Hoffman Amplifiers Tube Amplifier Forum

Other Stuff => Solid State => Topic started by: kagliostro on March 03, 2015, 07:42:10 am

Title: How works the current limiter on this circuit ?
Post by: kagliostro on March 03, 2015, 07:42:10 am
I've this schematic where, with a VVR function, is implemented a SAG function

EDIT: Filter capacitor added after the bridge


(http://i.imgur.com/4uAgeG0.jpg)


as I've very poor knowledge on SS circuits, please, someone can explain me how acts the current limiter section of the circuit ?


Many Thanks


K
Title: Re: How works the current limiter on this circuit ?
Post by: MakerDP on March 03, 2015, 01:11:38 pm
Do you have any of Kevin O'Connor's "The Ultimate Tone" books? Can't remember which one this is in... Maybe 5? I'll look and see when I get home tonight. It might be in a volume I don't have though.
Title: Re: How works the current limiter on this circuit ?
Post by: kagliostro on March 03, 2015, 05:42:54 pm
I've those books, but didn't remember if there are explanation about the SAG function and in which book they are

I read a lot but my brain refuses to collaborate and seems more like a colander than a strongbox ( :embarrassed: )

K

Title: Re: How works the current limiter on this circuit ?
Post by: Willabe on March 03, 2015, 05:51:38 pm
TUT5, chapter 9, The Standard. It's used in that amp build. It's the old version, works fine.

TUT4 and TUT6 have the details in the Sag/Compression chapters.


                    Brad    :icon_biggrin: 
Title: Re: How works the current limiter on this circuit ?
Post by: MakerDP on March 03, 2015, 08:32:44 pm
Hey Willabe... I don't have 4 or 6. Which one do you think I should get, if I could only get one, that will give me the best idea of how to implement KOC's Power Scaling tech?

I do have vol. 5 and someday I will build a Standard. Is what is in that build sufficient for any application? I'd like to do a 50-ish watt fixed-bias build with Power Scaling (duo EL34/KT77/66) and was just thinking of just copying what's in the Standard schematic for it.
Title: Re: How works the current limiter on this circuit ?
Post by: PRR on March 03, 2015, 08:56:53 pm
.
Title: Re: How works the current limiter on this circuit ?
Post by: kagliostro on March 04, 2015, 05:28:38 pm
Thanks for the explanation PRR

on which I've understand the part relative to the 2N3904 base controlled by the differential of voltage due to the drop on the 15R resistor and managed by the 25k pot

then ... the facts are still a bit obfuscated to me

the voltage on the 2N3904 base turns on the transistor and till here I understand

but when the 2N3904 is in conduction ..............  :dontknow:


---


Thanks Brad

Quote
It's the old version

I don't have TUT 6, is there the new version ?

Franco



Title: Re: How works the current limiter on this circuit ?
Post by: MakerDP on March 04, 2015, 05:55:44 pm
Yes Vol 6 has the new power scaling version...

http://www.londonpower.com/books/tut6cont.html (http://www.londonpower.com/books/tut6cont.html)

Sadly, I don't have that one either.
Title: Re: How works the current limiter on this circuit ?
Post by: PRR on March 04, 2015, 10:36:22 pm
> when the 2N3904 is in conduction ..............

The MOSFET conducts when its Gate is positive. Turns-off when its gate is negative.

With light load, the Gate "follows" the Tensione Anodica potentiometer wiper. 100% to 3% of the raw voltage.

When load is large enough to turn-on the 2N3904, it pulls current in the 10K resistor. Pulls the Gate down, more negative. MOSFET turns off.

In actual operation, the MOSFET is usually partly-on. Conducting just enough to pass the voltage set by Tensione Anodica or the current set by %SAG.
______________

I just noticed a possible error. There is no large capacitor at the rectifier output. All of the circuit over to the right-most BYT13 rectifier runs on pulsating DC. That may be what they intended. It seems to me there would be a lot of 100Hz ripple. And this would interact with the %SAG action. However it "will" work the way it is drawn.
Title: Re: How works the current limiter on this circuit ?
Post by: Willabe on March 05, 2015, 12:47:37 am
Quote from: MakerDP on March 03, 2015, 08:32:44 pm
Hey Willabe... I don't have 4 or 6. Which one do you think I should get, if I could only get one, that will give me the best idea of how to implement KOC's Power Scaling tech?

I just buy his PS kit with a PCB board.

TUT 4 and 6 go into deep analysis of the circuit, but it's way over my head.

Quote from: MakerDP on March 03, 2015, 08:32:44 pm
I do have vol. 5 and someday I will build a Standard. Is what is in that build sufficient for any application? I'd like to do a 50-ish watt fixed-bias build with Power Scaling (duo EL34/KT77/66) and was just thinking of just copying what's in the Standard schematic for it.

Pretty much but it depends on how big the amp is and it's B+ voltage.

The new PS is refined and has improvements over the old style. Like less voltage stress on the PS mosfet and it's pot.


                        Brad     :icon_biggrin:   
Title: Re: How works the current limiter on this circuit ?
Post by: kagliostro on March 05, 2015, 02:54:00 pm
Many Thanks for the explanation PRR

Quote
EDIT: I forgot to say that a filter cap is present on the circuit, after the bridge, but not shown on the schematic  :embarrassed:


(http://i.imgur.com/4uAgeG0.jpg)

@ MakerDP & Brad

I've not decided 100%, but may be I'll decide to get the TUT volume 6

Grazie

Franco