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preamp tubes in paralell

5/29/2000 3:36 AM
preamp tubes in paralell
I just finished a preamp that uses either a 12ax7 or a 6sl7. the sockets are wired in paralell. what would happen if I put them both in at the same time?  
5/29/2000 1:58 PM

This circuit sounds supiciously like the Super Single Ended amp from the Angela site, eh (?)...  
Can't see any harm in trying, just keep an assistant's hand on the power switch if it goes ballistic...  
You'd essentially be running two tubes in parallel, so the anode and cathode resistances would be off by a factor of two one way or the other... but that might be cool! You also might find that one tube dominates the other.  
Also, you'll be pulling another bit of amperage from the PT, so a little headroom in the iron would be nice.  
That's all I can think of, but I defer to the wiser among us...  
... Whit
5/29/2000 6:07 PM

you're right, it is the angela project. mine is only a preamp though. the PT is the one for a matchless hotbox so it should have plenty of amps for 2 tubes. Incedently, the 6sl7's are awesome, they sound so much better than a 12ax7 they are mellow, smooth, and fat. you cant get the level of distortion you can from a 12ax7 though. I have a sneaking suspition that 2 of these set up with a cathode follower would be the best preamp you could build. Josh
5/30/2000 2:46 AM
Re: preamp tubes in parallel - great!
Hey Josh, you beat me to the punch by a day or two. I just finished "finalizing" a schematic that I've been working on for quite some time - putting two preamp tubes in parallel, controlled by a balance pot that can select between the two preamp tubes or mix the signals. I'm planning on using a 12AX7 and 6SL7 (although I'm still open to suggestion) and last week, after looking at the site, added some "bright/deep" switches. I'm also considering using two 6V6 tubes in single-ended parallel configuration, similar to angela's schematic. I'll likely be posting several questions in the next few days or weeks. I'll be happy send you (or anyone) a pdf file (Adobe Acrobat) of the schematic I drew up if you're interested in sharing notes -- Dan
5/30/2000 5:00 AM

you know, an idea I had was to wire the amp up to have 2 6sl7's (3gain stages and a cathode folower, like a marshall) and then you could get octal to 9-pin adapters and wire them up right so you could also use 12ax7's. This to me seems like the best option, because you could mix and match witch tubes to use in each position. the single 6sl7 doesn't have a lot of gain, about like a 12at7. but 2 of them sould sound great.  
as always, the best ideas come AFTER you build the amp.  
5/30/2000 5:09 AM

"as always, the best ideas come AFTER you build the amp."
That's why is best never to build one. It never stops keeps going, and going, and goi  
best of luck  
5/30/2000 7:21 PM
Pre-amp tubes in parallel
I'm planning on building an amp that can switch between (or blend) signals from two different-sounding pre-amp tubes. I'm hoping to share notes with anyone who has tried this. The (preliminary) schematic I drew up is in pdf format if anyone cares to look it over and comment, and let me know if it will work. In the next few weeks I'll probably be posting lots more questions. -- Dan  

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