Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Colas LeGrippa on June 27, 2012, 07:30:25 am

Title: VOLTAGE DIVIDER on heater taps ?
Post by: Colas LeGrippa on June 27, 2012, 07:30:25 am

Hi everybody, ( except the guy to whom I don't speak anymore :laugh: ),

The heater taps on my PT is too high: 7.5 V with all tubes fed. How could I hook up a voltage divider to get that voltage down to 6.3 ? A voltage divider on each side or just one ?
A resistor between CT and gnd ? Could I easily run the heaters on DC, with a regulator ?

Thanks for answers, suggestions and schem

Regards, Colas.

Title: Re: VOLTAGE DIVIDER on heater taps ?
Post by: kagliostro on June 27, 2012, 10:51:25 am

2 resistors in series, one for each branch

or

2 (or 4) diodes

see documentation here http://www.freewebs.com/valvewizard/heater.html (http://www.freewebs.com/valvewizard/heater.html)

K

Title: Re: VOLTAGE DIVIDER on heater taps ?
Post by: thelonious on June 27, 2012, 11:47:52 am

Quote from: kagliostro on June 27, 2012, 10:51:25 am

2 (or 4) diodes
see documentation here http://www.freewebs.com/valvewizard/heater.html (http://www.freewebs.com/valvewizard/heater.html)

I purchased http://r.ebay.com/knxTms (http://r.ebay.com/knxTms) diodes for this purpose, and they have been working like a charm.

T

Title: Re: VOLTAGE DIVIDER on heater taps ?
Post by: Leevi on June 27, 2012, 11:50:14 am

The resistor value must be very low.

Use Ohm's law (U=RI) to determine the value.

If your total heater current is 4A and you want to drop 1.2V the resistor value
is 1.2V/4A=0.3 Ohm. Furthermore it has to be a power resistor, in this case 5W.

/Leevi

Title: Re: VOLTAGE DIVIDER on heater taps ?
Post by: Colas LeGrippa on June 27, 2012, 05:04:27 pm

thanks guys !

Title: Re: VOLTAGE DIVIDER on heater taps ?
Post by: Colas LeGrippa on June 30, 2012, 08:31:23 pm

Hi, the PT was originally designed for a 6 preamp tubes amplifier and I am using it in a 2 preamp tubes. This PT was custom made for me. I have solved the problem with 2 diodes on each side of the heater supply. The voltage went down from 7.8 or so to 6.2 V. So every thing else in that amp is just fine. Ditto for the HV. By putting a VVR at the B+ out. I can lower the high voltage to 300V or so, for the 2 X 6v6 ( paralleled in a SE amp ). So , with a re-bias, I can swap to EL34's, 6550's or whatever I want.

Regards

Colas

Title: Re: VOLTAGE DIVIDER on heater taps ?
Post by: Colas LeGrippa on July 02, 2012, 02:44:14 pm

yes sir, too much a load drops the voltage.BTW in Florida with no air conditioned, your should be close to the melting point, no ?

Title: Re: VOLTAGE DIVIDER on heater taps ?
Post by: Colas LeGrippa on July 03, 2012, 05:19:56 pm

I believe that, Even in Montreal, barefoot on a concrete floor, I had the ''chance'' of being shocked..........my good lord thanks for keeping me alive !