CSA Thermal Protector for a Fender 100w Twin Reverb with master volume

[dangeneau]

Hi!

I'm repairaing a 100 watts Twin Reverb with master volume and I must change the broken CSA thermal protector, part no 010870. What is the value of this part? At what temperature should it open?

Thanks all fellow technicians.

Dan


http://www.webphix.com/schematic%20h..._100_schem.pdf

[drewl]

You see them alot in the transformers of solid state amps, they range from like 150 to 180 degrees I think.
Our local radio Shack has them so that's what I use although you probably don't even need it it's just a thermal fuse.

[dangeneau]

Thanks Drewl,

In the end, I'll change the part for the thermistor Fender used to put in many amps. Although it does not protect against overheating, it manages the current surge when you turn the amp on.


Thanks again

Dan

[Enzo]

It does not open at temperature, it starts out at a nominal resistance - I don't recall what - when cold, and as it heats up the resistance goes DOWN. SO when in series with the mains it reduces inrush current. I don;t have my references handy, but the thermistor is available from places like Mouser. "C60" is sticking in my head at the moment. Or just get one from a Fender supplier.

[dangeneau]

You're right about the thermistor but the original part in the amp I am repairing is a thermal protection, a thermal fuse that does open when it reaches a certain temperature. Check the schematic, it was like that for only a few years and then Fender put a thermistor that works as you said.

[jmaf]

You're right about the thermistor but the original part in the amp I am repairing is a thermal protection, a thermal fuse that does open when it reaches a certain temperature. Check the schematic, it was like that for only a few years and then Fender put a thermistor that works as you said.

By the way have you removed the death cap from the ground switch? Do your customer a favor and snip it

[dangeneau]

"By the way have you removed the death cap from the ground switch? Do your customer a favor and snip it"

I guess you mean that if it gets short, one might end electrocuted by the amp' living ground? Is it something that happened?

Thanks all for your comments.

Dan

[jrfrond]

It does not open at temperature, it starts out at a nominal resistance - I don't recall what - when cold, and as it heats up the resistance goes DOWN. SO when in series with the mains it reduces inrush current. I don;t have my references handy, but the thermistor is available from places like Mouser. "C60" is sticking in my head at the moment. Or just get one from a Fender supplier.

Welcome back Doug! I hope all is well.

I've always question the validity of the use of an inrush current limiter in a tube amp. I guess it can't hurt, especially the tube heaters, but whether it is really needed or not? Debatable.

[jmaf]

"By the way have you removed the death cap from the ground switch? Do your customer a favor and snip it"

I guess you mean that if it gets short, one might end electrocuted by the amp' living ground? Is it something that happened?

Thanks all for your comments.

Dan

Even when it's not shorted, a 47nF cap is a resistor of approx. 56K from mains to your body(@ 60hz). Would you stick a 56K resistor randomly into one of the mains outlet's pins right now and grab it with your sweaty hands? That is exactly what is going on when you put that switch to either one of mains and play your guitar.

Edit 2: When it's on neutral, it's normally ok until you touch some other instrument that is not on neutral. When it's on hot, microphones will shock you, other instruments will too, etc

Edit: Has it happened? I think so. I recall there were threads about it on this forum. Search for death cap, you'll probably find tons of discussions about it.

Edit 3: Sorry, not 350k but 56k. I forgot 2 PI on the impedance calculation. A slight "detail".

[g1]

The thermal fuse was a CSA feature. As far as I know the US models didn't have it and the Canadian ones only had it for a few years. Most of the amps I have seen with them have had them bypassed, otherwise a thermal fuse for appliances such as coffee makers and kettles would probably do the job (Radio Shack?).

JMAF: With regard to the "death cap" you are speaking of situations where there is no 3rd prong ground on the amp or wall outlet?

[jmaf]

JMAF: With regard to the "death cap" you are speaking of situations where there is no 3rd prong ground on the amp or wall outlet?

Unfortunately you must consider it a potential hazard even if you have the 3 way chord on the amp and the outlet at your place of practice, because when you go out you never know what installation you'll find. If you forget that you have that cap and go to a gig where the safety earth isn't quite good, or if you grab a microphone while holding on to the guitar strings, or touch another instrument, you see that cap just isn't supposed to be there when you have a 3 way chord. So instead of theorizing all the possible safety hazards, removing it is simplest and most recommended IMO.