#26 pre amp

[stajo]

Erik: I dont think he has any current thru the tubes at all atm. Surely the cathode needs to find ground somehow.

Merlin. Swich on once more and see if you have any current between filament pin and ground.

 

[merlin el mago]

I have 1,485V in each heater

 

[andyjevans]

If Rod's board is working correctly you should have about 1.5v between the two filament pins of the 26. You should then have around 11volts or whatever across the cathode resistor. You should check that these voltages are correct BEFORE you fire up the B+. Check all the wiring: Rod's board output has - to ground and + to one side of the 26 filament. The other side of the filament is connected to ground via the cathode resistor, and this should have about 11v on the top of it.

 

[merlin el mago]

Rod's filaments are working OK in both tubes.

 

[ErikdeBest]

Hi Merlin, just to confirm, how much voltage are you measuring between (one end) of the filament and ground - that is the voltage over the cathode resistor, as Andy is asking.

 

[merlin el mago]

Rod's filament are floating.

 

[stajo]

Rod's filaments are working OK in both tubes.

How many volts exactly do you have between each filament pin and trafo center tap/ground?

 

[ErikdeBest]

So you have the + and - of the filament regulator across the filament of the #26? In other words, you do not have it across the filament AND the cathode resistors?

 

[merlin el mago]

Filament trafo haven't center tap. I use one separate for each tube filament.

 

[stajo]

Rod's filament are floating.

filament trafo shall float, not the filaments themselves. if it all floats, you dont connect to ground and no current can pass the tube

 

[stajo]

Filament trafo haven't center tap. I use one separate for each tube filament.

I ment B+ trafo

 

[vgeorge]

If the tubes are OK, check your wiring on the cathode, as suggested. There is no current draw.

 

[merlin el mago]

So you have the + and - of the filament regulator across the filament of the #26? In other words, you do not have it across the filament AND the cathode resistors?

+ reg goes direct to filament, - reg goes to 10R and continues to filament

 

[merlin el mago]

I ment B+ trafo

I have two 125VAC to get 250VAC, so between each trafo is the center tap for B+?

 

[stajo]

I have two 125VAC to get 250VAC, so between each trafo is the center tap for B+?

Yes

For filament circuit check your own schema #2597

It must go to ground as in that schema, not float

 

[ErikdeBest]

+ reg goes direct to gilament, - reg goes to 10R and continues to filament

Hi Merlin. I just checket your pictures in post 2593 and it looks as if you do not have a connection from the end of the resistors to ground. As you said: the whole thing is floating.

So, + reg goes to one side of the filament, other side of the filament goes to 10R resistor, other side of the 10R resistor goes to - reg. This - reg should also be connected to ground of the amplifier!

 

[vgeorge]

You are saying that you are using two 2x125ac transformers? Kindly clarify you setup exactly.

 

[merlin el mago]

Yes

For filament circuit check your own schema #2597

It must go to ground as in that schema, not float

I haven't grounded the cathode resistors, Rod told me his filaments regs must be connected floating never connected to ground.

 

[merlin el mago]

You are saying that you are using two 2x125ac transformers? Kindly clarify you setup exactly.

George I don't see any difference using 2 x 125 VAC or 1 x 250VAC, I don't understand what's the difference?

TIA

 

[vgeorge]

Have you taken the center of the two transformers to ground? Are the transformers 125ac or 2x125ac? How have you wired them?