Troubleshooting first build

[Codymobley]

When you do get it up and running that speaker jack right next to the 6SQ7 might make for a oscillation problem.

Also unless I missed it I only see one speaker jack, so how as you have stated do you have it wired for 8 and 16 ohms?

Also in your post from Friday you seem to be confusing mill volts and milliamps .

I built it in a 5E7T chassis and had to add the hole for the tremolo tube. I'd be happy at this point to hear oscillation, but can move them after the fact once I actually get some noise out of the circuit.

The chassis has output jacks on either side of where I placed the 6SQ7. I have 8ohms to the jack on the left and 16ohms on the right with the common lead connected to both.

[Codymobley]

Is the red wire coming from the recto tube socket the CT of the OT?

Yes, it is the CT of the output transformer.

[Stevem]

Where’s the power supply section of your hand drawn schematic?

I don’t see how any of your power supply filter nodes are reviving and voltage from the rectifier where you said you have the red wire of the OT hooked up.
There needs to more then that one wire there.

[Codymobley]

Where’s the power supply section of your hand drawn schematic?

I don’t see how any of your power supply filter nodes are reviving and voltage from the rectifier where you said you have the red wire of the OT hooked up.
There needs to more then that one wire there.

I only drew out the diagram to assist in wiring up the eyelet board. I used the schematic for wiring the transformers and power. The power transformer is connecting to the rectifier at pin 2 and 8 ( 5v), Pin 4 and 6 (330v). The CT (B+) from OT is connected to the rectifier at pin 8 where the filter cap is also connected. The OT is connected to 3rd pin of the power tubes (6v6) at pin 3 with the blue and brown leads.

There are two additional leads (white and gray PL as shown on the OT datasheet I posted earlier) that I have rolled up and out of the way and not connected.

[Codymobley]

I've attached the data sheets here for ease of reference.

[Codymobley]

Where’s the power supply section of your hand drawn schematic?

I don’t see how any of your power supply filter nodes are reviving and voltage from the rectifier where you said you have the red wire of the OT hooked up.
There needs to more then that one wire there.

If I'm looking at the schematic and understanding you correctly I am missing the B+ being connected to the rest of the filter caps/circuit and plates. Is this correct?

[maxkracht]

On your schematic, the 3H directly after the rectifier is a 3 Henry choke. If you do not have this in place, nothing but the power tube plates are getting power. If you do not have a choke, you could replace it with a resistor, somewhere around 2-5k 5W is probably ok.

Edit: be sure you are measuring the DC voltage of ALL of your filter caps and make sure they are discharged before you make any changes. They can store a charge and possibly kill you. This is especially dangerous when you are uncertain what is working/connected.

[Codymobley]

On your schematic, the 3H directly after the rectifier is a 3 Henry choke. If you do not have this in place, nothing but the power tube plates are getting power. If you do not have a choke, you could replace it with a resistor, somewhere around 2-5k 5W is probably ok.

Edit: be sure you are measuring the DC voltage of ALL of your filter caps and make sure they are discharged before you make any changes. They can store a charge and possibly kill you. This is especially dangerous when you are uncertain what is working/connected.

I've been bleeding the filter caps each time I work on the circuit. I have a 5w resistor that I'll insert between the .22uF and .10 uF caps in place of the choke. Thanks!

[Codymobley]

Attached all of the B+ points and we have sound (sounds like a grounding issues, but still...), there is an issue in the preamp that the pop test revealed that I'll chase down but for now I'm happy with sound.

[Codymobley]

The above “pop test” is useful for finding where the signal is lost, but I would start with a DC voltage survey. Measure voltages at each of the power supply nodes (at the positive end of each filter cap). Then, measure voltages on the tube pins, plates, grids, and cathodes. Record those and post them. The problem area will be often be revealed. Sounds like the heater circuit is working, but measure AC volts to be sure that it is in the right range.

Here are the voltage readings, the B+ at all points measured 378v:
5Y3 plate 349 vAC
6v6 plate 374v, grid 0v, cathode 24v
6v6 plate 374v, grid 0v, cathode 24v
12ax7 plate 349v, 309v, grid 0v, cathode 0v
6sq7 (tremolo) plate 8v, grid 1v, cathode 0v
5879 plate 375v, grid 34v @pin 7, cathode 6v
5879 plate 376v, grid 63v @pin7, cathode 1v

[Stevem]

Good to hear that you’re making progress, but note that the power supply filter caps on either side of that 5 watt resistor to added are not .22 uf and .10 uf, there 22 uf and 10 uf.

There’s a thousand times different between those values!

If you really had those in place there would be no filtering taking place .

[martin manning]

- Power transformer has too much AC voltage (+49V) so B+ is high (+70V)
- 6V6's are running very hot. You need a larger cathode resistor to bring it down to a reasonable operating point.
- Your phase inverter tube is not conducting at all, 0V on the cathode. Maybe a missing ground?
- You should be seeing some voltage drop along the B+ rail since the preamp tubes are drawing some current. If you keep the current PT I would increase the first dropping resistor to get the preamp voltages back in line with the original.

[maxkracht]

This is unrelated to the current problems, but I believe you are also missing a ground reference for the 6.3v heaters. The typical way to do this is with a pair of 100 ohm 1/2w resistors, one going from each side of the 6.3v winding to ground or to the power tube cathode.