Problem with startup

[jckid649]

I just finished a new express build. I checked everything multiple times and all was wired fine but threw the power switch for the first test and blew the fuse.

I'm puzzled.

I do see a discrepancy with how Ken wired the heaters and how Ron Worley's diagram goes.

I followed Ken's way. Would that have blown the fuse? Should I have just wired the heaters the way it is in RW's build guide or could it be something else?

[RJ Guitars]

Did you start with all the tubes pulled and the standby off?

We will need photos please.

[vibratoking]

+1 on RJ's comments. BTW, the reverse polarity of the heaters will not cause fuses to blow.

[jckid649]

I figured out what was wrong. I had one of the 280v tranny wires wired in the wrong position. However, now all the tubes glow but I get no sound at all. I suspect that I have something wrong at the bias board. No matter how I adjust the trim pot it doesn't change the bias rating at pin 5 of V4.

I'm reading about 415v at D8 but past that point is where the bias trim is and that's where my first improper reading comes in. Can someone look at this and tell me what's wrong?

(forgive the sloppy soldering here...i've pulled and reinstalled it several ways trying to figure out what I'm doing wrong)

[xtian]

The two outside legs of your bias pot should not be wired together.

Can I ask you to take a step back, slow down, and follow the first-time startup procedure? You're really rushing things if you have not first verified voltages, especially the bias voltage, BEFORE you install any tubes!

[jckid649]

The two outside legs of your bias pot should not be wired together.

Can I ask you to take a step back, slow down, and follow the first-time startup procedure? You're really rushing things if you have not first verified voltages, especially the bias voltage, BEFORE you install any tubes!

I've tried to follow the layout in Ron Worlely's guide and gut shots of francesca but it's very confusing. I can't tell which leg is connected to what.

[cbass]

http://www.paulrubyamps.com/info.html
Read this and follow the first time powerup procedure.

[cbass]

The two outside legs of your bias pot should not be wired together.

Can I ask you to take a step back, slow down, and follow the first-time startup procedure? You're really rushing things if you have not first verified voltages, especially the bias voltage, BEFORE you install any tubes!

I've tried to follow the layout in Ron Worlely's guide and gut shots of francesca but it's very confusing. I can't tell which leg is connected to what.

You shoulde be checking the schematic against the layout not trying to copy pictures

[jckid649]

I know this may be heresy here but I cannot read a schematic. That's why I follow the layouts and gut shots. I've built 3 amps this way that have worked fine. I will follow the start up procedure properly.

But at the moment I just need to know how to connect the bias trim.

[jckid649]

ps I was following the startup procedure in the build guide. It was when I realized something wasn't right with the bias trimmer that I decided to see if any tubes would work in the amp using throw aways.

[rock_mumbles]

You need to hook up the bias pot as a variable resistor, with an outer lug and wiper connected together to the caps and the other outer lug to the resistor ...

[cbass]

Well I have to admit I've never read the build guide.
One thing to check before installing tubes is your bias voltage.If you arent getting -30 to -50 vdc or so on pin 5 then there should be no reason to install tubes.Till you get in range.
With the way your pot is wired you praobably arent getting near the negative voltage for bias.Wich is really dangerous for your amp

[jckid649]

Well I have to admit I've never read the build guide.
One thing to check before installing tubes is your bias voltage.If you arent getting -30 to -50 vdc or so on pin 5 then there should be no reason to install tubes.Till you get in range.
With the way your pot is wired you praobably arent getting near the negative voltage for bias.Wich is really dangerous for your amp

Yeah I am assuming that is probably the problem. I've checked and rechecked every other connection and point over and over and the bias trim is the only thing that was in question at this point.

[cbass]

So what is your voltage at pin 5 ?

[martin manning]

xtian says it above... the bias trimmer is wired incorrectly. The center and one outside leg should be shorted together, not the two outside legs.