Tweed Tremolux build 5G9, need some help !

[tweedmarmot]

Hi guys, I have been building a 5E9A that is amazing and I didn't get any issues building it.

Now I am building a 5G9 with Mercury Magnetics PT, OT and choke. All voltage looks fine except the Bias (near the 10K Pot I have +58V !?) as I am suppose to have -69V...

What could be wrong ?


Thanks !

[tweedmarmot]

And of course, I have no sound at all, no humm, nothing. :S

[Daver]

Reversed diode in the bias supply?

[tweedmarmot]

Hi Daver, That bias supply Diode, would it be the 10K potentiometer ?

tremolux_5g9_layout.pdf

[Daver]

No. On that schematic it's the square next to the pot labeled "Sel. Rect." (silicone rectifier) It looks like from your picture that you're using that style. The picture is a little unclear but it looks like it's just to the left of the pot. I'm not sure how or if it's marked with polarity. You can remove the power tubes, reverse the wires on the rectifier (diode) and measure the voltage again to make sure it's negative.
Dave

[tweedmarmot]

Actually, it is a mounting bracket that is on the left of the pot.

is that "Sel.Rect." can be replace by a potentiometer like i did or is there something missing ?

[Daver]

Looking at the picture again.... It looks like you have the bias wire coming from the power transformer going directly to the bias pot. Is that correct? If so you will only get positive voltage. You need a diode to rectify that AC voltage into negative DC. You can use a 1N4007 diode with the stripe end connected to the bias supply wire coming from the transformer. Is this a kit or something you put together from scratch?

[tweedmarmot]

This is something I put together from scratch.

So yes the power comes from the PT and goes right through the bias pot. I am looking at a weber kit schematic right now, it looks like they have a circuit for the bias, should I copy that or only a diode connected between the 10K bias pot and the PT would work ?

[Daver]

You could copy that schematic but it would be extra work for you. There are two eyelets on your board near the bias caps. You can put the diode there. Look at this layout.... https://taweber.powweb.com/store/5f6a_layout.jpg Wire your's like this. You'll need to move the 56K resistor going to ground. Skip the pot until you're sure you have negative voltage. You can replace the 56K resistor with a 50K pot in series with a 10K resistor to get a good range of adjustment.

[tweedmarmot]

Should I keep the 82k resistor or should it be replace by a 15k like on the 5f6a layout ?

[Daver]

If you have a power transformer that is exactly like the 5G9 keep the 82K. You may have to change that resistor anyway depending on how much negative DC you actually get. Fire it up without power tubes and check what you have. You can adjust that value to get the voltage you want if you have to.

[tweedmarmot]

Thank you so much Dave, I'll order some parts and get back here with updates.

Stephane

[Daver]

Sounds good. Pay attention to the Weber layout. Note where the wire under the board connects from the bias caps to the 220K bias splitter/power tube grid resistors. You may have to move that wire on your amp depending on where you have it connected now. Good luck!

[tweedmarmot]

I have it connect exactly as the layout is showing (through the depth pot). So I can probably just connect the diode reverse than on the weber layout and I wouldn't have to move the 56k resistor.

Again, Thanks !!!

[tweedmarmot]

Hi there, I have it connect correctly with the diode and now I have a good negative voltage. But still have no sound, I wonder if that could be a bad OT issue .. !?