Rocket first fire up...not so much

[studiodunn]

I finished this build today, went to fire it up and things didn't go well.
As I brought the power up on my variac before getting very much AC input at all I could hear the variac wasn't happy. It had the electrical moan that said things weren't going to go well, so I unplugged and tried to find a mistake.

This is actually my first tube rectifier build, so I'm looking there first. I have the PT secondaries going into pin 8 and 2 and pin 8 feeding the first caps and into the standby switch.

Does my 5v tap need an artificial CT?

Taylor Rocket Schematic- Updated 6-5-08.pdf

40-18065.pdf

IMG_7618.jpg

IMG_7620.jpg

IMG_7623.jpg

[martin manning]

5VAC (yel) goes into 8 and 2, with 8 continuing on to the reservoir cap. HT (red) leads go into 4 and 6.

[studiodunn]

5VAC (yel) goes into 8 and 2, with 8 continuing on to the reservoir cap. HT (red) leads go into 4 and 6.

Wow thank you Martin. That is a pretty embarrassing mistake....and I've made a few.

[Stevem]

For a easy added filament noise reduction mod run a wire from pin 3 of any output to to the still jointed but lifted from ground end of the 100 ohm resistors that now form the artificial center tap .

[studiodunn]

For a easy added filament noise reduction mod run a wire from pin 3 of any output to to the still jointed but lifted from ground end of the 100 ohm resistors that now form the artificial center tap .

I don’t have an artificial CT at this point. The 6.3v tap on the PT I’m using had a CT.

Are you referring to the 5v tap and should I create a CT there?

IMG_7625.jpg

Amp is up and running. It sounds pretty good right off the bat, but is pretty noisy. It is fairly clean and has gobbs of bass, but I was expecting both.
I'm sitting right at 300v on the plates which I know is higher than the voltage chart I got from the Rocket docs. I'm carrying that extra 15v all through the B+.

[martin manning]

Are you referring to the 5v tap and should I create a CT there?

No! That 5V winding is sitting at B+ voltage!

[studiodunn]

Are you referring to the 5v tap and should I create a CT there?

No! That 5V winding is sitting at B+ voltage!

I see that now Martin. After staring at the schematic just now I finally understand what I thought vs. what it is.

[Stevem]

So lift that heater center tap and apply the DC voltage sitting on the Cathode ( pin 3 of EL84s ) of the output tubes to it.

[studiodunn]

So lift that heater center tap and apply the DC voltage sitting on the Cathode ( pin 3 of EL84s ) of the output tubes to it.

So I can just take the Heater CT and connect it to the + end of my 50ohm/220Uf bias circuit? I have 8.8v on the cathodes of the el84s

ct.PNG

[dorrisant]

So lift that heater center tap and apply the DC voltage sitting on the Cathode ( pin 3 of EL84s ) of the output tubes to it.

So I can just take the Heater CT and connect it to the + end of my 50ohm/220Uf bias circuit? I have 8.8v on the cathodes of the el84s
ct.PNG

Yes. It is called an elevated center tap.

[Phil_S]

On the non technical side of this, there is only room to applaud. There is no need to feel embarrassed by an error like this. You followed good practice, which is intended to 1) keep you safe, 2) keep your house safe, and 3) keep your build safe. All 3 goals were met because you did what you should. Fixing a wiring error or misunderstanding is no big deal!

[studiodunn]

So lift that heater center tap and apply the DC voltage sitting on the Cathode ( pin 3 of EL84s ) of the output tubes to it.

So I can just take the Heater CT and connect it to the + end of my 50ohm/220Uf bias circuit? I have 8.8v on the cathodes of the el84s
ct.PNG

Yes. It is called an elevated center tap.

can a hum balance pot be used as well with the elevated CT?

On the non technical side of this, there is only room to applaud. There is no need to feel embarrassed by an error like this. You followed good practice, which is intended to 1) keep you safe, 2) keep your house safe, and 3) keep your build safe. All 3 goals were met because you did what you should. Fixing a wiring error or misunderstanding is no big deal!

Much appreciated Phil. I still feel like such a newb with so little knowledge when it comes to some very simple things.

[Stevem]

No on that .
Once you place that Cathode voltage on the center tap you can not just then basically short it to ground as is done with what most of us call a humdinger.

[pompeiisneaks]

No on that .
Once you place that Cathode voltage on the center tap you can not just then basically short it to ground as is done with what most of us call a humdinger.

But if that's the 'center tap' that new elevation, couldn't you do a humdinger 'grounded' to that tap instead? I.e. balance the heaters between the dc reference center point?

I'm just throwing it out there, that could be very wrong for many reasons, just wanted to ask the question.

~Phil

[sluckey]

can a hum balance pot be used as well with the elevated CT?

Yes, just connect the wiper to the elevating voltage. No problem, unless it's a two terminal pot with the wiper connected directly to the metal casing by the manufacturer. These two terminal pots were very common in consumer electronics in the '60s. See pic for an example...