Tube DIY Asylum

Do It Yourself (DIY) paradise for tube and SET project builders.

Use this form to submit comments directly to the Asylum moderators for this forum. We're particularly interested in truly outstanding posts that might be added to our FAQs.
You may also use this form to provide feedback or to call attention to messages that may be in violation of our content rules.

You must login to use this feature.

Inmate Login

By default, logging in will set a session cookie that disappears when you close your browser. Clicking on the 'Remember my Moniker & Password' below will cause a permanent 'Login Cookie' to be set.

Moniker/Username: The Name that you picked or by default, your email. Forgot Moniker?	Examples "Rapper", "Bob W", "joe@aol.com".
Password:	Forgot Password?
	Remember my Moniker & Password ( What's this?)

If you don't have an Asylum Account, you can create one by clicking Here.

Our privacy policy can be reviewed by clicking Here.

Inmate Comments

From:
Your Email:
Subject:

Message Comments

Original Message

Re: Hum pot in DHT preamp ???

Posted by dave slagle on November 1, 2001 at 09:35:52:
lets assume more traditional R/C coupling....the filamnet has a 7.5V dc potential across it.... now tie one side to ground (through the RC) and build two different supplies a +7.5V one and a -7.5V one the two different filament supplies will considerably change where the tube biases up, and for the same operating point two different bias resistors will be needed...
i think the negative supply will require a smaller bias resistor for the same current... the down side is grid current will start to flow when the grid hits -7.5V rather than zero...this is a problem in output tubes, but in drivers and such were we tend to keep well clear of the 0 bias point... maybe this is a place to make a small gain???
in other words with the -7.5V supply when one 1/2 of the filament is at -7.5V the other half is at zero and some grid current will start to flow. but with the +7.5V supply when one 1/2 of the filament hits 0 the other 1/2 is still at -7.5V so the grid current will start flowing with a difference of bias of 7.5V
is this making sense???
dave