Firefly Clone Build

[shortfuse]

Ok I wimped out on the Hoffman 50 for a 1st build i think i have tried to download to much info too fast and have gone to max overload.  So after some research I decided to go with a Firefly Clone (wired not PCB) to get my feet wet.  I posted some of this on Bigdaddys thread and jojokeo answered some of my tone stack questions there but decided to start a Firefly thread as I could not find one in the archives.

So I received my order from Doug last night and guess what I forgot stuff, ordered a few wrong things (gotta keep an eye on the decimal point) and on top of that I ordered a few things that were not even on the list,  must have been Black Forest Gnomes on the computer when I ordered helping me out.  You all jinxed me because you said it would happen LMAO!!!!  Guess there will be order #2 going out tonight, and probably #3 by the time that gets here.  Growing pains

The Schematic calls for a Hammond 269EX PT and a Hammond 125A OT.  I guess I am confused because the 125A spec's as a PP and not SE, can it be used for both or is this a PP design?  I thought a PP has to have 2 output tubes to be a PP and the PT center tap would go to the cathodes of those 2 tubes?  Or is running through a 12AU7 like running through 2 power tubes because of the way they are configured?  I thought maybe the 1750A which is a SE 3w reverb trannie 8ohm @22,500 would be the one but the schematic shows using lug 2 & 4 for the OT @ 8ohm which is what the 125A has.  Either way I have both.

[OldHouseScott]

The Firefly is indeed P-P, so the 125A is correct. The 12AU7 is a dual-triode in one bottle and it's using both sections to create the push-pull arrangement.

[shortfuse]

Is there any reason I should not put the filter caps under the the board at the B1, B2, & B3 locations instead of to the far right side of the board as shown in the layout in my 1st post.  I want to do this to save space as I am using a smaller chassis?  I could use a larger one if it will cause me a problem.

I also finally figured out how to change the pdf to a jpg to throw up the quick view.

[stingray_65]

Is there any reason I should not put the filter caps under the the board at the B1, B2, & B3 locations instead of to the far right side of the board as shown in the layout in my 1st post.  I want to do this to save space as I am using a smaller chassis?  I could use a larger one if it will cause me a problem.

I'm not sure I understand you. do you mean to move the entire filter cap board under the component board?

or do you mean to say you want the caps on the underside of the filter cap board?

Maybe I'm tired or more likely I'm dense. cut and paste the JPG to give me an indication of your intent.

Ray

[shortfuse]

Its a pretty crude sketch but this is the idea.  I will have a scale size sketch tomorrow. My chassis is 9 X 5 X 2 1/4 the one in the JPG is larger.
Basically remove the cap board and mount the caps under the main board, move diodes to far left of main board and place PT where cap board and diodes were before.  Main board will be deeper front to back  and a bit wider to accept the caps underneath and diodes to left and slide toward the front to get away from tubes.  I guess the main question is can the filter caps go under the main board or will it cause my problems?

[stingray_65]

I get where you're going.

The only issue I see is there MAY be a chance of picking up unwanted filter hum.

I'll look it over closer and give you my opinion.

In general, you want to keep filtering as far away from signal processing, but our venerable Mr Hoffman has shown us bravely we CAN mount filter caps right on our main board with great results.

Ray

[Ritchie200]

Shortfuse,

You could add a couple of 50uFx2 multi cans on top of the chassis and leave one unused.  That might give you additional room down below.

Jim

[shortfuse]

Humm, that sounds like a good idea is there a specified distance they would need to be from the tranny's or tubes?

[shortfuse]

Ok I solved my own problem (which most likely was not a problem) and used a slightly larger chassis so it is pretty much like the layout.  I have drilled and Pre-fit all the parts in a mock up build before wire and it is now time to wire.  
I have searched this site and came up with 20ga solid core for heaters and 18ga stranded for board chassis.  Is the solid core used for anything else in the amp besides heaters and maybe the wall plug socket to the power switch?  I think that is even 18ga stranded.  Ok I just went back and re-read Dougs info and it says 18ga from the bulb to the power tubes and then 18ga for the pre amps.  Is solid core even necessary?
Is there an industry standard for wire color for certain areas?  I see all colors on projects in this site.
Another question out of curiosity looking at a lot of the projects that have pic's on here, I see some shielded wire like RG59 (solid core w/ shielded jacket) but I believe smaller used on some of the components across the board or chassis.  Wondering what that use is for and why?  And where is the shield tagged too when using it?
Will post some pic's tomorrow forgot the camera at work tonight.

Steve

[stingray_65]

Shortfuse,

My apologies for not getting back to you. Sorta fell thru the cracks.

First: shielded wiring is used for low signal runs Like from your input to V1 or to and from volume and tone pots to the board.
ONLY ONE SIDE OF THE SHIELD GETS WIRED TO GROUND!
When you make a shielded wire it should look like the pic below.
Most agree that you ground the shield at the signal source end. So if you're coming off the input jack, ground it at the jack. some times its not practical to ground it at the source, like coming off the board to the volume pot. Most will ground it at the pot.
Although it isn't strictly necessary you should use heat shrink at both ends.

As far as solid VS stranded there are a lot of personal preferences.
My personal preference is to use solid wire most places.
For me it holds bends neater and it is easier for me to rout the wires for least interference. Also with my failing eyesight I don't run the risk of a whisker not going through a lug and causing a short.
I do use stranded in my mains run and a few other areas where flexibility is needed.

Colors, that too is a personal preference.

I've got about a quarter mile of 12 twisted pair 19ga western electric solid wire. so I have lots of colors to choose from. Most guys buy a spool or 2 and use what they have,

I make all my high tension runs in solid red, all my grounds I run in black. Jumpers on the board I am willy nilly about and use what trimmings I have except red green or black. Green is almost always used in heater wiring, I always try to add a contrasted color when I make my twisted pairs, like a green and a white wire. The reason for this is that I keep my heaters in phase. the green wire lands on pins 4,5 on my preamps and pin 7 on my octals, white lands on pin 9  on the pre's and 2 on the octals. This is a hum reduction technique and is easier with 2 colors.

from my tube sockets, I run orange from the plates, brown on my cathodes and blue on my grids. some times i mess it up, BUT because I follow that prescription, it is easy to spot.

Pretty much tho only "industry standard" is on the mains, Green or green w yellow trace for ground , black for hot and white for neutral.   

transformers have their own "standard", but it is not written in stone and seems to be voluntary.

Ray

[stingray_65]

As a side note.

If you ever get a chance to get your hands on an old solid state organ, you will have a treasure trove of quality shielded wire that can last you for a hundred amp builds.

Ray

[shortfuse]

Progress finally.  Hope to be playing it tomorrow night as I will have all day to work on it.

I am leaving room for a tone knob possably later.  I like the moonlight one that Fresh Start put a link to on Big Daddy's Post. http://amps.zugster.net/articles/tone-stacks#Overview  I guess if i don't like it I will just leave it in bypass.  It says push pull knob DPDT would I just use a guitar tone pot as I can not find an amp pot like that or would I be better off using an amp pot and just use a mini DPDT sw?  Would you use a 500K or 250K?

[jojokeo]

Looking really nice fuse! It appears you mounted things before finishing the drilling? It doesn't matter if you use a pp pot or a switch, both work the same and you have plenty of room. Personally, I only have gain/vol for each stage since this amp is usually played cranked. But, it does sound nice w/ only the first stage engaged and set moderately low. The tone control is purely your choice for something like this. You can voice it to be however you want w/out one & retain all of the gain or put it in w/ a bypass. I noticed this design being a bit noisy w/ the high gain and turned up so raising the heaters helped a lot.
Here's what mine looks like, maybe it'll help you?

[shortfuse]

What size is your chassis?  You seem to have much more room than I.  Mine is 9X5X3 and the board just fits.  I questioned myself on how close I put everything but let it rip anyway.  Maybe the fact that you did not use a board makes it look bigger.  The tube stagger isn't something i gave a thought to. 
I have a spot for the tone but i am going to play it first to see what it really does 1st.  I saw your post for the lil giant and took that into consideration but the thought of the by pass intrigues me to give it a try.
Actually I pre-fit everything before I laid out the front and rear panels because being my 1st attempt at an amp I was not real sure on the elevation of the board in relation to controls and switches.  Last night I pre-fit all the other stuff took it all apart again and will start soldering tonight.  Board, transformers, and tube sockets all came out before I drilled the front and rear panels.
I probably made a good decision to try this out 1st before something with much more components bigger.  And thanks for the comments.

[jojokeo]

My chassis is 10x6x2 so not too much difference. You're getting a jump on things if you ever decide to build a 5E3 deluxe or similar. It's tight like that too. 
You can put the tone control(s) in w/ a bypass or lift so you can have the option of both (not sure if you understood this?)
It appears you have two options soldering your tube sockets. Either cut the board down close to the turrets to expose things better so you can solder to the sockets or solder wires to the sockets first leaving enough lead length to get around to the board. The idea of soldering switches or pots, etc. is a good idea to do out of the amp or chassis first whenever you can, and then install them. It makes things easier than fighting for room to work once inside a tightly spaced chassis.
One other note for you - get yourself a 12BH7 for the output tube. Put this in instead of the 12au7 and you'll find extended pleasure. You can even sub in a JJ ECC99 and it will work great w/ even more headroom and volume. But, you can also bias this tube better if that's something you like one of these days down the road? But, once you change the bias resistor, you may not be able to go back say w/ a 12au7 (just so you're aware of this).
It looks like you're doing a great job for your first build! 
This amp is really fun to play and experiment with. Enjoy the building phase, it's one of my favorite steps.

[shortfuse]

Ok finished soldering tonight and obviously did something wrong.  Powered up pilot light came and everything seem ok no smoke no smells.  Flipped the stand by switch on and immediately the 12AU7 power tube started to turn white from the bottom side.  I killed the switch as soon at I saw it start coming from the bottom of the tube.  Flipped it over and the the 2 100ohm for pin 4&5 - 9 resistors are smoked, bulged, burnt ect....  It appears that they are the only thing affected.  I have it hooked up like it is shown on the wiring diagram (attached) although I used a 470 cathode resistor instead of the 440 shown on the diagram.  Looking at it it seems I have it hooked up correctly.  I have the output transformer hooked up as follows Red hooked up to B1, Blue hooked up to Pin 6, Brown hooked up to pin 1.  Or should I be checking for something back feeding from the (-) side of the resistor.  I will have to  look again tomorrow I am getting tunnel vision now and may be overlooking the obvious.  Any ideas or starting point would be appreciated.  Maybe I should have filled out the voltage chart can i still do that with the tubes out?  My mind is fried along with the 100ohm resistors tonight.
  

[jojokeo]

it's not the 470r resistor, that's fine for a value. double check your heater layout carefully. pull your tubes. turn it on and check your voltages. an actual pic would be of greater help going forward. the 100r resistors should not have that issue. always double and triple check everything before 1st power up & make a current limiter w/ a light bulb to save your stuff.

[sluckey]

Recheck your wiring. There is either a wiring error or something on the + rail is touching the filament circuit. Look for something like a short between pin 5 and 6 on the 12AU7.

[shortfuse]

Well I officially smoke my 1st pt on my 1st build loaded full of 1st's maybe more damage than I thought last night.  I checked all tube sockets terminal connections.  Went over each wire connection twice and really didnt any thing wrong.  Replaced the 2 100ohm resistors and was preparing to check voltages and fill out the form when the PT got very hot and I shut it down.  Now after this happened I went over everything again to see where the wiring error is and went back to reading in the library.  From what I was looking at in the library should the 100ohm resistors have gone to chassis ground or to the (-) side of the board as shown in the layout diagram or should it not make a difference?  I will post pic's best I can but you can barely see the tube sockets.

[eleventeen]

I'm not on top of every detail you've posted, but why are there green (heater?) wires going near the filter caps?

Wait, maybe it's a depth perception deal and the twisted greens are going to the pilot lamp. Ne'mind.

Did you skin/puncture any transformer wires going thru chassis holes?

Transformers are usually pretty tough things...they don't smoke that easy... but on the other hand, obviously there is/was something ghastly wrong with the wiring.

[shortfuse]

The heaters and pilot light are above the filter caps it just looks that way from the angle I took the pic. 
I could not find any where the wires were cut or touching. 
The 12AU7 is the power tube on this amp its what connects to the OT.  3w amp

[shortfuse]

I have been scratching my head all day trying to think of what I did wrong.  1st I though maybe it was when I twisted the wires for the heaters but I held them before they enter the transformer and the 1st time i powered it up nothing really happened until I turned on the stand by switch.  Last night i pulled the board back up to double check everything wiring, continuity between (-) & (+) ect...  The only thing I found last night was I forgot to hook up the ring side of the input jack to the board.  Then when I turned the power on the filaments did not glow & the transformer got very hot, and I am sure damaged.  There must be something going on between the tube sockets and the board being place back down.  Although I did look with a mirror at all the pin connections on the bottom side of the tubes and did not see any thing touching each other.  I also checked for continuity between the pin sockets and ground.  The damage is done and I really want to find my mistake before I take it apart again.  Otherwise I have learned nothing from my mistake.  I am going to check for a short between power and ground again or bleed between socket solder points.  Could i use a 6v DC Bat with a circuit breaker to find the short.  What amp circuit breaker should i use?  Also and obviously a 1amp fuse will let a transformer cook although the fuse is on the 110 side not the 6.3 side would it be wise in the future to install a fuse on the filament side also?  Any suggestions as to where to start or sequence I should take would be appreciated.

[shortfuse]

I have figured out the problem and all I am going to say is I had a major case of dyslexia and will probably never wire a 12AX7 or 12AU7 wrong again.  I wired all 3 in the complete opposite rotation.    Very embarrassing!!!!!

[RicharD]

I was fixing to say look for a short around a socket.  Everything else looks purdy.  EVERYBODY reverses a tube socket on their 1st build.

Counter top / clock bottom.

[darryl]

EVERYBODY reverses a tube socket on their 1st build.

Some of us are still doing it... 

Even after 40+ years of amp building, I still occasionally swap the cathode and anode pins on 12AX7's.   

[RicharD]

I wired a 5U4 backwards.  Lamp limiters rule.  No harm done.  My favorite is to stick an output tube in the rectifier tube socket.

[eleventeen]

Oh crap! That's a fair amount of work to undo. One of the advantages of turret-build is that you're just clipping and moving wires instead of components as you'd be in P2P.

Look at it this way: You'll likely never do that again, although you are STILL eligible for the "one-pin-off" snafu. That one never goes away, as far as I'm concerned.

[jojokeo]

Fuse, let us know about the amp once you get things fired up again. Your work looks nice too. Hopefully the PT is still okay and maybe not all of the tubes blew?

[shortfuse]

The PT is toast new one on the way along with 3 new tube sockets (bottom mount this time) a the 12AU7.  I tested the 2 12AX7's last night with a 6v lantern battery and had 2 red dots so hopefully they are ok.  The 12AU7 did the white flash again with the battery and now does nothing.  Probably irreversible damage from the 1st time i fired it up.  I just hope everything else on the board is ok.

[bigdaddy]

Don't feel bad I did the same thing building a firefly, PT fired. That's when I realized at that time I can no longer do this.

I do miss it though and I am trying to figure a way to do it again. But I need backup in terms of working usable amps... . So I have an EAST Studio 2 and am waiting for the Lil' Night Train 2 watter. At least I have something to play through since most of my big watt amps are gone, yes those huge 5 watt Champ amps!!!!..ha ha.

[eleventeen]

I will tell you that I have had some 12AX7/12AU7 where the heaters light up VERY brightly, alarmingly on startup. And I have had others which just calmly, ho-hum, warmed up in a perfectly civilized fashion. It has not, to my recollection, affected tube life, but it's not as if my memory is a primary data-logging device.

I have a big Hewlett Packard power supply which has multiple 12AX7 in it. ONE of them looks like it is going to absolutely freaking explode on startup. The others, ho hum.

I guess it would behoove me to note the mfr of the Jumpin' Jack Flash 12AX7 and compare it to what brands the others are and whether they are different and what happens when I swap 'em around & report back.

I have seen this before. It's alarming when you see it but I can't recall any impact.

Now, if the tube went berzerk due to the socket miswiring, that's a different story. If you put B+, even reduced preamp-type B+ on the cathodes, then no doubt you've blasted the tubes way the heck out of heater-cathode specs. And it wouldn't surprise me a bit that the tube arced or otherwise got destroyed.

[stingray_65]

These Amperex's "flash" on start up.

Thats to say the suddenly glow bright then fade to red.

Ray

[eleventeen]

Well, of course I could not resist investigating the situation discussed in my prior post.

It appears that ALL the 12AX7 in this supply are OEM...because the points on the tubes are all dipped in red paint. They all run off 12.6 VAC. (The main power transformer in tube-type HV power supplies typically have loads of heater windings, because
1: One high-current [6-10 amp] one goes out to the front panel;
2: The pass elements (4 qty 6L6 in this case) supply the HV output (up to 500 VDC) directly from their cathodes, which implies that heater-to-cathode specs will be exceeded. The way this is handled is to short the cathodes of all the 6L6 to one side of the heater winding for that group of tubes, meaning, the heater winding is lifted to big volts)
3: Same can be said about some of the 9-pin control tubes; often some of their cathodes are at -200 to -300 volts so their heaters would also exceed H-to-K specs in the other direction.
4: The beefier supplies of this type either incorporate an electronic delay (via goofy heater-relay tube) or warn in big front-panel lettering to allow 30 seconds before turning on the big B+. before HV is turned on. This makes sure the heaters are all fully heated before slamming the tubes with big volts. It's thus quite possible that upon turn-on, the power transformer is sort of in a no-load condition, which means as we all know that volts could be high.


The Jumpin Jack Flash was a Telefunken 12AX7. The sleepy ones are Amperex. The Amperex ones are marked "made for hp by Amperex" The Telfunken is not so marked, but it's tip is red-painted so IMO it's OEM.

An RCA 12AX7 placed in the socket for the Telefunken doesn't flash on startup. Conclusion? Some do (flash), some don't. 

[jojokeo]

I would be glad to trade you for those old stinkin scary flashers??? 

[shortfuse]

Ok received my replacement transformer last night.  I did not ask this before but now i am gun shy should I use the 125v tap or 115v tap on the primary side of the PT?  Hammond 269EX
Hope to be making music with it tonight and not smoke again.

[RicharD]

should I use the 125v tap or 115v tap
Start with the 125V tap.  If you need more secondary voltage, swap to the 115V tap.

Hope to be making music with it tonight and not smoke again.
Lamp limiter is your friend.

[shortfuse]

Can someone please look at the DPDT boost switch and tell me if it is wired correctly on one of the layout dwgs in a previous post?  And if it should be an On On Switch.  I think I have something wrong here.  Would it be connected like doug shows here http://www.el34world.com/projects/hotswitch.htm except i dont think pin 6 would be utilized on my application.  The problem is the guitar signal is not making it to the pots the way the firefly diagram has it or would i just jump the guitar input straight across the switch Continuous i n conjunction with the diagonal jumper which switches stages.

[sluckey]

Can someone please look at the DPDT boost switch and tell me if it is wired correctly on one of the layout dwgs in a previous post?  And if it should be an On On Switch.

The switch is wired correctly, ---EXCEPT---, there should be a ground connection on the top left lug. A DPDT switch is an ON/ON switch.

I think I have something wrong here...    ...The problem is the guitar signal is not making it to the pots the way the firefly diagram has it...

Wire it like the layout and the guitar signal should make it to the pots in either switch position, unless something else is wired wrong.

[shortfuse]

Alas my 1st amp is complete.  I put the ground on and i now have very very minimal noise with with everything on, boost switch engaged, Vol and Boost Vol to 11,  & the guitar plugged in.  It sounds great for a 1.5w amp.  If i roll the boost vol to about 8.5 with the Main vol to 10 it is dead quiet so I am happy.  Now to build a cab for the chassis.

Thank you, Thank you, Thank you to all who posted here & IM'ed to help me out.  I also want to say thanks to those that didn't post here but post all the time, their other posts I have been reading over time along with all Doug's info was a huge help and wealth of information.  Hopefully in time I will be able to give back with information and not just be a sponge.
This was definitely a learning experience for me.  A am now glad that I listened to several of you that encouraged me to start small, low watt and simple or should I say not as many components.  Although picking a small chassis like I did didn't help matters any and I may have saved myself had I been able to see the tube sockets the 1st time (most likely not those tubes were destined to be wired backwards by me).  Even though it cost me (2) PT transformers and (2) 12AU7's the outcome was good in the end.

I can post the BOM and costs if anyone wants to see them otherwise I am going to let this thread sink to the bottom of the forum.

Again Many thanks Steve