HELP!! No B+!

[jkey04]

I am building a single-ended EL34 amp using a Hammond 370fx PT and a 1630sea OT. I got it ready for initial power up, and when flipped the power switch the pilot light flickered and fuse (1.5A) blew. I replaced fuse with a 2A slo-blo because that was all i could find. On my second attempt to power up, rectifier arced internally. So i replaced the two series connected 100uF filter caps (measured roughly 58uF) with a single 40uF cap and replaced the GZ34. Now, rectifier seems to be fine, but I do not get any B+. I get 275VAC sitting on pins 4 and 6 of the GZ34 and heater supply to all tubes, but no DC output on pin 8 of GZ34. Also, after about 30 seconds the PT starts to hiss and crack so i turn it off to find that it is HOT. Seems like i have a short somewhere, but so far i cannot find it.

If you verify that the 370fx is wired correctly that would be great! Wired as follows...

On Primary:

Blue and Black--tied together connected to power switch
White and Brown--tied together on the fuse

White/Blk, Brwn/Yel, Blu/Yel, and Blk/Red are all loose

One thing to note is that the Black/Red and Black wires are both just Black. I used the one that measured the most resistance from the White wire. Is this correct?

On Secondary:

Two Red wires--connected to pins 4 & 6 of GZ34
Red/Yel--grounded
Two Yellow wires--connected to pins 2 & 8 of GZ34 (5v heaters)
Yel/Blk--grounded
Two Green wires--connected to heaters for pre and power amp
Green/Yel--Grounded

Violet wire--loose

Thanks in advance for your help!

[M Fowler]

I don't like the way the AC is wired? Why is Neutral side fused?

Should have white wire from IEC neutral to one side of PT AC primary usually black wire. Other black wire from PT AC primary to switch. IEC Load to fuse and then to the switch.

[Firestorm]

You can't ground the yellow/black wire. You may have toasted the PT.

[jkey04]

Thanks for the quick reply!

I rewired the AC...see how it looks now.

I still have NO B+ though. What could cause this?

[ToneMerc]

I still have NO B+ though. What could cause this?

ac input at rectifier, but no dc output.... a dead rectifier

TM

[Firestorm]

I still have NO B+ though. What could cause this?

ac input at rectifier, but no dc output.... a dead rectifier

TM

I bet he has no 5VAC anymore.

[ToneMerc]

I still have NO B+ though. What could cause this?

ac input at rectifier, but no dc output.... a dead rectifier

TM

I bet he has no 5VAC anymore.

Yeah, he may have fried that winding.

TM

[jkey04]

I have 5v between pin 2 and 8 of GZ34. I have 6.3v on the rest of the heaters and i have 275vac on pins 4 and 6 of rectifier. PT seems to be fine. I am just not getting DC output. I have a Sovtek and a Ruby rectifier and both work in my Bassman, so they are functional.

The troubleshooting continues....

Thanks again!

[ToneMerc]

I have 5v between pin 2 and 8 of GZ34. I have 6.3v on the rest of the heaters and i have 275vac on pins 4 and 6 of rectifier. PT seems to be fine. I am just not getting DC output. I have a Sovtek and a Ruby rectifier and both work in my Bassman, so they are functional.

The troubleshooting continues....

Thanks again!

At the rectifier, you need to take B+ from pin 8, not 2.

TM

[jkey04]

I am taking B+ from pin 8.

[Tillydog]

You can't ground the yellow/black wire.

You may have toasted the PT.

^That

The rectifier heater is at high voltage. By grounding the yellow/black wire, you're shorting b+ to ground.

[jkey04]

Thanks Tillydog for pointing out what Firestorm said. I completely overlooked that comment. As soon as I get home, I'll remove the yellow/black wire from ground. Hopefully nothing was damaged! I knew it had to be something silly.

[jkey04]

OK...removing the yellow/black wire from ground solved the B+ issue! Thanks Tillydog and Firestorm!

BUT...I still have no audio output and cathode voltage on EL34 starts out around 32vdc and slowly rises. It got up to about 60vdc before i shut the amp down. I also noticed that when this was happening, the B+ voltages were dropping. I tried this several times and the B+ didnt drop every time..or maybe i didn't wait to shut the amp off as long as i did the first time therefore not noticing a drop in B+.

Any thoughts?

[Tillydog]

I completely overlooked that comment.

I thought you might have done! Props to Firestorm for spotting it.

...cathode voltage on EL34 starts out around 32vdc and slowly rises. It got up to about 60vdc before i shut the amp down.

What schematic are you working to? In particular, what value grid leak resistor do you have on the EL34 (grid to ground)?

[jkey04]

This is a design of my own. It's a single ended el34 with Hammond ultra linear 1630sea transformer. That being the case, the UL tap from the OT is connected straight to the grid of el34. Should I try a grid resistor between the two?

Also, the preamp is a single ef86.