12ax7 heater voltage problem

[bent]

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

[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/

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?

[davent]

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

[bent]

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/

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 !

[bent]

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

[bent]

Find IT !!!!

cold joint at the turret board, jonction of the 100nf (input) and the pin 2 of the tube...

[bent]

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?

[engelheimer]

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+...

[PRR]

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.