CL-80 question

[Diverted]

Hi,

I've just finished up a Scott 299B, which uses a GZ34 rectifier.
I've seen people commenting that a CL-80 should be added in the AC line to slow the inrush. Having never really used these (and this being my first Scott) I'm wondering why that would be necessary in this set, given the use of a GZ34. Can anyone school me in the pros of installing one of these in this set?

Thank you!

 

[Dave451]

I did put one in my 299B. Even with a tube rectifier, conventional wisdom is that it helps the power switch contacts by limiting inrush current. It also knocks almost exactly 2VAC off the line voltage, which can help with the line voltages running 120VAC plus these days, compared to what the original circuit was designed for.

 

[mroboto]

Slowing startup is good for capacitors also.

Check the VA rating of your amplifier vs the CL-80

Don't know if it's is 3A @ 120V or @ 240V for the CL-80 ?

You may want to use two series of two in parallel (4* CL-80) to acheve the right 47 ohms value with 6A curent raiting, you don't want one to run to his max, it will be very hot.

NTC 47D15 are similar but cheaper, body is little smaller, less precise, sometimes you find 70 ohms at room temperature in the 47 ohms package, that could be good if you want one with more current limiting on startup but smaller in quality (real max current rating maybe).

 

[kward]

It also knocks almost exactly 2VAC off the line voltage

This is likely the reason it was added--I suspect to knock down the filament voltage to spec given a 120V line.

 

[Diverted]

Knocking 2VAC alone is enough to justify putting it in. But I may not anyhow as my filament voltage is right on spec with AC mains at 120V +/-

 

[tube-a-lou]

Does anyone have a picture of one of these in the circuit?, I installed a power switch on the back's of two of my Fisher
and my Eico.

 

[Dave451]

Here is a shot of the CL-80 in my 299B. Wired into the power transformer primary off the fuse holder. It's a little cramped, but there's more space around the CL-80 than the picture indicates. You need to keep it away from other components as it gets hot during operation (power dissipated by the 2VAC drop). The leads are quite stiff, so I haven't used terminal strips for mounting. You also see the silicon rectifier bridge that replaced the Siemens selenium unit.
Dave

 

[Kingfisher]

I installed a CL-80 in my Fisher 400, but the voltages coming out of the wall measure anywhere from 124-126vac., so I doubt it will do enough. I'm considering running it on a variac or power conditioner to bring the VAC down to at least 120.

 

[Dave451]

That or a bucking transformer.

 

[Brice]

Yes, for that a bucking box is what you need.

 

[larryderouin]

I use the CL-80's strictly as a slow startup part. My wall voltages vary during the day from 122V to a high of 126V. I "Tune" all my heaters to run @ 6.2V when @ 124V. I haven't had any problems with any of the chassis' in the last 8 years due to high voltage. A lot of it has to do with using caps & resistors that have a higher working voltage than spec'ed, and setting the heaters to run @ their normal voltages @ higher than spec'ed line voltage. On the caps I use 630V films, and electrolytics 1 to 2 higher voltage ratings as appropriate. I do keep a close eye on output tube voltages and they are generally higher by less than 5% of spec.