"SHAKA TUBE" - almost working ??

[Paul Marossy]

Any progress MartyMart? I'm a hotel called Ayres in Los Angeles today, they have a computer, so I thought I'd check in...  

[markr04]

MartyMart,

Just a hunch... try a 10K resistor between the audio board ground and the AC "ground". It cleared up this problem for me.

[puretube]

does this look like your build?


additionally to the components in my PSU schem:
GND (0V) is connected to inputjack-sleeve, outputjack-sleeve, chassis.
GND (0V) also goes to:
2µ2 cap;
470k res;
0.01µ cap;
10k vol-pot.
in Aron`s schemo - nowhere else.

and also:
the IC`s powersupply pins go:
pin4 to V- ;
pin7 to V+ if using a TL071 only (single opamp);
OR:
(pin8 to V+ if using a TL072 only (dual opamp));

pin2 is neg. input;
pin3 is pos. input;
pin6 is output for TL071 only;
OR:
(pin1 is output for TL072 only);

all other pins: not connected anywhere.

(if in doubt, compare pinout from this 900kB pdf file:
TL071/72/74)

when this all applies point for point to your build,
please explain, where your 680 Ohm inline-resistor is situated,
when you would draw it into my schem...

[EDIT] R3 in my schem (above) should read 1k instead of 470R!
(for the rest, it corresponds exactly Aron`s schem, viewed "european style".

[MartyMart]

Ton.
That's EXACTLY what I have here !!
All other pin connections are also correct for TL071

The 680 Ohm resistor is in line with the PSU BEFORE it hits the board
top far left :

PSU centre pin --> 680 Ohm 1 watt --> power board/tube pin 4
PSU barrel ---> power board Ground/tube pin 5

AC value hitting the power board 10 Ohm 1 watt connection 12v
Op amp pin 7 +12v DC
Op amp pin 4 -12v DC

Connecting power ground to opamp board/jacks ground produces NO output
at all ..... SILENCE !!

Thanks,
Marty.

[puretube]

so that would be inserted xactly where I marked "x" ?
while the transformer is 16V instead of 12V.

in that case you only have ~ 1.7V AC across the filaments (tubepins4/5)...

[16V:(680+80)Ohm]x80 Ohm = 1.7V;

>those 80 Ohm is the filament (heater) resistance<

and I wonder how those 1.7V rectified come out as +/- 12V

Be sure of measuring V+ and V- against GND in DC-mode!
and measuring ONLY tubepins 4 and 5 against each other in AC mode!

the tube won`t lite up clearly visible with 1.7V...

[puretube]

you probably had measured the V+/- against the AC GND at the xfmr,
before you had the connection of all grounds completed.

The right value for the input-inline-series resistor ought to be between 22 Ohm and 68 Ohm, to reduce 16V to 12V when loaded by the 150mA of the heaters, and the few mA of the plates and IC.
This R should be rated at least 1W (better: 2x1W parallell with appr. values; e.g. 2x 100 Ohm).

[MartyMart]

so that would be inserted xactly where I marked "x" ?
while the transformer is 16V instead of 12V.

in that case you only have ~ 1.7V AC across the filaments (tubepins4/5)...

[16V:(680+80)Ohm]x80 Ohm = 1.7V;

>those 80 Ohm is the filament (heater) resistance<

and I wonder how those 1.7V rectified come out as +/- 12V

Be sure of measuring V+ and V- against GND in DC-mode!
and measuring ONLY tubepins 4 and 5 against each other in AC mode!

the tube won`t lite up clearly visible with 1.7V...

OK, interesting stuff :
The AC transformer ( Peavey ) is rated at 16.5 v AC, but supplies between 16 and 20 v AC. ( 1.2 amps max so it's quite muscle bound )
               **** Unloaded it reads 18.4 v AC ****
It connects via the 2.1mm power socket to a tiny piece of perf, with the
680 ohm resistor on, then out via small lead to point "X"
At the "board" side of the 680 Ohm resistor, I read 12 v AC ..... unless by
your calculation, I have 1.2 volts ?? !!!
So ... to drop 18.4 volts to 12 volts, you are saying that a resistor between 50 and 80 Ohms is required ? ?

Cheers,
Marty.

[MartyMart]

Hmm ... this is making no sense now  :?
I just tried 100 Ohm 1 watt between PSU and power board :

AC readings : 16.8 volts at the board/tube ref power board ground

DC readings : + 16.8 volts at op amp pin 7 ref ic board ground
                    - 16.8 volts at op amp pin 4 ref ic board ground

I guess the op/amp and tube could be dead now  !!

Marty.

Calculation :

18.4 (volts) divided by 270  ( 100 ohm + 150 tube +20 ic board) = 0.0681481

0.0681481 X 170 = 11.58 volts
Correct ?

[puretube]

if xfmr stays at 18,4V when delivering 150mA for the heaters (which have a resistance of 80 Ohm),
a series-resistor of 43 Ohms is needed,
to bring down the voltage across the heaters to 12V.



(forget about the low consumption of the DC circuit for a moment...)

[MartyMart]

OK. 680 ohm resistor back in :
AC reading from tube pins 4 /5 ONLY .......  is at 12.4 volts !!

Circuit works again, when the "ground" between the boards is disconnected    :?  :?  :shock:

It will intermittantly "cut out" but a "touch" on the floating board ground
cable ( still connected at power board end )  ... kicks it back to life  !

My god this is so close to working now ??   grrrr

Marty.

[puretube]

either the tube`s filaments are broken, or connected by cold solder joints/broken wire,
or the meter needs a new battery.
What resistance do you measure between the naked tube`s pins4 & 5?
(tube taken out of socket)
What resistance do you measure (wallwart un-plugged / out of the circuit;
caps discharged) between the points in your build, from where the wires to the tube-heaters origin (tube in socket, now).

[MartyMart]

Disconnected tube, across pins 4&5 I have about 11.2 Ohms resistance

Disconnected psu and caps discharged :
Between the power boards 11.7 Ohm resistor and tube pin 4 I have 11.7
ohms reistance.
This is as close too the power board 10ohm/1 watt as i could get
between power board AC entrance point and tube pin 4 "0" resistance

Meter measuring a new 9 volt battery, gives me 9.26 volts DC, so seems
to be working !!

M.

[puretube]

how about disconnecting the wallwart again,
and measure the resistance across the leads of theof the 680 Ohm series-resistor?

68 Ohm?

[EDIT]: those ~12 Ohm for the tube is an OK value, when it`s cold...
will go up (to ~ 80 Ohm, when hot)

[puretube]

the only other cause for the strange behaviour is a mis-wiring,
i.e.: it doesn`t really look like Aron`s/my schemo... (IMHO).
:?:  :shock:

[Paul Marossy]

Man, you are so close to getting this thing to work!  :?

[puretube]

RS is the inline series resistor (your 680 Ohm);
RH is the tube`s heaters nominal resistance;

On the left side you plug in the transformer,
the right side (dotted) UF goes to the diodes via a 10 Ohm resistor on the top-,
and is GND on the bottom-side...

my proposal comes from equations 1 & 2
(depending how much the xfmr voltage goes down, when loaded).
(I`m ignoring the current draw from the rest of the circuit, which I
calculate to be ~ 5mA)

[MartyMart]

Ton,
Thank you SO MUCH for going to all this trouble on my behalf, it is VERY
much appreciated  

I promise you that I am making the correct and relevent AC/DC readings
I did check that 680 Ohm resistor and a few more from that batch and
can confirm that they DO read 680 ... not 68 !!
The meter is working correctly.
I've gone through both boards/schems/layouts with a finr tooth comb and
can find nothing "wrong" in the values/connections ....

As I said yesterday, I have the circuit almost "working" now, the gain/tone/volume controls behave normally and the circuit is producing a
healthy amount of level ...
It's just that the "cut off" and seemingly "rail to rail" stuttering continues
but can be "fixed" by a connection from the "power board" ground, to
MY SKIN ..... and whatever explination for resistance/ground that gives
seems to be the answer .
I realize that in comparison to your calculations for the voltage I should
have, it makes NO SENSE whatsoever ...! and I just dont have a reason
for that .
If I only had 1.9 volts at the tube, I'm presuming that I would not have
any "gain" nor a working "overdrive"  circuit  .. correct ?

I do now have approximately +12 and -12 volts where it needs to be and
I have 12.3 volts at pin 4 of the tube ref to pin 5/power board ground
I will try to connect the "grounds" again with some resistance, as this
seemed to solve Mark's problem, but so far, whenever I reconnect the
two boards ground rail, I loose all signal .. not even a "hum" remains !!

I know, its wierd and the more I think about it, the  more it hurts my very tiny brain

Marty.

[puretube]

doesn`t the sound appear when you slowly turn the bias-trim in that last case?

[puretube]

is that "SKIN-connexion" ( ) while you`re holding/playing the guitar?

and: do you use a bypass-switching or directly guit>shaka>amp?

[MartyMart]

is that "SKIN-connexion" ( ) while you`re holding/playing the guitar?

and: do you use a bypass-switching or directly guit>shaka>amp?

Yes,
Strumming guitar with fingers/toes holding the end of the power board
ground lead ( floating )
No switch as yet, just gtr --> circuit --> amp

The only other "grounded" components are :
1M pulldown resistor at input, 470k from pin 3, in/out jacks and lug 1 from the volume pot.

M