Transformer question on filament amp

[Redfishbum]

I have a basic question.  I'm thinking of putting together a Ricktone Type 19.  He uses two back to back transformers for isolation....his have 120V primary and then 12-0-12 secondary.  He then takes the center tap and one of the secondary leads to then go to the filaments of the tubes.

I happened upon a couple of low buck transformers with that have 120v primary and 12V secondary as 6-0-6 with center taps.  My thought is to connect the 6 volt secondary together and then take each of those to the filaments of the tubes and also ground the center taps.

Am I on the right track?

Thanks!

[shooter]

My thought is to connect the 6 volt secondary together and then take each of those to the filaments of the tubes and also ground the center taps.

You mean twist the 2 blue wires together, and ground the yellow?  If so that will probably give some stinky results.

I believe you can do something like this, but you won't have 3-0-3, it's just be 0-6

[Redfishbum]

Thanks for the response.  Not exactly.  I will have two of the same transformers back to back....each blue on the secondary will be connected to the corresponding blue.  I think i need to ground each center tap?

Then I will go from the lug where I solder each blue and treat run to the filaments as a twist, just as I would if I had a step down transformer.

I'm just trying to get some clarification because the Ricktone19 schematic uses a 24 volt secondary (12-0-12) and he connects one side of the 12 and the center tap to get 6 V.  I would not need to do that.

Just really need to figure out what I do, if anything, with the center taps.  Based on my champ build that had a center tap grounded from the 6.3V wires, I would think I need to do that as well.

Sorry for the ramble.

Bart

[mresistor]

Ricktone 19 first PT seems to me to have 6.3-0-6.3 secondary ...  and schematic says 12.6 VCT..   I don't know why not wire like the schematic...


http://el34world.com/charts/Schematics/files/rick_tone/RickTone19.pdf

[mresistor]

in the Rt 19 schematic the 6.3vac looks to be floating, not referenced to ground.

[shooter]

the 6.3vac looks to be floating

Yup, I wouldn't be putting any 100ohm fake grounds in that config.  I think it's called a *bucking* configuration?  any easy way to get your 6.3vac, while still getting B+ from a tranny without Fil taps.

I happened upon a couple of low buck transformers with that have 120v primary and 12V secondary

wire them just like the schematic, and I believe all will be well, get creative and, well, Steinbeck? comes to mind, about best laid plans......

[sluckey]

Just really need to figure out what I do, if anything, with the center taps.  Based on my champ build that had a center tap grounded from the 6.3V wires, I would think I need to do that as well.

On the PT that will be connected to the wall socket... Connect the CT to ground. Just tape off the CT on the other PT.

This will give your filaments a ground reference to reduce hum and will not interfere with the second PT that is used for B+.

EDIT... Ignore that. It's wrong.

[Redfishbum]

Perfect.  Thanks guys.

B

[sluckey]

Whoa! Wait a minute. I misunderstood about your transformers. Disregard what I said in my previous post. Wire your PTs exactly like the schematic that mresistor posted. Sorry

[Redfishbum]

Thanks a ton for the follow up.  One thing that has caused me confusion is the attached schematic for a RickTone Tube-o-Drive.  Why is there a difference in the primary transformer wiring compared to the Ricktone19?

[sluckey]

Why is there a difference in the primary transformer wiring compared to the Ricktone19?

Because the tube requires 12V for filaments. The tubes in the other circuit required 6V for filaments.

For the ricktone19 you can still create an artificial center tap for the filaments by using two 100Ω resistors, one from each line that goes to the tubes to ground. Still leave the CT of the second transformer taped off.

[shooter]

For the ricktone19 you can still create an artificial center tap

So that doesn't mess up the 2nd tranny output for B+ and ground?

[sluckey]

So that doesn't mess up the 2nd tranny output for B+ and ground?

I don't see how it could. 12.6v is still being supplied to the second transformer. What would change? Am I missing something simple (like earlier)?

EDIT... added pic

[mresistor]

I think the only thing that might happen with the artificial center tap is that some of the 12.6v might get decreased... dependent upon the current rating of the transformer. But than again, the floating filaments are pulling current too. So maybe not.

My question is, what is the advantage, if any, of adding an artificial canter tap on the filament string? It's more parts and really I haven't seem many of these tubes fail with a filament short.


Are EL84s running modestly prone to screen/filament shorts? or plate filament?

[shooter]

Am I missing something simple

That's why I asked! somehow - without any *logic* it didn't seem correct, which should be clue that it IS right

what is the advantage

you have less potential for hum to be big, 3-0-3 insures lower hum leaking than 0-6, at least that how I understand it

[mresistor]

you have less potential for hum to be big, 3-0-3 insures lower hum leaking than 0-6, at least that how I understand it

Ah yes   forgot about the hum factor..