New AB673 deluxe reverb combo build

[aussietim]

Ah I see it now I have had a good look at first I thought the wrong schematic was posted

[aussietim]

OK there seems to be a lot of argument about using various resistors and how much mojo they have, I have pretty much decided and purchased metal film resistors, as I like quiet amps
So my question is how much mojo do capacitors give? I went and purchased mainly jupiter sprauge and f&t caps for this build, but I have seen a lot of " boutique" amps use orange drops and even no name caps, so have I wasted money? I always use the best rated quality I can get and afford at the time, but I sometimes wonder on the necessity of this or if any old components will do.

[martin manning]

Capacitors are not simple. Generally, if I'm looking to replicate something that has been done before, I focus on dielectric type. Fender used a combination of polyester film caps and ceramic discs in the signal path.

For the film caps, common dielectrics are polyester and polypropylene, and there are film/foil, and metalized film constructions. Personally, I prefer to use good quality polyester caps from the larger manufacturers, and either construction type. For the recent DR build, I used Mallory Type 150 metalized polyester, but polyester film/foil Orange Drops (6PS, 418P) are often used in Fender builds. Polypropelene is really a better (more stable) dielectric material. Examples are 715P and 716P Orange drops. Some people say PP sounds brighter.

Ceramic discs, which are used for the smaller values, are available in several dielectric types: Class 1, e.g, NP0/C0G, Class 2, e.g. X7R, X5R, Y5V, Z5U. Class 1 are much more temperature stable than Class 2, and Class 2 produce measurable harmonic distortion. I prefer NP0/C0G for all ceramics, but some people like to add some ceramic cap character. The treble cap is probably the most sensitive in that regard. Some people use a silvered mica cap there, which are near ideal like NP0/C0G, but seem to be expensive and less reliable lately.

[pdf64]

Has the class of ceramic cap used by Fender in the 60s been investigated / identified?
As well as the treble and bright caps, on the DR and bigger, ceramic was sometimes used for the 1nF at the LTP signal input.

I found a LarMar / type 2 master volume, channel link for fx on both channels, and a 50k audio mid pot on the normal channel, useful mods on my Fender based build.

[martin manning]

Has the class of ceramic cap used by Fender in the 60s been investigated / identified?
As well as the treble and bright caps, on the DR and bigger, ceramic was sometimes used for the 1nF at the LTP signal input.

Vibrato channel output coupling cap, reverb driver input, dry signal bypass, and reverb recover coupling caps were also ceramic. Photos of original boards might help identify the type(s) if they are marked and visible, but I'd think the more temperature-stable Class 1 or at least the better Class 2 parts (X7R) would be preferred. As always cost would have been a factor, but they would have been readily available due to extensive use in television sets.

[aussietim]

Hi pdf64 which model Fender was your build based around?
I have got the full compliment of caps just curious as to how much is magic pixie dust and unicorn tears and how much is actual added value to the sound? I may have gotten caught up in the moment when I ordered but Ill live with it, just wondering
I have or have ordered everything I need except the power transformer and a cabinet which will happen in the next few weeks then I will start assembling, so any late tips and ideas are welcome

[aussietim]

OK almost ready to start and doing a lot of reading and googling on how these things work and what to tweak and not to tweak etc.
My current thoughts and question is how do different types/ brands of bypass capacitors affect tone?
I have been looking at a lot of builds lately in preparation and have noticed a lot of builds that use brand name caps in the coupling eg sozos jupiter etc but orange drops in the bypass, is this because the bypass caps do not affect the tone so much so they are using the cheaper caps there? or they do affect the tone to one that people prefer?

[pdf64]

Hi pdf64 which model Fender was your build based around?
…

Apologies, I overlooked your query
I wanted 1x12” combo, so to try keep the amp power low enough for s 50W speaker to be safe-ish, I used a Vibrolux Reverb transformer set, so the aa964 was the starting point
https://el34world.com/charts/Schematics ... ematic.pdf

Which film caps are you referring to as decoupling?

Whatever, I’m not sure that rationals used to make the distinction that coupling applications are more critical than decoupling are always good.

[aussietim]

https://robrobinette.com/images/Guitar/ ... _small.png
This is the layout that I am basing my build around the terminology I am using is from Robrobs site
This will be my third full build and I am slowly learning how the electronics work, I am self taught on this stuff coming from a mechanical engineering background so my knowledge is a bit scattered, so I have a tendency to ask some strange questions at times in my quest for knowledge

[pdf64]

Ok, so he’s only describing the cap to the LTP common grid section’s grid as decoupling, that seems fair enough.

Are the snake oil caps available in lower voltage ratings?

Bear in mind that all the ecaps are also in decoupling applications.

[aussietim]

PXL_20230426_080127850.jpg

OK so I have been busy doing life a bit and this build has been put on the backburner but now Ive got all the bits I need plus some extra stuff.
Now all I have to do is pop it all into the cabinet and Bobs your uncle
This will be a pretty much stock build, with a three way negative feedback switch, Reverb on both channels, with serious consideration to Sluckeys TremO Nater and Marshall bias.
I have got some extra 1M pots with push pull switches with the view to maybe switch the bright cap, is this useful on a Deluxe reverb?
I have 2 layouts One from RobRobinette and one from Mojotone, they are essentially the same but I have noticed the buss for the preamp is different with the Mojo one being split for each channel, and each pot being individually connected from the case to the buss bar, is there any benefit or problems with either? which is preferable? or is the difference negligable?
Thanking in advance for any feedback, Ill probably ask some silly questions but I will get this thing working and it should sound good
Tim

*

AB763_Deluxe_Reverb_Layout_DIYLC_small.png

IMG_20230426_173012_01.jpg

Almost finished my last build just waiting on some piping haven't done woodwork since high school and have never upholstered before so I'm pretty happy even though there are a couple of flaws

Deluxe_Reverb_WD.pdf

[aussietim]

Hi All Getting into the build one question, is there a preference for routing the wires from the input jacks and pots etc to the valves? as in do builders generally go under or over the fibre board?
Thank you
Tim

[sluckey]

I use shielded cable and route underneath the board. Looks neater to me. Here's an example...

http://sluckeyamps.com/6v6plexi/6v6plexi.htm

[martin manning]

On the originals, those leads were routed through holes in the top board and trapped between the eyelet and backer boards.

[sluckey]

I just realized your Mojo board provides holes to route the wires through the board as Martin's pic shows. Using shielded cable under the board as I suggested will not work with the Mojo fiber board.

Here are some '64 DR pics that may be helpful with this project...

http://sluckeyamps.com/64DR/index.htm