ampage
Tube Amps / Music Electronics
For current discussions, please visit Music Electronics Forum. The sunn still shines online!

ampage archive

Vintage threads from the first ten years

Search for:  Mode:  

Anyone with Power Scaling Experience?


 :
8/15/2004 8:23 AM
Dave B.
Anyone with Power Scaling Experience?
Hi,  
 
I've been reading TUT4 and am contemplating adding power scaling to a new amp build and was wondering if anyone could share some insight as to how to impliment this feature.  
 
I remember reading some threads regarding this topic but can't remember...was it, power scale the the B+ for the power tubes, or power scale the B+ for the entire amp? I can't remember, but I know there are a few out there that have done some experimentation. I'd really like to hear what results you found to be most satisfying.  
 
Thank You in Advance,  
 
DB
 
8/15/2004 11:58 AM
Cole Davis

Is TUT4 out already? I thought it wasn't going to be released until the Fall.  
 
Anyway, check out this site:  
 
http://bruceclement.com/music/psk.htm
 
8/15/2004 6:27 PM
Yannick Dupont
Hi Bob,  
 
I Think you're talking about TUT5?  
 
I've been designing an amp with Power Scaling. All the ideas were taken from TUT2. As for witch part of the amp you want to scale, scale the whole B+, that is:  
- VA (Anode)  
- VS (screens)  
- Vb (Bias: should be tracking VS)  
- VD (Driver, or the Phase Splitter B+ if you prefer)  
- VP (Preamp B+)  
 
As for the preamp, scale it if it's part of the same unit, other wise, just having an "INPUT" pot in the power amp unit will do the trick (you wont have to touch any knob in the preamp).  
 
You also want to consider intalling a Post-PI Master Volume when having PScale control.  
 
I think there should be an example of the London Power Standard preamp with PScale in TUT5???  
http://www.londonpower.com/tut5.htm  
 
YD
 
8/15/2004 8:50 PM
Dave B.

You're right, TUT5 is the one I have, it does have the London Standard amp with power scaling in it. I just want to use the power scaling.  
 
Thanks for that page about Power Scaling. Sounds like you really need to have some kind of master volume before the PI do do it right.  
 
DB
 
8/18/2004 2:57 PM
CraigR

Dave  
 
I have built Power Scaling into several amps. I really like it.  
 
Based on my experience, I disagree with Yannick about the "scale the whole amp" approach. If you scale the output tubes only (V+, screens and bias) and use a master, you will get the best results. That is subjective I know, but an opinion based on having done it both ways. I think the Bruce Clement article on the website noted in an earlier post came to the same conclusion.  
 
I have used several different versions of master volumes and have fixed on a pre-PI as the one I like the most. The Post-PI ones affect the NFB loop too much for my taste. The "Ultimate Master Volume" in the 800 section of TUT3 works really well, and is my favourite for when the master directly preceeds the PI.  
 
I am just starting to build the Standard Amp as outlined in the Standard chapter of TUT5, but with three modifications;  
 
- use an anode mixer to isolate the two preamp channels (see TUT)  
- add a "both channels on" feature, per TUT  
- use the concertina splitter and power amp from the Doppelsonde chapter in TUT5 so I can mix in different sets of power tubes with volume controls.  
 
These additions require an extra tube, but that is OK.  
 
Good luck,  
 
Craig
 
8/18/2004 4:18 PM
jaysg
Q's: Craig
quote:
"If you scale the output tubes only (V+, screens and bias) and use a master, you will get the best results.[/QUOTE]Where's the PI in this scheme - scaled or fixed?[QUOTE]I am just starting to build the Standard Amp as outlined in the Standard chapter of TUT5"
Since you have this and you've obviously bought at least one kit from Kevin: is there enough information in TUT5 to do it up right?  
 
I had been planning on waiting for TUT4 until I heard there was Power Scaling info in TUT5.
 
8/18/2004 11:12 PM
CraigR

>>Where's the PI in this scheme - scaled or fixed?  
 
Fixed. That way you actually have the option of scaling the output tubes only in order to increase compression (by maintaining the amplitude of the signal it gets fed) or decreasing the input signal in proportion to maintain the tone, but at a lower SPL. The latter is where the master comes in.  
 
>>Since you have this and you've obviously bought at least one kit from Kevin: is there enough information in TUT5 to do it up right?  
 
Yup. I have to hand it to Kevin, he didn't play "silly buggers" in TUT5. The circuit is exactly the same as in my London Power Session amp. I actually didn't buy the kit, I got the design from reverse-engineering that amp. I modded my first amp well before Kevin came out with the kits, and just kept on doing it. Since I only do it for my own amps, Kevin has been cool with that.  
 
There is a schematic and layout for both Power Scaling and his Sag control in the Standard amp chapter of TUT5.  
 
I have used several layouts of my own in the amps I have modded for Power Scaling, since they were all on different platforms. I have to say that I really like the suggested layout that Kevin uses in TUT5. It is very modular, and makes good use of space.  
 
If you build amps from scratch, TUT5 is a great book to own. The Power Scaling and Sag circuits in there are worth the price of the book on their own.  
 
Cheers,  
 
Craig
 

  Page 1 of 5 Next> Last Page>>