Question about transparency in ab763 style amps

[sluckey]

Yes, both resistors are the correct resistance value. But both resistors are the wrong tolerance value. The schematic calls for 5% tolerance. Both of those resistors are 10% tolerance.

[espinete]

I've been checking the value of every single resistor . Everything seems to be right.
The amp is brand new, only three or four gigs.

Caps are all right too. Except five or six ones wich don't have eather brand or value written in anywhere.

A couple of things are not the same compared to original layout ( apart from the modifications that I made ) :

1. Two resistors in v4 going to vibrato pedal jack ( rear side )


2. 6800 NORMAL channel bass pot resistor going to vibrato channel low gain input instead of going to ground in the same pot

[sluckey]

Everything is right. Even the 10% tolerance as indicated in original ab763 bf super reverb layout.

No. You don't understand. The tolerance for those resistors is clearly 5%, not 10%.It's right in front of you in the partial layout you posted. If you don't see it, then look at the pic I posted. It's circled in red.

3. I don't understand 200 value showed belove. The cap i guess is a .1uF ( near v6)

Yes, the cap is .1µF and it has a voltage rating of 200 volts.

SR_AB763.png

[espinete]

Ups!
Yes,Sluckey. You are right

[espinete]

What about the multitap ot NFB connections ?

One of the yelow wires comes from 100 resistor and then to the mini switch where 820 ohms NFB resistor is. Then another yellow cloth wire goes to the 8ohms tap jack on the left. Jacks from left to right : 8 ohms, 4 ohms and 2 ohms outputs.
Is it connected properly ? I thought nfb goes in the 2 ohms jack. Because the original ab763 super reverb.

[sluckey]

Is it connected properly ? I thought nfb goes in the 2 ohms jack. Because the original ab763 super reverb.

But your amp is not an original AB763 Super Reverb. It may be best to stop comparing your boutique amp to the original Fender documents. Contact your boutique builder and ask him these questions. Better yet, get him to give you a copy of his working schematic and layout, and post them here.

[espinete]

Yes, it's an ab763 circuit. The builder followed original schematics. Every component has exactly the same value and connections. Builder doesn't know where the issue is coming from. And i repeat , no good technnicians in my area. When i have time i'll go far away to see a good tech guy that i know.
If you are tired of my messages, just ignore them. I know very well your opinion. I respect that. But if you have a look in the tittle of the thread , you will see ab763 style amp, not original. If you can't help because it's not original , eather you don't like comparing to the original or you are just tired of this thread, don't help me.
But in this particulary question, i found information from people saying that in a multitap situation, nfb goes to original 2 ohms tap. The last amp that i had ( it has been stolen from my car this year ) was a copy of an ab763 super reverb too.with an OT multitap too. A Headstrong King Reverb amp head. It is very possible that amp was connected in a different way(jack speaker outputs) than my current one.

It is exactly like a bf super reverb. Except : fan, OT multitap ( but original 2 ohms tap available.Like many bf current builders ) , tubes specs the same except v2 5751 (srv) and power tubes, rectifier switch also includes original gz34, reversible switch wich turn on/off normal channel. The point is , the headstrong had exactly the same mods as this one. And the Fender super reverb from 1966 that i sold a couple of years ago, too. All these three amps , exactly the same mods, circuit, etc,. The only different thing could be this one. I don't know. That's why i'm asking to see if anyone knows something about this particular question. The current amp doesn't like pedals while the other ones loved them.
I saw a post saying that if the nfb is connected to the 2 ohms instead of to the 8 ohms one, that will clean up the 8 ohm output signal. But maybe it's not a right info. Or i didn't understand it properly. I share this information here because I have the hope that maybe is possible.
Cheers

[sluckey]

Use the 2Ω tap for the NFB. This will be less NFB and the amp won't sound quite as clean. You may like it better.

[pompeiisneaks]

I don't think sluckey's being negative, he's given you tons of information, and he's just calling out the fact that this amp can't be compared apples to apples to an AB763, it's got some modifications, and therefore, not being identical, trying to compare the two isn't the best way to go about it.

He's one of the most helpful and knowledgable people I've seen on these forums, and he's definitely worth your time to listen to, and learn from.

My 2c anyway.

~Phil

[tubeswell]

Is it connected properly ? I thought nfb goes in the 2 ohms jack. Because the original ab763 super reverb.

But your amp is not an original AB763 Super Reverb. It may be best to stop comparing your boutique amp to the original Fender documents. Contact your boutique builder and ask him these questions. Better yet, get him to give you a copy of his working schematic and layout, and post them here.

^This^. We really need to see a schematic with working (idle) voltages, so we can usefully help you analyse your concerns.

Otherwise we end up talking past each other.

[espinete]

Anyway thank you all for your patience. I've been stressed because i'm currently playing almost everyday with this amp and i wanted to fix it ASAP