50s Stancor - Anyone have any info on these amps?

[MCK]

Been looking at the 5E3, 5B3... Can't help but wish for something a little sexier... I have 2 slots for the preamp tubes. I'm wondering if I can do something like pulling the octal sockets out for the 6SL7s and putting in 2 x compactron tubes in these to give me a total of 6 triodes to play with... Thoughts?

Ref... 6C10 = 3 triodes similar to the 2 in 12AX7.

[Cliff Schecht]

6C10's weren't made for very long AFAIK and are quickly escalating in price and scarcity. I think we should save those for the Super Champs of the world (a VERY cool Fender design from the 80's).

I've for whatever reason never built a 5E3. Something about the fact that everybody builds on as their first tube amp seems to deter me. I admit this is a stupid reason to have not build one and I surely will someday but there are other amp designs that interest me more.

The 5B3/5C3 is to me a more interesting amp. There is some unique things about these amps. Grid-leaked inputs, no grid stoppers anywhere and an ancient form of a differential amplifier that was used before the LTP was general practice. I think they went with this setup partially because of the common-cathode connection inside of 6SC7. Had they had separate cathodes the 5B3/5C3 amps might have had a completely different circuit!

I like the 5B3 better now that I've built both (5B3 and 5C3) but one big change I made was to have one channel be cathode biased. You'll find the grid-leaked side sounds hella cool but there is virtually no headroom. With a cathode-biased channel I get a great clean side (biased for cleans in my case) and the grid leak side gets a nasty, dirty, raunchy distortion that doesn't sound like any other Fender I've plugged into.

I probably will build a 5E3 soon as well as a 6G3, both are relatively unique circuits to the Fender line. I also played a brown Princeton recently that was really fun (but dark with whatever speaker was stock) but probably won't build one soon. I also have my eye on a pretty clean real 5E3 Deluxe which has my name written all over it. The guy thinks it's worth $4000, I'd like to talk him down to about $1200-$1400..

[Cliff Schecht]

Also don't scoff at a BF type amp. You add a 10k or 25k pot instead of that 6800 Ohm resistor to ground in the tonestack and you have yourself a pretty versatile amp. Open up the negative feedback loop for another world of fun. Maybe not the highest gain, sexiest amp available but you have something that can take pedals extremely well. My new rig consists of a pedalboard with a wah, phaser, 3 or 4 OD/distortions and some chorus/delay into a Deluxe. Maybe I don't look super cool without a 4x12 behind me but I sure have been getting a lot of compliments on my tone lately .

[MCK]

Thanks for the input. I will try 5B3 then and see how it turns out. Wasn't putting BF sound down at all. I have a 67 SR at home which I love and cherish. Great tone and platform. I was just thinking I could do something more ambitious thats all but you are absolutely right. There are so many addons or mods that can be tried.

The schematics I am seeing call for 6SC7 though. I have on hand 6SL7s and would like to use them. I understand these are almost the same tubes with an internal connection difference. Did you build yours with 6SC7 or 6SL7?

Appreciate your help.

[Cliff Schecht]

You probably won't be doing too much modifying. The 5B3 is less troublesome simply because the lack of negative feedback prevents the bias shifting problem (whose fix is the Paul Ruby Zener mod) that the 5C3 suffers from. I think Mark Fowler and a few others have built the 5B3 successfully and I'd love to hear what others think about their builds. I don't want to sway you into an amp that you don't enjoy.

6SL7's are almost an order of magnitude cheaper. I use them in all of my octal builds. As I mentioned in another thread I pay $2-$3 for NOS or nearly so examples regularly at ham radio meets and such. The other nice thing about using these is you can sub in a 6SN7 to knock down the gain while still getting that great octal preamp flavor.

I need to start a thread for my Deluxe builds soon. Both turned out great and I haven't shared any of my builds in a while.

[MCK]

5B3 it is then... It will be nice. My chassis has a Bass & Treble pot marking so I'd like to squeeze in a Bass pot in there as well somehow. Also will incorporate Dana's VVR for cathode bias as I already bought it for this amp long time ago. Will try to put this all into schematics and revert

[MCK]

I like the 5B3 better now that I've built both (5B3 and 5C3) but one big change I made was to have one channel be cathode biased. You'll find the grid-leaked side sounds hella cool but there is virtually no headroom. With a cathode-biased channel I get a great clean side (biased for cleans in my case) and the grid leak side gets a nasty, dirty, raunchy distortion that doesn't sound like any other Fender I've plugged into.

Cliff, would you happen to have the schematics for your modified 5B3 running on 6SL7 with one channel cathode biased? Would love to see some shots of your layout as well if at all possible. Thanks so much!!!

[Cliff Schecht]

I feel like you're making me do homework! I come to this website to escape school/work!

JK (minus the escaping school/work part)

Here's a schematic I drew up real quick. Looks right at 2 in the morning but you might want to double check it for glaring errors. I'll list my voltages soon but your target for B+1 is 340-350V. I did a SS rectifier on this build out of necessity but I like tube rectifiers when I can fit 'em.

IN1 is the cathode biased input and IN2 is the grid leaked input. Channel 1 gets a lot cleaner because I left off the cathode bypass cap. You can put this on a switch if you want for added gain but I don't think the amp needs it. In2 gets enough gain to make most metalheads happy..

[MCK]

Thanks so much!!! Most appreciated. I will fill in the blanks using the original 5B3 drawing : http://www.blueguitar.org/new/schem/fender/5b3_sch.jpg

and modify the original layout : http://www.blueguitar.org/new/schem/fender/5b3_lay.jpg

and start a new thread with the more appropriate title. All creds go to you!

Thank you very much once again. Hope you get some good sleep before work or school hits you in the morning. All the best

[MCK]

Ok. I went through your schematics and applied your changes to the original 5B3 schematics just to learn. Here's the result (attached). I think I can use most of the original layout as well. Next I will work on that. Thanks for any guidance you might have.

[Cliff Schecht]

That's funny that you copied the part designators too. Those are what Eagle spit out automatically, not anything that I took the time to do. They mean nothing with respect to the Fender schematic.

I don't know if others would put on some sort of screen resistor but I think at these voltages (~350V B+) they aren't necessary. Plus (maybe IMO) part of the tweed sound comes from the lack of screen resistors, especially when pushed into heavy distortion.

Everything looks right to me in your drawing. I really just adjusted the values for modern standards. I had the choice between 2.2k/220k or 2.7k/270k for the cathode/plate resistors and I went with the latter option. In my 5C3 build I used the 270k plate resistors and that amp had way more than enough gain. I think the 220k resistors are a better choice, at least IME and for what I want from these tweed amps.

I'll try to take some pictures tonight before I finish up the headshells for this and the BF Deluxe.

[MCK]

Heheh. Where do you do your schematics? I will try to do a better one using an online service etc later. I need some part identifiers anyways so took on what you had. It works! I am going through the parts to create a BOM of sorts. This will be fun! Thanks for all your help.

[MCK]

Quick question if you don't mind... what should the voltage rating on the

C5 15nF
C6 470pF

be? 600V as well? Thanks

[MCK]

Here's the rough BOM I worked out from the schematics... Decided to use 1W resistors unless higher is called for. The original schematics list 10K 1W for the dropping resistors but I like to overdo things so I'll put in 2W or 3W etc. Just not sure about the voltage rating for C5 & C6.

Next will be to source all this along with a suitable generic eyelet board. Thanks for all your help.

Input Jacks
Speaker Jack[s]
3 x 20uF Multi-Section 450V or better Cap
clamp & insulation for above cap
C1, C2, C3,
C4, C8, C9 47nF - 600V
C5 15nF - ?V
C6 470pF - ?V
C7, C10 22uF - 25V
R1 1M 1W
R10, R11, R12 1M Alpha Audio Pots
R14 6.8K 1W
R16, R17 1.5K 1W
R18 250R 5W
R2, R3, R7, R9, R13, R15 220K 1W
R20, R21 10K 3W Resistor
R4, 19 2.2K 1W
R5 51K 1W
R6 5M 1W

[Cliff Schecht]

Change C5 to 0.01uF (10nF) instead of 0.015uF, that was just what I used because it's what I had on hand. Both this and the 470pF caps need to be rated at 400-600V (higher is fine but caps get massive in the 1000V-1600V ratings).

Also the cap on the cathode of the power stage (22uF) could stand to be raised to 50V for more margin. If you don't want to order both 25V and 50V 22uF caps then don't, just order the 50V ones. They're still very small.