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Baby Bassman?


 
7/16/1999 5:32 PM
Doc
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Baby Bassman?
I've been thinking about building a circuit similar to the 5F6A bassman, but using 6V6GT finals rather than 6L6/5881s. The 6V6 is a baby brother to the 6L6, both beam tubes with some similar sonic characteristics. (A "Baby Marshall" version could be built using small pentodes, like EL84s.)  
 
 
 
That is, the preamp & cathode follower tone control setup of the bassman, but with a lower gain long tail inverter using a 12AU7 (or 6SN7) so as to not swamp the 6V6s with more grid signal voltage than they can sensibly handle. Using 6V6 instead of 6L6 would allow that power tube distortion we all love, but at a lower stage volume than with a 6L6-based 4-10 bassman cranked up. Sort of the same reasoning why you might choose a Deluxe Reverb over a Pro Reverb in certain situations.  
 
 
 
I figure that this might make a good harmonica amp, as well as guitar amp, using multiple 10" or maybe even 8" speakers. With multiple speakers the bass response should be adequate.  
 
 
 
Has anyone built one of these yet?
 
7/16/1999 6:50 PM
Michael
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Doc,  
 
 
 
I took a trashed Vibro Champ and made (almost) what you describe. Three differences... 1) I did use a 12AX7 for the driver, 2) I don't have the cathode follower, and 3) Solid-state rectifier. I converted what was the rectifier socket to be the 2nd power tube socket. I had a friend build a cabinet (from solid mahogany) big enough to use a single 10" speaker.  
 
 
 
This is my favorite amp. The tone is great (if I say so myself). The clean tone just sparkles, and as you drive it harder it responds beautifully. I even left the original markings on the control panel, so that the mid pot is labeled "speed" and the presence is labeled "intensity". (I thought it still "worked".)  
 
 
 
I used a Hammond 1608 output xfmr and the stock power xfmr. The voltages were a little high for 6V6s, so I did the zener trick on the power xfmr center tap.
 
7/18/1999 12:03 PM
well...
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I built a Fender Tweed Deluxe  
 
and added a gain stage(12AX7)  
 
and a master volume(before phase  
 
inverter).  
 
 
 
In fact, I hated 6V6. But I changed my mind  
 
as soon as I heard the sound of this modified  
 
Fender Tweed Deluxe.  
 
 
 
But you must give attention to the overflowing  
 
gain. There is so much gain. Between 2nd and 3rd  
 
stage, add a 500k Variable Resistor (one is  
 
to ground)  
 
 
 
I am going to reset up plate voltage of 12AX7.  
 
 
 
PS@REMEMBER! IT IS NOT FOR CLEAN SOUND,BUT  
 
FOR BOOSTED SOUND. CLEAN SOUND OF THIS MO  
 
DIFIED AMP IS SO SMALL.
 
7/16/1999 9:03 PM
moocow
This sounds like my first amp project. I started with a Heath EA-3 w/EL84 output tubes (cathode biased). It uses a VOX preamp/cathode follower/tone control with a Bassman phase splitter and presence control. So it is more of a VOX/Bassman than a baby Bassman. The amp had EL-84s to begin with, some VOX influence was unavoidable.  
 
 
 
Just for fun, I made no attempt to limit the amount of signal to the output tubes. There's no lack of gain in this amp. I haven't noticed any problems from overdriving the EL84s, and they are more sensitive than 6V6s.  
 
 
 
Like Michael, this is my favorite amp, but it isn't loud enough for me to gig with. It now lives the life of a studio amp, driving a 12" Oxford.
 
7/16/1999 9:13 PM
SpeedRacer
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I built a baby VOX like this.. really the Marshall pre-amp, Bassman & AC30TB are so close I almost don't distinguish between them anymore! :-) It's a VOX valued pre-amp with a 15W output stage built in an old Gibson GA20RVT cabinet. I used an old HK PT from a stereo integrated amp so I have the essential EZ81 tube recto-mojo.. I run 1x12 with it and it's a great recording amp. I also did a version initially with a basic BF pre-amp linked to an AC30PI. that worked pretty well too. FWIW I used a Dixie "Marshall" turrret board to build the amp.  
 
I think the 6V6 Bassman is a great idea.. I should try 6V6's in my 2x10 Pro.. I'll let you know how it works.. I think 2x10 would be good for the Bassman style as well if you really want to cut the volume.
 
7/16/1999 9:21 PM
Richie
I have a 6v6 type amp your wanting to build.  
 
You can use a 12AX7 in the PI/driver circut.. if you want it cleaner then just do as the CBS fender and change the circut.  
 
But I like the oldd style.. You could do tweaking tin the pream and make it cleaner too.Many possibilites with this amp.  
 
And they sound great.. I think Benjamin made a Baby plexi using the EL84 power tubes. But I like the 6V6 tubes alot. The seem to break up nice. Richie
 
7/16/1999 9:22 PM
Bill R
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Doc: I did a 6V6 PP amp very similar to what you're considering. Long tail PI (12AT7) with a fixed bias AB1 output stage. 410 plate volts on the pwr tubes. Fender Deluxe reverb pwr and output transformers. Classic 59 bassman preamp/tone stack, cathode follower, except; I doubled up the first stage preamp running both sides of a 5751 in parallel with a 1W 100k plate load and a 1K cathode resistor with a 5uf bypass. This was a very sweet non-reverb small amp. Cleaner than a tweed deluxe type amp, but with a toothy distortion as it was turned up. I ran it into a single 12" alinco speaker. I would like to build another but with a slightly heftier output transformer running two 10" spkrs. Sort of a mini tweed twin! Bill R.
 
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