Negative Temperature Co-Efficient Resistor(s)

[Dave Ed]

Hi All,

I wish to build a 'soft start' into my Maplin Millenium amp which I finished a few years back.
Can anyone recommend and tell me where to source a suitable NTC thermistor? (With suggested electrical/temperature values if poss)
A few questions for those of you who have done this:
Have you installed it in the Primary side of the power t/x, thus bringing up both the heater volts and H.T. slowly, or on the rectified H.T. alone=470v.
I understand some guitar amps use an H.T. standby switch, another possible option as I understand it.

Feedback appreciated.
Dave

[John Caswell]

Hi Dave,
They are available from Farnell in various ratings, but the types I generically use are 118-6603 (3A 10R > 0R2), and 170-4470 (4A 15R > 0R4).
They must be mounted on a separate tag strip with longish leads (say 25mm) in free air away from any components and make sure that the leads are mechanically sound before soldering as they get quite hot.
I always instal mine on the primary side of the power tx but there is no reason why you cannot place them on the HT side solely or in conjunction with one on the primary side.
Bear in mind that they will really not provide much protection on the HT side as no current is drawn through them until the valves start to warm up!

John

[bob orbell]

Don't think that I am being funny John, but arn't the part no's you quoted, RS no's? BOB

[John Caswell]

No all correct.
All taken off the Farnell labels. Farnell have had to change a lot of their numbers due to the ROHS farce.

John

[Dave Ed]

Many thanks for the info John

I have always found this site to be invaluable for advice.

Regards,

Dave