[Mjork]

Hello TubeTown friends,

I am new here and Dutch therefore I hope English will work,,,,
I did learn something about electronics but it has been a while, now I an rediscovering all that.

I have built the Emma kit and found the output was noisy and undefined.
I checked all the DC voltages, grounds and of course the elements, but all seemed fine.
Then I started using a scope to trace a 110Hz signal from my looper through the circuits.
I found out it worked all fine incl the signal going into the grid of the ECC99 (pins 2 and 7).
Strangely enough the signal from ECC99 to the push-pull transformer (pins 1 and 6) looked different.
The frequency was doubled. the amlitude weakened a bit at the same time.
When checking the speaker out put I indeed saw 215Hz coming out while sending 107Hz in.

Does anyone recognize this issue maybe?
What is the next thing to check here?

[Mjork]

I think also the signals coming from pins 1 and 6 should be in counter phase?.

On checking the push-pull Hammond 125C that the resistance between B2 (DC feed) and signal leads in not the same. red-blue is 128ohm and red-brown is 159ohm. I would expect equal resistance, as the windings should be the same.

Ich denke auch, dass die Signale von den Pins 1 und 6 in Gegenphase sein sollten.

Bei der Überprüfung der Gegentakt-Hammond 125C, dass der Widerstand zwischen B2 (DC-Einspeisung) und Signalleitung nicht gleich ist. Rot-Blau ist 128 Ohm und Rot-Braun ist 159 Ohm. Ich würde einen gleichen Widerstand erwarten, da die Wicklungen gleich sein sollten.

[cca88]

I think also the signals coming from pins 1 and 6 should be in counter phase?.

On checking the push-pull Hammond 125C that the resistance between B2 (DC feed) and signal leads in not the same. red-blue is 128ohm and red-brown is 159ohm. I would expect equal resistance, as the windings should be the same.

Ich denke auch, dass die Signale von den Pins 1 und 6 in Gegenphase sein sollten.

Bei der Überprüfung der Gegentakt-Hammond 125C, dass der Widerstand zwischen B2 (DC-Einspeisung) und Signalleitung nicht gleich ist. Rot-Blau ist 128 Ohm und Rot-Braun ist 159 Ohm. Ich würde einen gleichen Widerstand erwarten, da die Wicklungen gleich sein sollten.

Hi Mjork
the doubling of the frequencies is part of the behavior of the kathodyne PI when the powertubes start to draw grid current. I'm a bit astonished, that this even happens with a ECC99, but with 6V6s it is perfectly normal >> 5E3 Tweed Deluxe.

regards
Jochen

[Mjork]

Hi Jochen, thank you for picking this up.
OK, I must say I am a bit new with all this.
But putting in 107Hz and getting out 215Hz surely could not be the desired effect? It gives you a different sound I would think?

I started my investigations on the Emma when after building it I had noticed:
- I do get sound when playing a string but only when putting the volume over 50%
- when I play more strings or when I hit one string harder the output becomes really scrambled, like the speaker is ripped
- when I connect one of the two ECC99 grids inlets to ground sound comes out as I would expect.

So surely something must be not OK as I do not get the proper sound, but what?
Even, when I connect one of the two ECC99 grids inlets to ground, the output signal on BOTH output pins doubles when I use the scope to  observe.
See attached pics. It not only sound better, it also looks better

[Mjork]

So what does happen ther?
I would expect loss of output signal when connecting on of the inlet signals to ground, but here I gain output instead?

[Dirk]

Hi,

I started my investigations on the Emma when after building it I had noticed:
- I do get sound when playing a string but only when putting the volume over 50%
- when I play more strings or when I hit one string harder the output becomes really scrambled, like the speaker is ripped
- when I connect one of the two ECC99 grids inlets to ground sound comes out as I would expect.

As I wrote already earlier I guess that you have a problem with the ground somewhere. I know you said that you checked everything twice and everything is connected correctly but it is not otherwise the amp would work as it should.
Now you have a scope so use it to troubleshoot the amp. Check the first stage, is it okay then the next etc. If you do not understand how the amp, the PI or something else works then you must learn the basics first otherwise you can not make sure that the amp is build correctly and works safe and stable.

Easy but helpful: enter the circuit in Spice a simulate it and compare the result of the simulation with your measurements. This could help a lot.

Best regards, Dirk

[iefes]

If you provide us with some high-resolution images of the wiring inside the amp we may be able to trace out what is wrong with it. 
Apart from that I agree with Dirk.

[Mjork]

Goodmorning,
I did indeed check the other circuits in the amp, see attached log file.
I have no list of values that could be expected but the AC signal seems to nicely increment, what do you think?
Will try that Spice simulation software when I have some more time, good tip.
Attached the wiring pics. The component connections like R15 to R16 are made on the back side, not touching the housing/ground.

[günther]

The signal on the grids is absolut 400mVpp. Far away from any overdrive Kondition.
But the plate-signals are heavenly distorted.
I also see no gain.
Try to check the heater current & voltage on this tube
If this OK than the ECC99 maybe faulty.

[Mjork]

No, no, the grid on that picture is much higher: at 1 (V/division) x 2 (divisions) x 10 (pen setting) = 20VAC. And close to 0 VDC

Only when I close the volume pot from 50% to approx. 20% then finally the plate signal looks like a perfect sine again.
At that point the grid voltage is 9VAC and the plate voltage is 1,5 VAC.

Heater voltage: 6.6V between pins 4/5 and pin 9.

[Dirk]

Hi,

I just run Emma thru the simulator with these settings:
All potentiometers a 50%
Input Signal 100 mV @ 1 kHz Input Chanel 2 Low
8 Ohm Load

Curves
red: Testpoint Grid V2B
blue and green: Testpoint C8-R17-R20 and C9-R18-R21

Maybe this helps.

Best regards, Dirk

[alexradium]

Hello TubeTown friends,

I am new here and Dutch therefore I hope English will work,,,,
I did learn something about electronics but it has been a while, now I an rediscovering all that.

I have built the Emma kit and found the output was noisy and undefined.
I checked all the DC voltages, grounds and of course the elements, but all seemed fine.
Then I started using a scope to trace a 110Hz signal from my looper through the circuits.
I found out it worked all fine incl the signal going into the grid of the ECC99 (pins 2 and 7).
Strangely enough the signal from ECC99 to the push-pull transformer (pins 1 and 6) looked different.
The frequency was doubled. the amlitude weakened a bit at the same time.
When checking the speaker out put I indeed saw 215Hz coming out while sending 107Hz in.

Does anyone recognize this issue maybe?
What is the next thing to check here?

the doubling effect can happen in a push pull OT when it is wired incorrectly,the 2 halves are in phase,i don't know if you have access to the center tap junction to try reversing one side

[Mjork]

Dirk, thinks for taking the efftort of simulation.
I was starting with this, nbut it is more complicated then I thoought.
--> Where can I find the .sub files or the data therein for these: 12AY7, 12AX7 and ECC99?

I changed my input to 1kHz at 0,1 V and measured all points again, see attachment.
The 3 curves you got from LTspice are spot on in my amp.
It is the  ECC99 where things seem to go wrong.
What i first thought to be doubled frequency is actually a dent pulled in the positive wave of the output sine which makes it look like doubled.
When i measure it I see frequency peaks at 1000 and 2000Hz.
If I turn the vol pot back the dent disappears and at about 25% it is close to a sine,  see pics. At all  volumes the amplification is negative.

[Dirk]

You can use a 12AU7 instead of a ECC99 for testing. Maybe you got one.

The PI is working correctly ? This is what you should first check.

Google knows where you can get the models for the tubes. I also posted a sim a few days ago including some models and a potentiometer lib which you need.
Here it is: https://www.tube-town.de/ttforum/index.php/topic,24782.0.html

Best regards, Dirk

[Mjork]

I managed to get my hands on a new ECC99 but the result is the same, so the tubes all seem OK.
The PI works good I think, it shows two perfect sine waves in counterphase as output, 15VAC.
The input is a 15,5VAC sine. Voltages as in Dirks simulation. The DC voltagesare as per the drawing.

So that leaves the ECC99 outpput signal still to be strange.
Grid has perfect sine 15VAC as input, the output plate voltages is no longer a perfect sine and around 11VAC.
DC voltages are close to 260VDC (plate) and 8.5VDC (cathode).
What more can I check?

And what can I check on the push-pulll trafo?
I noticed there is a difference in the resistance between the two inut sides (red to blue = 124 Ohm, red to brown is 160 Ohm), is that relevant? The number of windings must be the same on both sides.