bad tube or what

[Seegs]

i'm back at this bogen chb 20a . and everything seems to be working beside one thing.. and i am pretty sure one of the ecl86 tubes is bad. But i thought i would run it by you guys first.

the issue i am having is that the amp cannot get cleans, it's always slightly distorted no matter if i have the volume just were you can hear it. there is almost no bass, and when i turn the treble up the amp starts to squeal. i've ran through the circuit over and over. everything checks out. my voltages are about 15+ of what the schem says. i taped the tubes to check if they were microphonic. and the 6eu7 seemed to be so i rewired the socket for a 12ax7 cause i had one laying around and it helped a little. also one of the power tubes when taped gives me a rattling/noise from the speaker. leading me to believe the preamp section of the tube has gone bad or in fact both sections have.

other things i have tried.. i ran a 12ay instead of the 12ax and it cleaned the signal up alot had much more headroom, but the distortion still was there and the signal wasn't clear at all.

i'm tempted to find a pre amp tube with a little more headroom for the pre amp to give me some more cleans before break up. the 12ay was way to much.

so the question is.. is it a tube.. or is it something else.. i have a new tube coming tomorrow and can test it out but before i order a whole new set and have spares i want to be sure this is right.

[PRR]

Clean/re-tension sockets.

Verify every grid is at ZERO volts (unless it is clearly supposed to be otherwise): leaking caps.

[Seegs]

checked all the voltages again, and checked the grid.. nothings leaking by.. got the new tube today.. let it warm up .. put it in. and nothing no sound no nothing pertty sure they sent me a bad tube. crappy thing is that i need to be able to play for sunday.

[DummyLoad]

voltages at plate pin? g2 pin? cathode of power tube & triodes? - if output stage was left alone (autobias) and you have no voltage measured from cathode to ground, that would indicate that the element is not conducting and therefore not working. measure voltage at all pins & post with a schematic that includes any modification(s).

lastly, are all the filaments of the triode section and pentode section lighting?

--pete

[Seegs]

alright here is a pic of the mods done




voltages are as follows

v2
pin 1 - 0 volts
pin 2 -1.9v
pin 3 - 414 ( running hot today)
pin 4 - 0
pin 5 - 0 ( this makes no sense because the heaters turn on and so does the lamp)
pin 6 - 424
pin 7 - 0 volts
pin 8 - -16.5
pin 9 - 198 volts

v3
pin 1 - 42.5 ( shared ground with others voltage now 0)
pin 2 - 267 ( should be 1.3 volts from schem taking another look at that ) fixed ground issue now down to 1.3 volts
pin 3 - 414
pin 4 - 0
pin 5 - 0
pin 6 - 424
pin 7 - 0
pin 8 - - 15.8
pin 9 - 293 ( also fixing ground issue droped the voltage to 130)

no dc voltage on pots or any dc voltage coming from any of the grounds

that helped solve one problem.  sound is very distorted and all around bad sounding

[HotBluePlates]

Did you use a 6EU7 or 12AX7 for V1? If you used a 12AX7, the heater wiring is wrong; pins 4/5 should be connected and soldered to one heater wire, pin 9 should be soldered to the other heater wire.

Well, you must be getting heater voltage (0v measurements aside) because the ECL86 triodes appear to be passing current.

The different voltages for bias (pin 8 of V2/V3) is troubling. These should be exactly the same. Unsolder the leg of C11 and C13 that have wires running to pin 8 of the output tubes and see if the bias voltages now match. If so, one or both are leaking and should be replaced.

Also, R18 and R19 should be the same value, 150kΩ each. I know the schematic floating around is smudged on R19 and looks kind of like 100k; it should be 150k. Or, switch both to be 100k if that's the value you have on hand.

[Seegs]

the voltages are about 1v off with the v1 being higher. with the caps disconnected. i'll put a resistor in tomorrow that might help with that also. would it be safe to assume at this point that the tubes are shot?

i am using a 12ax7 and yes both pins 4 and 5 are connected the run to ground as shown in the schem

[HotBluePlates]

would it be safe to assume at this point that the tubes are shot?

Only if you have known good tubes that you can swap in, and that fixes the problem.

If you don't have a known good pair to swap in, shame on you and go order some now. You'll use them sooner or later.

got the new tube today.. let it warm up .. put it in. and nothing no sound no nothing pertty sure they sent me a bad tube.

That's HIGHLY unlikely. It's just rare to have bad tubes, swap in a new one, and that be bad too. I haven't had a bad tube in 20 years of amp-tinkering, and only had 1 tube failure ever.

If you did any of the modifying, suspect your wiring, solder joints, etc.

Did the amp ever work properly? If yes, what changed between when it worked and now?

[Seegs]

Yes the amp did function before mods were done to it . I wanted change the front end and decided to redo the whole board because the layout from bogen was driving me crazy .  I did have one of the tubes red plate for about 5 seconds if that. But I don't have a spare set for the bogen . 6gw8 tubes are not super common and have put off buying a spare set  I know excuses excuses . I've gone over the wireing . But ill check it out again and highlight the schem as I go through it . And order a set of tubes .

[Seegs]

also i put the new tube in and checked the voltages.. and pin 8 gets + 7 volts and pin 9 is getting about 250 and one the other tube it's about -7 volts instead of 15..

EDit: also went through the wireing again re did all the ground solder joints fixed some lead dress issues i thought might be an issue.. this fixed the disotrtion in all the notes.. new problem is.. if i dig into the strings on the guitar with the volume any were near were it could distort .. instead of distortion i get this crackleing sound.. it happens more with the treble side then anything

[HotBluePlates]

... I wanted change the front end and decided to redo the whole board because the layout from bogen was driving me crazy ...

... went through the wireing again re did all the ground solder joints fixed some lead dress issues i thought might be an issue.. this fixed the disotrtion in all the notes.. new problem is.. if i dig into the strings on the guitar with the volume any were near were it could distort .. instead of distortion i get this crackleing sound..

The are good clues!

Okay, you should assume a build/wiring problem or poor solder joint (or maybe loose socket). This is not a knock against you, it's just a matter of probability in new builds and major modifications. For example, in my last amp build I made a dumb wiring mistake that turned the amp into an oscillator. I played 1 note... VERY loud (and no negative feedback in the output stage, so it wasn't swapped plate wires).

Try to gently wiggle each tube in its socket. The socket should grip the pins firmly; if that's not true, turn off, drain filter caps (and verify 0vdc) and retension the contacts.

Assuming that's good, check solder joints and grounds. If you have to ground to the chassis, don't solder to it (unless you have a 100w+ solder gun to do it). Instead, solder a ring terminal on the ground wire and bolt firmly to the chassis with a nut and star washer or Keps nut (which has a built-in star washer).

Solder joints: no connection should be held in place by solder; it should be held in place by a firm mechanical connection (wire wrapped through pot lugs, component leads bent where they contact eyelets/turrets so they hold themselves in place). Solder should be applied minimally, by heating the junction of the parts and allowing the wire/component lead to melt the solder. The solder should only ensure that your good mechanical connection can never move later.

Noise on big signals sounds like a poor or intermittent connection, but it is conceivable it could be a wrong resistor value. It's common to use a 470Ω where a 470kΩ should go (the yellow and brown bands on Xicon carbon comps look very much alike, especially under yellow light).

I think you're on the right path. Assume you made an error or got too excited and hurried. It happens to us all! 

[Seegs]

thanks, i'll have to get some new grounding locations. i used self tappers and a 5 lug strip to ground  but i think i'm going to change that soon. also i noticed when i turn the treble pot i get a hiss then it goes away but when it's all the way up it crackles and hums.. and the single is a lot louder and one would say.. crisper... but with a huge hum in the background.

and now when i turn the amp on i get this odd... like power up sound right before the sound kicks in.. almost sounds like a capacitor charging or something along those lines if that makes any sense. one might describe it as a smoothing out of the signal. and now when i shut it off i get a nice loud pop which is new.

also.. the .1 uf cap off of pin 7 of the pre amp i am getting negitive voltage there.. i tried bypassing the tone controls to see if my hum was from there.. most def not.. i got a high screeching noise when i did that.. leads me to believe i am having an issue with my pre amp circuit. and now i'm having a low freq hum. grounding issue i re did the grounds leads. what would be the best way to ground? star ground? or ? right now i have a 5 lug strip joined with a copper wire soldered across it and the grounds going to a different lug.

I also ordered some NOS tubes and a new JJ 12ax7 should be here next week

[Seegs]

update.. i decided to fix the soldering jobs and re do them all.. after doing that today. i have new issues.. i must have really messed this up somehow. but now the problem seems to be the preamp circut and i have a grounding hum. if i touch the chassis it goes down alot.. but new problem consists off. when i have the preamp tube in and i turn the volume at all i get the loudest screaching high pitched noise. as if someone were blowing a dog whistle and it really hurts your ears. i've traced the circuit back but i still can't find anything.

voltages as follows

12ax7
1 -30
2 - -.13
3 .6
4 0
5 0
6 52
7 0
8 2.1
9 0

v2
1 .004
2 1.5v
3 335
4 0
5 0
6 425
7 0
8 -18.5
9 145

v3
1 -1
2 1
3 330
4 0
5 0
6 425
70
8 -43
9 130

i'v looked at everything on v3 and have no idea why it's pulling that much negitive voltage.. everything checks out.. voltages coming in resitance checked solder joints. also to note without the tubes in i get a perfect -15.5 and the rest of the voltages seem to be right on.

[Seegs]

well, if anyone is still looking at this.. i have fixed the negative voltage, a resistor went bad and was showing 1m ohms. swaped out to a 150k. and now am gettin -19 volts on each side. a little high but the same.. have a little hum when amp is on but no pre amp tube in.  here is the current issue the pre amp is getting alot of noise.. just form somewere.. i have disconected the input wire and yet it still there. and when i touch the input wireing the noise gets super loud. i'm going to try and clean and re do the solder joints and check the tension on the socket but there really is nothing that i can see wrong with it

[HotBluePlates]

... have a little hum when amp is on but no pre amp tube in. ...

I'd probably stop there and try to sort that out before going any further. You should have no noise with no preamp tube. Leave the tube out until you solve that problem.

[Seegs]

tube amp fixed, thanks for the help, i was finding alot of challenges with the layout i was using and decided to move all the tubes to the back. and be able to clean up my lead dress. the tone is good, and has a very warm smooth feel. suprisingly i have little to no break up till i get well into the 5+ volume. as it use to break up at maybe 2. over all i like the amp i still think i'll try and tweak it here and there and maybe try a new OT later. and maybe try the fender style tone controls over the bogen ones. But i think i'll build a 5e3 next.  time to button everything up and put it in the cab i built for it.

also was playing through a WGS reaper 12" 30w

[HotBluePlates]

Moving the tubes (and therefore the wiring) fixed it? Do you think the wiring layout was causing oscillation, and that was the problem all along?

I'd guess so from the dog whistle comment you made earlier.

Congrats on getting it sorted! I bet there were some good lessons in there!