Boutique blowing fuses

[Pryde]

Hello,

I have Divided by 13 amp (13/29 model) that is instantly popping mains fuse when main power switch turned on (standby in off position). Unfortunately they wont provide a schematic so that is a limitation.

It is not a tube issue, have all tubes removed (GZ34 rectifier, KT66 power, preamp tubes) and still blows instantly. Hooked up to my current limiter bulb and it is glowing bright with no tubes in.

No visible filter cap distress that I can see, dropping resistors ok as well.

I am checking resistance on the PT primary leads and getting about 4-ohms. When I check each primary lead resistance to ground I get nothing on the meter. PT toast? I don't want to assume that but I think I should be seeing high resistance from primary to ground right? Any ideas on what to try next?

Only a pic sorry:

[The Dude]

......When I check each primary lead resistance to ground I get nothing on the meter.......

Please don't use "nothing" to describe a meter reading. The meter reads "something". Is it infinite, or shorted? "nothing" can be interpreted either way.

[lowell]

Abide by the Dude. Also,
"I am checking resistance on the PT primary leads and getting about 4-ohms"

From primary end to other primary end? From primary to secondary? From primary to ground? Please be very specific as to where both probes of your meter are.

We ask because we're trying to help.

[Pryde]

Abide by the Dude. Also,
"I am checking resistance on the PT primary leads and getting about 4-ohms"

From primary end to other primary end? From primary to secondary? From primary to ground? Please be very specific as to where both probes of your meter are.

We ask because we're trying to help.

Sorry fellas:
Primary end to other primary end= 3.4 ohms
Primary end (either one) to ground = OL

[The Dude]

We don't have a schematic. I'm posting this one only to show a typical/similar tube rectifier power supply.



You'll need to verify that your amp's PS is "similar". Until then, some presumptive ideas.

If you have the tubes removed (including rectifier tube) and are still blowing fuses, likely suspects are the PT or something in the bias rectifier circuit. Without knowing your exact layout, this is a bit of "guessing". First I would check to see if there is a primary to secondary short. Then, I would probably remove the winding that goes to the bias rectifier and see if the amp holds a fuse or lights the light bulb limiter brightly and continue to unsolder windings until the light goes dim. If you get to the last secondary winding and the bulb is still bright or the amp isn't holding a fuse, then you know the transformer is bad.

Saying all that, 4 ohms across the primary seems awfully low and probably not good, but before you spend big money on iron, I would verify.

[Justin Thomas]

Then it seems something on the secondary end is shorted or close to it. Disconnect the secondary wires, insulate them, and see if the fuse still blows. Basically, if it blows with all the 2ndaries disconnected, the tranny is toast. BUT: there may yet be hope...

More info here: geofex.com top left corner, click on "tube amp debug page." Steps on tranny testing all spwlled out clearly & safely.

Justin

PS: what The Dude said...

[lowell]

Is there anything, like an MOV, across the primaries? Otherwise The Dude abides.

[The Dude]

Is there anything, like an MOV, across the primaries? Otherwise The Dude abides.

I thought of that too, but I didn't see one in the picture.

[g1]

Wow, an expensive boutique amp that fits in the shell so "well" that the front panel bends when the bolts are tightened up.
Some kind of heater winding short like a pilot lamp socket issue could also cause problems.
Simplest check would be disconnecting all secondaries as mentioned above.
2 reds, 2 orange, and 2 greens. Green/white and red/white can stay connected.
If it still blows fuse, PT is toast.

[Pryde]

Wow, an expensive boutique amp that fits in the shell so "well" that the front panel bends when the bolts are tightened up.
Some kind of heater winding short like a pilot lamp socket issue could also cause problems.
Simplest check would be disconnecting all secondaries as mentioned above.
2 reds, 2 orange, and 2 greens. Green/white and red/white can stay connected.
If it still blows fuse, PT is toast.

i thought the same thing when I first eyed the bent chassis

I am getting OL measuring resistance from primary lead to any secondary lead (greens, oranges, reds).

I will unhook all secondaries as suggested and see what I get

[Pryde]

OK I have all the secondaries disconnected and still toasting fuses so I guess we have our answer. Seems odd it would give up the ghost as the owner plays it low only at home for maybe an hour or so per session. Definitely does not abuse it in any way.

[Enzo]

With the rectifier tube out, the filter caps never see any voltage anyway.

I'd unhook the green 6v wires from the lamp socket first. But the advice to disconnect all the secondary wires and see if the transformer still blows fuses is valid.

[Enzo]

Sorry, you beat me to it.

Most circuit failures are not the result of anything someone "did".

[Pryde]

gotcha.

It is going to be interesting to see if they will warranty or give the guy a break on a new transformer. I don't really know much about the company other than they charge A LOT of scratch for their amps.

So 100% confirmed toast

[The Dude]

Glad you figured it out, but bad news. Are there any numbers on the transformer or a company name perhaps? You might be able to source it from somewhere else at a lower cost if they aren't willing to help. I would definitely contact them first to see what they will do......BUT...... If they charge as much for their parts as they do their amps, I'd consider alternatives.