Bottlehead Forum

General Category => Technical topics => Topic started by: vetmed on March 21, 2012, 06:27:10 AM

Title: DC coupling
Post by: vetmed on March 21, 2012, 06:27:10 AM

I am having difficulty understanding how DC coupled circuits work in SETs. I can see that the plate voltage of the preceding stage has to appear on the grid of the following stage. After that I find it confusing. How is the value for the bias resistor calculated? Does it have any effect on heater to cathode values? etc... Thanks




Robert Lees

Title: Re: DC coupling
Post by: nullspace on March 21, 2012, 06:57:54 AM

Hi Robert,

There was an excellent article in VALVE back in the day on just this topic. The issue is available for download here: Blues Master (http://www.bottlehead.com/VALVEarchive/1998/va011998.pdf). Pretty much walks you through step-by-step on all the details. The output stage is a DHT, though, so no heater-to-cathode issues to speak of -- if you were looking at a IDHT, then yes, you would need to bias up the heater to be within the h-to-k ratings.

Regards,
John

Title: Re: DC coupling
Post by: vetmed on March 29, 2012, 04:09:47 PM

Hi
   Really appreciate your response, and the link was very useful. My concern regarding heater to cathode limits had to do with the more usual 100volt limit, but the tube I am working with has a 200 volt limit so of course is less of a concern. Thanks




Robert Lees