Newcomb M-5

[Guitarzan]

OK so I might have exaggerated a bit in my frustration with cleaning up that socket but the really thin wire from that weird wafer thingy and the almost as thin hookup wire they used were stuck thru the lug, plus wrapped once. So when there were more than 1 in a lug is seemed like it was wrapped around it forever.
I gotta remember the flick-trick.

[John]

Lol... that's old school wiring technique, coming from (I believe) the military. The idea was that even if the solder joint broke completely, you at least had intermittent contact at the wire/component junction, and that would keep the plane from falling out of the sky. As you run into more often it gets easier to desolder.

[Guitarzan]

Lol... that's old school wiring technique, coming from (I believe) the military. The idea was that even if the solder joint broke completely, you at least had intermittent contact at the wire/component junction, and that would keep the plane from falling out of the sky. As you run into more often it gets easier to desolder.

when I wired homes I was taught to make a good mechanical connection with wires, then put a wire nut on it. So in a j-box we'd always twist any connections with a lineman's pliers then trim and cap it. But we weren't using any solder. But I suppose if it kept the plane in the air it made sense.

[Guitarzan]

On a champ turret board the 1st 2 filter caps have the grounds tied together but the 3rd one is grounded separately from those 1st two.
Why aren't the 3 filter caps tied together on the neg side?

The first two caps supply the power tube plate and screen. They are considered the 'power' ground.

The third cap feeds the preamp tube and is considered the 'preamp' ground. It's good practice to keep the two separated so the preamp current does not flow thru the same path as the high current power ground.

Those two grounds are electrically connected together thru the chassis, but the currents flowing thru each ground circuit is kept separate.

That theory goes by the wayside when using a cap can tho, right?

[Willabe]

It's good practice to keep the two separated so the preamp current does not flow thru the same path as the high current power ground.

Those two grounds are electrically connected together thru the chassis, but the currents flowing thru each ground circuit is kept separate.

It's about keeping the B+ 'loop' current isolated then you run 1 'loop' to the next 'loop'.

Here's a few drawings that may help. (G*1 = ground star #)


                           Brad                              

[Guitarzan]

It's good practice to keep the two separated so the preamp current does not flow thru the same path as the high current power ground.

Those two grounds are electrically connected together thru the chassis, but the currents flowing thru each ground circuit is kept separate.

It's about keeping the B+ 'loop' current isolated then you run 1 'loop' to the next 'loop'.

Here's a few drawings that may help.


I was looking at the drawings, when all of a sudden they disappeared. I closed and reopened the browser and they're just not there anymore.
?!?




                         

[Willabe]

Sorry I reposted them.


                Brad   

[Willabe]

That theory goes by the wayside when using a cap can tho, right?

Maybe, maybe not.

If you use a dual 50uF cap can and use 1 section for the power tube B+ plate supply and the 2nd section for the power tube B+ screen supply then no.


                Brad   

[Willabe]

Here's a link to a very good grounding explanation;

http://www.valvewizard.co.uk/Grounding.html



                         Brad     

[Guitarzan]

thanks for the link Brad.
Looks like valve wizard has all sorts of good inf on that site.

[DummyLoad]

On a champ turret board the 1st 2 filter caps have the grounds tied together but the 3rd one is grounded separately from those 1st two.
Why aren't the 3 filter caps tied together on the neg side?

The first two caps supply the power tube plate and screen. They are considered the 'power' ground.

The third cap feeds the preamp tube and is considered the 'preamp' ground. It's good practice to keep the two separated so the preamp current does not flow thru the same path as the high current power ground.

Those two grounds are electrically connected together thru the chassis, but the currents flowing thru each ground circuit is kept separate.

That theory goes by the wayside when using a cap can tho, right?

it does.


--pete

[Guitarzan]

just doodling... based on princeton 5F2-A preamp. drawing generated with visio 2010. if you'd like to have it in native visio format, PM an email address.


hoping others here will help check for errors.    


happy rosin smokin'. 


--pete

Holy cow! That Visio drawing is just what Jane and the monkey said I'd be needing to get this done and they were right.


"Tanks, tanks, and ever tanks"
-Max Calvada

[DummyLoad]

you're welcome. check it for errors.

--pete

[PRR]

> I really can't get my head around how they're separate, when they ultimately go to the same PT post an inch away.

Remember we don't have clean power, we get the peaks of 50/60 Hz wall power.

So the PT-Rectifier-main Cap loop is FULL of BIG buzz. Jackhammer racket.

Illustrative digression:

My father says when he was young there was a Juke Joint dance-hall far outside of town (where the sheriff didn't go). Converted from a chicken shack. Skinny floor beams. When the joint got jumping, the floor would bounce up and down six inches.

Now say you see all these customers and want to open a tattoo parlor there. Do you set up....

1) middle of dance floor?
2) shack hanging from the edge of the dance floor?
3) new shack on new blocks a foot outside the dance hall?

With #1 you will be tattooing places the customer doesn't want tatted. Even #2 will foil good workmanship. If I was the artist (and especially if I was the customer!), I'd want to haul in new blocks and be well outside the bounce zone. On the same ground, but not on the same blocks and beams.

In the diagram below, note the jackhammer pulse-path through rect and main cap, and the smooth current through the stage taking your sweet (but weak) guitar input signal. They do connect, but not so the input stage gets the full brunt of the wall-power system.

[Guitarzan]

LOL!
If you don't teach this stuff (outside of this board) you really should. You have a knack for making it fun as well as understandable. The mark of an exceptional teacher.

[Guitarzan]

Well I made a little progress today. It looks a lot grungier and more ham handed in the picture than it does in person.
It also doesn't look like a lot of progress but I'm partially disabled and can only do a little at a time before pain tells me it's time to quit for a while.
Anyway, here's what I have so far...

[Willabe]

Looks good to me!


             Brad     

[Guitarzan]

Thanks Brad.
Next time I'll try & finish the preamp socket and do the pots.
A 220k resistor is still needed from stock. I'll have to go thru my stuff & find one.
I have everything else. The tube (6sl7) I ordered arrived yesterday along with the Jensen P69R so as soon as I can finish up I'll be able to fire it up.

[Willabe]

The tube (6sl7) I ordered arrived yesterday along with the Jensen P69R so as soon as I can finish up I'll be able to fire it up.

                   

[Guitarzan]

I have to say that the really nifty color layout that Pete made up really made the difference on this for me.
Thanks a bunch to DummyLoad for his help.
Connecting the resistors and caps right to the tube socket makes their function clearer in mind as opposed to making up a turret board and connecting everything that way.
I only hope I can go long enough on this next leg to get the thing done. Either way, I'll post my progress

[Guitarzan]

Well, I've finally got it close to being done. No pics just now, but if you guys really want 'em I'll snap a couple & post 'em later.
I'm just fixin' to smoke test it now. Maybe a poor choice of words?  So, I was gonna power it on w/o tubes first, then put the tubes in and see if it actually passes a signal & works correctly.
Any other initial power on suggestions would be much appreciated. I'll wait a while & see if there are any replies. The guy across the street is a harp player & tomorrow night is his band's practice night so if all goes well before then, I think I'll have him put it thru the paces for me. He's playing one of my Champ clone builds now. Has been for the past year & loves it. I'm really interested in hearing this one in an "A-B" comparison test with that one. This will be my fist experience with an octal preamp tube.

[Guitarzan]

It was a bit of a blivot but here it is.
A blivot is 10 pounds of s**t in a 5 pound bag. It's what my mother used to threaten to give us for Christmas back in the day...

[Guitarzan]

The good news is...no flames, smoke, or tripped breakers.
The bad news...no sound. Nuthin. A barely audible hum....if that.
Back to the drawing board I guess...

[DummyLoad]

possible short? see pic.


--pete

[Guitarzan]

Good eye!
I'll have a look & let you know.

[Guitarzan]

Wow! That was an amazing piece of spotting the/an issue from a distance man! That was a great call Pete.
Only now I have something else going on. As it warmed up it began feeding back and the FB just got louder and nastier as it got warmer.
I pulled the plug right away because I didn't want to fry something. I can't fiddle with it anymore tonight, but tomorrow I'm going to have to try & figure this out.
Any ideas?

[Willabe]

It looks really good to me!

You'll find what's wrong.

And Yes Pete's very good at drawings and coming up with mods to amp builds isn't he? He's helped many members here through the years, me included!     

Wow! That was an amazing piece of spotting the/an issue from a distance man! That was a great call Pete.

Must be that good fresh Texas air and sunshine that makes his eyes so good.      hehehe


                    Brad     

[Guitarzan]

I'm positive I never would've gotten this far if it hadn't been for his Visio drawing and other help. Not to mention the rest of the help I got from this bb.
So for the record, as it warmed up it started making a high pitched, steady, feedback sort of noise. Not a screech but just like a mic too close to a speaker sort of noise that got louder and louder 'til I killed it.
Actually, it's probably a good sign. If I can get this runaway FB under control, it sounds like it's gonna be just as loud as my 5F1 builds.
That, after all, was the point of this entire exercise, right?

[DummyLoad]

does it feedback when both controls are at "0"?

aside from a wiring error  - things to ponder:
1) the 250k resistor that hangs off of pin 5 of the 6V6: is it grounded on the input jack?
2) if yes, then move the 250K to pin 5 of 6V6 ground end: ground it on the 6V6 socket.
3) the input jack may be too close to the 6V6: rotate the input jack so that the tip lug is closest to pin 1 of the 6SL7 and make that wire as short as possible.

--pete

[Guitarzan]

That resistor is grounded on the socket lug. it goes from pin 5 on the 6v6 right to the ground lug below it on the 6v6 "frame".
Tomorrow, I'll try moving the input jack and let you know. That wire is only about an inch long now but if it can be shortened any, I will.
If you can think of anything else, Please feel free to let me know. For example, if you can think of what kind of wiring error could cause this symptom.
Thanks again and again, and I'll report back tomorrow.

[Guitarzan]

Oh...maybe you saw that black ground wire on the input jack & thought it was the 6v6 pin 5 resistor?
That ground wire does go to one of the tube socket ground lugs. i don't recall which one I soldered it to.
Should I move it?

[DummyLoad]

It looks really good to me!

You'll find what's wrong.

And Yes Pete's very good at drawings and coming up with mods to amp builds isn't he? He's helped many members here through the years, me included!     

Wow! That was an amazing piece of spotting the/an issue from a distance man! That was a great call Pete.

Must be that good fresh Texas air and sunshine that makes his eyes so good.      hehehe


                    Brad     

thank you for the kind words... 

it's the heat. that unbearable 100 degree humid heat. 

--pete 

[Willabe]

it's the heat. that unbearable 100 degree humid heat. 

NO,  it's not the heat Pete (hehehe), your a good man and it's been proven MANY times here by how much you've contributed here to all of us, just a tip of the hat to you.   

Now back to our regular programing..........   and a 1 and a 2.......    'Do the hip shake thang', a do the hip shake thang', a do the Texas Zydeco hip hip shake thang.......   


                  Brad       

[Guitarzan]

it's the heat. that unbearable 100 degree humid heat. 

NO,  it's not the heat Pete (hehehe), your a good man and it's been proven MANY times here by how much you've contributed here to all of us, just a tip of the hat to you.   

Now back to our regular programing..........   and a 1 and a 2.......    'Do the hip shake thang', a do the hip shake thang', a do the Texas Zydeco hip hip shake thang.......   


                  Brad       

LMAO!

[Guitarzan]

Upon doing a search for feedback problems I ran across this..


Some causes of squeal...

• Tube going microphonic - most often first preamp tubes.
• Shorting contact on input jack (esp #1) not making contact; the "squeal" is from sound vibrations vibrating the chassis and the contact making and breaking contact repeatedly, making a little 'click' each time.
• Power tube shorted (this only happens for a short time - the amp squeals and then dies.)
• Lead dress - the leads carrying the signal around inside the amp have been moved around somehow so that the signal is causing internal electrical feedback. You can find this by running the amp with the chassis open and moving the wires around (gently! with a wooden stick) to see if the squeal changes or goes away. Once you locate the critical wire(s) you can figure out where they have to be to keep this from happening and tie them there. Another option can be to substituted shielded wire for the sensitive ones, with the shield connected at one end of the run only.
• If the amp has been modified, the squeal may be caused by poor lead dress in the modification, improper grounding in the modification, parts layout too close, or just that the new (usually higher) gain has pushed things over the edge. Higher gain makes a lot of things more critical, including grounding, bypassing, lead dress, and signal shielding.
• Wrong polarity/ incorrect hookup of a replacement output transformer.

I bought two used 6sl7s so I can try swapping the one that's in there for the other one.
I didn't hear any clicks but #2 could be it I guess.
#3 scares me the most since they don't specify the cause of death. I'll check & re-check my work & hope I don't fry anything. Before I found the short that Pete pointed out, it was powered on for a few minutes not making any sound. So if the 6v6 was in fact shorted, wouldn't it have failed catastrophically? Or did that short at pin 5 of the 6sl7 somehow prevent it from going up in smoke? Again, I wish they'd have said in what way it dies.
#4&5 are similar and could be the problem. It's the blivot syndrome.
I don't see how it could be #6 since I didn't change that.

So I guess I have my work cut out for me. I don't wanna cook anything in the process. Tips are encouraged at this point.
Please and thanks guys!

[Guitarzan]

Well, just to update this thread, I did wade back into the amp yesterday and found that I had misplaced one of the connections on the volume pot. Pete was also of the opinion that the input jack might be too close to the 6V6 so I fixed that too. I wasn't really pleased with the way that little piece of shielded wire turned out either so I redid that as well. I took a forceps and generally tried to tidy things up too. The amp works but I have 2 6SL7s that I bought used and both are micro-phonic. It amplifies the sound of any jostling or tapping of the cabinet, and pings like a wine glass if you so much as touch the 6SL7. Plus it seems untable since it wants to try and squawk a little intermittently. Pete tells me that's an indication of "one or more of the grid wires in the grid element is sagging and touching another." So I can't really report on what it sounds like until I can get that issue resolved and test again. However, it the mean time, Here's the latest looksee.

[Willabe]

as it warmed up it started making a high pitched, steady, feedback sort of noise.

That's a drag about the 2 6SL7's but it's not doing the above any more, that's good.


                       Brad     

[Guitarzan]

Yeah, I thought that I was hedging by buying 2 of 'em. One is decidedly worse than the other but they're both totally unacceptable in the amount of microphony. I didn't want to buy any current production 6SL7s because I've heard too many bad things about them and NOS are just too darned expensive. I suppose I'll have to go with one or the other though. I have a friend with boxes of that kind of stuff. Maybe I can find a good one there and make a swap or something.
It still feeds back at high volume, but couldn't that be another function of the microphonic tube? I mean, with a good tube, maybe it'll settle down?

[Guitarzan]

OK. I got some more 6SL7s and boy do they make the difference! That little amp sounds pretty darned good. It's very close to being there except for one more thing.
At full volume and with the tone control turned all the way to bass, it just barely keeps from feeding back with no input, and then when you turn the tone control towards treble, it starts motor boating.
In doing a search for motor boating I've seen it blamed on too much gain, and on filter caps just for a couple of possible causes.
So what do you guys think?

[Guitarzan]

Does anyone have an opinion on changing that 220-ohm cathode resistor on the 6V6 to a 470-ohm like a tweed champ?
Going that direction with the value of that resistor will do what?
If I do that, will I also need to change anything else?
Please & thanx as always.

[sluckey]

Increasing the value of that resistor will decrease power out and let the 6V6 run cooler. You should not have to change anything else.

[Guitarzan]

Thanks Sluckey!!
I'm trying to dial this thing in to where it doesn't want to feedback when dimed, like my tweed & bf champs

[Guitarzan]

Well, it's finally working and WOW...is it ever a killer!
After the initial mods it was still not right. It was motor boating as the volume control went beyond about halfway. Sort of blub, blub blub noise. The B+ at the 6V6 was off a little so a resistor adjustment corrected that.

That motor boating was persistent even after making sure the voltages were all correct. It only became more defined and rather than blub, blub, it started making an articulate sounding putt, putt, putt.
Pete gave it some thought and determined that the "C" tap from the cap can was bad. This was the power supply filtering for the 6SL7 and so he helped me to make the necessary changes to add one 8uF 450v cap (cuz it's what I had handy) and BINGO! It sounds great!
It gets just as loud as any 5F1 clone that I've built, with maybe a little less clean headroom but hey..who needs a bunch of amps that all sound identical? The distortion at full volume is fantastic! Think Led Zepellin's Moby Dick. Just my Les Paul with DiMarzio humburckers and nothing else.
I'm not thrilled with the tone control as it gets harsh very quickly as you roll it from bass to treble but I think I leave it alone for now.
I have to find a way to extend the pot shafts yet but that's minor. The little amp's a real sleeper. You can crank it and rattle the windows. Didn't take long for Jane and the monkey to start complaining. I'll have to hook it up to a couple of different speakers to see how the old Jensen AlNiCo 6X9 compares to say a Weber 8F150.
Thanks again to Pete and all of you guys who contributed ideas. I learned a lot from this project.

[Willabe]

All right!!!!!     

Didn't take long for Jane and the monkey to start complaining.

Send them out to get some bananas.     



             Brad     

[Guitarzan]

Looking back, I see that I never offered up any pictures of the thing in it's entirety. So...here it is..
I swapped out that speaker with an old Jensen AlNiCo I had, in addition to the other mods.
Ain't it cute?

[DummyLoad]

nice looking little thang. glad you're happy with the mods.

--pete

[sluckey]

I really like this kind of project. Thanks for sharing.

[DummyLoad]

schematics of what was built.


hope you're diggin' on the new groove...shock the monkey.



--pete

[Willabe]

I read Tone Quest Report mag (have all the back issues) and they had a couple of interviews with west coat blues guitar players who LOVED oval speakers as a sleeper for mojo sound.

Those guys searched under every rock, once they stumbled across them in old pawn shop buys and bought every one they could find.     

I've been spending hours, literally searching for the last year for amp cab coverings and grill cloth to get away from the normal tradition in color schem.             

The tolex on it looks great, the depth of grain and the depth of color!!!!!  The cab it's in looks way cool all the way around, I love it!!!!!!  Plus the cab locks!!!!!         


                       Brad             

[Guitarzan]

Thanks once again to Pete for the schemo! I can put the as-built in the box alsong with the original for some future tube guy. If there ever is such a thing as a future tube guy. 
 
I'll been on "Large item collection day", if your town's trash collection offers one, you could find old TVs and consoles on the curb for the picking. Old speaker and tube chassis heaven! A wire cutter and set of nut drivers is prolly all you'd have to carry.
 
I've tried looking for that Silvertone style of tolex with no luck at all. I think some of the old tolex, y'know, the really unusual stuff might be best approximated with wallpaper. You might find something that'll meet your needs at home improvement place or, if you're lucky enough to have a very old decorator in your town, 3rd ot 4th generation or even older, they may have really old out of print stuff that could be used to cover a cab. Old radio guys often have grill cloth that's different from the usual oxbloody tweedy stuff that's so popular right now. I'll bet there are other sources too if one thinks outside the box as they say. I think the trick is to find a cloth that's sonically transparant. I read in one of the forums that a guy improved the sound of his reissue champ 600 by replacing the grill cloth. It seems the stuff they put on that thing in the factory could make pretty good soundproofing if used in a couple of layers. I don't know this to be fact but it seemed like the thread had some creedance. I'll bet an upholstery shop would be a good place to hunt for unusual cab covering and grill cloth too.
 
BTW and FWIW
I've found that the old radio people aren't nearly as high priced as the old tube amp people when it comes to selling parts and stuff. I've seen some really interesting and unusual old radio cabinets on flea bay with asking prices that way below what a run of the mill 5F1 cab goes for. With a little imagination I think one might use all of the exsisting openings in one of those and make a cool little combo out of it. If you had to do any surgery on it, obvously it would get a lot trickier and then you're back to trying to find an appropriate covering mat'l.
Anyway, that's been my experience to date.