5C2 question

[armillary]

I'm building a 5C2 Princeton from the Fender schematic. There's no layout page for the 5C2, so I'm left to figure out a few details, and looking for help.

The RCA tube manual shows Pin 1 of the 6SC7 as shell, so I assume that grounding it is correct. (I assume this because the Champ 5C1 layout shows pin 1 of the 6SJ7 grounded, and it is also shell.)

But the RCA tube manual also lists the Direct Interelectrode Capacitances for the 6SC7, with a note that says "with shell connected to cathode." My reading suggests that keeping interelectrode capacitances low is a good thing.

So my question is, ground pin 1, or connect it to pin 6?

Thanks in advance for your help.

[pops]

Check here

http://www.webphix.com/schematic%20heav ... _schem.pdf

[armillary]

Thanks. That's the schematic. The layout sheet for the 5C2 is what I can't seem to find.

[Phil_S]

The 5C2 probably has less than 20 components (excluding tubes, sockets, and transformers). If you are relatively new to this, I can understand wanting to have a layout diagram. The simple truth is that with so few parts, layout is not going to be that critical. There is a layout attached to the 5D2 (uses 12AX7, not 6SC7) which should give you a decent starting point and should be relatively easy to adapt. You might also look at the 5?1 (Champ series) for hints as well.

I'm just an amateur builder. I think I'd ground the shield on the 6SC7. This is a simple and relatively low gain amp, which means it should be fairly forgiving. I'd be concerned that connecting it to the cathode might introduce something new/unintended/unwanted.

Good luck with your project.

[armillary]

Thanks Phil, I take your point. I guess the designers felt it was more important to ground the shell (create a Faraday cage) to minimize external electrical fields than mess with interelectrode capacitance. Maybe that's more RF anyway.

My layout is point to point with a ground buss bar, so I don't need the Fender layout for that. But I like the layouts for seeing the voltages, and the wiring tricks that aren't obvious in the schematic. I agree it's a simple layout. I'm looking forward to some resistors arriving so I can finish it up.

[M Fowler]

Well there is the Weber 5c1 layout.

[armillary]

The resistors arrived in the mail yesterday, so I finished up the 5C2. I grounded pin 1 of the 6SC7 preamp tube, following the 5C1 schematic. The 5C2 worked great on first try. It's got nearly the tone of a 5C3 with the volume of a 5C1. I used the 4/8 ohm Champ-style OT I got from Triode, USA, it's a bargain. I've been playing it through a 15" Jensen 8 ohm alnico speaker, but will try it with a 4 ohm 10" next.

For anyone who has a 5C1 clone that they like but don't love, it's an easy mod to make it a 5C2, and much more fun to play.

[rp]

I love the 6SJ7 pentode in the 5C1. I also prefer the 5C1s lack of a tone pot. IME with low power amps no tone stack is way better, not that a simple pot dumping treble to ground is much of a tone stack, but still. If I ever build an other 5C1 it may not even have a volume pot, just to piss people off.

The OT appears this: http://store.triodestore.com/tfchxfwi48oh.html you have no idea how bad (muddy) that OT is till you junk it. Maybe their 15W upgrade option is better, the Allen Champ is much better and Fendery. The Edcor is excellent but not fendery (more clangy like a tiny Hiwatt).

[armillary]

Thanks rp. Do you have an opinion on the Hammond 1750C OT? That's what I used in my 5C1. The 5C2 has a better bass, fuller sound and more overdrive tone than the 5C1, especially in the high E and B strings. But that may be due to the two stages of gain in the 6SC7 versus the single stage in the pentode. I agree that these SE 6V6 amps sound best on 10.

[rp]

Thanks rp. Do you have an opinion on the Hammond 1750C OT? That's what I used in my 5C1. The 5C2 has a better bass, fuller sound and more overdrive tone than the 5C1, especially in the high E and B strings. But that may be due to the two stages of gain in the 6SC7 versus the single stage in the pentode. I agree that these SE 6V6 amps sound best on 10.

No idea, never tried the Hammond guitar line disliked their 1600 series for guitar but even that was a limited experience. I found out the 1700 line has some wound w/ paper so Hammond appears to have made the extra effort here, though the 1750C is bobbin wound. I'll point out it only has a 4 ohm tap, they make a 1760C w/ 4/8/16, I really like having at least an 8 ohm tap for versatility in Champs, they sound pretty smoking through the right 12". If I could only have one tap I'd choose 8R. The Allen has 4/8 BTW. The 15W MC has 4/8/16, Edcor GXSE10-8-5K just 8R. For kicks you should try the Edcor one day, just for the cool different but good Champ sound.

The extra gain stage of the 5C2 appealed to me too, maybe it'll be my next little amp. Do you find you need the tone control or never used it at all?

[rp]

BTW with octals I'd always ground the shell, never know if you use a metal tube, mis-wire or something bad weird might happen and you'd have HT on the shell - yikes.

[armillary]

So far I've set the tone to 7 and controlled it from my guitar. Check out my guitar's new tone caps. I don't remember what I re-capped years ago, but these sat in a baggie of junk caps until figured out what they were a few months ago. They measure .030 uf but sound good with the guitar tone on 3.

The 5C2 tone control is pretty crude, but it's almost identical to the 5C3 Deluxe tone control. It might be electrically identical, but it's wired a little different in the schematics.

Finally, I have to ask bout your meme photo. Could it be Ed Norton in his Captain Video space helmet?

[rp]

Finally, I have to ask bout your meme photo. Could it be Ed Norton in his Captain Video space helmet?

Good place for bumbles, but avoid in amps as the pretty much all leak compared to later greenies, blues, reds, blacks, and other bennies and goofballs we like.

Official space helmet on, Captain Video!

[armillary]

You can see in the photo that the chassis I'm using has some empty octal sockets. The PT is a 340-0-340. I doubt the PT or the 6X5 recitfier has the capacity to handle a pair of 6V6 in push-pull, so it will never be a 5C3 clone, but it's happy to be a 5C1 or a 5C2 (it's been one and now it's the other).

So the next thing is for it to be both. Here's a rough schematic for your consideration. It's a Princeton with two channels. One is the standard 6SC7, the other is the 6SJ7 from the 5C1 Champ. The volume/tone stack is directly from a 5C3 (which also has 2 channels). You could call it a Champston, although I won't be offended if you call it a Chump.

I'm going to work on it this weekend. It will be easy to reverse if it doesn't work out. Comments appreciated.

[rp]

maybe also try the 6SJ7 cathode biased to compare the the dual triode pentode thing? which tube you like best? but don't forgo the grid bias if you never tried it, it's strawberry rather than vanilla or chocolate.