Re: Single Channel AB763 no verb/vib

[samato]

Thanks Sluckey.  These jacks are not wired like the Switchcraft jacks.  That must be my problem - I didn't realize that, I just followed the diagrams you listed but these jacks have the switch and tip reversed compared to the Switchcrafts.  


1. With nothing plugged into either input you should read 34KΩ from V1-2 to chassis.
I have 1.068M ohms.

2. Plug your cord into the Hi jack. You should read 34KΩ from V1-2 to the free end tip of your guitar cord plug and you should read 1MΩ from V1-2 to the sleeve of the guitar plug.
I have 1.068M ohms & 1.068M ohms

3. Plug your cord into the Lo jack. You should read 68KΩ from V1-2 to the free end tip of your guitar cord plug and you should read 68KΩ from V1-2 to the sleeve of the guitar plug.
I have 70.8K ohms & 734K ohms

I plan on swapping these jacks out with some I got at Radio Shack.  They seem sturdier and the switch makes better contact with the tip than the ones I'm using now.  The Radio Shack ones also have the switch and tip opposite from the Switchcrafts - interesting.  

Thanks for the warning on the output jack tips being too close to the screen resistors.  They are very close and I was a little worried but it doesn't look like they could make contact.  Still, I'll see if I can rearrange that or at least insulate the resistor leads.

I hope I didn't damage anything by running the amp with all the jacks wired wrong.  There was no smoke and nothing seemed excessively hot, in fact the transformers didn't even seem warm.  I did get kind of a spark inside my V4 when I switched the Blue & Brown OT leads but when I put them back everything seemed normal.  I have plenty of 6V6's though so if I ruined a tube, oh well.

[samato]

With Sluckey's help I got my input and output jacks connected properly and now the amp works.  I think it even sounds good but it's hard to hear the tone over all the hum and buzz.  I think my bass and treble controls are a little weird too but that is the least of my worries at the moment.

I did a little chopsticking and didn't find anything.  I'm worried the noise is from the orientation of my transformers.  I hope not because there might not be much I can do about that short of doing a complete rebuild. 

I'm open to any suggestions as to how I can figure out the cause of the noise and what I can do about it.  The amp is not usable like this.

[samato]

I've gotten absolutely nowhere with trying to determine the cause of this noise.

I've tried moving wires while the amp is running, jumping filter capacitors with others of equal or greater value, jumping ground wires to other ground points, swapping all the tubes, plugging the amp in in other locations/outlets, and probably some other things I can't remember.  I even tried moving the OT but I was only able to remove one mounting screw and rotate it a few degrees - to move it any more I'd need to remove my board and disconnect a lot of stuff.  

None of this has even altered this constant hum/buzz.  My voltages are fine and bias is good.  I have a very closely matched set of output tubes in now, within 1.5mA of each other.

The only thing left that I can think of is to run the filaments off of a 6V lantern battery, which I will try tomorrow I guess.  Can the AC filament winding cause a loud, constant noise like this that doesn't change when the wires are moved?

I'm thinking of making a video with good audio quality to post on YouTube so maybe you guys can see/hear what I am and give some ideas.

What makes this even more frustrating is that behind all the noise I think I can hear the sound I was after when I started this project.  

[samato]

I just needed a virtual center tap for my filament winding with (2) 100 ohm resistors to ground. Somehow I missed that lesson in all my research. I don't think I'll forget it in the future.

I read about this before but I misunderstood the purpose. I thought it was for providing filament voltage for a PT that doesn't have it, not for grounding an existing filament winding. I shouldn't have missed it though, it's on the schematic.

This means I only made 2 mistakes in the whole build:

1) Not noticing the jacks I'm using have a different pinout than the Switchcrafts Fender used.

2) Not knowing about grounding the filament winding.

The amp is now much quieter than my Pro Jr. and gets the louder, spongy clean sound I was after.

There might be some tweaking to do but now my focus is on finding the right speaker for it.  I think I blew or almost blew the 25W speaker I've been testing it with.

Thanks to everyone here for all the help and to Doug for maintaining this site and all the information it contains.  There's no way I could have done this without it.

[Willabe]

samoto,

Thats great to hear! I hope you have a lot of playin through it.       


              Brad     

[topbrent]

Pictures of the finished product or you're lying!....Just kidding! 

-  Good job on getting it working to your satisfaction. 

[samato]

Pictures will come soon.  I'll post them in the new gallery section and post a link here I guess.

It won't be a work of art like a lot of what I see here.  That was never my goal and I don't think I'm capable of that.  I'm working on a top to enclose my chassis/head and a speaker cabinet I'm building from scratch.  Neither will be pretty but hopefully they'll work well and be durable.

On another note, I like the sound of this amp but I haven't really heard it properly yet.  I'm running it through an Eminence Rajin Cajun 10" until I make my cabinet for a 12".  One thing I notice is I think I prefer the extra grit provided on the Vibrato channel on a real Deluxe Reverb.  I can't expect my amp to have that since I don't have those extra gain stages and added components.  I think it answers my question about how much that stuff adds to the character of the amp (a lot).  It's not really about more or less gain, it's just more something - mojo, character, grit?

I might look into building a stand alone outboard unit for reverb and tremolo.  If so I'd like to make it as close to the Deluxe Reverb circuit but I don't know the first thing about how that works or how I would connect my amp to it yet.  Can anybody point me in the right direction for some info on this?