Reduce filament

[sbirkenstock]

Hi there,

I´d like to reduce my filament slightly.
I currently have a variac in front of the amp and optimized for 6.3 volts filament.
If I raise the variac to the full 122.5 my line is giving me, the amp sounds harsher and colder.
Filament goes up to 6.9, which is technically still ok.

This article describes the use of 2 diodes
http://www.valvewizard.co.uk/heater.html
I would love to simply try it, but I don´t know what diodes to use.
Are 1N4007 ok here?
And I don´t know why this is reducing voltage by 0.7. Any explanation on this?

The other method I know about is using 5 or 10 Watt resistors, usually with less the 1 Ohm.

Any other methods?
I´d love to find a method to set filament voltage to the optimum.

thank you,
Stephan

[tele_player]

First, when you reduce the AC voltage with a variac, all voltages are reduced, so the filament voltage may not be causing the change in sound.

The reason adding two diodes drops .7 volts is that .7 is the voltage drop of a forward-biased silicon diode. 1N4007 is good for this.

Robert

[drew]

Is it? Merlin shows 60S1 diodes, which are 6 amp diodes.

[Charlie Wilson]

Sbirkenstock, I would suspect preamp tube plate voltages before filament voltages.
CW

[glasman]

Is it? Merlin shows 60S1 diodes, which are 6 amp diodes.

I would suspect your going to want to use at least a 6 or 7 amp diode if your power tubes and preamp tubes are chained like a normal D-Style amp.

In my Matchbox, a stereo style D-later, I use 12.6VDC on the filaments. I get this by using a 1N4001 in the ground leg of a 7812 voltage regultor. Raises the regulator to the sweet spot.

Back to the original question on Harshness, I would be sure to measure the plates on each stage. I find harshness comes when the plates of V1 are pushing over 200VDC. I usually settle for a V1a plate of 185 to 190.

Just my two cents.

Gary

[tele_player]

Is it? Merlin shows 60S1 diodes, which are 6 amp diodes.

My error, 4007 isn't good for that much current.
Robert

[DonMoose]

Is it? Merlin shows 60S1 diodes, which are 6 amp diodes.

My error, 4007 isn't good for that much current.
Robert

Do NOT make the mistake of trying to parallel diodes to add current capacity - because of inherent mismatches in Vf, one will wind up trying to pass the full load and smoke, then the next and so forth. You could give each diode a 1-2ohm series resistor to help force a match, but you're way better off just buying a diode of the capacity you need.

Hope this helps!

[sbirkenstock]

Hi there,

tried it out.
Got 6A diodes (actually from amazon.com.... very fast delivery).
It drops the voltage by almost exactly .7 volt.
I have been at 6.6, now it is 5.9.

Makes the amp sound pretty different.
At 5.9 it gets noticably warmer and softer.
In this case too much for my taste, so I´ll go back to the 6.6 volt.

Any other way to change it by .3 volt (other than resistors)?

Thank you very much for your help!

Stephan