• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Building a Aikido preamplifier

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#121
Think I've got it.



I connect the heater bias point to the centre point of the 2 resistors which are soldered between the hot and neutral cables of the secondary.

But I have 2 secondaries.

1 x 6.3V going to the 6X5 rectifier
1 x 12.6 V going to the 4 tubes on the Aikido main.

Do I connect the heater bias point on the psu to the virtual CT on the 12.6 V 4 tube heater?

If so, then I just connect the 6.3V 6X5 heater direct to the psu board?
 
#122
Yes, I think you've got it 🙂

I connect the heater bias point to the centre point of the 2 resistors
Correct!

But there is no such thing as phase and neutral after the transformer!
The primary windings on the transformer are phase and neutral. (Hot and neutral)
On the secondary winding (6,3V) there is no such thing as hot and neutral! Just 6,3VAC separated from earth!

Skip the tube rectifier! You don't need to lock this potential.

Do I connect the heater bias point on the psu to the virtual CT on the 12.6 V 4 tube heater?
Yes!

If you use 12,6V I would use higher resistance on the resistors in my schematic.
Maybe 200ohm each... 47ohm:s would be a little warm...
 
#124
But there is no such thing as phase and neutral after the transformer!On the secondary winding (6,3V) there is no such thing as hot and neutral! Just 6,3VAC separated from earth!
Click to expand...
Well that is something I didn't know. Thks for the clarification.
On my tranny I have no color coding. So one has the voltage and the other is the earth?
I will need to test which one with my DVM then.


Skip the tube rectifier! You don't need to lock this potential.
Click to expand...

So my 6X5 can be hooked up directly with no bias/resistor point.

Thank you
 
#125
Brit01 said:

Well that is something I didn't know. Thks for the clarification.
On my tranny I have no color coding. So one has the voltage and the other is the earth?
I will need to test which one with my DVM then.




So my 6X5 can be hooked up directly with no bias/resistor point.

Thank you
Click to expand...


Brit,

"On my tranny I have no color coding. So one has the voltage and the other is the earth"
on the primary side yes, (actually it's the neutral not the earth ground, there is a difference! ) on the secondary side no

Do you have a 5V A/C or D/C for your rectifier? You mention 6.3V and 12.6V............?

"But there is no such thing as phase and neutral after the transformer!On the secondary winding (6,3V) there is no such thing as hot and neutral! Just 6,3VAC separated from earth! "

Correct, thats why its A/C. After it has been rectified there is a + and - Voltage as referenced from 0 (zero)

Ron
 
#126
"On my tranny I have no color coding. So one has the voltage and the other is the earth"
Click to expand...
on the primary side yes, (actually it's the neutral not the earth ground, there is a difference! ) on the secondary side no

Sorry yes, wasn't thinking when I was writing. In the UK we use Blue for Neutral, Red/Yellow for earth and brown or red for live.

Now what I understand is that the primary and secondaries have polarities, which can be in or out of phase with each other.
at this point I do not know which they are or which cable is positive or negative.
When I referred to hot I meant positive sorry.



Do you have a 5V A/C or D/C for your rectifier? You mention 6.3V and 12.6V............?
Click to expand...

I'm going to use the 6.3 V AC winding to heat the 6X5 on Bas's psu.
And the 12.6V AC to heat the 5687/6N1P heaters.
 
#127
Brit,
Do you have a 5V A/C or D/C for your rectifier? You mention 6.3V and 12.6V............?" ------by Renron
My mistake....too many open pages on the computer, I was thinking about something else while I was typing this...I was thinking 5V for the 6x5gt. It is 6.3V for the heaters like you said..
Sorry.....multi-mistaking LOL
Ron
 
#128
I was wondering what you mean by: "I had connected the shield of the input wires on both sides." Isn't this how it should be?
Click to expand...

Thanks Ollebelle and Stixx: I know what you mean now. There was a misunderstanding. You were using 2-core + shield as input wire and you connected the shields on both sides.

In my case I use shielded single core wire. The core is connected to + on the phono socket and input stage, while the shield is connected to the - ve of the phono socket and input stage.

So far I'm still living with the hum. Probably I'll place the preamp in a larger box and pay more attention to cabling, especially heater-carrying wires.

Thanks and regards to all.

Joe A
 
#129
Joe,
If you are using a single core shielded wire for signal transmission, you are not using a shielded wire you are using an antenna. The shield is acting as an antenna and could even be a source of a ground loop. Try replacing that signal wire with a twisted pair.....say from Cat5 network cable and see what happens..
Good luck,
Ron
 
#134
Now I have figured out where the hum comes from! The power supply!
I disconnected my power supply, and temporarily connected another power supply built by me. I used it for my very first projects... It's a simple CRCRC-supply.

This helped a lot! The hum is pretty low now 😉 I will go on making a good CRCRCRC supply instead! 🙂
 
#140
Question: If JB recomended a transformer with 120mA will I be ok with 200mA? Thats just what it is capable of correct?
Click to expand...


Yes this is the maximum rating. I've just had some tranny's built for my JB project rated at 200mA (0-275V).

Another tranny rated at 0-12.6V @ 4 Amps. Loads of extra headroom for 6N1P's and 5687.

I have the 5687 JB board.
 
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