290BX PT - d'lite 22 6V6 powering up issue

[mehfuzhoss]

Hello Sir,

I built the mentioned amp and powering up first time. No lamp or tubes glowing.

The 290BX has a black and white wire on the primary side. Please take a look at my wiring and tell me if you see mistakes.

How i connected is like this :
The white wire from 290bx goes to pw sw left lug (shown in pics)
The yellow wire is connected pw sw right lug, coming from fuse.
The black wire from 290bx goes to neutral in IEC plug.


Any help is appreciated!

[pompeiisneaks]

what are you doing with the 5v yellow wires I see going under the rectifier diodes?

Other than that, it seems like it should work yes... You've got the switch and the fuse in line with the power to the transformer's white wire, and it looks like black just connects to the IEC adapter.

You can use a DMM to test if you're getting AC 120V on the switch on both sides, you can also see that you have high voltage AC on the red leads going into the diodes.

Basically, you should start with AC volts and test you're seeing 120V at the IEC side, then check that you get it across the switch. Make sure something didn't blow the fuse immediately... etc.

If there was something wired dead to ground it might not have even gotten to the light bulb limiter and just blown the mains fuse.

~Phil

[mehfuzhoss]

I connected the 5v yellow wires to diode and capacitor for the relay power. two boards are stacked and not showing in the pic.

please take a look at the layout attached. two black arrows are pointing to the wires coming out of the PT. are these the same as the 0v and 120v in 290BX PT? please confirm.

[mehfuzhoss]

it looks to me the pilot light is blown. all the tubes are powering up okay.
I can see 120V on both sides of the power switch. and the rectifier diodes has 350V AC
6v6 power tubes has 488 on each.
but i get no sound when i plug in the guitar.

is the OT at fault?

please advise.

[pompeiisneaks]

It seems right to me per the photos, as mentioned.

No sound can be caused by many things. I would write down voltages of all B+ nodes, and of all the pins of the different tubes so that is may be clear/unclear what's right/wrong... that's always a good starting point.

~Phil

[rootz]

Most likely not the OT. I had problems like these before, it never was the OT.

Best thing to do: start tracing the signal in the amp. Make sure there is absolutely a load connected to your amp if you do this with the power tubes in the amp. I’d pull the power tubes though, especially when tracing signals in the power amp.

Put a signal, guitar or otherwise at the input of the amp. Controls at 12 ‘o clock (except master). Do you get a signal at the coupling cap of v1a? And at the CC of v1b? And so forth.

Work SAFELY! If not sure how to do that, ask for some tips here.

[fred.violleau]

As rootz mentionned, tracing your signal is a great way to debug the preamp.

Another approach would be to plug your guitar into the return jack of the FX loop. You should hear sound if the power amp functions correctly (signal path would be guitar -> PI -> 6V6s -> OT->speaker)
Then you can try to work your way up : inject a signal into the preamp and check where the signal disappears or gets weak.
Check all your connexions to ground with a DMM. you should have a very low ohmage on each of those connections.
Check for any wire touching the chassis (on my fisrt build I had no sound and realized that one of the output speaker jack connection was grounding on the chassis )
And as mentionned before, can you post voltages for all tubes all pins ? that would help also to diagnose if something is wrong.

Be patient and methodic, you will find what's wrong.

Fred.

[sluckey]

By far, the most common problem with a new build is a wiring error.

[mehfuzhoss]

yes, i am also guessing a wiring issue. looking at the layout, the rectifier board (the small one on the left side of the chassis), the large capacitor's positive side is not connected or grounded.

[pompeiisneaks]

That's to filter the power for the negative bias, You'd still have a semi operating amp, but it would be probably going in and out of bias constantly due to the dirty power coming from there...I rarely have a perfect first power up. Something always gets missed somewhere even with multiple checks and re-checks. I had a failure in my recent build due to a transcription error from my schematic to the layout. Once found it was super easy to fix, but that was a day or more of tinkering, trying things etc.

~Phil

[sluckey]

Your pilot lamp is definitely not wired correctly.

[mehfuzhoss]

pilot light has been fixed. i removed both the 1M resistors. so the capacitor doesn't need to grounded? I have it grounded.

[pompeiisneaks]

It does need to be connected to ground I must have misunderstood your point. I can't see a ground in the pictures, and I thought you were saying that it wasn't grounded. It definitely needs to be.

~Phil

[dbharris]

Do you have an artificial center tap? A 100r to ground on each side of the heaters. That PT does not have a CT for the 6.3v wires, right?

-Dan

[pompeiisneaks]

Do you have an artificial center tap? A 100r to ground on each side of the heaters. That PT does not have a CT for the 6.3v wires, right?

-Dan

The PT doesn't. I can't tell if there are any dual 100R to ground either. If not, though usually you just get horrific noise on the amp due to the lack of the center tap. I.e. it works, but there's tons of 60Hz hum.

Still a very important thing to check for sure.

~Phil