UPDATE: Finished my Express build last night > it's working!

[prairie]

Yeah, I tried taking the indicator light completely out of the circuit, and it gets me the same result. Power on: blown fuse.

[johnnyreece]

Sorry, I wasn't suggesting that was the cause of the blown fuse; just why the lamp would blow.

[prairie]

No absolutely. I was just troubleshooting and figured I’d try taking the light out of the circuit. Definitely realize the issue is elsewhere.

If there’s value in photos of specific things, let me know and I’ll snap some!

[johnnyreece]

Not sure this would cause the issue, but is C22 grounded? Can't tell from the pic, but it looks like it isn't.

Edit: I also can't tell from the pics, but are the flyback diodes installed with the correct polarity? Might be worth taking them out during this testing phase.

[prairie]

C22 is not grounded. Good catch. I’ll correct that.

Regarding the diodes: Yeah, after my first attempt at startup, it was flagged that the diode connected to C21 was backwards, so I went through and checked them all when I corrected that.

[prairie]

Took out the flyback diodes, no change.

[romberg]

I redid my entire PS section and I’m still blowing fuses (the indicator bulb blows too when I turn it on, no tubes).

When I run it through the voltage limiter, everything fired up fine, but straight into the wall, poof.

Carefully measure some voltages while it is on the limiter and post them. That may give folks a clue as to where to focus in helping you out. Measure the DC voltage on the power supply nodes along with the tube pins.

Mike

[prairie]

Will do today. Thank you!

[johnnyreece]

Also, what wattage bulb are you using? It raises red flags to me that the bulb tester is fine, but it pops fuses. You're *sure* you're using slow blo fuses?

[prairie]

Hi again,

I'm using a 65w bulb as the limiter.

I took some voltage readings around the circuit. Numbers in parentheses are with the standby switched off (to the "operate" position).

C21 + side: 0v
C21 - side: -35v

C22 + side: 0
C22 - side: -28

Bias terminal: -28.45v
B3: 0v (300v)
B4: 0v (286v)
B5: 0v (271v)

D11: 358v
D7: 0v
D8: 0v

R25: 0v
R26: 0v
R27: 0v
R28: 0V

V4 pin 5: -27v
V5 pin 5: 27v


One thing I noticed that was interesting was that the 300v windings from my transformer are registering as having continuity with ground, both on standby and off. I'm not sure what that's all about.

I also registered continuity with ground on the pilot light terminals, despite the light still working. I traced it back, and the 6.3 windings are also registering as ground.

Any idea what that might be about?

[martin manning]

One thing I noticed that was interesting was that the 300v windings from my transformer are registering as having continuity with ground, both on standby and off. I'm not sure what that's all about.
I also registered continuity with ground on the pilot light terminals, despite the light still working. I traced it back, and the 6.3 windings are also registering as ground.

Both windings have grounded center taps. Measure the resistances to ground and you should get something significant from the 300V leads, a few tens of ohms, and very little resistance for the 6.3V leads, almost nothing.

[prairie]

One thing I noticed that was interesting was that the 300v windings from my transformer are registering as having continuity with ground, both on standby and off. I'm not sure what that's all about.
I also registered continuity with ground on the pilot light terminals, despite the light still working. I traced it back, and the 6.3 windings are also registering as ground.

Both windings have grounded center taps. Measure the resistances to ground and you should get something significant from the 300V leads, a few tens of ohms, and very little resistance for the 6.3V leads, almost nothing.

That that makes sense. I called Heyboer and they told me the same thing.

[romberg]

I took some voltage readings around the circuit. Numbers in parentheses are with the standby switched off (to the "operate" position).

C21 + side: 0v
C21 - side: -35v

C22 + side: 0
C22 - side: -28

///

Without knowing which layout/schematic these R and C numbers refer to, it is difficult or impossible for others to follow. Can you post the layout and schematic you used for your build? Or a link to them?

Otherwise, how about measuring just the voltages on the tube pins with the standby switch in the operate position only (when off the numbers are not interesting):

V1 (first tube the signal goes in)
pin1:
pin2:
pin3:
pin4:
pin5:
pin6:
pin7:
pin8:
pin:9:

Pins 4, 5 and 9 should be your 6.3VAC heaters. They will be ac and not DC.

repeat this for V2 and V3.

V4 (power tube)
pin1:
pin2:
pint3:
pin4:
pin5:
pin6:
pin7:
pin8:

Here pins 2 and 7 will be the 6.3v ac heaters.

repeat for V5 (second power tube)

[johnnyreece]

Also, you've got B+3 through B+5, but no B+1,2. Those would be the voltages on C15/16 (B+1) and C17 (B+2), according to the RLW layout. B+1 should have voltage even when the standby is not in the operate position.

[prairie]

I took some voltage readings around the circuit. Numbers in parentheses are with the standby switched off (to the "operate" position).

C21 + side: 0v
C21 - side: -35v

C22 + side: 0
C22 - side: -28

///

Without knowing which layout/schematic these R and C numbers refer to, it is difficult or impossible for others to follow. Can you post the layout and schematic you used for your build? Or a link to them?

Otherwise, how about measuring just the voltages on the tube pins with the standby switch in the operate position only (when off the numbers are not interesting):

V1 (first tube the signal goes in)
pin1:
pin2:
pin3:
pin4:
pin5:
pin6:
pin7:
pin8:
pin:9:

Pins 4, 5 and 9 should be your 6.3VAC heaters. They will be ac and not DC.

repeat this for V2 and V3.

V4 (power tube)
pin1:
pin2:
pint3:
pin4:
pin5:
pin6:
pin7:
pin8:

Here pins 2 and 7 will be the 6.3v ac heaters.

repeat for V5 (second power tube)

Apologies. This is the layout I'm working from:



I'll take the above readings right away and post them.

Thank you for all your help! This is definitely my first amp build (I've built plenty of pedals) and all the help is greatly appreciated.