Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Craftyjam on November 03, 2021, 02:20:19 am
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I know that this topic has been harped on in many different threads already, but I'm curious about a very specific situation I've encountered.
In one of my builds, I'm using an unisolated boost converter for the HT supply that uses FB from the secondary of the flyback transformer to the primary side without optoisolator.
For the heaters, I'm using a buck converter to drop 12v to 6.3.
Both SMPS's use the same 12v supply voltage and are referenced to the same ground.
How can I elevate the filament voltage without using another transformer to isolate it from the B+ ground?
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Can you post a schematic, not a layout drawing?
Really not clear by your description.
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....12v supply voltage and are referenced to the same ground.
How can I elevate the filament voltage without using another transformer to isolate it from the B+ ground?
By using isolated converters.
I know you don't want to hear this.
Do you have hum?
Or are you trying to protect cathode insulation? (Then maybe just one bottle? Maybe just one isolated 12V supply?)
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Or are you trying to protect cathode insulation? (Then maybe just one bottle? Maybe just one isolated 12V supply?)
Yeah, just need to protect the cathode insulation for one CF. If I were to use an isolated DC heater supply for that one tube, how would I make it elevated with respect to the B+? Or will the problem fix itself by both voltages having different ground references?
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The second, fully isolated, DC supply for the CFs can be connected to any decent source of +180V, or whatever.
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The second, fully isolated, DC supply for the CFs can be connected to any decent source of +180V, or whatever.
Thank you for your wisdom.
Just to be clear, how exactly would it be connected? Say for instance I have a fly-buck converter (with optoisolated FB) outputing the 6.3v dc on its secondary, would I connect the ground point to +180v and then connect the +6.3v dc to the filament (basically just treat +180v as the common connection for the filament and flybuck)?
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Why are you making this so complicated? :think1:
I think you would get more help/ideas if you would post a full schematic of the amp and what you want to do.
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I think you would get more help/ideas if you would post a full schematic of the amp and what you want to do.
Sorry, heres a block diagram of what I think I need to do. I should tap off some point of the HT with a resistive divider and connect it to the common connection on the isolated side of the 6.3v buck converter, and then wire it to the filaments.
(http://)
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No, not a block diagram, a schematic.
That block diagram is not clear at all for showing what you have and what you want to do.
You see it in your minds eye because you have the amp there and have thought about it a lot. We don't see it in our minds eye.
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That block diagram is not clear at all for showing what you have and what you want to do.
Alright, does this help? You can assume that the buck/boosts are black boxes that do what I say they do and are isolated (don't have the schematics for the modules, but I've load tested and checked for isolation). Does this scheme for applying the elevated voltage work? The point I chose on the B+ rail was arbrituary, I know that you can get a good reference from the cathode bias resistor of a power valve.
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Here's a link from Merlin's web site on heaters. It has info on elevating heaters.
http://www.valvewizard.co.uk/heater.html (http://www.valvewizard.co.uk/heater.html)
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That should work provided the 6.3V supply output remains floating (except for the elevated reference).
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That should work provided the 6.3V supply output remains floating (except for the elevated reference).
Thank you for the answer. I'm gonna try it out soon and let you all know the results.
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You can assume that the buck/boosts are black boxes that do what I say they do and are isolated (don't have the schematics for the modules, but I've load tested and checked for isolation).
Are the black boxes transformers?
Not enough to go on to assume much, can't tell what your PT is, black boxes, isolated. That's not clear.
Need to see grounding of PT, does it have a CT? Are you running PT's back to back? Do the other PT's have CT's? What's your rectifier set up for B+? What amp is this for? How much B+ and heater current do the PT's have? How much will the amp need?
Lots of missing information. :dontknow:
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Are the black boxes transformers?
Not enough to go on to assume much, can't tell what your PT is, black boxes, isolated. That's not clear.
Need to see grounding of PT, does it have a CT? Are you running PT's back to back? Do the other PT's have CT's? What's your rectifier set up for B+? What amp is this for? How much B+ and heater current do the PT's have? How much will the amp need?
Lots of missing information. :dontknow:
You don't need to know any of that stuff. All you need to know is that the B+ output (pos and neg) is isolated from the 6.3V output (pos and neg).
Think of it as a 300V battery in one box with positive and negative leads coming out. And another box with a 6V lantern battery with positive and negative leads coming out.
Both boxes are totally isolated from each other.
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You can assume that the buck/boosts are black boxes that do what I say they do and are isolated (don't have the schematics for the modules, but I've load tested and checked for isolation).
Are the black boxes transformers?
Not enough to go on to assume much, can't tell what your PT is, black boxes, isolated. That's not clear.
Need to see grounding of PT, does it have a CT? Are you running PT's back to back? Do the other PT's have CT's? What's your rectifier set up for B+? What amp is this for? How much B+ and heater current do the PT's have? How much will the amp need?
Lots of missing information. :dontknow:
The boost converter is in flyback configuration with optoisolated feedback, stepping 12vdc up to 350vdc, can supply 150mA. The heater supply is in flybuck configuration outputing 6.3vdc also completely isolated, can supply about 3A. Theres no power transformers or center tapping required. The amp I'm working on is my own design but the power output is cathode biased PP 6PS3's (biased at about 85% PD).
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Yes, I know how to elevate heaters and keep them isolated. It's what he's hooking it up to, we don't know.
He's being to vague. I think we do need a lot more info. Maybe it will work, or maybe he'll blow something up. :dontknow:
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The boost converter is in flyback configuration with optoisolated feedback, stepping 12vdc up to 350vdc, can supply 150mA. The heater supply is in flybuck configuration outputing 6.3vdc also completely isolated, can supply about 3A. Theres no power transformers or center tapping required.
I have no idea what your talking about, absolutely none. :think1: :laugh:
In all my years here and on other forums, and in books, I have never seen this before;
"boost converter is in flyback configuration with optoisolated feedback."
Are these switching power supplies? Where do you get the 12v that feeds the black boxes, a transformer?
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The boost converter is in flyback configuration with optoisolated feedback, stepping 12vdc up to 350vdc, can supply 150mA. The heater supply is in flybuck configuration outputing 6.3vdc also completely isolated, can supply about 3A. Theres no power transformers or center tapping required.
I have no idea what your talking about, absolutely none. :think1: :laugh:
In all my years here and on other forums, and in books, I have never seen this before;
"boost converter is in flyback configuration with optoisolated feedback."
Are these switching power supplies? Where do you get the 12v that feeds the black boxes, a transformer?
Here is a good video on the topic of flyback converters. I'm using a 12v 5A power supply like you would use for a laptop or LED strips.
https://www.youtube.com/watch?v=ycT-PItAzNk&ab_channel=GreatScott%21 (https://www.youtube.com/watch?v=ycT-PItAzNk&ab_channel=GreatScott%21)
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He says right at the end it's a "modern switch mode power supply."
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I take it your in a country where standard guitar amp transformers are hard to get and/or very expensive?
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I take it your in a country where standard guitar amp transformers are hard to get and/or very expensive?
I live in the U.S, but I am a student so PT's are pretty expensive for me. Especially since I want to build a lot of amps!
I'm also trying to make my builds as compact as possible, so PT's are out of the question.
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...I have no idea what your talking about, absolutely none...... , I have never seen this before;
"boost converter is in flyback configuration with optoisolated feedback." ...
You have been living in the tube age. Flyback conversion has been routine since 1980. Optoisolated means there is some chance it has galvanic isolation equal or superior to tube-age wound-iron.
Crafty may know what he is doing. Stuff could smoke. Your stuff sometimes smokes. Smoke is educational. Do it out in the driveway on a long cord, and run the YouToobe camera just in case it gets interesting.
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Hi Crafty,
Very Clever :icon_biggrin: Obviously you have given this some thought.
+1 with PRR and Sluckey re "TOTALLY ISOLATED/Floating Heaters"
You state "+350V @150mA" and "+6.3V @ 3A" maximums running off a 12V 5A computer type Power Supply.
Just beware as you hit the upper limits, as your total consumption will be:
Pmax=(350x0.15)+(6.3x3)=52.5+18.9=71.4W plus a little extra for losses (5% ??Switchmode).
This exceeds your Power Supply rating of 60W (12V x 5A) :laugh:
Keep us posted
Kind Regards
Mirek
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Hi Crafty,
Very Clever :icon_biggrin: Obviously you have given this some thought.
+1 with PRR and Sluckey re "TOTALLY ISOLATED/Floating Heaters"
You state "+350V @150mA" and "+6.3V @ 3A" maximums running off a 12V 5A computer type Power Supply.
Just beware as you hit the upper limits, as your total consumption will be:
Pmax=(350x0.15)+(6.3x3)=52.5+18.9=71.4W plus a little extra for losses (5% ??Switchmode).
This exceeds your Power Supply rating of 60W (12V x 5A) :laugh:
Keep us posted
Kind Regards
Mirek
Thank you for the warm welcome and warning, Mirek. :icon_biggrin:
As of right now, I'm running the 6PS3's at 80% PD so they are drawing about 100mA + screen current, so I'm just BARELY coming under the limits of my 12v 5A supply. Definitely gonna upgrade to a 12v 10A supply for these bigger builds! :worthy1:
Crafty may know what he is doing. Stuff could smoke. Your stuff sometimes smokes. Smoke is educational. Do it out in the driveway on a long cord, and run the YouToobe camera just in case it gets interesting.
I'll be sure to film the explosion for your viewing pleasure!
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Are these switching power supplies?
The answer is yes.
You have been living in the tube age. Flyback conversion has been routine since 1980. Optoisolated means there is some chance it has galvanic isolation equal or superior to tube-age wound-iron.
Yes, and I like it. :undecided:
I was trying to get an answer to what the black box modules are. You could have just told me it's an isolated switching power supply. :laugh:
Both of you are talking about the circuits refinements, instead of just saying it is a switching power supply, which was not clearing up anything, at least for me. :laugh:
So I did a quick search and it seems that "boost converter is in flyback configuration with optoisolated feedback" are refinements of a switching mode power supply.
For anyone interested;
https://www.monolithicpower.com/en/switching-power-supply (https://www.monolithicpower.com/en/switching-power-supply)
Stuff could smoke. Your stuff sometimes smokes.
Only when cooking, grilling and using the BBQ smoker. Electronics, nope, nothing so far, not even a resistor. But it could happen the next time, ya never know :icon_biggrin:
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I'm also trying to make my builds as compact as possible, so PT's are out of the question.
I hope they work out for you.
We have seen a number of compact builds have problems. It can be done but, shrinking the chassis size and jamming everything close together can be asking for trouble. And it can make an amp sound thin from parasitic capacitance's. :think1:
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....You could have just told me it's an isolated switching power supply.....
First post used the cryptic "SMPS". I didn't know you didn't know that. Sorry.
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Craftyjam,
I am following this with interest as I have also been interested in building a compact amp. I have access to a lot of free to me, surplus computer power supplies. Not sure if you have looked at the purpose built Nixie tube PSU's, but they may be an economical and clean way of accomplishing some of what you described as your end goal without all the headaches? I have seen some SMPS PSU's on ebay that provide HV and an adjustable filament tap. Of course that defeats the whole learning concept as a student. You may want to look at this thread. Your path has been trodden by others in the past and this may offer some valuable insight. https://www.diyaudio.com/forums/power-supplies/335839-powerful-smps-tube-ampifier.html
You might also study some of the micro tube preamps such as the Fender MTG, and the Effectrode Blackbird SR-71.
Only when cooking, grilling and using the BBQ smoker. Electronics, nope, nothing so far, not even a resistor. But it could happen the next time, ya never know :icon_biggrin:
My theory is that smoke is what gives everything flavor. I usually apply liberally whether cooking, grilling, or electronics. I also find it is more exciting that way. :l2:
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I designed and built my own flavor of power tube boards for the Pvy Classic 50. I used DC Heater Standoffs and it worked out great. The amp as it is now is very much silent with regards to AC heater hum. Also Im posting this to see if I can post in this thread as I have had trouble posting just in this part of the Forum. Maybe I can read it after I post it? LoL
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Welcome! :icon_biggrin:
Also Im posting this to see if I can post in this thread as I have had trouble posting just in this part of the Forum. Maybe I can read it after I post it? LoL
I see it. :icon_biggrin:
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This board I made for the Classic 50 Has 4 way bias, DC heater standoff, proper grid leak resistors and plugs in just like the original. I admit I did have to abandon my bias and make that off the board as real estate was an issue. Ok I can finally post a pic LOL. Did not mean to get off track here but it is partly about how well DC Heater Standoff can work and it is simple to do.
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The DC Stand off side components
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...Im posting this to see if I can post in this thread as I have had trouble posting ....
Yes, two of your threads are "stuck", look blank to other people (including moderators). We have to ask the Boss to use his tooth-extractor to get rid of them.
Are you just typing in the Compose Box? Or are you copy/pasting from another program, such as a word processor? The format codes in MS Word are known to confound forum postings.
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I think the issue is a corrupted set of schematic pictures I have. I posted successfully then added a 2nd pic and it all went bad again. So Sorry for that