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PostPosted: 29 May 2010, 12:20 
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I did abit more research and turns out I wired the 12au7 tubes wrong, so I think I fixed that. For the DC3 out for the 12ax7's, I have two wires coming off the positive, each wire going to pin 4 on the two 12ax7's, i then have a wire connecting pin 4 and 5 together on each 12ax7. I then have two wires running back to negative on the DC3 out. Each negative wire coming from pin 9 of each 12ax7. Is that the right way to do it for parallel 6.3v wiring? The tubes light up nicely exept that I still read 12ish volts, even though the two 12ax7's are running off one 12.6v output. Also the heatsink is getting really really hot, like you can only touch it for a few seconds, is that normal?

Now the 12au7's. These are not meant to be in parallel and are meant to have 12.6v to each tube. So I have two DC 12.6v outputs for each 12au7. On each, I have a wire from positive of one DC output to pin 4, then a wire from pin5 to negative on the DC output. The problem is, they are not glowing barely at all, they get slightly warm aswell as its heatsink.

Now for the rectifier tube. 6.3v does go into the filament, and I measured pin 7 at 337v (red from multimeter to pin7 and black from multimeter to ground on power supply board, think that may be wrong) but the tube isnt glowing and Im not reading any high voltage at the B+ out. No idea whats going on.


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PostPosted: 31 May 2010, 03:57 
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Hi again,

i think there is some misunderstanding for the wiring.

Basically, the tubes can be heated with 12.6V OR 6,3V. There is only one choice.
You got 12,6 (12V) from the outputs. So - pin 9 must not be connected anyway. It's only for use with 6,3V.
It doesn't matter if you parallel the tubes or single connect them. The 12,6V must be present, even if you connect
them in parallel. The current (0,3A per tube) must be available from the PS. That should be the case on your project.

I attached a drawing, how to connect the tubes in parallel or single. You can use one wire, coming from the PS
and split the ends to both tubes or you can use two wires, one for each tube.. The same to the negative side.
The drawing shows the two kinds of wiring.
Attachment:
heater.gif

Don't expect that the tubes light up like a christmas tree. The filament glow is barely visible, if you power up the tubes at daylight.
In a dark room the filaments glow slightly red or orange.

You can take a look on another guide here (figure 2 - tube pinout): Rogers' 12AU7 (ECC82) / IRF510 Headphone Amp.

You wrote:
Now for the rectifier tube. 6.3v does go into the filament, and I measured pin 7 at 337v (red from multimeter to pin7 and black from multimeter to ground on power supply board, think that may be wrong) but the tube isnt glowing and Im not reading any high voltage at the B+ out. No idea whats going on.
Now - that doesn't read bad. 337V at pin 7 is a good reading from
a dual 250V transformer. The filament power is hooked up properly. If not, you would have nearly no voltage at pin 7 on the
rectifier tube. As meant in a post before, you have to regard the transformer's outputs. There are several "0" pins on the transformer. All this "0" pins are responsible for the "ground" connections. Let's take a look on the HV (high voltage) section.
(Marked Orange):
Attachment:
tranny.jpg
The transformer has 3 pins for the "High Voltage". This are the two
250V (AC) and the pin "0" for the grounding. The two 250V pins must connect to "H . AC" on your HV supply board.
The transformer's high voltage "0" (which is also shown in the orange rectangle - picture above) connects to the pin "E" or
you can solder it to the pcb hole "gnd" on the HV supply pcb. This 3 transformer pins build the high voltage.
If the transformer pins are hooked up properly to the HV pcb, you should have a reading of about 340V / DC on the "+B1".
The voltage is measured between "+B1" and the "ground" (The pin next to +B1 - on the right side OR the pin "E").
This voltage is measured without a connected load, so it's way higher, until you connect the load circuit which
drops down the HV supply voltage in a second. Measurings without a load circuit are usually 1,2 to 1,414 times higher
than load connected...

The things will turn for good in a while. ;-).


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Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 31 May 2010, 17:01 
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Joined: 22 May 2010, 08:01
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Thankyou soooo much! I will fix all this this arfternoon and see how it goes. Just one thing about the transformer. The three high voltage pins are labelled 280v, 250v and 0v. But the 280v pin reads 310v on the multimeter and the 250v pin reads 280v. The company that sold me the transformer also sells a 280-310v transformer, so Im assuming that they put the wrong label on it. So in this case, how would I have it connected?


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PostPosted: 31 May 2010, 18:46 
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Location: Duesseldorf, Germany
Barrington wrote:
The three high voltage pins are labeled 280v, 250v and 0v

Oh my, sorry, i thought this transformer is a double 250V with one "0" for ground
and i didn't take a second look onto the power supply schematic. Sorry - my fault!

OK - everything still goes fine.

The heaters for the tubes still have to be connected like meant before..
Some more informations: http://en.wikipedia.org/wiki/12AX7


The transformer really has 2 different HV sections. You'll need the pin with the measured 280V (AC) output.
Maybe the transformer has a wrong label... You wrote you've already measured the AC-output.
The schematic shows that 280V (AC) is recommended.
So - we use the pin that gave you the 280V (AC) output. (Measured from 250 / 280 to "0").

Your HV pcb is stuffed with a "hybrid" tube rectifier circuit (i double checked it to be sure and checked the schematic again).
Hybrid configurations work with one tube for the high voltage supply and two solid state diodes to build the ground (0).
So - the transformer does NOT provide a "0" or a pin for the "ground" by itself.
The label shows a "0", but this 0 can not be used to build the PSU ground.
In this case, "0" is used for the second AC connection.
This hybrid configuration works in the same way like a "graetz bridge rectifier" or "diode bridge"
http://en.wikipedia.org/wiki/Diode_bridge

OK - connect the 280V (measured) pin and the pin "0" (from the transformers HV section)
to the "H . AC" on the HV board. That's all for the HV supply (and the right connection now].
The circuit ground "0" or "ground" is provided by the 2 solid state diodes and is on pin "E" or "GND" or next to the "+B1" pin.

If you now go to measure the HV board now, you should read about 340V (DC unloaded) and 280VDC regulated / with load.

Please be careful - HV is very dangerous - treat it with respect!

I hope i could help you a bit further now...

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Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 31 May 2010, 21:19 
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Ok so 280v and 0v connected to the H. AC on the power supply, is that all thats needed to be connected (besides fixing the heater wiring)? Because that was how I always had it wired, and I dont get any voltage at the B+ out on the power supply board. So you are saying that it is already grounded by the two diodes so I dont have to worry about grounding anything? For the primary voltage on the transformer, (coming from the wall), I have the earth connected to 'GND' on the transformer, does this also have to be connected to the chassis? Also, because Im still wiring the preamp, I havent put any of it in the metal chassis yet, meaning that nothing is grounded to it. Could this be a reason why Im not getting a B+ reading?


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PostPosted: 01 Jun 2010, 16:40 
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Yep,

280 and 0 to H. AC is definately right.
The circuit ground is provided by the HV supply board at pin E or GND.
(this will become the common ground rail for the speakers, OPTs and the other stuff)

The reason that you don't get the B+ voltage on the pins might be another...

Today i've thought that you didn't connect the choke or a filter resistor to the board.
On the schematic are two pins to connect a choke or a filter resistor...
With non of them connected to the board, the circuit is open and there can't be any voltage at the B+ pins...

Yes, you can connect the mains "earth" to the transformer's "GND". When you've put all the boards into a chassis
this tansformer "GND" connects to the chassis and the chassis also connects to mains "earth".
Grounding the chassis and the transformer to "earth" prevents you or other people from getting injured by
a short circuit or HV on the metal parts.

This pin on the transformer is the output from a shield / screen winding in the transformer.
It also makes sure, that the level of stray inductions or HF inductions and other junk stays low.

Again to the failure of B+ out...
Choke connected??

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Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 01 Jun 2010, 16:57 
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yep choke is connected


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PostPosted: 03 Jun 2010, 18:02 
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I've no idea at the moment why you don't get the voltage at the B+ pin. The setup seems to be OK so far.
How did you measure the B+ pin. Only with the Multimeter? Without a resistive load?

It's hard to guess what's going on there. You wrote that you've read 337V at pin 7 on the rectifier tube. That's a good start.
There must also be a lower voltage at the resistor R1 (white 1,2K), the choke input / output (w. connected choke)
and the capacitors C1 and C3, R2, R3, D4 and D5 (reference to pin "E" - "GND").

At the moment i'm not very sure, if the 240K bleeder resistor (R4) lets pass enough current to enable the
solid-state voltage regulator. To be sure, i'ld connect a resistive load at B+ (to GND), to enable a current flow.

I don't have any further ideas what could cause the fact that you don't read a voltage at B+.
The solid state devices are backwards protected, they should be OK so...

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Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 03 Jun 2010, 21:23 
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Joined: 22 May 2010, 08:01
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Could it be a faulty 6x4 tube? I have the 6.3v voltage connected directly to the heaters and it doesnt heat p or glow at all.


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PostPosted: 04 Jun 2010, 12:12 
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That sounds like a problem with the tube heater. You can confirm this by checking the resistance across the tube heater pins with a DMM.

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