I'm planning another Hammond AO39 build. This time I'm moviing the tube locations around to make room for an eyelet board, and I want to try the 12ax7 channel of a Trinity TC-15 as a base. This design calls for 3-12ax7s vs the two I used on my previous build. The question is, does the Hammond PT have the heater current to handle the extra tube.
The original Hammond schematic labels the heater tap as being 1.8 amps, which on paper is just barely enough for the 2-el84, 1-12ax7 configuration it supported. It seems unlikely that Hammond would really cut things that close, and we already know that the PT supports a 2nd preamp tube just fine, so the rating in the schematic must be very conservative,
I know I can add a filament transformer, but in the spirit of beaks and feet building if I just go ahead and add the 3rd preamp tube how would I know if it is OK? ( or not) Would I be looking for voltage dropping below 6.3v, the PT getting obviously too warm or..? Note that I will be using SS rectification so the 5v tap will be unused. I have read conflicting info on whether that matters or not.
Hammond AO39 PT heater current
Moderators: pompeiisneaks, Colossal
-
lord preset
- Posts: 447
- Joined: Tue Aug 27, 2013 3:06 am
- Location: San Diego
-
Stevem
- Posts: 5144
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: Hammond AO39 PT heater current
Well if you find the heater voltage goes below 6.1 not only will That current draw be taxing that filament winding too much, but the tubes cathodes will not be putting out enough electrons and you will end up with the gain level just like weak tubes have!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Hammond AO39 PT heater current
It will handle 3x12AX7 plus 2xEL84. I'm using EF86 plus 2x12AX7 plus 2xEL84 which is 2.42A current (same as your config).
-
lord preset
- Posts: 447
- Joined: Tue Aug 27, 2013 3:06 am
- Location: San Diego
Re: Hammond AO39 PT heater current
sluckey wrote:It will handle 3x12AX7 plus 2xEL84. I'm using EF86 plus 2x12AX7 plus 2xEL84 which is 2.42A current (same as your config).
Excellent news. That saves me $12!! Woop!
As I was busy cutting, welding and punching away on the Hammond chassis to get it ready for the build my wife asked me how much it would cost to just buy a new chassis. I told her she was missing the point.