6SJ7, 6SL7, or 6SQ7 for input in Masco MA-17 to 5C5 project?

[Matt D]

.....so I got my GA-20/40ish amp sounding pretty good and now I'm moving on to a new project.

This time to start with I have a Masco MA-17 chassis with transformers and a choke. The original tube compliment was a 7C7 input, 7F7 PI, 2 6L6's and a 5y3. The amp is already gutted of everything but the transformers and tube sockets. The chassis is pretty small so this time I need to be much more careful about my layout.

What I'd like to do is make the simplest possible 5C5 type amp to produce a nice warm, mostly-clean-but-fuzzy-around-the-edges sound for my 1953 Fender triple 8 custom steel guitar. Something like the steel sound on a Hank Williams record.

I'm thinking about using a 5v4 rectifier, 5881's, and a 6SL7 PI.

Since I have a serious lack of real estate in the chassis I want to make this a single input amp with a volume and tone control. I could use a 6SL7 similar to the 6sc7 in the 5c5, but I'd be wasting one half of the dual triode. Also, I don't have very many of these and they are getting harder to come by on the cheap.

I have a ton of 6sq7's. I could just use the high mu triode and ignore the diodes in these.

Alternately I could use a 6sj7, of which I also have quite a few lying around. I worry that the pentode would be too gainy for the warm but clean (not crunchy) sound I'm looking for.

I also have 6sn7's and 6sc7 metal cans I could try.

Also, should I stick with grid-leak or use cathode biasing in the input stage? Both the masco and 5c5 use the grid-leak. Though I'm not really planning to use anything other than a volume and perhaps a delay pedal though this amp, it might be nice to use the tube screamer occasionally.

What do you think?

More info about the masco including transformer specs here:

http://blikethetubes.blogspot.com/

Thanks

[Phil_S]

There's every reason to use the 6SQ7, cheap and about the same as half of a 12AX7 or 6EU7. Internal plate resistance is high. It make the tube a great candidate for a tremolo oscillator tube.

The 6SJ7 input won't sound like the 5C5.

AFA grid leak vs cathode bias in the input, I think that's a matter of taste. Maybe when you build it, you will plan ahead some to allow for one or the other or for an easy mod to be done. If you want the 5C5, follow the schematic and use the grid leak.

[ampgeek]

I am big fan of the 6SL7 tone in the preamps of Fender circuits. Big, fat, warm and round. Even fatter/warmer when paralled with another 6SL7. Better with stomp boxes than 12AX7s IMHO. Probably due to a bit lower gain.

Consider a parallel 6SL7 in V1. Single input to both grids, separate plate load resistors and separately biased cathodes. Set one side up as normal and one side as bright. Two separate volume controls so you can blend in a little of each. Three knobs as currently configured for the Masco chassis.

Later versions of the 5C5 used 12AX7s in the PI. I have played with 6SL7s in the PI of 5F6As with 6SL7s in V1 and V2 and, truth be told, can't say that I heard/felt a huge difference. So.....I would probably stick with the noval in the PI slot if you are going for a 5C5'ish build.

Cheers,
Dave O.

[Phil_S]

The cheap tube, half of a 6SL7 is the 6AQ7. Get the 6AQ7-GT. You can find these cheap on eBay. There are people who sell them for more than you should pay. Hold your wallet close. You won't be disappointed.

Here's an example, buy several to spread out the shipping.
http://cgi.ebay.com/ONE-NEW-6AQ7GT-6AQ7 ... 3cace3aa27
Same seller, "free" shipping:
http://cgi.ebay.com/ONE-6AQ7GT-6AQ7-GT- ... 3cb0c5a9f2

Perfect for when you only need one triode, and well under 50% of the cost of a 6SL7.

[labb]

Take a look at the old Fender 5B3. Change the 6SC7's to 6SL7's.