ampage Tube Amps / Music Electronics	For current discussions, please visit Music Electronics Forum.	New: view Recent Searches. New: visit Schematic Hell! The sunn still shines online!

Listen to great tunes streaming live right now!

ampage archive

Vintage threads from the first ten years

DC voltage drop Q

12/21/2004 11:11 PM
wayneosdias	DC voltage drop Q Useing 5v3a winding to a ss fwb to a 10m cap I get an unloaded voltage of 6.6vdc. Running this to a single 12ax7 heater drops this to 5.4vdc, I know that dc req's 40% more current than ac, but even at 420ma Im still way under 3a, why such a large voltage drop? Is there any way to get the minimal 5.7vdc 12ax7 req out of a 5v winding? wayne

12/22/2004 6:58 AM
Don Symes	It's all about the transformer's source impedance ... at least that's the impression I get fiddling with it under Duncan's PSUD-II (Power Supply Unit Designer). With the load down to 10mA, you get 5.5-ish volts, adn darned noisy at that. ...geeze - with the load at 500k ohms, you don't quite get to 5.7V. Pick up a copy at http://www.duncanamps.com in the software section. Measure your 5V winding's DCr and enter that (I was using 3 ohms). HTH!

12/22/2004 6:58 AM

Don Symes

It's all about the transformer's source impedance ... at least that's the impression I get fiddling with it under Duncan's PSUD-II (Power Supply Unit Designer).

With the load down to 10mA, you get 5.5-ish volts, adn darned noisy at that.

...geeze - with the load at 500k ohms, you don't quite get to 5.7V.

Pick up a copy at http://www.duncanamps.com in the software section. Measure your 5V winding's DCr and enter that (I was using 3 ohms).

HTH!

Monday

Book Of The Day

The Ultimate Tone, Volume III by Kevin O'Connor

Have you ever wondered if there is a better way to build a Bassman, Champ, Plexi, an 800, AC-30, Bulldog or Portaflex? Or you wanted to build an SVT with off-the-shelf parts? How about a master-volume amp that doesn’t change tone with the master setting? Everything you need to know is right here, including: proper grounding techniques, wiring methods, and mechanical considerations. Eighteen chapters cover the “iconic” amps everyone knows and loves, with schematics and layouts for each, along with the technical history of the product. Eyelet-board and chassis-mounted tube socket construction is used throughout, for easy servicing and modding. TUT3 is very accessible even if you cannot fully read a schematic and is a "must have" if you are going to build an amp for your self.

Note: The Ampage Archive is an Amazon Associate site. A small commission is paid to the site owner on any qualified purchase made after clicking an associate link such as the one above.

12/22/2004 7:39 AM
Wild Bill	10 Mfd? Way too low, IMHO. These are low voltage 5vac rectifier pulses and you are asking much more current than you'd draw from a plate B+ supply. So that 10 mfd can never charge up very much - essentially it's not enough to be a cap input filter. Hang a 470 mfd or even a 1000 mfd in there and see what happens. I find that when using these windings for DC filaments 500 or 1000 mfd is the minimum value, especially to reduce ripple. With only 10 mfd I'd expect to get a bad filter hum in the 12AX7. ---Wild Bill

12/22/2004 7:39 AM

Wild Bill

10 Mfd? Way too low, IMHO.

These are low voltage 5vac rectifier pulses and you are asking much more current than you'd draw from a plate B+ supply. So that 10 mfd can never charge up very much - essentially it's not enough to be a cap input filter.

Hang a 470 mfd or even a 1000 mfd in there and see what happens. I find that when using these windings for DC filaments 500 or 1000 mfd is the minimum value, especially to reduce ripple. With only 10 mfd I'd expect to get a bad filter hum in the 12AX7.

---Wild Bill

12/22/2004 8:34 AM
wayneosdias	Thanks Guys Im going by KOC's TOT filter supply that should be able to feed 2 12ax7s same PT, same bridge same cap 2200u, i played w/whis value a little but w/little of no chnage I just dont get why Im not replicateing KOCs loaded voltage. I tried dong this in the past w/the 6.3 winding and not having any success. Can some one point me to a solid method of a good dc supply for 2-3 12ax7's? Getting a dedicated filament xfer a choke and a bunch of hi u caps is no problem, I just want to get a clean dc heater supply thanks wayne

12/22/2004 8:34 AM

wayneosdias
email

Thanks Guys

Im going by KOC's TOT filter supply that should be able to feed 2 12ax7s

same PT,
same bridge
same cap 2200u, i played w/whis value a little but w/little of no chnage

I just dont get why Im not replicateing KOCs loaded voltage. I tried dong this in the past w/the 6.3 winding and not having any success. Can some one point me to a solid method of a good dc supply for 2-3 12ax7's? Getting a dedicated filament xfer a choke and a bunch of hi u caps is no problem, I just want to get a clean dc heater supply

thanks
wayne

12/22/2004 10:38 AM

Don Symes

quote:
"Getting a dedicated filament xfer a choke and a bunch of hi u caps is no problem"

Choke? What's the choke for (except to drop some voltage)? Just my stupid opinion, but that seems like like overkill.

12/23/2004 12:22 AM
wayneosdias	Ya a choke if itll smooth things out. Ive got 2 small spares from early tweed builds, whether their appropriate or not I dunno. Thanks for the PSUD Ive been screwing around w/it, but must confess Im haveing difficulty interpreting the results. I did however figure out the heater has a resistance of 5r, why this totally escaped me I dunno. Just a noob taking baby steps wayne

12/23/2004 7:30 PM
Don Symes	It's not the MOST intuitive tool, but if you screw around with it a bit using PSU circuits you know or understand, the light slowly comes on. In the tool, you select a (major) section and tell it what topology you have in mind. Then you can select individual components in each section and get fairly detailed about its properties (try double-clicking in the various menus). Once you've completed a run, you select the V or I node(s) you want graphed - like in some SPICEs - and you get a semi-usable picture. You may find it useful to futz with the time parameters to delay and scale the graph.

12/23/2004 7:30 PM

Don Symes

It's not the MOST intuitive tool, but if you screw around with it a bit using PSU circuits you know or understand, the light slowly comes on.

In the tool, you select a (major) section and tell it what topology you have in mind. Then you can select individual components in each section and get fairly detailed about its properties (try double-clicking in the various menus).

Once you've completed a run, you select the V or I node(s) you want graphed - like in some SPICEs - and you get a semi-usable picture. You may find it useful to futz with the time parameters to delay and scale the graph.

Page 1 of 3

Next>

Last Page>>