Captain Coconut wrote:I use a ST-35 amp with a CL-90 thermistor. The voltage is 121-123 at our place. I like the idea of a softer start-up with the thermistor and the fact that it knocks down the line voltage a few volts. However, I have read somewhere that a thermistor is not a great idea to have "running" all the time, and to have some sort of bypass if possible.
I know there are thousands of ST-35's out there that have run fine for years without a thermistor, and the tubes have survived hundreds of "hard" startups. Also, the original manual states: " It is intended for use with the 120-volt a.c. power supplied to most homes. Although variations of several volts above or below this figure will have no pronounced effect upon performance or component life ...". It goes on to say that there is no guarantee on the amp if operated above 130 volts.
It looks like the 123V at my place is not an issue therefore, but wonder if the thermistor is a good idea anyway. Any thoughts?
PS - I made a similar post some time ago, but wonder if there's any new insight on the matter.
4 posters
use of thermistor
Guest- Guest
- Post n°1
Re: use of thermistor
GP49- Posts : 792
Join date : 2009-04-30
Location : East of the sun and west of the moon
- Post n°2
Re: use of thermistor
If it makes any difference, McIntosh used thermistors for decades in their tube amplifiers, in exactly the same application. The only ill effect I ever saw was when they failed...physically broke apart. Dead amp, but an easy fix.
Jim McShane- Posts : 237
Join date : 2011-10-19
Location : South Suburban Chicago
- Post n°3
Re: use of thermistor
As well, keep in mind the CL-** series parts are not standard thermistors. They are made with a very long time constant so the resistance stays higher longer than with standard thermistors, giving you increased protection against the initial surge at turn on. They are a VERY good idea, I've used them for 12+ years with great success and zero trouble.
1973shovel- Posts : 45
Join date : 2009-12-13
- Post n°4
Re: use of thermistor
Both Jim McShane and Eli Duttman recommended using CL-90's in my SCA-35. Interestingly (to me, anyway) they suggested not only placing one in series with the incoming AC line, but also in series with the B+. This serves not only to offer a little extra B+ voltage drop, but also delays the B+ (however slightly), giving the filaments a bit of a head start.
They're not a game changer, or as good as Roy's time delay circuit, but they're only $2 each, and do what they're designed to. I plan on adding them to both my ST-70 and MkIII's eventually.
They're not a game changer, or as good as Roy's time delay circuit, but they're only $2 each, and do what they're designed to. I plan on adding them to both my ST-70 and MkIII's eventually.
sKiZo- Posts : 1530
Join date : 2013-04-01
Location : Michigan USA
- Post n°5
Re: use of thermistor
Hadn't thought about putting one on the B+ line. Seeing as how ONE will drop the voltage a couple or three points, I assUme TWO would drop it five or six?
My power averages 122+, so that would put me down to around 117, which I keep hearing is some sort of magic number for tube equipment.
My power averages 122+, so that would put me down to around 117, which I keep hearing is some sort of magic number for tube equipment.