Forums
New posts
Search forums
What's new
New posts
Latest activity
Members
Registered members
Current visitors
Log in
Register
What's new
Search
Search
Search titles only
By:
New posts
Search forums
Menu
Log in
Register
Install the app
Install
Audio and Video Talk
Valves / Vacuum Tubes
How to bias split-load phase splitters?
JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding.
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an
alternative browser
.
Reply to thread
Help Support AVForums:
This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
Message
<blockquote data-quote="handsome" data-source="post: 847947" data-attributes="member: 772"><p>you should aim to have 25% of your HT across the anode and cathode resistors of your splitter and 50% across the phase splitter tube itself. so you would aim to find an operating point for the first tube that is approximately 25% of your HT, the problem as you no doubt have found is operating your first tube at such a low voltage. EL84s and 6V6s have a maximum HT voltage of ~300V so this means your first tube is operating at ~75V a very low voltage. This is one reason to use a pentode in this position (gain being the other) and a good reason NOT to use a 12AX7 if the ultimate in linearity is your goal. Solutions to this particular conundrum are: a) AC coupling which allows you to set the operating points of the tubes independently, b) having an separate high voltage power supply for the first two stages or, c) for the first stage use low Rp triodes (might not have enough gain), high Gm triodes or pentodes all of which can be more linear at low plate voltages. Most design work is managing compromises, in this case you have headroom vs linearity fortunately EL84s do have a low drive voltage requirements so you can fudge the HT rules a bit.....</p></blockquote><p></p>
[QUOTE="handsome, post: 847947, member: 772"] you should aim to have 25% of your HT across the anode and cathode resistors of your splitter and 50% across the phase splitter tube itself. so you would aim to find an operating point for the first tube that is approximately 25% of your HT, the problem as you no doubt have found is operating your first tube at such a low voltage. EL84s and 6V6s have a maximum HT voltage of ~300V so this means your first tube is operating at ~75V a very low voltage. This is one reason to use a pentode in this position (gain being the other) and a good reason NOT to use a 12AX7 if the ultimate in linearity is your goal. Solutions to this particular conundrum are: a) AC coupling which allows you to set the operating points of the tubes independently, b) having an separate high voltage power supply for the first two stages or, c) for the first stage use low Rp triodes (might not have enough gain), high Gm triodes or pentodes all of which can be more linear at low plate voltages. Most design work is managing compromises, in this case you have headroom vs linearity fortunately EL84s do have a low drive voltage requirements so you can fudge the HT rules a bit..... [/QUOTE]
Insert quotes…
Verification
Post reply
Audio and Video Talk
Valves / Vacuum Tubes
How to bias split-load phase splitters?
Top