Blowing fuses.

[CBL]

Back in december my Dynaclone st-35 blew a fuse. The amp had been running for several hours without problem. I put it away and hooked up my stereo 70.

As I prefer the sound of the st-35, I've recently tried to figure out what is wrong. Within 1 or 2 seconds of power up the amp will blow a fuse. This has occured with all secondary taps connected, all secondaries open, and only the heater windings connected.

I'm thinking it might be a short on the primary side, but cannot detect anything. Possibly something internal to the transformer? No continuity between primary and secondary. Primary resistance 3.3 ohms, secondaries 120 B+ and .8 heater.

Transformer (dyna clone) worked without issue for four years.

Stumped. Any help would be appreciated.

[Geek]

Hi,

Is the Cap verified OK? maybe time for a recap.

Pull the rectifier. Does it still blow?

Bad cap or rectifier most likely...

Cheers!

[TomMcNally]

Hi CBL ...

Since you tested the ST-35 with the secondaries open, and the
fuse still blows, you've pretty much narrowed it down to a bad
transformer. I remember reading someplace that they did have
a batch of bad ones at one point.

... tom

[CBL]

Transformer is what I've suspected. But It seems odd that it would suddenly fail after four years of use.

I guess the tranformers are supposed to be a disposable item. This would be the second power transformer to fail on this amp. The first, however, ran hot and vibrated lots.

I'm thinking it's time to switch to Hammond. Thoughts?

[TomMcNally]

Transformers can last forever ... I think you got some bad ones.
While waiting for a backordered PA-774 for a get*set*go, I bought
a couple from Dynakit Parts http://www.dynakitparts.com
here in my state of New Jersey, so they came next day by UPS Ground.
You might want to try one, although I haven't heard of any problems
with Triode's PA-774's for a few years, I've used about 6 of them with
no problems.

Oh - anything can fail instantly ... everything doesn't "wear out" slowly
like a car tire.

[CBL]

I looked at their site yesterday. I had assumed their transformers were from the same supplier but I noticed the leads are a different colour. Might be the best option.

Now if only they could get Mk 3 covers in stock.

[CBL]

Disregard statement about lead colours. I was mistaken.