Circuit breaker vs fuse ?

[Fuzzbuster]

Howdy all...Fuzz here again. Loving this site...So I have a Stromberg Carlson ASR 433 in my bedroom system. Like the amp a lot...quietest phono stage I've ever heard. My question: it has a circuit breaker instead of a fuse. Are they reliable or would switching to a fuse be better? First amp I've seen personally with one. Thanks.

 

[Tom Bavis]

I had a 6BQ5 arc over on my ASR333 and it tripped, so at least ONE of them can be trusted. Other ones have fallen apart - I replaced with a fuse.

 

[I LIKE MUSIC]

The time to clear versus current is well know for both quality fuses and circuit breakers.

Fuses start fresh each time. Circuit breakers that have been repeatedly tripped may exhibit pitted contacts and some degradation in performance.

There are those that will say that there is an audible difference between fuses and circuit breakers. That is another can of worms. I take no sides.

 

[gadget73]

You may be the only person I've ever heard say something good about the ASR-433 phono stage.

 

[Fuzzbuster]

Thanks. I think I'll put a fuse in place of the breaker...I'd feel more comfortable.

And yes, I've read a lot of negative comments about the 433's phono stage. It is lacking in the dynamics department. It is dead quiet though.

 

[trobbins]

The time to clear versus current is well know for both quality fuses and circuit breakers..

It doesn't sound like Fuzzmaster has the model # or datasheet of the existing CB or probably the fuse that will replace it. A simple 'current rating' leaves a lot of latitude for the performance of an unknown part. Even a known part has a large variation in nominal performance.

Fuses start fresh each time. Circuit breakers that have been repeatedly tripped may exhibit pitted contacts and some degradation in performance..

Lets hope the OP doesn't purposefully reset the CB more than once or twice in its service life.

There are those that will say that there is an audible difference between fuses and circuit breakers. That is another can of worms. I take no sides.

A larger range of fuse models and ratings are typically available for low current applications, than with CBs, so if one knows what performance is needed, then a fuse will likely offer a better outcome.

I would suggest that changing a part meant for protection, due only to a hope of feeling more comfortable, is an unsafe outcome.

 

[Fuzzbuster]

It doesn't sound like Fuzzmaster has the model # or datasheet of the existing CB or probably the fuse that will replace it. A simple 'current rating' leaves a lot of latitude for the performance of an unknown part. Even a known part has a large variation in nominal performance.


Lets hope the OP doesn't purposefully reset the CB more than once or twice in its service life.


A larger range of fuse models and ratings are typically available for low current applications, than with CBs, so if one knows what performance is needed, then a fuse will likely offer a better outcome.

I would suggest that changing a part meant for protection, due only to a hope of feeling more comfortable, is an unsafe outcome.

Actually I do have the data sheet for the CB and the unit. I wouldn't willy-nilly throw in any size fuse. I have had this connected to my variac which has an ammeter and it pulls about 3/4 of an amp at the line. I would use a 1 1/2 amp fuse which is pretty typical for an EL84 PP amp. Thanks for your input though.

 

[I LIKE MUSIC]

Even a known part has a large variation in nominal performance.

While UL and other ratings are rather wide, fuse and circuit breaker manufacturers can and do supply detailed information for those that need it. I have been involved professionally obtaining this information.

It appears that the OP does in fact have the data on the circuit breaker and his post indicates that he is more comfortable choosing a fuse. Is that not what you recommend.

 

[gadget73]

I have a 433 myself. Not sure if thats a 1.5 or 2 amp breaker, but a fuse in that size range seems reasonable. Likely needs to be slow-blow to deal with transformer inrush.

Mine still has the CB installed, but the amp has been in pieces as one of those "round tuit" projects for longer than I care to admit at this point.

 

[trobbins]

Well done Fuzz for measuring the static AC line current.

A vintage manufacturer may have sized their mains protection to cope with worst-case static current, such as from allowed max AC line voltage (and hence heater and B+ levels) and max design centre dissipation of output stage, and part tolerances (such as heater current at a set voltage), and to be consistent with the long-term current where the CB or fuse won't trip. And if using a fuse, then they may also have determined that a generic fast or slow blow characteristic is required for the given circuit arrangement.

Some fuse and CB manufacturers just show a characteristic I-t curve, somewhat similar to a valve's bogey parameter values and anode curves, but many will also show a tolerance range (or a compliance to a UL or IEC standard which includes tolerance limits). The equipment manufacturer then has the option to target the tolerance limits, or the bogey characteristic, or something in-between.

One hassle with fuses (eg. small 5x20 and 3AG) is that they are often purchased without a datasheet reference, or get mixed with other fuses from different manufacturers, and depending on the country then the fuse is either aligned with a UL or an IEC standard (where the same current rating fuse is not directly interchangeable between standards).