New 5e3 build voltage check

[Ledvedder]

I'm just wondering if these voltages are acceptable on my new 5e3 build? B+2 seems a bit high at 333V, which is also affecting pin 4 on the power tubes. Also, the v1 voltages seem a bit low. I've noted my voltages in pen on the attached image.

[sluckey]

Look fine to me.

[bmccowan]

When I get that close to spec, I am extremely happy and have a beer. Since its election season... they are all within the margin of error. Play it yet?

[Ledvedder]

sounds ok. Not great yet. I think I'm having an issue. The NFB switch works in only position 1. In the center position, the sound just fizzles out. In the 3rd position, I get sound, but as soon as I whack a note, it fizzles out.

I'm, also having a hard time deciphering which side of the bias switch is stock 5e3, and which is fixed bias.

[sluckey]

I'm, also having a hard time deciphering which side of the bias switch is stock 5e3, and which is fixed bias.

In the stock position there will be zero vdc on pin 5 of the output tubes and some positive vdc on pin 8.

In fixed bias there will be some negative voltage on pin 5 and zero volts on pin 8.

[Ledvedder]

I'm, also having a hard time deciphering which side of the bias switch is stock 5e3, and which is fixed bias.

In the stock position there will be zero vdc on pin 5 of the output tubes and some positive vdc on pin 8.

In fixed bias there will be some negative voltage on pin 5 and zero volts on pin 8.

This is with the output tubes installed?

[thetragichero]

fixed bias with or without tubes installed. cathode bias there won't be negative voltage on the grid but there also won't be positive voltage on the cathode without tubes installed

[Ledvedder]

I'm, also having a hard time deciphering which side of the bias switch is stock 5e3, and which is fixed bias.

In the stock position there will be zero vdc on pin 5 of the output tubes and some positive vdc on pin 8.

In fixed bias there will be some negative voltage on pin 5 and zero volts on pin 8.

This helped me determine which switch position was fixed vs cathode. Thanks!

Now to figure out what's going on with the NFB switch.

[JPK]

You may need to flip the OT primary leads for the NF. With my 18 watt AX84 October I had to do that. It will make a nasty noise if it's wrong. I had a switch to turn NF on or off. I haven't looked at what your three way does.


 Also had to increase tail resistor for fixed bias. It was a little too hot even with the pots dialed all the way down (I had one for each tube).

[Ledvedder]

You may need to flip the OT primary leads for the NF. With my 18 watt AX84 October I had to do that. It will make a nasty noise if it's wrong. I had a switch to turn NF on or off. I haven't looked at what your three way does.


 Also had to increase tail resistor for fixed bias. It was a little too hot even with the pots dialed all the way down (I had one for each tube).

My 3 way switch is doing stock mode/no v2a bypass cap/56k NFB with no bypass cap. I've attached the diagram.

I haven't gotten to the fixed bias adjustment yet. Did you just use the instructions here, https://robrobinette.com/Tube_Bias_Calculator.htm?

[JPK]

You may need to flip the OT primary leads for the NF. With my 18 watt AX84 October I had to do that. It will make a nasty noise if it's wrong. I had a switch to turn NF on or off. I haven't looked at what your three way does.


 Also had to increase tail resistor for fixed bias. It was a little too hot even with the pots dialed all the way down (I had one for each tube).

My 3 way switch is doing stock mode/no v2a bypass cap/56k NFB with no bypass cap. I've attached the diagram.

I haven't gotten to the fixed bias adjustment yet. Did you just use the instructions here, https://robrobinette.com/Tube_Bias_Calculator.htm?

I can't remember if I used that since I built the amp 10 years ago. I ended up using 24ma for my 6V6GT's. I used 1 ohm in line resistors and had test ports on mine which were really handy. Whatever you measure in mv is the ma bias current.


PS: I ordered my 5E3 kit from Boothill today. My build is going to be super stretched out time-wise. I like taking my time especially since I'm retired. Hopefully it's not done before xmas.