Help with new build: Vibrolux Reverb

[ratgon]

Hey all! I hope everyone's doing well; it's been a long time since I've been around but here's the first place I always come to when I find time to get back to building. I just finished a second build of Sluckey's AC-15 for a friend and it came out as great as the first one. Thank you again Sluckey.

I want my next build to be a BF Vibrolux Reverb ina 2x10 combo. Seems like a really fun build and I just love everything about them. I've assembled the trannies, chassis and most of the hardware but now I'm stuck. I hope I'm corect in assuming I'll be working from the AA964 schematic/layout but my God, I can't find anything legible enough to work from. Has anyone built one of these? Any tips? Any redrawn schematics or layouts?

Any help in any way will be truly appreciated. Again, I hope everyone's doing well and I thank you all in advance

[ratgon]

I think I've already seen one potential blunder. Is there any reason why this can't be built from the AB763, which there seems to be tons more resources for? Again, thanks for the hlp for a guy who's back at the drawing board with all of thi stuff again. Happily, but still....very rusty.

[AlNewman]

https://el34world.com/charts/Schematics/files/Fender/Fender_vibrolux_reverb_aa964_schematic.pdf

This is a pretty legible schematic, no?

It is very similar on paper to an AB763 Super Reverb. The Super reverb has a couple tone stack tweaks, a slightly higher voltage PT, slightly different filtering, but very different dropping resistors in the power section.  The bias voltage of the Super reverb is set higher, which makes sense for the higher voltage, but the PI, preamp, and reverb recovery show much lower voltages in the Vibrolux.  So you would probably have a lot more breakup prior to reaching the power tubes in the Vibrolux.

I would think most of the secret sauce between Fender amps of the day besides voltage tweaks at the front of the amp was probably stiffness of the PT's and the impedance of the OT's.  You say you have your transformers set up, what are you stuck with?

[ratgon]

Al! Thank you man/ I really appreciate it. And yeah, I've been looking at that schematic and it's not too bad at all truly. To be honest, the real issue is a combination of 60+ year-old eyes and having become spoiled by all the schematics I pore over here and the other usual sites. The fruits of all the labor guys put into making computer rendering of these things. So, thank you.

As far as being stuck, I think it's another case of being spoiled by options. At this point I have the chassis and all the basic hardware and here's what I'm working with transformer wise. As a perpetual newcomer to this beautiful hobby/passion, my sleuthing has brought me here:

Hammond 290cx for power with 650vct
Hammond 1760j for output with 4, 8 and 16 taps
Hammond 184A with 4H and 50ma for the choke

I have a set of  eyelet boards for an AB763

I need to choose to either go along with these and tweak as neccessary or by one of Doug's AB 763 two channel short boards with turrets.

A lot of the builds I've taken on have centered around Doug's turret boards.

I def still have a lot of studying to do; I haven't even really delved deeply into the real differences between the AB763 and the AA964.

So that's where I am with the whole thing. The idea of using another one of Doug's boards is def a huge drawer and I hadn't even really even considered it  as an option until today.

In any case, thank you for your reply and I am all ears if you have any other thoughts or input into the whole thing.

Thanks,


Mike

[AlNewman]

Yeah, the Hoffman board should work, or the eyelet board you have should work also.  Hoffman's AB763 board includes documentation and a parts list for the Vibrolux.  Either way, you'll need to make it work with your chassis.  Your eyelet board may or may not include provisions for the bias circuit, and either way you'll have to decide how to place your filter caps, either in a dog house or the chassis.  One thing about the eyelet board to consider may be the length of the leads for the parts you choose, I would think there's modern parts which will not work well in a classic eyelet board set up.
But your transformers and choke should work great, they're all recommended for that circuit.  Hammond builds quality transformers.

[ratgon]

Thanks man, I really appreciate it. I've decided to go with Doug's short turret board and use the bias and filter cap eyelet boards. I'm going with MOD filter caps so they should fit the boghouse eyelet board nicely. I'll keep you posted.

Thanks again and always open to any suggestions or wayward thoughts.

Mike

[RoadShow]

I would suggest using the 1750Q instead of the 1760J .  You can read the issues I had here:
https://el34world.com/Forum/index.php?topic=32741
Hammond info had recommended the 1760J.

I had used the 1750Q on JTM45 builds and it was rock solid.  When I switched I no longer had problems and have maybe 200 hours on the amp.

Just sayin...

[ratgon]

Hey there Roadshow and I appreciate the reply. I can't say I've read EVERY word of your thread but I spent a good bit of time there and I'm missing what the issue you found with the 1760J was. Can you maybe help clarify? I really do appreciate it.

[RoadShow]

Hey there Roadshow and I appreciate the reply. I can't say I've read EVERY word of your thread but I spent a good bit of time there and I'm missing what the issue you found with the 1760J was. Can you maybe help clarify? I really do appreciate it.

As stated in the thread, I decided to go with what I had used in a couple of builds using KT66 P-P  per one of my attachments and it's been perfect since.  The primary and secondary resistances on the 1760J were close to spec.

If you look at the input impedances on the transformer attachment notice that the 1760J was about half of the other two which included the 1750Q, I'm leaning there. Maybe it had an intermittent defect, I don't really know, and I didn't feel like tearing it open to find out.  My swap observation and hunch panned out and I stopped there.