5E3 build

[Twin]

Disconnected both green & yellow wires & measured to ground - same 1(non reading) Also same for both the pins(pin 3 of 6V6's)

[soundguruman]

It was not 1. It was OL open load. No reading.
Now follow the power supply measuring to ground...with the ohm meter.
at some point in there you may find a low resistance to ground.

[Enzo]

has your resistor now burnt to open condition? If you have 266 ohms at pins 4, if that 4.7k resistor is OK, you OUGHT to get 4.7k plus 266 ohms or 4966 ohms.

If your wires and sockets read open to ground, that is good here. Your 266 ohms at pin 4 is not good. But 266 ohms is also not a dead short, so you likely do not have a wire touching ground. That makes me suspect the cap even more. Unsolder the + wire of that second cap, the one meassuring 266 ohms, and pull if out of the eyelet. Now what does pin 4 read to ground? and measuer the cap itself while it is disconnected, does it measuer that low resistance? Or does it read like it is charging up?

[Twin]

Will do later. I'll get those readings & post tomorrow... Thanks for all the help Soundguruman!

[g1]

Pin 3 to pin 3 is 650 ohms. From either pin to ground measures 1ohm

What is?
When I took a measurement it was the same as a "no reading" like Enzo mentioned earlier.

do not report "not getting anything" on a meter reading. Unless your meter is turned off, you always get SOMETHING. it reads zero ohm, that is not the same as "nothing." If it reads open, that too is not "no reading." Tell us what it says.

So please be more specific, did it measure 1 ohm or not. Meters do not use "1" to indicate no reading. They typically read "OL" to indicate the reading is out of range.
If you got a measurement of 1 on ohms scale, from pin3 to ground then you have a short.
All that being said, however, a short at pin 3 to ground would be before the resistor and not cause it to burn.

[Bruce / Mission Amps]

Try lifting the screen node wire from the eyelet board.... the one between the 4k7 and 22k resistor.
Measure that eyelet to ground.... and the wire with it removed.
Should be Zero ohms on the wire. If not, you have miswired one of the 6V6 sockets or have a short on a socket.

On the eyelet board, once the filter caps start to charge up from your Ohm meter's little 1.5vdc... that number should go very high.... if not there is a short on the eyelet board, topside or underside.

[Twin]

Hey Bruce, Thanks I'll give that a shot & get back to you ASAP...

OK, so I pulled the screen node wire to the 6V6 at the tagboard... Wire is OL(0ohms) BUT the eyelet is picking up sporadic readings only the moment I probe it then it goes OL... I think we've found it fellas!!! I should also mention that I lifted the positive side of the cap but left the 22k resistor... should I pull the 22k also?
Thanks.

[Twin]

has your resistor now burnt to open condition? If you have 266 ohms at pins 4, if that 4.7k resistor is OK, you OUGHT to get 4.7k plus 266 ohms or 4966 ohms.

If your wires and sockets read open to ground, that is good here. Your 266 ohms at pin 4 is not good. But 266 ohms is also not a dead short, so you likely do not have a wire touching ground. That makes me suspect the cap even more. Unsolder the + wire of that second cap, the one meassuring 266 ohms, and pull if out of the eyelet. Now what does pin 4 read to ground? and measuer the cap itself while it is disconnected, does it measuer that low resistance? Or does it read like it is charging up?

The 4k7 might be toast at this point & I can put another one in there if needed...
Assuming I should still keep all the tubes out of the sockets, I just measured pin 4 to ground & got the OL reading.

[Enzo]

Look underneath.

That node is leaking heavy to ground. The 4.7k comes into the nose, the cap goes to ground from the nose, the wire to pin 4 comes from the nose, and the 22k goes from the node to the next node. One of those paths is messing with you. If your pin 4s are not measureing 266 ohm, that is a good sign. You now have the + end of the cap disconnected? Measure the cap wire itself - up in midair - to see if it has that low resistance to ground. If it does, the cap is toast.

[Bruce / Mission Amps]

As Enzo so eloquently points frequently here with hammer in hand... learn all about simple Ohm's law...

If your 360vdc B+ rail is accidentally grounded through that 4K7 resistor....then:
360v/4700ohms = about 77ma.... right to ground.
Power is, current squared times resistance
77ma^2 is
.077A x .077A = .0059
.0059 x 4700 ohms = 27 watts.... you think that little 2 watt resistor could handle that?
That is probably all the power transformer can deliver without grossly over heating, but not quite enough to blow the fuse.

Think "Forbidden Planet" and you released the Krell's Id with nearly unlimited power behind it... well, limited by the 2 watt 4k7 resistor.


Every once in a while I'll have a novice builder assemble one of my 5e3 amp kits and, after fully populating the board, including flying lead wires,... forget to snip off some of the extra leads lengths under the eyelet board, causing all kinds of problems... or they'll snip a piece off and not take notice where it lands... of course sticking some place under there and shorting the power supply or audio path.

Also... the date code on your two Sprague filter caps is mid-late 1975!! Jeeze man, over 36 years old. You should get rid of those no matter what you find later.

Confirm your volt/ohm meter is working right too...
Measure across your power tube cathode biasing resistor.
If it also measures 266 ohms that should be a red flag with respect to the 266 ohms you measured at lug 4 of the power tube socket.

[Twin]

Hey Bruce - I finally found the source of the problem as you & Enzo suggested... Pulled the tagboard & had a clipped lead that was barely bridging the 2 first eyelets...doh! As far as the old Sprague caps go, I had a fresh set of TAD's in there to begin with, but just to rule out that it wasn't a shorted cap I swapped them out for a few I had lying around... not ideal, but certainly better than waiting a week for new ones to show up & delay the troubleshoot... Thanks for helping me with this head scratcher, I couldn't have done it without you guys steering me in the right direction!