Another MoFo
#61 Re: Another MoFo
No, I meant make a 120ma CCS using the 317 or mosfet and then use that to provide the filament bias current.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
#62 Re: Another MoFo
You're right Phil. I had completely taken my eye off the 20mA at the 2P29L anode
That makes sense now, with the schematic with the filament bias resistor I just adjust the Andrew DHT supply so there's 2.2V across the filament and the rest takes care of itself.
Last edited by Ray P on Mon Dec 28, 2020 3:03 pm, edited 1 time in total.
Sorry, I couldn't resist!
- pre65
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#63 Re: Another MoFo
Well done Ray.
It took a while for filament bias to penetrate one of my two brain cells, and because my valve (on the 833a driver circuit) is transformer coupled I also need to use a cap with the filament resistor. Only found that out last night.
I'm watching with interest as my MoFo could benefit from a gain stage.
It took a while for filament bias to penetrate one of my two brain cells, and because my valve (on the 833a driver circuit) is transformer coupled I also need to use a cap with the filament resistor. Only found that out last night.
I'm watching with interest as my MoFo could benefit from a gain stage.
The only thing necessary for the triumph of evil is for good men to do nothing.
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
#64 Re: Another MoFo
Cheers Phil
I've just placed an order for the parts to build a MoFo to test the bandwidth limiting.
I've just placed an order for the parts to build a MoFo to test the bandwidth limiting.
Sorry, I couldn't resist!
#65 Re: Another MoFo
If a more powerful version of the MoFo is of interest, Andrea Ciuffoli's developments might be of interest;
http://audiodesignguide.com/Inpol/index1.html
He uses the 100mH Hammond 195T5 capable of handling 5A.
He includes a valve-based voltage gain stage and offers the files to get PCBs fabricated (or they're available to purchase from Jims Audio) - might be of interest to some here (Phil?).
Ray
http://audiodesignguide.com/Inpol/index1.html
He uses the 100mH Hammond 195T5 capable of handling 5A.
He includes a valve-based voltage gain stage and offers the files to get PCBs fabricated (or they're available to purchase from Jims Audio) - might be of interest to some here (Phil?).
Ray
Sorry, I couldn't resist!
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#66 Re: Another MoFo
This confused me. My understanding was that filament bias enabled the removal of the cap bypass on the filament resistor at the cost of a beefier and hotter cathode resistor as it was a much lower value. Especially applicable for a transformer loaded stage.pre65 wrote: ↑Mon Dec 28, 2020 12:19 pm Well done Ray.
It took a while for filament bias to penetrate one of my two brain cells, and because my valve (on the 833a driver circuit) is transformer coupled I also need to use a cap with the filament resistor. Only found that out last night.
I'm watching with interest as my MoFo could benefit from a gain stage.
- pre65
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#67 Re: Another MoFo
The "problem" with filament bias happens when the valve is transformer coupled.
I read this piece and it explains why.
https://vinylsavor.blogspot.com/search?q=filament+bias
It could, of course, mean I have totally misunderstood the article.
I read this piece and it explains why.
https://vinylsavor.blogspot.com/search?q=filament+bias
It could, of course, mean I have totally misunderstood the article.
The only thing necessary for the triumph of evil is for good men to do nothing.
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
#68 Re: Another MoFo
There is nothing magic about transformer coupling or for that matter choke loading and fill bias. It's just as the link says the cathode AC impedance is my multiplied by gain and is seen at the anode. So will form a LR filter. It's just a matter of the numbers.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
#69 Re: Another MoFo
I received all the parts for the test (bandwidth limited) MoFo build today so I'll aim to get it up and running soon, hopefully over the coming weekend.
Sorry, I couldn't resist!
- pre65
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#70 Re: Another MoFo
Looking forward to a picture, or two.
The only thing necessary for the triumph of evil is for good men to do nothing.
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
#71 Re: Another MoFo
DIY chores today so time a bit limited but I have managed to recycle a heatsink as the 'chassis' for my test MoFo build - just caught the last of the decent daylight.
Sorry, I couldn't resist!
- pre65
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#72 Re: Another MoFo
Is the "yellow thing" your inductor ? If so it's a tad smaller than the MOT (microwave oven transformer) like wot you sold me.
The only thing necessary for the triumph of evil is for good men to do nothing.
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
#73 Re: Another MoFo
Yep, but you don't seem to be paying attention Mr. Frogg! The aim is to build a bandwidth limited MoFo for a full-range driver, smaller inductor is part of rolling off the bottom-end at around 180Hz
Sorry, I couldn't resist!
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#74 Re: Another MoFo
Yes Ray, I was paying attention, but trying to inject a smattering of humour. I obviously failed miserably.
The only thing necessary for the triumph of evil is for good men to do nothing.
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
#75 Re: Another MoFo
Finally took delivery of the missing MoFo parts today so, hopefully, I'll get some music out of the test MoFo this weekend. If that works out I'll knock out cheap baffle for the full-range speaker unit and try to measure the FR (and have a listen).
Sorry, I couldn't resist!