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Svetlana 6BM8 SE Amp Schematic


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11/26/1997 7:49 AM
Bill Harbour
Svetlana 6BM8 SE Amp Schematic
On the site http://svetlana.com/appnoteNO.10.html is a schematic (figure 2) for a single tube single ended amp (1.5 watts or so).  
 
I think this would be a great starter project for me to learn about building tube amps.  
 
The schematic shows anywhere from +150 to +450 volts supply. What would be best for a guitar amp application?  
 
Also...the schematic shows not tone or volume controls. Where should they be included and what values for the pots?  
 
The schematic also mentions that the filaments could be run off of DC. Is that best for low hum and what transformer should I use to do this?  
 
What power transformer would be best?  
 
Thanks for the help all!!!
 
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11/26/1997 9:55 AM
Bruce

Bill,  
Pop over to the schematics section of this site and look up the Champ schem.  
It is a super easy weekend amp project.  
It will run anywhere from 3-5 watts output and be suprisingly loud in a good quality speaker cab with a 10" to 12" +93dB/meter/watt speaker.  
If you need some help with parts, get with me via E-mail {my call at aol.com).If you have packet radio it is KB0TJ@W0GVT.  
I have a real good supply of great low power amp stuff in my junk boxes at the shop. Well, they are hardly junk, but being a Ham, you know what I mean.  
 
Bruce
 
11/26/1997 12:22 PM
Bill Harbour

I do know what you're talking about...I'm KD4PWB and I'm the same way. The reason I picked this is because it only uses one tube and I'd use fewer parts...but if I build for one tube I can probably build for more with a little more effort.  
 
I can round up all the caps and resistors (and the tubes eventually) but what I'm usually short on (including toroidal kind for ham projects) is transformers.  
 
I'd like to graduate to something larger that I can use on gigs (I'll build it like a tank).  
 
I appreciate your offer of help and I will drop you a line by email.  
 
Thanks!!  
 
73 OM!
 
11/26/1997 10:13 AM
John Martin

I am familiar with that circuit. I bought a Hammond power transformer with a HT of 250-0-250v for my project. This should end up giving you over 300 volts on the plate of the 6BM8 pentode section using solid state rectification. Keep in mind that the Svetlana schematic is intended to be as general purpose as possible. You can add a volume control right up front that will work ok. If you wish to go for a tone control section, another stage may be needed to overcome the signal loss. It might be interesting to use the EF86 small signal pentode in front of the tone stack for that. You can always address the hum problem, if any, after the amp is working. As I remember those filaments were biased in that example anyway. My own project remains unfinished because I work on other people's amps six days a week. If you are interested in following this up, send e-mail.  
 
JM
 
11/26/1997 12:25 PM
Bill Harbour

I sure will drop you a line. I'm a cookbook builder so I know little about figuring where tone circuits should go.  
 
I appreciate your help!!
 

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