few final firefly qs

[jimmy]

hi all

ive been working hard on my firefly and im almost done!!! i got the output transformer (Hammond 125A) and the tubes (Electro Harmonix) in the mail today and i have a few quick questions.

1) on the POWER transformers primary side, i have two wires. one is blue, the other is brown. which one goes to the Live or Neutral side of the AC socket?

2) on the POWER transformers secondary side, there are 3 wires, 2 are yellow, and the middle one is white. i am using two power transformers back to back, and the transformer is marked 6.3, 0, 6.3 so i joined the 0 and top 6.3 wires together. is this correct?

3) on the OUTPUT transformers primary side there are 3 wires, a blue one, a red one in the middle ( i assume this ones where B+1 goes) and brown. which wire goes to the 1KV cap and which wire goes to the 5W resistor?

thatll do,
Cheers
Jim

[Peter Snowberg]

1) on the POWER transformers primary side, i have two wires. one is blue, the other is brown. which one goes to the Live or Neutral side of the AC socket?

The blue is neutral and brown is hot.

2) on the POWER transformers secondary side, there are 3 wires, 2 are yellow, and the middle one is white. i am using two power transformers back to back, and the transformer is marked 6.3, 0, 6.3 so i joined the 0 and top 6.3 wires together. is this correct?

That should be just fine in this application, but I would tend to connect the 6.3 leads from one to the other and leave out the white center taps (assuming you are powering the tube heater with 12V). Either way will be fine here since you are not using much current from the step-up, but if you use the entire low voltage winding on both transformers, it will be easier on the windings.

3) on the OUTPUT transformers primary side there are 3 wires, a blue one, a red one in the middle ( i assume this ones where B+1 goes) and brown. which wire goes to the 1KV cap and which wire goes to the 5W resistor?

You are correct about the red getting B+, and you could go either way with the blue and brown. Take your pick.

Pardon me if you already know this, but the most important thing to keep in mind is that you MUST have a speaker or at least an 8 ohm resistor connected at all times. If you don't have a load, the smallest noise that would be coming out the speaker gets reflected back into the output tube and that will eat it alive. I use a switching jack (SwitchCraft 12A) and put an 8 ohm 5 watt resistor on the switched contact. That way if you don't have a speaker installed, you're still safe. It also makes for an easy way to use the amp for silent direct recording if you add a line-out jack too.

Best of luck! I'm looking forward to your success report.

-Peter

[petemoore]

I'm just happy that you decided to build a tube amp. Just talking about tubes brings to mind that warm inner glow...lol !!!

[jimmy]

cheers!! all is looking good. tube amps just look so cool... although i was crying with laughter when i had a look at the tubes. they look like hat for live elves or something. comedy gold.

ive added in a marshall tonestack as well, that should be good. now i have to wait till tomorrow, i ran out of wire  :evil:  

thanks!!
Jim

P.S. pics will be coming soon

[Doug H]

Let us know how it turns out!

Doug

[Ansil]

sounds cool i am trying to get a pcb done for one. to make it easier.

i hate perf!!

[Prive]

Hey Ansil, do it point to point, is easy and "vintage" hehehehe!!!! :lol:

Saludos, Marcelo.

[jimmy]

hi all.

its FINISHED!!! but...

i think ive stuffed the transformers. i asked the question about the colour of the leads going where because i had it hooked up previously to check if i was getting the correct voltage at the heater, and i wasnt. this may have had something to do with me getting the leads mixed up. i was thinking hmmmm blue, as in electric blue? and brown. dirt. earth. ground = neutral yay.

i now know that this is wrong. do i need to make another trip to jaycar?

cheers
Jim

[Peter Snowberg]

Hmmmm..... sorry, I answered based on standard European color codes for AC cords. I was thinking cords and didn't think you were speaking of transformer leads for some reason. :? Maybe I shouldn't post so early in the morning.

How many primary leads are there? If there are only two it shoud work either way. Too bad the Jaycar site only shows the secondaries.

Jaycar 12.6VCT @ 500 mils

The heater pulls about 150ma at 12.6VAC so you should have plenty to spare. What voltage are you seeing in-circuit?

-Peter

[jimmy]

hmmm yep theres only 2 primary leads, blue and brown.

my voltage reading is (assuming your multimeterleads go from heater pin 4 to filament pin 9)

errrrr 0.0V

thats no good. i dont seem to be getting any voltage anywhere. i have a 240V led as my on light. it goes IEC socket, DPDT Mains Toggle, Led, Transformer A, Heater Wires, Transformer B, Power Supply etc...

what i mean is i have a solder joint between two wires coming from the mains switch, and transformer a. at the same joint, i have 2 wires going to the LED. do i need a current limiting resistor?

cheers
Jim

[Ansil]

Hey Ansil, do it point to point, is easy and "vintage" hehehehe!!!! :lol:

Saludos, Marcelo.

i don't know where i can find the good strip board or whatever you call it around here.

[Peter Snowberg]

my voltage reading is (assuming your multimeterleads go from heater pin 4 to filament pin 9)

errrrr 0.0V

thats no good. i dont seem to be getting any voltage anywhere. i have a 240V led as my on light. it goes IEC socket, DPDT Mains Toggle, Led, Transformer A, Heater Wires, Transformer B, Power Supply etc...

what i mean is i have a solder joint between two wires coming from the mains switch, and transformer a. at the same joint, i have 2 wires going to the LED. do i need a current limiting resistor?

OK, with just two primary leads you don't have the option of wiring it wrong so lets look at it step by step.

When you say 240V LED I'm assuming this is a panel indicator made for mains voltage. If you connect an LED to mains voltage that doesn't already have a limiting resistor, it will simply explode in the first milisecond you have the circuit powered and everything else should still function.

Do you have voltage showing at the IEC socket? Some of those buggers have filters and/or fuses inside. Then is there juice at your mains switch? And then is there juice at the connections to the LED and transformer primary? If you answered yes to all those questions, the transformer is starting to look suspect. Check for continuity across the transformer primary. You should see a couple of K there. If you don't see that, the primary is open. It could simply be dead from the factory.

I'm assuming you're using one yellow and the white center tap for powering the heater and that you have pins 4 and 5 tied together. That should be fine, but I would use both yellows and apply power between pins 4 and 5 while leaving pin 9 and the white center tap unconnected. Either way should work.

It sounds like the problem is on the primary side.

Good luck,
-Peter

[jimmy]

im sure ive got juice at the led/transformer connection because the light works!! i checked the transformers and i get about 500 ohms on each one.

suggestions?

cheers
Jim

P.S. when im checking voltages, my multimeter has to be on the side with the little ~ on it doesnt it?

P.P.S. when im checking the heater pins, the multimeter leads have to be on the heater pin and where exactly?

[Peter Snowberg]

Great; sounds like the primaries are functioning....

The next spot to check would be across the secondary of your 1st transformer. Look for voltage (with the meter on the ~Volts setting ) across the yellow secondary wires. You should see anywhere from 13-18 (or so) volts with no tube plugged in.

There are two ways you could wire the tube so I'll cover both:

(1) If you are using one yellow and the white center tap, you should have one wire going to pin 9 and the other going to pins 4+5. Measure voltage between these two wires. You should see roughy 7-9 volts.

(2) If you are using the two yellows, pin 9 should be unconnected, pin 4 should get one yellow and pin 5 should get the other. You should see roughly 13-18 volts between the yellows.

In either case you just want to make sure you have voltage across the secondary wires. The voltages above might sound funny, but that's reality for you . When you add the current draw of the tube heater it will drop down a bit to what looks like a more real value.

If you have low voltage, next check for high voltage AC on the output of the 2nd transformer. If you see that, I think it's time to install the tube, connect your speaker, and try powering it up.

The next next question becomes, do you have glowing heaters?

It sounds like you're really close!

-Peter

[jimmy]

riiiiight im getting 3.1V on the secondarys, no heater glow,  and nothing on the second transformers primarys. i dont know if i have it hooked up right now, ive got the transformers wired back to back, as in the secondarys are tied together, yellow to yellow and white to white. correct?

cheers
Jim

[Peter Snowberg]

Just to make sure I'm on the same page.... this was a 12.6 VCT transformer, wasn't it?

That's the voltage I would expect to see on a 6.3 VCT transformer and that would explain the lack of visable glow on the heater because it's just too low. If the transformer is actually a 6.3VCT (measure across the yellow wires), you'll need to use both yellows instead and wire the heater with one yellow going to pin 9 and the other yellow going to pins 4 and 5. That should get your heater glowing.  :? (realizing I've never said that to a guy before. LOL!)

What I don't understand is why you don't have high voltage coming out the second transformer. That is quite strange.

Take a look at this illustration:
http://www.freewebs.com/qrp/snippits.html

That's how I would wire them. It makes use of the whole secondary winding of each transformer to reduce stress.

What voltage do you see across the yellows?

-Peter

[jimmy]

yeah im sure its a 12.6VCT. ill have to get back to you on the voltages as my multimeter only has those stabby probes and i need some clips to get reliable readings.

till tomorrow,
Jim

[jimmy]

right good news and bad news. i got some readings on the secondary yellows - 9. something volts. i refered to a previous post an you said that would mean a 6.3V transformer. hmmmm. different to what the box said. anyway i wired it up as you said, and pluged the tubes in, and as is daytime, i cant really see if there is a glow, but when i went to remove them, they were quite warm. and i also got a reading on the secondary transformer primarys. errr 0.5V. that aint right. so i looked about and after close inspection i determined that my transformers were hooked up like this:

--------| - |-------to heaters====| - |=======
         | - |                                | - |
==== | - |====to heaters-------| - |-------------

rather than

--------| - |-------to heaters-------| - |-------------
         | - |                                | - |
==== | - |====to heaters====| - |=======

so i made a swap and there was no difference. i then decided to give the whole thing a go so i plugged the speaker and my geetar in and nothing happened. frustration.

cheers
Jim

[Peter Snowberg]

That's a bummer.

That 9V reading could be explained in a couple ways I could think of. It could be the first transformer is a mislabeled unit of an unknown voltage or current, or the second transformer is bad, and the first one is OK.

In any case, that reading from the second one is sure wrong and the first is suspicious.

I would say the next thing to do is to check the transformers out by themselves. Disconnect them from the circuit and wire up the mains on each one, then check the secondary voltages. If you aren't seeing 12.6V+ across the yellows, I would return them to Jaycar with a complaint. Without the proper readings, you could damage the tube and the FireFly is just too cool of a circuit to get discouraged over.

Was that 9V with the tubes plugged in? With a 12.6V 500mA transformer you should be seeing pretty close to 12.6 volts with the tubes in. Each tube takes 150mA at 12V for the heater which is more than enough load to have a stable output near the rated voltage. You should have 200mA left over to power the step-up unit and get a high voltage reading.

Wait a second..... :shock:

Let's call the wall input voltage the mains voltage, the output of the first transformer as the filament voltage, and the output of the second transformer as the HT output.

You're seeing .5V on the HT side?, I'm wondering if you have a problem with the bridge rectifier shorting the HT out through a diode. That would show you the .5 volts and it would load down the first transformer so you wouldn't get the full 12 filament volts. That could explain everything, even with known good transformers. The first test should be to disconnect the HT transformer secondary with the tubes installed and check the HT voltage, then check the filament voltage. Remove the tubes (leaving the HT output disconnected), then check the filament voltage and the HT output again.

That should shed light on the transformer condition.

The .5V and 9V reading suggest a short in the HT section.

Good luck,
-Peter

[jimmy]

AHHHHHH HAAAAAAAAAAAA!!!!

took the short circuit advice, duct taped the bottom of my stripboard up, 220V on the second transformers primarys. peter snowberg = smartest man alive. in about an hour ill be having dinner to the romantic lighting of tubes. dont know about music but, we'll see.

cheers
Jim