Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Vlada on October 12, 2020, 06:05:35 pm

Title: Two heater secondaries
Post by: Vlada on October 12, 2020, 06:05:35 pm

Hi guys, I have a transformer that I plan using for my new build. Transformer has two heater secondaries, one of them is center tapped and I thought about using that one for tube heaters and other one, which isnt center tapped, for indicator lamp. My question is should I implement artificial center tap, or it doesnt matter since it will be only used for indicator lamp?   

Title: Re: Two heater secondaries
Post by: shooter on October 12, 2020, 06:31:38 pm

I like creating an artificial CT that will burn up before the PT


the indicator side just put 2 wires to 2 leads making sure they touch nothing else.

Title: Re: Two heater secondaries
Post by: sluckey on October 12, 2020, 06:33:42 pm

Quote from: Vlada on October 12, 2020, 06:05:35 pm

My question is should I implement artificial center tap?

no

Title: Re: Two heater secondaries
Post by: AmberB on October 12, 2020, 08:06:27 pm

Are both heater secondaries 6.3 volt?

Title: Re: Two heater secondaries
Post by: Vlada on October 12, 2020, 08:43:15 pm

Thank you for the answers.
Yes, both are 6,3
One is center tapped (3,15-0-3,15), other one is not (6,3-0)

Title: Re: Two heater secondaries
Post by: 2deaf on October 12, 2020, 11:24:21 pm

Sometimes a PT will have one heater winding for the power tubes and another heater winding for the preamps.  If you try to use the preamp heater winding for the entire amp, it may be under powered.

Title: Re: Two heater secondaries
Post by: tubeswell on October 13, 2020, 11:03:18 am

What 2deaf said. One of the windings may’ve been a separate winding for a 6V rectifier and may only be rated for that, e.g. 1A. (and if this is the case here, it’s likely to be the winding without the CT)

Title: Re: Two heater secondaries
Post by: Vlada on October 13, 2020, 12:32:15 pm

6,3-0 is rated 500mA. My main concern is will it add noise because preamp is high gain. Is there going to be any diference in hum if I dont put artificial ct in use with that secondary?

Title: Re: Two heater secondaries
Post by: tubeswell on October 13, 2020, 12:54:55 pm

Quote from: Vlada on October 13, 2020, 12:32:15 pm

6,3-0 is rated 500mA. My main concern is will it add noise because preamp is high gain. Is there going to be any diference in hum if I dont put artificial ct in use with that secondary?

If you use the winding for a signal tube filament, then you should put the ground reference resistors in, otherwise you have no h-k voltage reference for the tube, and it will probably hum quite noticeably.

Title: Re: Two heater secondaries
Post by: Vlada on October 13, 2020, 12:56:26 pm

I thought using it for pilot light  :dontknow:

Title: Re: Two heater secondaries
Post by: pdf64 on October 13, 2020, 01:06:01 pm

Quote from: Vlada on October 13, 2020, 12:32:15 pm

6,3-0 is rated 500mA. My main concern is will it add noise because preamp is high gain. Is there going to be any diference in hum if I dont put artificial ct in use with that secondary?

It can only support 1 preamp tube, eg 12AX7.
Heaters that aren’t balanced or smoothed dc will cause hum.

Title: Re: Two heater secondaries
Post by: Vlada on October 13, 2020, 01:49:09 pm

I think my question is misunderstood  :BangHead: I wouldnt use that secondary for any of the tubes, just for the pilot light

Title: Re: Two heater secondaries
Post by: pdf64 on October 13, 2020, 01:57:14 pm

Haha, unless the wiring to the lamp runs near the preamp circuit, they can be regarded as completely separate things.
Sono need / benefit for any type of 0V reference on it.

Title: Re: Two heater secondaries
Post by: sluckey on October 13, 2020, 02:57:49 pm

Quote from: Vlada on October 13, 2020, 01:49:09 pm

I think my question is misunderstood  :BangHead: I wouldnt use that secondary for any of the tubes, just for the pilot light

I thought your intentions were perfectly clear. Hence my very short answer in reply #2.  :wink:

Title: Re: Two heater secondaries
Post by: shooter on October 13, 2020, 03:13:38 pm

 :laugh:


yup, I understood, just more coy about it in reply #1