Bassman 5b6

[M Fowler]

Smoked glass so can't see innards and glass is marked Haltron Made In England so anyone's guess repackaged EU tube packed in Haltron tube box.

I can post a picture if anyone wants me to.

Mark

[Blackburn]

I've got the same 6sc7 and do think they are less prone to microphony than metal ones, those of which are RCAs in my octal deluxe build. The 6sl7 is a Raytheon. Interesting though, my first 6sc7 from TubeDepot came DOA suffering from an apparent breach of its vacuum.

[M Fowler]

One of my tubes went bad very quickly.

[Blackburn]

Which one?

Before my rebuild, when this thing was ptp, I could just about dime it with it directly on the speaker cabinet and would only hear the microphony with the bassy notes and playing softly. With the new build I'm having a motorboating issue. Sounds great until I hit the strings hard then it's off to the water!

When I first realized the sensitivity of the 6sc7 I used to tap it gently with my pick and was amazed how it registered through the speaker.

[M Fowler]

A Haltron 6SC7GT dropped voltage for some reason so I had to use another NOS tube.

[Blackburn]

Good thing they're cheap! I've been thinking of rewiring for another 6sl7 for more gain, though I really do like the tone of the Haltron, if it's not acting up, which is more often than not.

[M Fowler]

I saw this info on another forum and thought it was helpful maybe

Preamp tube and PI change:

Octal tube comparison:
Commonly available octal dual triodes are 6SN7 (very much like a 12AU7) and 6SL7 (like a 5751 and probably closest octal sub for a 6SC7). One big difference between 6SN7 and 6SL7 vs 6SC7 is that the 6SC7 has a common cathode for both sections, making it less flexible.

The 6SN7 might not have enough gain and to low a plate resistance to drive the circuit, but it will clean up a bit due to much lower gain. The 6SL7, while about the same gain factor as the 6SC7, has a lower plate resistance, and just might be the ticket you are looking for. Since the cathodes are split on the 6SL7, you can just put a jumper on the cathode pins and that will work.

6SN7 and 6SL7 have the same pin out. 6SC7 has a different pin out, so you will need to rewire the grids and cathodes. Plates and heaters are the same.

[Blackburn]

So sad to report that my 5B6 is no more.

I rebuilt it with a board and all on a different chassis which led to differing locations of things, i.e. the preamp's vicinity to the OT. That, along with exponentially longer leads because of the board were the real demise of this thing. The amp was oscillating itself to death and even caused arcing at a point. It was so messy before as a rat's nest so I felt the need to rebuild in the style I have adapted to, nice and tidy with a board. Long story short, I finally got together with a friend who's experience vastly encompasses mine and we got it on his scope. My rebuild made the 6SC7 even more microphonic than it was. If I ever build one of these again, and I likely will, definitely PTP like the first time, just neater.

Good news is that after ripping stuff out I've got a good bit of an amp built and am building something else... PT specs are perfect and OT should be a good fit. Clips will be in line when it's done.

[rp]

This old circuit sure gives people a lot of trouble, strange. I'd like to give it shot when I can.

[Blackburn]

This old circuit sure gives people a lot of trouble, strange. I'd like to give it shot when I can.

You're right about that. It's funny though, when I had mine PTP, I could leave it just in the chassis and literally crank it sitting right on the cab I was using and things were fine. The bass notes would cause subtle ringing but all else was okay. Talking about this thing more gives me the urge to do it again in the new chassis PTP. Maybe a few other tweaks as well...

[rp]

The bass notes would cause subtle ringing but all else was okay.

Likely the 6SC7, try shock mounting it on grommets, pretty easy to do. Actually I doubt that helps much but what hell, worth trying. And test it reasonably away from the cab. Initially my 5c8 had me freaked but it has just having the test speaker right next to it. Those octals ain't novals - you heard it here first!

[Blackburn]

When we hooked up mine to the scope, simply talking in normal volume conversation voices would register on it... Then I clapped my hands while I was 5 or 6 feet away and man that was really something! I'll build one again soon enough, but next time I'm thinking two 6SL7s. They seem to be far less microphonic than the Cs.

[rp]

if you're using metals the glass are a little bit better.

[Blackburn]

I only used glass with my 5B6. I have metal 6SC7s in my octal Deluxe. Not too bad, not that great either. Nice cleans.

[M Fowler]

I read that Little Walter now is running two amps each with pair of KT120 tubes to get some clean headroom.