1482Esq

[orangehead72]

That all looks really good Shooter. I even like that Jackson P.

[DummyLoad]

yo mon! i dig on de zydeco chassis. NoLA is calling to you. 

--pete

[shooter]

here's the link to the switches;
https://www.parts-express.com/parts-express-spst-large-rocker-switch-w-blue-illumination-125vac--060-704

and they don't light like yours 

Pete, I am a closet zydeco listener 

got carried away and mixed Pollack's dark period with his splatter years 

[shooter]

crappy day, tired of watching paint dry, bored watching for tanks, decided to solder some 

[shooter]

nuther coldwetgrayday
so I clear-coated a couple layers n busted out the install tools 
here's the eye candy side 

[davidwpack]

That's awesome! Cool way to combine visual art and aural art!

[shooter]

aural art

Long way to go in that genre' 
Odd note though, as I was drifting to black last night I "heard" the amp
"Memphis style" bluesy funk 

[shooter]

the SUN showed up, without heat but hey;

starting the Yang side 

[shooter]

messed up my BOM and my spares are low, parts on  order 

I can't recall if there's a "downside" flipping the secondary wires if she's a screamer 
since it's UL, I'd much rather swap 2 than 4

thanks
dave

[sluckey]

I can't recall if there's a "downside" flipping the secondary wires if she's a screamer 
since it's UL, I'd much rather swap 2 than 4

Swapping secondaries is fine if there is only one impedance tap to deal with. Multiple taps is a no no. Much easier to just swap the grid wires.

[shooter]

Multiple taps is a no no.

thanks, I had the fuzzy thought there was a downside, I only got 1 tap though!   

[shooter]

gray cold only broke even on scratch offs, so I added a few yellow marks on the layout and parts inside, waiting to replace the 2banger tone with a singlewide 

[shooter]

just a note for those gleaning insight;

I've caught n fixed 4 problems and the power switch still ain't installed!
I "find" the problems by doing a "mental install" 1st, that caught a mis-draw on V2.
once I do a bunch of soldering, I walk away n play, then come back and "re-do" the same work with my eyes, That found a missed solder point, 2 R's wrong values 

remember the turtle always wins 

[shooter]

3+ inches of new snow! after some tracking managed to get the power switch installed n tested, red wires 265vac, brown 6.44vac and zero smoke 

think it's time to refresh my reading on "the folly of man", maybe play some Nero fiddling tunes while I wait for the bridge to come 

[shooter]

cold gray no snow but more state boys than I've seen in 2 weeks!
bridge is in the mail!

nothing left to add until I can shoe-horn the bridge in.  then....

I have a major design flaw that just might be a "happy mistake" or epic fail.
My pre ends into a DCCF, which feeds a Cathodyne PI, so 2 "buffer" stages 
don't recall ever seeing that.  shouldn't be a problem just converting the DCCF to a DCPI and V3A becomes a floater, gain, light flasher, something, or not 

[shooter]

played outside, got a bridge in the mail, went inside 
the command n control side is about done, the working class side next 

found the neutral wire jumped when I got it hot, re-doing 
still gotta solve the roach but it's music with crayons now

[shooter]

working class side wired 99%.  missed a couple wires during layout so flying   

still sorting the roach, doug says "bulb" in description, is that right, or LED?
probably cut it open IF I can find it, got it isolated to a room 

to have "proper phase"  do I want the PI in to match the speaker +?

thanks
dave

[sluckey]

still sorting the roach, doug says "bulb" in description, is that right, or LED?

It's a NE-2 neon glass bulb. It's the copper colored leads on the right side in his pic. The bulb is approx 3/16" dia x 1/2" long. Very obvious in Hoffman's pic. The bulb will have infinity resistance. The photo cell (LDR) will have very high resistance. May be able to measure it with your 87V. I've never tried.

In the old days I have used a razor blade to cut a tiny hole directly over the bulb to see if it was flashing. Paint the hole with a drop of fingernail polish when done.

[shooter]

Thanks Steve

I'm down to a corner 
might have it soldered tonight!

[shooter]

LOTS to check but;

quiet as any amp I've built, maybe quietest!!!
1st pass;
Vp = 331
Vk = 20.5
Diss = 14.6W/tube oops
moved B+ to second tap
Vp = 217
Vk = 12
Diss = 5.4W /tube safe.
Nice tones, clean with small edge at the 10's.  Trem doesn't seem to be there, find out with scope later.
NFB not hooked up so i'll clip it and see about screams.

todo:
run a signal through, gain/volume pretty low, might need to bump V1 to AX
address trem n NFB
overall;
  

[sluckey]

Which trem circuit are you using? Schematic please. Don't need a scope to check the trem. Your 87V works just fine.

[sluckey]

I just checked the schematics you posted in the first few posts. That Fender roach ain't never gonna work in the schematics I saw!

[shooter]

That Fender roach ain't never gonna work

used the 87, nice constant vdc
nope.  I have LEDS and photocells and heat sink, does that get me close?

done for tonight
got good clean from in to out, good start
 
something wonky in PA, IF my #'s are correct, I have ~~ unity gain from PA tubes 

one tube doesn't like me getting close, the AC on the PS taps starts bouncing.  got 5 more tubes, + a new 6V6, might just buy the next one, for tweaking using the  6K6's

[sluckey]

Set the trem aside. Fix the amp. Come back to trem.

[shooter]

Set the trem aside

 
I read that in ANOTHER thread 

already jumped it out, not ready for the on switch yet, coFFEE! 

[shooter]

trem gone, jumped Grid leak 330k's to ground instead of INT pot.  (only change from initial checks)

Here's initial current schematic with vdc and Vacrms.

noted changes from last night, gain went up starting at V2a into grid PA, speaker out is same 

[sluckey]

Looks like the amp is working. Is it? Why are you using 12AU7s in places where everyone else uses 12AX7s?

[DummyLoad]

That Fender roach ain't never gonna work

used the 87, nice constant vdc
something wonky in PA, IF my #'s are correct, I have ~~ unity gain from PA tubes 

not possible in grounded cathode fixed bias P-P or cathode bias P-P stages - IOW: you'd need 400V g1 drive with 400V+ B+ to make full power. your math is way off. 


--pete

[shooter]

Why are you using 12AU7s

The AU seems to be better at keeping "too much gain" at bay, the signal comes up better than noise, so less hiss n other related "hi gain" issues.

as long as I can get a drive signal bigger than "bias" to the PA, I'm good.

It sounds like a 5F1 champ as far as loud goes, nice tone, good lows to highs, just not a 10W PP sound like I'd expect from a Gibson skylark kinda amp.

cathode bias P-P stages

you'd need 400V g1 drive with 400V+ B+

lost now;
the datasheet suggests ~ 300 plate, AF peak G-G ~50v  (I'm pretty low there), dissipation design center ~ 8+W  I'm at 8.6W/tube

Game plan;
roll PA tubes
change V2 to AX for more gain
bypass V1a some
evaluate

[DummyLoad]

Why are you using 12AU7s

The AU seems to be better at keeping "too much gain" at bay, the signal comes up better than noise, so less hiss n other related "hi gain" issues.

as long as I can get a drive signal bigger than "bias" to the PA, I'm good.

It sounds like a 5F1 champ as far as loud goes, nice tone, good lows to highs, just not a 10W PP sound like I'd expect from a Gibson skylark kinda amp.

cathode bias P-P stages

you'd need 400V g1 drive with 400V+ B+

lost now;
the datasheet suggests ~ 300 plate, AF peak G-G ~50v  (I'm pretty low there), dissipation design center ~ 8+W  I'm at 8.6W/tube

Game plan;
roll PA tubes
change V2 to AX for more gain
bypass V1a some
evaluate

when you state unity gain: output = input, IOW a gain of "1".


--pete

[shooter]

Ya, I'm less than unity PI out to speaker out (13vac out Pi to 5.7 speaker) so that's an issue.
I believe getting more drive to the PA will open it up, but I'll probably bust out the HV probe and see what the PA plates are up to.

and i DID screw up my DCv pa calcs, forgot to subtract Vk from Vp 

once I mess with drive, I do wanna try n bump B+ at plate closer to the 285vdc

[sluckey]

Ya, I'm less than unity PI out to speaker out (13vac out Pi to 5.7 speaker) so that's an issue.

How is that an issue? The power amp ain't about voltage gain. It's about converting voltage to current. 5.7V on an 8Ω load produces .7A and that is 4 watts. That's the important stuff.

[shooter]

That's the important stuff.

I'm still learning Yoda 

made V2 an AX7, got a good bump out, well above what I need to drive the PA with 14.5v bias.  more a yawn bump at speaker as to loudness
starting to discern a kinda reverb, empty room "echo-y" sound.  the spectrum shows a couple IM signatures (in red) 

[DummyLoad]

what are DCV measurements at pin1 & pin3 of 12AU7 V3A cathodyne?

IMD may PS related - try 100nF node D to GND, may or may not help. 


--pete

[shooter]

 
I caught a snore bug, then;
replaced the 1K, 1st tap R, with 750, dialed plate right at datasheet 286vdc
Rk might need a tweak, but for now running 9.2W/ tube.
swapped in 2 other PA tubes and changed speaker cabs and the amp IS alive!
much closer to what I was expecting.  Pam's watching B&W movies so.......real sound test in AM.

Pete, the plate is 156vdc, the cathode 125vdc

probably scope it out once more and re-do vdc's since I changed the PS rail, I'll glue in another 47uF also.

[shooter]

just yawn changes with vdc, shows AX gain bump at V2 n right.

probably done for the night, the AM i'll play awhile, then tweak bypass caps, maybe test NFB although I'm not pushing to distorting and I have no gain to give up, yet.

[DummyLoad]

stuff a 1K under the cathode of V2B (cathodyne) to bias it proper. Vk is too high.


--pete

[shooter]

 
I started playing with paint, but it's noted on schematic, thanks.
got 10 more minutes guitar in, it's there, 90% sure the cab did it.  still needs 20% more loud, but that can be had with 6V6's, but I like a challenge 

[shooter]

Ok Pete, I put the 1k in, you do know where it was right, down in the bilge room, way at the bottom, under lots of stuff!! 

for fun I changed my speaker DL from 8 to 14, Volts at DL went from 8.3VacRms to 10.  Next I'll re-config my cab from 8 to 16ohm and play some.

Ready for help with new roach for my TON then I can call the build a success 

[shooter]

I tried it, and liked it!  V1 is now an AX7.  I lost some sparkle, but the 90's grunge/hard rock came alive!!
ordered the proper vactrol, even went with new old stock, also a 2nd 6V6 for even more bark!

musician/design question, this amp really doesn't like single pickups, but the bridge dual pickups really makes it happy.  Is that a "hot" pickup thing 
(It is a cheap guitar :)

[SILVERGUN]

musician/design question, this amp really doesn't like single pickups, but the bridge dual pickups really makes it happy.  Is that a "hot" pickup thing 
(It is a cheap guitar :)

Yes...in some cases more output V from the pickup = more better. Those dual pickups are called humbuckers and almost always have more oomph.
 
As a player (hack), I have found that I prefer a lowered B+ in V1 because I don't play clean enough to like/need hi-fi response at the input stage. One of my favorite dirty input stages used a low B+ and split load where the signal was tapped off the middle as an experiment....that wound up feeling like home to me. Add some sweet humbuckers to that and viola, plenty of room to hide. Plug singles into that stage and it sounds anemic.
 
You'll see a lot of old washed up strat players using a boost pedal for those whimpy little single pickups. It's usually to overcompensate for something else....
 
One of the old tricks of the trade mods was to double(and more) the plate load on V1(leaving all else the same). This makes some voltage gain but also pushes the bias point and makes the stage more likely to clip - some guys like that. V1 obviously has a lot to do with how the amp feels with different pickup types.
 
More than you asked for but I know you like food for thought.
 

[shooter]

I know you like food for thought.

Thanks SG, ya, regular food isn't my thing 

and I'm finding V1 IS the "key" to keeping things simple AND getting "that sound"

the 6K6 is a great sounder, the problem, drive is almost 2X a 6V6, so as soon as you roll off volume for those teary eyed guitar sounds, the amp just goes yawn n the pretty girls go home with the drummer 

[SILVERGUN]

One more morsel while I'm donating.
Have you tried bootstrapping V2a with V2b?
 
I know it sounds silly to use a low mu tube and then bootstrap it for more gain but it's never been beyond you to be silly.
 
Thanks to Merlin for the snip:

[shooter]

all my latest builds use the straight DCCF.  I did try the bootstrapped version awile back but I drew it up wrong, fortunately Sluckey caught it, N slapped my hand 
the DCCF is where I try and get enough gain boost to get my "pre-amp distortion".
V1 I try and get the "mojo".  I also want enough signal to spank the PA into being part of the "mojo" crowd, wait, can I still say crowd 

[sluckey]

Here's a pic showing where I would connect the TON circuit. May need a 250K or higher INT pot.

BTW, what is your reasoning for using a low Z cathode follower to drive a very high Z cathodyne? V2A plate is very capable of driving that cathodyne. Not logical to me.

[shooter]

what is your reasoning

simple epic fail on my part 
I worked on the design over many months and many states and simply didn't double-check, the up-side, it sounds better than my last build!, I love a happy mistake 
Same fail with the TON.  I did go back and found the thread by Trox on trem in a SE build, Tubenit gave an example of inserting it where I have it drawn, since his build and mine are both self biased PP not fixed, looked good, "cut-paste" here we are 

[shooter]

when I scoped this out the 1st time, my thought was she's clean enough to do audio if guitar sucks.  I rolled the AU's back in, plugged in my "test tape" and it beats my SS monoblock!!!  The pauses are silent, my hearing is ZERO above 12k so can't call that part, the fidelity is real transparent, the only "cork-sniff" complaint;  there is a very subtle "hall effect EQ" but on all the songs it didn't take anything away.

throw in the AX's and jamb to Pearl Jam    win/win

[shooter]

Here's a pic showing

I was gonna "walk" a .0047uf in place of the .01uf's to see if I could shave a tad bass in guitar mode.   Any problem just adding another .01uf at that junction, kill 2 birds 

[sluckey]

Use whatever values you like. But you gotta use two caps, one to block voltage from the CF, and the other to block dc from the PI.

[shooter]

soldered in LED, lights, no flash.  Current vdc on schematic.
1st passed didn't find wiring error, back for 2nd pass soon.
guessing B+ might be to low, so If I don't find wire error, i'll move tap to A, ~340vdc