5687 filament question

[tone]

hi all,
attach is the preamp circuit that im building,
how to connect the filament supply?..im using a 12.6@2A secondary..after rectify 17+volts..do i need to regulate it to 6.3volts?pls help..thanks

[tone]

hope this time will load

[jim]

tone,

you can use 12.6v to heat up the 5687.
that way the voltage drop over the resistor isn't that high.
Connect the heater voltage to pins 4 & 5.

Greetz
Jim

[Original Burnedfingers]

What is the advantage of supplying the heaters with 12vdc instead of 12vac here in this situation?


Joe

[jim]

I think you better use AC in this situation.
I overlooked it, but when you use AC, there's no rectifier noise
to cope with

jim

[Brett]

Originally posted by jim
I think you better use AC in this situation.
I overlooked it, but when you use AC, there's no rectifier noise
to cope with

jim

Agreed. As you've already biassed the centre of the filament up 30V or so, hum shouldn't be a problem in a linestage, even with very high efficiency speakers. If you find hum is an issue, I'd check all your wiring, and maybe reverse the filament wires on the heater pins.

When built, measure the filament voltage under load. It might be a bit high with only one 450mA filament in use. In that case, add a small series resistor to each leg to get it to the correct voltage.

The only place I use DC filaments are my phono stages, where I use a series reg, shunt and current source.

Cheers

[Original Burnedfingers]

You might want to consider this circuit also. http://www.netaxs.com/~vkalia/5687.html

There seemed to be a problem with this tube with respect to AC hum that was solved by using a battery supply. I realize I haven't built any tube gear yet but I think this is worth your consideration .

Joe

[tone]

guess ill go AC supply.
thanks guys for the helps..

cheers.
tone

[fdegrove]

Hi,

If you still experience hum problems and want to use DC on the heaters:

Use a full wave bridge (preferably a Schottky or hexfred) put a sizeable cap behind it (4700 microF or bigger) than use a LM317 or 7812 as a regulator and bypass the IC with about 10 microF.
Ground at the heater side.

Remember the reg. needs at least a couple of volts over its' regulation voltage to operate properly.
You will have this automatically no matter what diodes you use in full wave bridge:

12VAC *1.4 =16.8 VDC.

This may also improve the SN/R of the preamp.

Cheers,

[fdegrove]

Hi,

BTW,may I recommend the black (graphite) 5687?

I still have too find a black plate tube that sounds worse than its' regular counterpart.

Anyone else having the same experience?

While I'm at it:don't get those shiny nickel plates the sound awful.

Cheers,