Spring Reverb For Farfisa Organ

[sarakisof]

Thanks Rob once again for your help. Yeap i guessed it would be like that, so was my drawing like that, but just to be sure.
Ok so, yes as i ve mentioned above in previous posts i get about 160V at V2 pin1, seems V2 n other tubes work fine.

I would say the signal on the reverb side of C512 has a short

Checked n tested all "7" path seems no short anywhere. So last chance, i guess smthng may be wrong wit that C512 mustard 10nf cap? I was wondering in my previous posts about it if you remember. How could i test it, desolder and attach a new one and see what happens?

[Rob Strand]

Checked n tested all "7" path seems no short anywhere. So last chance, i guess smthng may be wrong wit that C512 mustard 10nf cap? I was wondering in my previous posts about it if you remember. How could i test it, desolder and attach a new one and see what happens?

A faulty C512 doesn't really explain why you get no signal on the plate of the tube V2 pin 1.   If there's not short on the reverb side of C512 and the tube is good then you would expect signal on V2 pin 1.  I have a small suspicion that the 50V cap might be the problem but the measurement on V1 pin 1 seems fine.

A simple test would be to turn the organ off and pull the plug.   Wait about 1 minute.  Short out the cap with a 1k resistor for about 10 secs. to make sure it is discharged.  Then measure the value with a cap meter.  Also check the cap measure open circuit with an ohms meter.

I wasn't actually sure what the green signal at the output of V1 pin 1 means.   Are you saying you can hear a non-reverb signal there?

[sarakisof]

I have a small suspicion that the 50V cap might be the problem but the measurement on V1 pin 1 seems fine.

Checked also with 1KV cap signal tracer but same results.

I wasn't actually sure what the green signal at the output of V1 pin 1 means.   Are you saying you can hear a non-reverb signal there?

Yes i get dry signal there, a little weak like in V2 pin7 (V2 pin6 gets louder), but yes i have signal there.    And no signal at V1 pin2.
PS. Tank is dissasembled, no cartridge connection at all ...

[Rob Strand]

Checked also with 1KV cap signal tracer but same results.

You could try pulling the tubes in V1 and V2 then swapping the positions.

Can you see anything odd with the wiring or soldering starting from V2 pin 1 at the tube socket through to *V2 side* of C512 ?  It should be the same wire but maybe a connection is broken alone the way.

[Rob Strand]

I was thinking you should measure the "235V" DC rail.

We are assuming the tube is good based on the DC voltage but we don't actually know the 235V is correct in the first place.   Also, do you know the input impedance of your multimeter, it is usually 1M or 10M (although there are meters are inside this range.)   The thing is a 1M input impedance meter will measure a plate voltage of 193V with the tube totally removed.  So if your 235V is low the meter without the tube will be less than 193V and maybe things are *not* as good as they seem.

[sarakisof]

As i said schem is different from Compact one. Foyer uses EZ81 rectifier tube. B+  goes to positive legs of two big filter capacitors  (33uf 450V) with the classic big ceramic "filter" box resistor in parallel. (classic tube amp circuit) There  i get 233-236V. Perfect.

Then,

V2
pin1: 160V
pin6: 150V

V1
pin1: 155V
pin6: 95V (is this ok?)

Point "7" and "12": Zero Volts either DC or AC. Point 7,12 are Rvrb's IN and OUT / send and receive tranducers in other words.

I have taken those measurements when i started the thread (if u see in a pic on first posts with 160V and 0V across mustard C512 legs if u remember)

You can see the voltages purple coloured in pic below.

You could try pulling the tubes in V1 and V2 then swapping the positions.

will do that later, actually the V1 from the time i got the organ home n fixed it, was the one that was lighting less than the other two 12AX7's, i was shy to ask this in the forum (spooky..."why this tube is lightning less?  )

Pics loading .....

[sarakisof]

You can see in the middle the three (smaller from others) 12AX7s. The two small on the bottom are V1 and V2. V1 is in the bottom right, V2 in the bottom left.
You can clearly see how V1 gets less lighted than V2 and the other upper one ...

PS. V1 is also a bit loose

[Rob Strand]

pin6: 95V (is this ok?)

I don't think so!

I can't make sense out of it.   If you look at V2 pin (1,2,3) and V1 (6, 7, it is the same circuit but the voltages are way off.

It might help to measure the gate and anode cathode voltages on those tubes ie. pins 2, 7, 5, 8.
Also power the unit off for about 10 mins then measure the resistors on pins 1, 6, 3, 8.

[Rob Strand]

You can see in the middle the three (smaller from others) 12AX7s. The two small on the bottom are V1 and V2. V1 is in the bottom right, V2 in the bottom left.
You can clearly see how V1 gets less lighted than V2 and the other upper one ...

Yes, it looks a little dim.  From what I can see it's a different brand tube.

[sarakisof]

Yes, it looks a little dim.  From what I can see it's a different brand tube.

Ok.

If you look at V2 pin (1,2,3) and V1 (6, 7, it is the same circuit but the voltages are way off.

i get 90-95V (actually it makes an instant peak at 120V and then reduces until gets stable at 93V) between V1 pin6 and R509 if that helps. After R509 i get about 195-200V. All the "purple" volt. measurements i have close to pins are measurements between V pins and their correspond resistors. I measure the pins.
The "big rail" is 190-220V depends on which resistor leg i measure.

So 93V is the most weak voltage i get from all V1,2 pin1,6  to their resistors ...

Also power the unit off for about 10 mins then measure the resistors on pins 1, 6, 3, 8.

you mean ohm resistance?

[sarakisof]

It might help to measure the gate and anode cathode voltages on those tubes ie. pins 2, 7, 5, 8.

all zero voltage.

Also power the unit off for about 10 mins then measure the resistors on pins 1, 6, 3, 8.

you mean ohm resistance?

[Rob Strand]

i get 90-95V (actually it makes an instant peak at 120V and then reduces until gets stable at 93V) between V1 pin6 and R509 if that helps.

If the change occurs at power-up/warm-up then it's normal for the voltage to drop.  When the tube is cold it is open circuit then when it heats up current flows and brings the voltage down.

i
After R509 i get about 195-200V. All the "purple" volt. measurements i have close to pins are measurements between V pins and their correspond resistors. I measure the pins.

If I understand you correctly, that doesn't sound good.  Are you saying at different points on the same wire you get different voltages?  That would point to a bad connection, or perhaps a resistor who's value is changing when you push on the legs.

It might help to measure the gate and anode cathode voltages on those tubes ie. pins 2, 7, 5, 8.
Also power the unit off for about 10 mins then measure the resistors on pins 1, 6, 3, 8.

you mean ohm resistance?

The first part of the test is to measure voltages.
The second part of the test, after powering down, is measuring resistance.

(To me, even on the original schematic the 1.3V on the cathodes don't match-up well with the anode voltages.)

[Rob Strand]

all zero voltage.

With the power on, yes?   

Zero volts on pins 3 and pin 8 looks like a problem.

I'm starting to think you have some open resistors.

[sarakisof]

[sarakisof]

Zero volts on pins 3 and pin 8 looks like a problem.

Ooops my apologies Rob now that i saw your post about 1.3V i realised i had my multimeter at big scale and remember i had smthng like 0001, so turned to 20V scale and i get:

V1
pin3: cannot get there its a mess of legs was scared to probe , no access  but i think i m good for V1
pin8: 1.3 V.

V2
pin3: Zero Volts !!
Pin 8: 1.4 V.

[sarakisof]

OK

[Rob Strand]

I think you need to measure the resistance of the resistors on V2(pin1 and pin3).  The 220k (R514) and the 2.2k (R516).  Don't forget to power everything down and wait 5 to 10 mins.

Before doing the measurement it's probably a good idea to check that the 200V rail has dropped to zero.  If not you might have to discharge the all the supply caps manually.

[Rob Strand]

Ok Rob look smthng strange. At V2 pin3 that i get zero voltage i measured the resistor(s) and get 2.2K but as you can see in the pic below there is a 2.2K on the bottom and in parallel with that another resistor (470K??) but i get 2.2K !
At other points resistors are as it should be, 3.3K for V2 pin8,  2.2K for V1 pin8 and 2.2K for pin3.

OK cool.  So at least those resistors are OK.

The zero volts on V2 pin 3 is the root cause.   Try to measure the 220k (R514).
-------------------------------------------------
The other angle is to swap the tubes.  If the weird voltage moves with the tubes you know it's the tube.

[sarakisof]

Resistance measurements

V1
pin1: 100K
pin6: 220K
pin3: 2.2K
pin8: 2.2K

V2
pin1: 220K
pin6: 100K
pin3: 2.2K
pin8: 3.3K

So all as it should be. Only prob is that i get that zero voltage at V2 pin3. But should this be the problem for reverb? I mean the organ works perfect, Rob i think it is smthng in the reverb tank itself and its carts. I still haven't try totally new different carts or two piezo's at same time, just one per time and swapped wires for transducers. 

[sarakisof]

The other angle is to swap the tubes.  If the weird voltage moves with the tubes you know it's the tube.

Rob i swapped the tubes and thats the result: For the first weird voltage issue at V1 pin6 95V the situation was about the same. Now it got at about 110V (instead of 120V before) and then reduces and gets stable at 95V (instead of 90V). But, about the second issue, at V2 pin3 zero voltage, now i got 0.9 V. ...