amp blowing fuses

[ernie_jr]

I need some help. My ampeg build with the 807s has started blowing fuses. Was working fine til one day turned it and fuse blows. I have taken out all the tubes so nothing is still hooked up, fuse still blows, so it seems as if the PT went bad. Before I put in a new one, what do I need to check so I dont fry a new PT. All the parts in the amp are new except some of the tubes.
Any advice will be a help.
Thanks,
Ernie

[sluckey]

Does it use a SS rectifier? If so, disconnect the HT leads from that. Still blow fuse? Post a schematic.

[ernie_jr]

Tube rectifier, no schematic, but it is basically an ampeg B15
Ernie

[sluckey]

How quickly does it blow the fuse? Immediately when you flip the switch? Several seconds later? Disconnect all secondary leads. Still blow? If so, disconnect the PT primary. Still blow? If not, you probably need a new PT.

[plexi50]

Ampeg B15 is a great amp.

[ernie_jr]

Fuse blows within 1 sec. Hum in PT just before it blows. All secondary leads have been disconnected. If it is the PT, what would cause it to blow? It has been used less than 50 hours. It is a Fender replacement 022798 bought from Antique Electronics.
Thanks,
Ernie

[ernie_jr]

http://www.el34world.com/Forum/index.php?topic=14573.0

if this link works, this is the amp with the problem.
Ernie

[kagliostro]

My two cents

have you tested electrolytic capacitors ?

K

[stratele52]

Fuse blows within 1 sec. Hum in PT just before it blows. All secondary leads have been disconnected. If it is the PT, what would cause it to blow? It has been used less than 50 hours. It is a Fender replacement 022798 bought from Antique Electronics.
Thanks,
Ernie

Fuse blow with ALL  secondary lead disconnect from the amp ; Transformer is short.

Why ? Amp need too much current.

1- Problem in the circuit ?

2- Not the good transformer for your need  ? Its a Bandmaster transformer 325 v at 200 ma , heater ; 6.3 V at 4A and 5 V at 3A .  I don't check your tubes need.

3- Fuse too high to protect transformer if circuit come defect ?

[kagliostro]

Transformer is short.

For sure, but why ?

K

[stratele52]

Transformer is short.

For sure, but why ?

K

ernie jr must do some check as I write . You want details ?

Problem in the circuit ; Too much heater current need ( I don't check tube's spec)
Bias too hot , over transformer spec .
Filter caps defective; I see cheap filter caps in this circuit board
Short to ground , building error.
Short output transformer / wrong speaker load.

Some test with current limiter whit a new transformer is a must . We must do that with a new build amp before.

[ernie_jr]

Thanks for the input.
 PT is 200ma at 325 volts. All caps are brand new, same ones I use in my Sunn builds and never had a problem. Heater current 3 preamp tubes 2 807's, way below PT rating. 6.3 volts at 4 amps, 5 volts at 3 amps. Dont think there is a short in the building as the amp was working fine for several weeks. Bias is (was) set to specs.  I am hoping that the 5v4 shorted out and that is what caused the problems. I hope to get it checked sometime next week.
Thanks.
Ernie

[DummyLoad]

I am hoping that the 5v4 shorted out and that is what caused the problems. I hope to get it checked sometime next week.

likely what happened or a cap fail-short taking out the recto and PT. did you install a B+ fuse?

btw, test the 807's, OT, and the rest of the power rail as well.

--DL