Second channel of AB763 behaving oddly

[sluckey]

This layout has a little arrow coming off that terminal.

That little arrow is not a ground symbol. It simply indicates the wiper of the switch. When you operate the switch that little arrow swings over to make contact with the other switch lug.

[evancorylevine]

I was mistaken about the tremolo. It was working with the footswitch connected before I disconnected that ground.

Disconnecting that ground wire from the switch has nothing to do with making the roach flash unless you have another wiring error.

Let's stay in sync with each other. Answer these three questions...

Does the VIB channel work now that you removed the ground wire from the switch?
Does the roach flash now?
Do you have a tremolo effect?

Holy moly!

the channel seems to work now. The roach flashes, unless I turn the speed down too low and then it kinda gets half lit and I lose the trem. If I turn the speed up too high, the intensity knob seems to kind of invert it's rotation?

[evancorylevine]

a little more clarity:

When I turn the speed up I get a pop as I approach ten, and then I get clicking on every oscillation, which seems to get louder as I turn the intensity down.

That loudness change seems to be related to a pretty serious volume drop as I turn the VIB INT up.

[evancorylevine]

also for clarity:

THANK YOU SO MUCH SLUCKEY! THIS AMP SOUNDS INCREDIBLE AND I OWE YOU ONE BIG TIME.

[sluckey]

That loudness change seems to be related to a pretty serious volume drop as I turn the VIB INT up.

Turn the trem off using the footswitch. Does turning the INT pot cause a serious volume drop now?

[evancorylevine]

That loudness change seems to be related to a pretty serious volume drop as I turn the VIB INT up.

Turn the trem off using the footswitch. Does turning the INT pot cause a serious volume drop now?

No, but switching the panel switch does. When the panel switch (which is a rotary pot switch) turns the trem "on" (even with the footswitch off) I'm operating at a lower volume.

[sluckey]

No, but switching the panel switch does. When the panel switch (which is a rotary pot switch) turns the trem "on" (even with the footswitch off) I'm operating at a lower volume.

That's the whole purpose of that switch. It's not meant to be an on/off switch for the trem (even though it will turn the trem off). That switch is supposed to be used for a GAIN BOOST for the VIB channel. The correct way to turn the trem on/off is using the footswitch. Only use the switch on the pot when you want a gain boost.

BTW, I've been in and out of the house for the last few hours, but I'm in for a while now. So I can respond more quickly.

[evancorylevine]

No, but switching the panel switch does. When the panel switch (which is a rotary pot switch) turns the trem "on" (even with the footswitch off) I'm operating at a lower volume.

That's the whole purpose of that switch. It's not meant to be an on/off switch for the trem (even though it will turn the trem off). That switch is supposed to be used for a GAIN BOOST for the VIB channel. The correct way to turn the trem on/off is using the footswitch. Only use the switch on the pot when you want a gain boost.

BTW, I've been in and out of the house for the last few hours, but I'm in for a while now. So I can respond more quickly.

Ah! That's great!

Any idea about the popping oscillator at high speeds? or why the oscillation stops at slow speeds?

[sluckey]

Any idea about the popping oscillator at high speeds? or why the oscillation stops at slow speeds?

Get a handful of 12AX7s and try each one. You can even swap with the other 12AX7s in that amp. The trem circuit needs a strong tube to work well.

[evancorylevine]

actually. I think the footswitch does make the output lower when the VIB is on.

[evancorylevine]

Any idea about the popping oscillator at high speeds? or why the oscillation stops at slow speeds?

Get a handful of 12AX7s and try each one. You can even swap with the other 12AX7s in that amp. The trem circuit needs a strong tube to work well.

on it...

[evancorylevine]

Any idea about the popping oscillator at high speeds? or why the oscillation stops at slow speeds?

Get a handful of 12AX7s and try each one. You can even swap with the other 12AX7s in that amp. The trem circuit needs a strong tube to work well.

on it...

I switched V4 and V5 and that seemed to fix the weird tremolo behavior mostly. I still get a little pop near the top speed, and a short cessation of flashing, but then it seems to start up again.

The volume is still lower when the trem is engaged.

[sluckey]

I still get a little pop near the top speed, and a short cessation of flashing, but then it seems to start up again.

That's a symptom that can usually be cured with a stronger tube. Keep on swapping. It's OK to use V1 and V2 also.

The volume is still lower when the trem is engaged.

That's what tremolo does. It varies the volume of the guitar signal.

[evancorylevine]

I still get a little pop near the top speed, and a short cessation of flashing, but then it seems to start up again.

That's a symptom that can usually be cured with a stronger tube. Keep on swapping. It's OK to use V1 and V2 also.

The volume is still lower when the trem is engaged.

That's what tremolo does. It varies the volume of the guitar signal.

I can live with the present quirks of the trem if it's not going to hurt the amp.

There's a pretty sizable overall volume drop when the trem is engaged.

[sluckey]

There's a pretty sizable overall volume drop when the trem is engaged.

You're talking about engaging the trem with the footswitch right? And you're not messing with that gain boost switch on the back of the INT pot right?

BTW, most people don't care for this trem circuit.

[evancorylevine]

Yeah, with the footswitch.

What trem circuit do people like? Why don't people like this trem? My AC30's trem is okay, but it has no reverb and I'm not gonna bring two amps to my gigs.

I was thinking about building a Princeton Reverb next. Is that circuit respectable?

[sluckey]

I think you are experiencing some of the reasons people don't like this trem circuit. But the biggest complaint is the chop, chop, chop, or tick, tick, tick sound. This neon bulb/LDR trem is just not smooth like the bias vary trem circuits.

The Princeton Reverb is a very popular build. And it has a bias vary tremolo circuit. I'd much rather tote a PR than a TR any day!

BTW, your workmanship on this amp looks fine. I'm gonna drop off for a while but I'll be checking in hourly.

OH, what about your reverb?

[evancorylevine]

The reverb sounds great!!

If there's no easy fix to get my trem circuit to volume, than I'm gonna call this build done and box it up!

Thank you about my workmanship. I've been doing electronics a decade as a hobby. Recently been building a lot of synth circuitry.

[tubeswell]

FWIW, apart from the bias-vary trem wiggle in the BFPR, the brown vibroverb, brown vibrolux and brown tremolux all use bias-vary tremolo (if you decide you want to change the type of tremolo albiet with 6L6 output stages).

[bnwitt]

This layout has a little arrow coming off that terminal.

I think Weber's intension was for that little tiny arrow to represent a switch contact rather than a ground connection.  Bad choice on their part if so.  Your Tremolo issues are common with the LDR preamp tremolo.  This is why I don't use that tremolo type.  I build all of my blackface amps with Hoffman layouts and brownface bias vary tremolo.  They sound great.  No ticking.

[evancorylevine]

The ticking of the trem is really only an issue at top speeds, but not really so much an issue anymore anyway.

The volume drop is really the only issue for me. It may make it really hard to use the trem and clean in the same song, the volume is so different.

[sluckey]

The volume drop is really the only issue for me. It may make it really hard to use the trem and clean in the same song, the volume is so different.

That's not normal. You probably still have a wiring problem.

[evancorylevine]

The volume drop is really the only issue for me. It may make it really hard to use the trem and clean in the same song, the volume is so different.

That's not normal. You probably still have a wiring problem.

:( Any idea where I should begin to pinpoint?

[sluckey]

Print the layout in black and white. Use a yellow highlighter to trace every wire on that layout as you verify the wire is connected properly. Don't overlook underboard jumpers.

[evancorylevine]

y'know. I've decided that the volume difference is probably not a wiring error, and that I have overstated its magnitude, and was more concerned with than I should have been.

I think that this amp is finished. I'm boxing it. Oh my god. I'm so excited to have this thing done and functional.

Thank you SO MUCH one and all, and especially sluckey. Please let me know if you're ever in Philly and what I can do for you.

[sluckey]

I'll have a Philly cheese steak. I'll bring the beer.   

[evancorylevine]

I'll have a Philly cheese steak. I'll bring the beer.   

I support this plan 100%.

[tubeswell]

Another possibility is it could be a bad coupling cap in that low-volume channel affecting the grid bias on one of the gain stages. I can't remember whether you addressed this question earlier in the thread, but have you tested the coupling caps for DC-leakage?

[evancorylevine]

Another possibility is it could be a bad coupling cap in that low-volume channel affecting the grid bias on one of the gain stages. I can't remember whether you addressed this question earlier in the thread, but have you tested the coupling caps for DC-leakage?

I haven't, but I'm calling this build for now. It's done! If it becomes problematic on the gig, then I may start troubleshooting.