: November 16, 2019, 10:30:21 AM »
I have a working breadboard rebuild of the BeePre and am working on dialing in the filament regulator (LM1085 board).  I have a bunch of questions that I'm hoping @PB and @PJ can help me with.  Any directions/pointers you can provide will be greatly appreciated. I am taking my time with the BeePre rebuild and really want to find an implementation that works well with my EML 300B tubes.

In stock configuration the reg board is set up so that Vin - Vout = approx. 3.5V.  Based on my best attempt at making sense of the TI datasheet for the LM1085 (attached), it looks to me like the LM1085 only needs about 1.5V difference between Vin and Vout, and even @1.5V there's should be at least a 200mV cushion at typical operating parameters.  But the stock config has an additional 2V of difference - which would otherwise suggest to me that there is huge cushion to prevent reg dropout,  but my past experience suggests that this isn't necessarily the case and that the reg can drop out even where Vin - Vout > 1.5V.

So my first question is: is some other part of the fil reg circuit dropping the additional 2V?  As best as I can tell, the first half of the fil reg circuit is identical to the TI "ripple rejection enhancement" model found at 8.2.9 of the datasheet, except for the use of 33uF caps where TI has 10uF caps.  But the last half of the reg circuit looks like its based on what I've learned is called a "Sziklai pair" -  close cousin to the "Darlington pair" but with reported thermal regulation, impedance and possible lower voltage drop benefits over the latter -- I dunno about any of this: trying to read about it made my head spin.  Related second question: What does the second half of the fil reg circuit do? / why is it there?

My next set of questions is about noise and ripple rejection.  When the regulator drops out, where does the resulting hum come from - is it power supply ripple being passed to the filament? or is it generated by the reg circuit itself?  If the former (passed power supply ripple), then my separate filament trafos with CLC filters that reduce ripple to a modeled (PSUD2) 8 mV pk-pk should help to keep things quiet if the reg drops out (for comparison, my PSUD model of the BP stock voltage doubler/rectifier shows about 2.25V of ripple being fed to the inputs of the reg board - all of which is eliminated by the reg circuit).  But if the reg circuit is the source of the dropout hum, then no amount of ripple rejection before the reg circuit will make a difference.

To minimize the incidence of dropout, I'm thinking of increasing Vin to 14V instead of 13.5, while keeping Vout at 10V.  I can't tell from the datasheet whether this decreases ripple rejection / increases noise. Does it?  And if it does, do you think some or all of the increased noise would be offset by the increased ripple rejection of my CLC filter? If my basic arithmetic and use of an online dB calculator is correct, then 2.25V pk-pk (stock) : 8 mV pk-pk (CLC) is 281:1, or about -24.5 dB.

I anticipate that increasing Vin by 0.5V will put more thermal stress on the regulator. I plan to deal with heat stress to the LM1085 via (a) replacing the stock mica spacers with "kerafol keratherm" insulators that are reported to be more heat conductive than mica and comparable to a combination of mica and thermal grease; (b) forced air cooling @ 400 cfm.  But this only takes care of the LM1085 (hopefully). Might other parts of the board - e.g., the transistors, need additional cooling if I bump up Vin?

Apologies for the numerous questions, but I really want to get this right.

cheers and many thanks in advance, Derek
« Last Edit: November 16, 2019, 10:49:46 AM by Deke609 »
Derek
______

Roon Intel NUC ->  Yggdrasil DAC -> BeePre (w/ BeeQuiet and EML 300B)  -> Kaiju (w/ DCFil and EML 300B) or Stereomour II (2A3 [EML Mesh] and 45 Conversion [EML 45B])  -> Audeze LCD4

Offline Paul Joppa

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Re: Adjusting 300B filament voltage
« Reply #44 on: November 16, 2019, 11:14:44 AM »
Congratulations! You are discovering the large amount of work involved in developing a detailed design! I'l offer a few comments,, but you'll still have to do the work.

There is some headroom on the dropout to allow for variations in powerline voltage, plus more to allow for ripple on the input line.

The second part of the BeePre regulator  is a broadband noise cancellation circuit. You should be able to estimate the voltage loss.

Power dissipation is easily calculated if you know the voltage and current in a component. Temperature is more challenging due to variation of the environment.

In my experience, you want to keep the junction temperature of silicon components below 100C for longevity, even though a specified maximum temperature is usually around 150C.
Paul Joppa