Hello!
you can see my other topic for reference:
http://www.diystompboxes.com/smfforum/index.php?topic=89461.msg759722#msg759722 (http://www.diystompboxes.com/smfforum/index.php?topic=89461.msg759722#msg759722)
i have build a lm350 circuit:
Adjustable Regulator with Improved
Ripple Rejection, page 7 http://www.national.com/ds/LM/LM150.pdf (http://www.national.com/ds/LM/LM150.pdf)
I have a nice 12.6vdc, and when i connect the heater (pin 4 and pin 5) of the 12ax7 , pin 9 unconnected :
voltage drop to 7.2 vdc at the output of the lm350 circuit ! :-\
I try 2 other tube (in case that the heater was malfunction)... they all do the same...
The rest of the tube is unconnected, i just try to solve the heater problem...
HELP !
Bent
This may help you : http://www.enotes.com/topic/12AX7
Quote from: thedefog on January 31, 2011, 11:08:28 PM
This may help you : http://www.enotes.com/topic/12AX7
Thank's :) , but no really helping me....
i was more wandering why the voltage is dropping (12.6vdc to 7.2vdc ) on the out of the lm350 when i put a load on it...
and how to correct this....
bent
Your regulator cannot supply more current than the raw unregulated DC supply before it.
When the output drops under load, what is the DC voltage on the INPUT to the regulator?
Here's the set up:
- 110 vac in
- from 110vac, goes to 229d24 transfo to get 24vac
- from 24vac --- go to 3 place:
- another 229d24 in reverse + bridge and cap/resis to get 307vdc
- phantom power circuit http://www.extremecircuits.net/2010/05/48v-phantom-microphone-power-supply.html (http://www.extremecircuits.net/2010/05/48v-phantom-microphone-power-supply.html) to get 48vdc
- another diode-bridge to supply 3 individual LM350 circuit to get:
- 12vdc for IC board ( not connected for this moment)
- 12.6vdc for heater
- 24vdc for vu meter ( not connected for this moment)
All ground connected together
The problem i see (or i think), is that the phantom power circuit is affecting the power of the other circuit.... cause i have 50vdc at the IN of the LM350...
I build 2 LM350 circuit to seperated the heater from the IC board to avoid HUM !
A BIG Thank's R.G. to drop by ;) , i'm totally lost....
Bent
I need:
- +/- 300 volt for 4 tube circuit, total +/- 30mA
- 12.6vdc for heating 4 tube, and 4 meter light, total +/- 850mA
- 12vdc for 4 IC board , total of +/- 500mA
- 24vdc for 2 vu meter board, +/- 5mA
- 48vdc for 4 mic phantom power
i got :
- 110vac in
- 229d24 (hammond) X 2
- TL783 ( few of them)
- LM350 (few of them)
Solution anybody?
Bent
Had the same problem never solved - i'm using AC for heaters. DC 12v 1.5A - LM5806 - 12AX7 (6n2p) heaters => voltage drop to 7.9 / 8.2 (heaters in both cases are drawing between 350-400mA so there is another problem that i don't see).
Best regards,
Gabriel Tudoran
Analog Sound
Thank's Gtudoran,
i just think in my shower (best place to think ;D ), i will remove the 48vdc circuit and take the 24vac in a diode bridge to supply the rest, if this work, i will order a 110v to 48v transfo, and make my phantom power from the transfo directly with diode bridge and rectifier like lm350 or TL783....
bent
YES!
so far so good....
i disconnect the phantom circuit... plug 24vac throught a diode bridge with a 1000uF cap on the exit....
now all my 3 lm350 circuit have the good power....12vdc, 12.6vdc, 24vdc
when i connect a heater on the 12.6vdc...it stay at 12.6vdc....heater work !
when i connect vu meter light on it, stay at 12.6vdc but after a minute overheat and lm350 switch off...
i didn't put compound between the lm350 and the heatsink....might be the problem !
can sustain 1 heater.... at 2 heater the lm350 switch off by the heat...
If you are not using a heat sink, I would consider adding one to improve heat dissipation. This solution assumes the circuit is working correctly, which may or may not be the case.
Or, omit the DC heaters and use elevated AC heaters. Four resistors and a cap and you're there.
i use a heat sink, but didn't put compound between the heat sink and the lm350...
can you tell me more about the 4 resistor and cap.... the Ac i have is 24vac....
Under "DC Elevation". http://www.freewebs.com/valvewizard/heater.html (http://www.freewebs.com/valvewizard/heater.html)
R1 = 1M
R2 = 100K
C1 = 22 to 47u. 100v.
All can be user adjustable, I just know these values give you about 30v elevation with 300v B+ and good decoupling. If that's not enough to eliminate heater/cathode coupling hum, increase R2 until you're in the 40-60v range.
thank's defaced....
very usefull page....
i just found a nice little transfo 115v to 12vac.... but its giving 14.3vac....how to drop it to 12.6vac...?
Quote from: bent on February 01, 2011, 01:35:49 PM
i use a heat sink, but didn't put compound between the heat sink and the lm350...
The LM3xx series will always shut down before dying from overheating.
Heat production is the product of the current through the regulator times the voltage difference across it - that is, Vin minus Vout of the regulator. Measure this difference, then multiply by the current through the load.
If it's overheating and you did not use compound, then... use heat sink compound. Heat sinks can be almost useless unless they are properly attached to the heat producing device.
Quote from: bent on February 01, 2011, 03:40:00 PM
i just found a nice little transfo 115v to 12vac.... but its giving 14.3vac....how to drop it to 12.6vac...?
For what use?
12vac transfo no good..... its 2.4vac....not enought current....
i use compound and.....one heater is good....but when i connect the second one it took about 1 minute to overheat...
i use the 229d24.....
the second parallel is 12vac.... so when i pass it in a diode bridge i got 12.3vdc.... do i need to put a 1000uF cap at the dc side of the bridge ?
cause when i do it rise at 19.6vdc, so i would need a regulator, and im trying to avoid since i got problem with heat... but the 12.3vdc without the cap would be nice for me......
except that everything will be connect on this .....would it cause humm?
just connect 2 heater and voltage drop from 12.3vdc to 10.9vdc.... :icon_confused:
well well well !
i took a chance and connect the 12vac on a bridge with 1000uF cap, then past it into the lm350 regulator....and the circuit can supply the 4 heater ! without overheat ! ( hot but not switch off)....but i need 24vdc so...
i think i will try to replug has it (24vac) then use a lm350 to drop to about 24vdc then use another lm350 to drop to about 16vdc, then lm350 to drop to 12.6vdc
OK !
So far so good !
24vac -> diode bridge + 1000uF ( 30vdc) -> lm350 to drop to 24vdc ( for vu meter) -> lm350 to drop to 16vdc -> lm350 to drop to 12.6vdc
all 4 heater are working for 5 minutes and still running...no shut down....
heat sink are hot ! but dont look overheat ! i will had a small fan for that !
i think ill will build another lm350 to drop 16vdc to 12vdc for the IC board....
and still have the 48vdc phantom power to find a way to get it...
Quote from: bent on February 01, 2011, 05:00:28 PM
well well well !
i took a chance and connect the 12vac on a bridge with 1000uF cap, then past it into the lm350 regulator....and the circuit can supply the 4 heater ! without overheat ! ( hot but not switch off)....but i need 24vdc so...
i think i will try to replug has it (24vac) then use a lm350 to drop to about 24vdc then use another lm350 to drop to about 16vdc, then lm350 to drop to 12.6vdc
If you already must have 24V
dc, then think about wiring your heaters in series. You'll use less current, and reduce your parts count. I'm not sure it is the way to go, and it does raise some concerns (if one of your heaters dies, you have got a problem!), but it would solve some of your problems. You can decide for yourself if the trade off is worth it.
Gabriel
Thank's for the reply G.Hoffman,
I did think of that, but the fact that one heater burn and the rest turn off, stop me for that option....
so i will go for dropping the voltage by step....more part but less problem ...
and i just order a 115/230v - 24v transfo for the tl783 circuit for phantom power... 162E24 hammond
ill keep posting for people that have the same problem of me...
bent
everything good so far ! 12.6vdc for heater...
but now i have another problem...
i build preamp based on this
http://diyaudioprojects.com/Tubes/12AX7_Preamp/ (http://diyaudioprojects.com/Tubes/12AX7_Preamp/)
first one work perfectly...
the other not... where is supposed to have +140 and +160 ( pin1 and pin6 of the tube), i got something like 46v and 70v....and before the resistors i have 245v (between the 47uF cap and the 68k & 270k)....
i checked the resistor but they are good....
all the rest look ok, cause i compared with the one that's working....
i change tube.. still not working...
any idea ? anybody?
If you could put a current schematic up it would be a big help in trying to sort things out. In the meantime there's a really good article on the creative use of wallwarts with a good section on using back-to-back transformers (eg. how to size them etc.) for powering tube circuits.
http://www.audioxpress.com/magsdirx/ax/addenda/media/stamler2874.pdf
dave
Thank's davent,
all my voltage are set and working...
for the schematic, i put this link in my last post:
http://diyaudioprojects.com/Tubes/12AX7_Preamp/ (http://diyaudioprojects.com/Tubes/12AX7_Preamp/)
my problem is that i drop from 245v to 46v and 70v where is supossed to have 140v and 160v on pin 1 and 6 on the tube....
the rest looks ok...and resistor are ok !
K...
I switch the tube between circuit, the one working and the one not working, problem switch of board...so i got a tube burn ( i think), but now on the circuit where's the working tube...no sound...all voltage are good, the sound goes to pin2 but dont exit by pin 1 so dont go to pin 7...
pin 1 is moving between 123v to 126v
pin 6 is moving between 130v to 200v
and where is the junction of the 47uF cap , 68k, 270k, 8k2 i got moving between 240v to 242v ...
before 8k2 is steady at 254v
Find IT !!!!
cold joint at the turret board, jonction of the 100nf (input) and the pin 2 of the tube...
Just realized that the tube that is not working is a ecc82 ( 12au7) , can it be the problem?
always thought that it can be swap without change on the circuit...
but can this circuit can accept this type of tube?
HeyLow, Am still reeling from the RG IQ Test. Did get a call last year from a local Vintage Vinyl Shop to repair and restore the older RCA, GE, and Zenith consoles and players. I flashed back to when I knew little or what was considered HiFi. All I knew or cared about back then was how to make it loud by finding and cutting out the NFB resistors. Anyway, In the schematics of all of the players I noted filaments were all ways ran in series with a selenium or silicon rectifier, and just had a few resistors and a 150/100/50uf all in one Can capacitor. It was used for the B+. and cathode bypass. The chassis and the floating signal ground worked well at eliminating any hum from the signal path. At 3W per channel, was loud enough to be irritating enough to the HiFi folks. On one restore I used a few simple IRF240 MOSFET's as the final stages and got a conservative 10W. On most of my restores added a headphone jack to Bluetooth® to let you go into whatever you got.
What I learned from working with the first solid state germanium output players was when overdriven, they smooth and compress the signal. NTE still makes the TO3 output transistors and other's, if any one is interested czech it out.
Am wondering if someone else could take this and take it to a new topic or keep this one and expand or improve on the filament/B+ circuit possibilities and potentials, add more tubes (pentode input). Maybe some kind of voltage doubler for the B+...
(https://i.postimg.cc/PNF5Q4tk/Series-Filaments.png) (https://postimg.cc/PNF5Q4tk)
(https://i.postimg.cc/wtV6y5WZ/RCA-speaker-redux.jpg) (https://postimg.cc/wtV6y5WZ)
This record player is HOT-CHASSIS. It is fairly safe as a record player. The MIC input skirts the old safety regulations with C3, which allows "only" 2mA of line-power leakage. If true, probably not lethal, but a significant shock. However the common break-down in the C3 part is Dead Short. This can be lethal.
Please be careful.
It is actually very odd for these things to run the heater on DC. In this case they "had" to because the wiring is on PCB and proper heater-wire layout is not possible.
This is a 2W/ch amplifier. Taking it to 10 actual measured watts audio output would be like turning my 100HP car into a 500HP car-- it requires replacing ALL the power parts.