variac - breadboard with choke input

[g(f(e))]

Hello,

I have been listening to my single channel breadboard amp for awhile now and decided that it will sound a little better if I stop using the variac. I am a little afraid to just plug it in and turn on because I am using a tube rectifier and a choke input. What components will take the most punishment without the slow ramp up and the slow ramp down when the variac is taken out of the circuit?

Or is this not a concern?

Thanks

Gary

 

[andRookie]

Hello,

I have been listening to my single channel breadboard amp for awhile now and decided that it will sound a little better if I stop using the variac. I am a little afraid to just plug it in and turn on because I am using a tube rectifier and a choke input. What components will take the most punishment without the slow ramp up and the slow ramp down when the variac is taken out of the circuit?

Or is this not a concern?

Thanks

Gary

To my basic understanding/ experience the tube rectifier will quite slowly bring the voltage up. So it is the anodes of the rectifier that will take the extra heat. It is designed for it, though.

 

[astouffer]

A variac is just another transformer so I don't think it would affect the sound very much. How big is the choke and the capacitor afterward? If you have a slow warm up rectifier like a 5AR4 or 5V4 then its ok unless you have a really large filter cap. The datasheet for the rectifier tube will provide more info.

 

[g(f(e))]

The choke is a 10H 200ma, and the cap after is 40uf. The variac has a slight hum, and I wanted to get that out of the circuit. The rectifier is a 5y3.

I am more worried about turning the amp off.

 

[Rundmaus]

Well,

you do not want to listen to a breadboard amp forever, do you?

The variac is a very good means to prevent damage in case of component or wiring errors when new or repaired equipment is powered up for the first time.

When the amp works correctly, there is no need for a variac. A tube rectifier will provide soft-start of the B+ and turning the amp off should be no problem either.

Greetings,
Andreas

 

[g(f(e))]

Thanks. I am going to give it a try without the variac.

 

[piano3]

I had to use a variac for about a year because of extreme voltage variations(now fixed fortunately) in my supply. It did not seem to have any negative effect on the sound and the hum you can hear is,of course,mechanical. I,too,use choke input supply so I turn the filaments supply to the amplifiers on about 30 seconds before the HT. If I did not do this the supply would be about at 550V instead of the 280V output under load. I don't think this would be terribly kind to the electrolytic caps in the supply! A 5U4G type of rectifier would certainly not give you long enough.I haven't used 5Y3 but isn't it directly heated as well? Don't worry too much about turning off as I don't think the voltage on the caps can rise significantly.

 

[nigelwright7557]

I use a SS rectifier for my B+ and have not had any ill effects.
The heater supply is also SS regulated and again had no problems.

 

[g(f(e))]

I tried it this afternoon and it seemed fine. The sound from the variac was mechanical, but in a small room it was easily heard in between passages and in quiet passages.