Newcomb M-5

[Guitarzan]

The monkey was surfing schematics and found these:
http://www.oldfrets.com/Valco/Schematics.html
And there, he found this:
http://www.oldfrets.com/Valco/Schematics/1950SuproSpectator.jpg
And then he came up with a couple of questions. He says he noticed that the Spectator didn't seem to have a cathode bypass cap on the 6V6, (Or so he says...we're dealin' with a monkey here.) and if that's the case, what effect does that cap have anyway?
It also appears to be minus on cap on the (second stage?) of the 6SL7.
What's up with that?
The monkey thanks you for your input in advance. He's thinking of building another version of my Newcomb from scratch in a blank chassis box using some ClassicTone transformers he has laying around and is wondering what the differences are between what I have and what the Valco version is.

[sluckey]

Valco built a lot of cheap stuff. The missing caps were probably a cost cutter. Installing cathode bypass caps will increase the gain and also make the amp sound more bassy. The cheap speaker that was in that amp probably could not handle the extra bass response, so just drop the caps from the circuit too. No one will ever know. We'll market it at Monkey Wards or Western Auto for $49.99 regular price.

[Guitarzan]

Valco built a lot of cheap stuff. The missing caps were probably a cost cutter. Installing cathode bypass caps will increase the gain and also make the amp sound more bassy. The cheap speaker that was in that amp probably could not handle the extra bass response, so just drop the caps from the circuit too. No one will ever know. We'll market it at Monkey Wards or Western Auto for $49.99 regular price.

 
LOL 
Actually he went to Jane 1st. She told him to ask me and since he seems to notice stuff like that before I do, I figure he's already ahead of me on it.
So I put it to you guys. He wonders because he's heard that these Valcos are often prized by harp players. In addition to singing boogie-woogie, he's thinking of taking up the harp. Jane's already screaming "Shut up baby I'm trying to sing!!" every time he open's his mouth so I have no idea what he thinks he's gonna gain by trying to blow a harp..

[sluckey]

We need to hear it straight from the Monkey. What does the Monkey really think?

[Guitarzan]

Back at the point where I mentioned that I needed to extend the pot shafts I sorta figured someone would say "DUH!, that's an easy one" and clue me in.
I'm still betting you guys have all sorts of ways for doing that and I'm fairly certain I'm not the first to think of this one. Still, I think it was a pretty decent idea I had this morning so I thought I'd share it. It wasn't the rods that I was stumped on but the couplings...
It suddenly occurred to me that guitar tuner bushings might just do the trick. So I went to my boxes of miscellany and found some plastic ones and they're perfect!
Just trim off the flange and they're like that was what they were made for.
The shafts from old unwanted or bad pots can make the extension or any hunk of 1/4" OD dowel or metal rods completes the deal.
I don't know if I'd try and use this method if you had to extend 6" or something like that, but I only needed to go about 3/8" to make up for the thickness of the wood cabinet and for that, this was just right. The right price too.
  

[sluckey]

1/4" couplers are very common. I got these on eBay for cheap. AL rods from Lowes.

[DummyLoad]

if you don't need them as long as steve's, the PEC brand of pots are available with 2" shafts. NTE also sources PEC pots, however, digi-key is the best source. PEC pots are expensive usually $8.00 or more depending on supplier. NTE packaged PEC pots are higher than a cat's ass, but they're available.


http://www.nteinc.com/pot_web/pdf/KU_series.pdf


--pete

[Guitarzan]

I knew that long shaft pots were available but I elected to go with what I had on hand. The knobs that the amp came with had the sort of hubs that kind of stick out past the skirt, if you can picture what I mean. So the short shafts weren't a problem for the original parts, but the hubs were mismatched, cracked and loose. I just figured on getting a couple of knobs like the ones it came with but then I was surprised to find out that they're not as common as I assumed they were. If I'd realized all of that before I soldered it all together I would have ordered a couple of pots with long shafts. Heck, I had all sorts of time. I fiddled around with that thing for days before I got to the pots. So, live and learn right? If I ever run into this situation again I will order the correct pots right off the bat.
Another thing I didn't do was to try the hardware store. I suppose one could find some thin walled, rigid 1/4" ID tubing in brass, aluminum, or any number of materials. I just don't get out much anymore and being on my feet for an extended period of time is literally a pain in the piriformis. So browsing a big box type of hardware store is pretty much out. Maybe a hobby shop. I can't imagine a piece of tubing being more than a few bucks and if you had a foot of the stuff you'd be set for at least a dozen extensions. Probably more.
I did try searching eBay for those couplings but everything I found looked like it way too thick.
Funny how the things that you figure will be cheap and simple turn out to be the ones that are the hardest to solve solve sometimes. The tuner bushings worked great in a pinch and someone working on a guitar amp might be likely to have those kind of odd parts sailing around like I did. So I thought I'd toss it out there in case anyone found themselves stuck.

[PRR]

> guitar tuner bushings might just do the trick

Sweet!

My go-to was always 1/4" rubber fuel-line. Pretty snug fit on traditional pot shafts. True, it will slip if you jam the knob past 10. But you just turn the other way to zero, and it's cool until you force it again.

I suppose if you forced it a lot, you could use hose-clamps. But that's more money and trouble.

Car-parts store. No walking-around (know what you mean about big concrete box-stores), you just say "a foot of 1/4" fuel line" and the counterperson cuts it for you. You hardly have time to pick up some fuzzy dice and some fine sandpaper.

The rubber may be useful in some settings. Steve's chassis may be an old radio, chassis deep inside a decorative wood cabinet. Old wood warps and twists. The holes in the wood could get out of line with the pots. With rubber coupling you could bush the shaft in the wood, then run a 2 degree flex in the coupling to the pot.

Much more elaborate couplings used to be common. Flex joints. U-joints. Some radio chassis have to put the tuning-cap in catty-corner to get the leads short, and U-joint the shaft to the front. There were even cables (like speedometer cables) where you have the knobs on the dash and the radio under the seat or under the floor. A lot of that stuff has vanished in this day of digital everything.

[Guitarzan]

WOW! Hooda thunk? Spedo cables! I suppose some creative engineering had to be employed in the radio-under-the-seat days.
Fuel line sounds perfect. Friction fit like push on knobs but less likely to crack.

[Guitarzan]

does anyone recognize this?

[sluckey]

I recognize the file names.   

[Willabe]

That's the amp you just rebuilt?


            Brad   

[Guitarzan]

No it's not the Newcomb. I have my eye on this as a possible for the suitcase amp. It's all octal, and the right size. 10 X 5 X 3. The tubes are 1-ea 6SN7, 6SJ7, 7Y4, and unkown.
I'll have to drill new holes for pots, pilot, & input(s) on one long side as the pot-on-the-end config won't do for this project. But that's not too bad. At least I don't have to drill everything as in a new blank box. The seller dosn't know what it is and I was hoping maybe someone here with vastly more experience than I might recognize it. If someone did happen to ID it for me, I could start hunting a schemo for it & start trying to figure out how to proceed should I end up with it.

[Guitarzan]

I was just wondering if it would be safe to sub a 6SN7 for the 6SL7 in the Newcomb just for the sake of experimentation. Also, are there any other tubes that can be subbed for the 6SL7?
I'm curious since there are so many 12AX7-types that can safely be swapped for an actual 12AX7 and wondered if the 6SL7 has a similar set up. Also, are there any other power tubes that can safely be swapped for the 6V6? I just wanted to experiment a bit but not if I have to go under the hood to do it.

[P Batty]

Here's a thread on 6sl7 vs 6sn7: http://alt.guitar.amps.narkive.com/cIdXB4fd/6sl7-6sn7-vs-5691-in-a-49-princeton

I've had good luck with 5881 instead of 6V6 in a BF Deluxe Reverb (with bias vari tremolo), you'll have to adjust your bias of course.

Is your PT beefy enough?

[Guitarzan]

I'm not sure about the PT. It's physically very small. Smaller than, oh, say a champ tranny but then it doesn't have the 5v windings. Minimal markings and what's there appears to be an oem number which matches part  number on the (original) schematic. When I was still shooting trouble on the mods I did to it, I checked voltages and cam up with the following:
6SL7
Pin 2 = 162
Pin 3 = 1.4
Pin 5 = 159
Pin 6 = 1.5
6V6
Pin 3 = 319
Pin 4 = 267
Pin 8 = 11.7
if that helps any.
The PT seems to run cool tho. Does a 6SN7 make the PT work harder than a 6SL7 does?

[P Batty]

6SN7 has twice the heater draw of the 6SL7, so that would be a definite yes. Give it a try, but watch your PT temps.