Need help on a YAHA build.
Oct 1, 2009 at 6:36 AM Thread Starter Post #1 of 4

928GTS

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So I finally got around to using one of my YAHA boards and I've got it all together and it works....nearly. The issue I'm having is that the sound out of the left channel is quite faint whereas I just hear a hiss out of the right channel. The interesting bit is that if I take one of my hands and place it on either the tip or ring of either the input or output jack and then take my other hand and place it on one of the tube pins I'll get sound in one of the channels though with some of the pins it doesn't sound like stereo sound for that channel. For example if I touch ring and tip on the input jack and pin 7 with my left hand and pins 3 and 4 with my right hand I get stereo sound through the headphones.

I need to work on getting my heater voltages down as they're a bit too high. I'm using the LM317T along with a 6GM8 tube which is a pin for pin analogue to the 6922/6DJ8. Below are my voltages as well as photos of the circuit.

Pin 1: 6.09V
Pin 2: 0.04V
Pin 3: 2.40V
Pin 4: 9.40V(too high,I need to increase the resistor size for the LM317T)
Pin 5: 0.04V
Pin 6: 5.06V
Pin 8: 0.04V

Pin 9 and 7 are not connected.

Pictures:


Twisted orange wires coming towards the camera are the + voltage supply.
dsc04842s.jpg


Close up of input jack.
dsc04844l.jpg


Tube socket wiring close up,pin 7 and 9 are not connected.
dsc04845t.jpg


PCB underside(I lifted a pad or two by mistake but all of the connections test well for continuity)
dsc04847pr.jpg


Circuit overview,red alligator clip is + power lead whereas white alligator clip is - power lead.
dsc04848u.jpg


Top circuit board view.
dsc04849c.jpg
 
Oct 1, 2009 at 8:51 PM Post #2 of 4

MrSlim

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Ok I'll take a stab..
Here's the tube data sheet :
6GM8 pdf, 6GM8 description, 6GM8 datasheets, 6GM8 view ::: ALLDATASHEET :::

Fa-Schmidt's YAHA page:
The YAHA amp

Digi's YAHA page (he made the boards...)
YAHA_v2 Head Amplifier

The Headwize YAHA thread: with a diagram of the pc board.
HeadWize: DIY Workshop > The YAHA amp thread part 2

Looking at the design, the input for each channel connects to the grid of one half of the dual triode, which are pin 2 and pin 7 (see the datasheet).
That means that both 2 and 7 need to be connected to work (and you say 7 isn't connected) The channel that only has hiss may be the one that is supposed to be connected to pin 7. I think you are missing the long jumper from Pin 7 to the connection beside R1R (which happens to be the right channel).

Fix that first and see what happens..

Get the voltage down on the heater also.

When you are touching the connections, your body might be acting like an antenna and picking up RF interference(basically radio signals) so that doesn't indicate anything.

As a matter of principal I would say shorten up the wires to the tube. You are going to get a lot of noise and crosstalk the way you have it right now.

IF you want to do it right, get a proper PC mount tube socket.. it will work much better.
 
Oct 2, 2009 at 2:43 AM Post #3 of 4

928GTS

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The long connection between pin 7 and R1R is already connected,it just runs underneath the board. I tried connecting pin 7 up and when I turn the unit on I get clear sound out of the left channel until the tube warms up and reaches full filament voltage and then it just turns to distorted mess. I tried switching to a 9V battery and the time where the output on the left channel stayed clean was longer but then it did the same thing again and turned to distorted mess. The power supply I was using originally was 12 volts supplied from a 7AH SLA battery.

I would use a PC mount except I want to have this in a case where the tube is lying down so I can put the enclosure in my pocket and not have to worry about a tube sticking out.
 

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