snap crackle pop (solved)

[mat]

OT secondary wires unsoldered:
green-black 0.4 OHM.
yel/green-black 0.3 OHM.

Does that mean I have fried the OT If so what might have caused this..

[Tonegeek]

OT secondary wires unsoldered:
green-black 0.4 OHM.
yel/green-black 0.3 OHM.

Does that mean I have fried the OT If so what might have caused this..

Maybe, but I am not sure your resistance measurment is reliable way to test tranny, especially since your problem is intermittent. Here is info on testing the tranny if you still think it is bad: http://www.geofex.com/ampdbug/outtrans.htm
BTW- I just measured my 4 ohm tap to ground and it measured .9 ohms so I think a fraction of an ohm might be a normal measurement. I don't think my old Fluke is very accurate so I may be off a good bit at that resolution. It does sound like something is arcing somewhere and it could be the trannies, choke, tubes, or sockets - even the standby switch. Standy is easy to check, just throw a jumper across it (CAUTION!). If your master vol is down and you still hear it then it does seem like the problem is near the output section but it could be the power supply. Try removing the PI tube and let it run. If it goes away, look for DC getting past the plate couplers on the PI or a bad PI tube. If crackle is still present with no PI and you know your output tubes are good, then you will have to test the OT and/or power supply.

[mat]

Here is info on testing the tranny if you still think it is bad: http://www.geofex.com/ampdbug/outtrans.htm

I did the simple OT test and to me the readings seem to be in range.

It does sound like something is arcing somewhere and it could be the trannies, choke, tubes, or sockets - even the standby switch. Standy is easy to check, just throw a jumper across it (CAUTION!).

I replecaed the standby switch - no help.

If your master vol is down and you still hear it then it does seem like the problem is near the output section but it could be the power supply. Try removing the PI tube and let it run. If it goes away, look for DC getting past the plate couplers on the PI or a bad PI tube.

With the PI tube removed = no noise. Swapped PI tube to different one = noise. Changed the .1uF PI couplers to fresh Xicons, still got the noise in there..

I measured the voltages with PI tube removed:

B+1 469

B+2 466

B+3 437

B+4 330

B+5 322

V1 196 1.84 202 1.77

V2 207 1.82 206 1.79

dlator 383 46 257 1.91

PI (no tube) 432 430


V5 463.5 462 -45 -45

V6 466 464 -45 -45

I just recorded this one: http://media.putfile.com/nhrmsizzle On 37sec I turned the clean master pot and got the noise go away when putting it to zero. After a while I tried same thing but the noise just stayed regardless of the position of the master pot.

Any further suggestios ?

[Tonegeek]

dlator 383 46 257 1.91



Any further suggestios ?

Its good news that the noise is gone without the PI as the problem is most likely back in the pre-amp although it is not 100% because you now also have removed negative feedback and you can't rule out some bad caps, resistors in the PI section but that is unlikely.

The plate of your dlator could be an issue.
If your dlator is a 12ax7 then it appears your voltage is too high. a 12ax7 maxs out at 300v. even subtracting the 46 volts the cathode is above ground, you have a potential diff of 337 on the plate. I bet it is arcing. Try bypassing the dlator and see if the noise goes away. (Unplug the tube till you get the voltage down so it doesnt kill your PS). Your dlator tube will need to be replaced most likely if you had that much voltage on it for any length of time. I put about that much voltage on mine (EH12ax7) early on and it toasted it after about a week.

Also, if the noise is still there after you get the voltage down on the dlator, then try this (with a new dlator tube): If you have another amp, run its send into the return on the one you are trouble shooting. If the noise is gone then you will know your power section is OK and you can concentrate on working your way back up the preamp.
whit

[tonelab2]

Glad you've posted voltages. I agree with Tonegeek that it's upstream from the PI. By the look of the voltages (and sound) your cooking that 12ax7 in the d'lator.

[mat]

Ok, thanks for the further information. I´ll check if I have some bad components connected to the D-lator plate.

The power supply to the dlator is like in picture: http://www.pichotel.com/pic/16028B31e/148313.jpg

I have changed the resistors in the PS for getting more optimum voltages for the dlator. Maybe the other plate resistor is fried..

[Tonegeek]

Mat,
From what I have read, the recovery plate should have about 220v and the follower plate should have 300v measured to ground. Your follower plate is ~22% too high and the recovery plate is ~15% too high. I would up the 10k resistor on the recovery filter cap to 15k and see what that does. It should bring both plates down. You may have to up the 30k resistor going to your follower filter cap too as the plate will still probably be too high. Try 33k - 43K. I see you are taking no chances on hum with the extra filtering for the dlator.

Also I noticed you have 10n across the bass pot. It should be 1n (.001 = 1000pf), unless you are experimenting here... makes a huge difference.

[mat]

Today I changed the last cheap tubesocket (dlator) to belton one but the voltages kept being too high (near 400V !) on the dlator first plate. Changed the dropping resistor to new one and bigger value (95k 7W) but again too high voltages. Then I measured the resistors of the dlator circuit and the grid resistor (1M) did not give a value so I replaced it and the amp was very silent again

The new voltages:

B+1 477

B+2 474

B+3 420

B+4 317

B+5 309

V1 192 1.76 196 1.72

V2 199 1.84 197 1.8

dlator 245 15 222 1.77

PI 285 277


V5 475 474 -46

V6 474 473 -46

Great sounds with HB's and SC's, will record a clip asap.

Big thanks for everyone helping me on this one

btw. the basspotcap is 1n. Wrong value on the layout.

[Tonegeek]

Good work. Can't wait to hear it! Are you still using 30k > 10k > 30k on your dlator dropping strings? I ask because I am thinking of changing mine since it is not deriving power in the best way. I will probably just stay with 2 caps though. The most current info I have on the dropping string for the dlator is 47k > 33K (for 2 caps). This is close to what you are using.

[mat]

Good work. Can't wait to hear it! Are you still using 30k > 10k > 30k on your dlator dropping strings? I ask because I am thinking of changing mine since it is not deriving power in the best way. I will probably just stay with 2 caps though. The most current info I have on the dropping string for the dlator is 47k > 33K (for 2 caps). This is close to what you are using.

I have to check the dropping resistors again but the last one is (was 86k 3W) 95K 7W (I have quite high B+1). The one berofe it think was 36k. I will check the next time I remove the chassis from the cab.

Dogears suggested me to use the additional cap and I think it is good to have one in there.

Btw. would be nice to know why the dlator tube eated so much voltage with the broken 1M (or cold solder joint) in there.

[mat]

here are two (mindles noodling) clips recorded with SM57 + Alesis microverb on the built in dlator (no prosessing):

Strat - http://media.putfile.com/nonhrm-with-strat

335 style - http://media.putfile.com/nhrm-with-335-style

At 1:35 I engage the bright switch, a bit too much bite I think.

cheers,