Has anyone here done the blackface mods to their Fender? (And general amp work)

[lincolnic]

A little while ago I posted a thread about my new amp, a 68 or 69 silverface Fender Pro Reverb. I bought it thinking that it was using the AA165 circuit (which would be blackface specs), but once I looked inside I saw that it was actually the AB668 circuit. I want to restore it to the blackface circuit, but I've never done any amp work before. The mods themselves don't seem that difficult, but I'm not quite sure how working point-to-point is mechanically different than working on a PCB. It seems like it might be easier to cut out a component and solder the new one to its existing leads, rather than to completely desolder and remove it intact, but I'm just speculating.

If anyone's done this before, I'd be curious to hear your experience. I'd also like to hear from any of you amp builders in general - what's the actual work like? What should I know beforehand? I already know how to properly discharge the filter caps, but what else?

Also, where do you buy caps and resistors of the proper values for this kind of thing? The usual pedal supplier suspects don't seem to carry resistors past 1/4 watt, and I'm not sure if Mouser has carbon comps anymore. Is it worth just buying a kit of everything from somewhere? (Like this: http://vintagefenderamprepair.com/mods-2/home/pro-reverb/) Or is that way overpriced?

I guess another important question would be: is it even worth doing this on my own? Is this a project that's better handled by an experienced tech? After around 30 pedals I feel confident that I can do the actual work properly, but amps are a new world for me. I'm ready to learn, but I also don't want to accidentally wreck a perfectly good amp.

[jkokura]

I've been thinking about blackfacing a silverface Vibro Champ I own. But I don't think it's very hard. I've even read that there's no difference between the black and silver champs.

Anyway, If I had a Princeton of Deluxe of some sort I'd really be looking at making it happen.

Jacob

[claytushaywood]

Its pretty easy and definitely worth it.  Ive done quite a bit of upgrading and revamping of fender amps.  I completely redid a silverface pro reverb a while back and really got it sounding good.  I am a huge jerry garcia fan and found some of the mods alembic did to his twin reverbs back in the day.  I would definitely blackface the amp.  But I also like to change out plate resistors, cathode bypass resistors, all the resistors replaced during blackfacing with high quality made for audio metal film resistors.  hand matched (though the ones I use are like .1% tolerance) I like PRP 1 watt metal films.  You can get these amps dead quiet- especially since yours is probably a drip edge silverface (if its actually a 68 it might have blackface guts honestly)
  and if the amp doesnt have the famous blue caps (mine were blue... read: famous blue) from the blackface era I would replace a good portion.  If you would like help with placing the lead with the outer foil the correct position I might have a blackface schematic marked. 

I replace the treble caps with polystyrene caps, like the 120pf bright cap (lower it to 80pf to make it more useable), the 250pf tone stack cap and any other small caps.  Match the caps before the phase inverter to as close as you can get.  The cathode bypass caps actually affect the tone a lot... one of the jerry g mods was to replace those with some old school sprague axial tantalum's. 

i know this is a lot, but i've seriously turned some old fenders into the absolute quietest amps youve ever heard.  Now i'm starting to think this post is redundant because if its actually a 68 it might have blackface guts with the revered blue caps and all, in that case, i would leave it.

that kit is definitely a rip off, i think it is pretty important to match the coupling caps at the phase inverter to really take advantage of the harmonics of the pro's power tube dirt. 

The best mod IMO, is putting an ANOS 5751 from kcanostubes in v1 (or v2 rather cuz u should be using the reverb channel), and getting a decent reverb driver 12at7, and changing the reverb pot to a linear pot. 

ive got a layout that shows where all these sections and exactly what you wanna change.  im telling you i can get a pro reverb to be absolutely dead quiet (with humbuckers) until you get the volume above 7.  and thats LOUD

http://www.partsconnexion.com/resistors_prp.html

[gordo]

It's very addictive (like pedals aren't...) and everything is on a larger scale.  If you can drain caps you're all set, just think twice before you do anything and don't be afraid to recheck voltages from time to time to make SURE they're drained.

I've done a bunch of old fenders (either rebuilds, repairs, or blackfacing) as well as a lot of newer ones (installed Fromel kits, BillM kits, repairs).  A few great parts resources are Antique Electronic Supply in Phoenix, and Triode Electronics here in Chicago.

Clipping parts is much easier but keep in mind that you might want to return the amp to stock if you decide to sell it...to...say...uh...ME...

[oldhousescott]

Doug Hoffman is one of the best amp parts suppliers in the biz. Not the cheapest, but he ships almost instantaneously. (I think he's actually either prescient, or a mind reader, he ships so fast). Plus, there's a great forum at his site. Lots of smart cookies with experience in this kind of thing.

[lincolnic]

Thanks, guys, lots of good info here!

claytushaywood, it is a drip-edge, and it's actually super quiet already! It does have the blue caps, but it's not the blackface circuit. I've got schematics and layouts for both versions, and I know what needs to be changed to restore it, so it's just a matter of getting parts and doing the work.

Two more questions for everyone: I probably need to replace the filter caps, but I don't have a variac. What's the best way to bring these up to full charge safely? And second, if I desolder and remove the parts rather than clipping them out, what am I actually going to be soldering the new parts to? Are there turrets underneath the solder joints, or are things just straight up point-to-point under there?

[gtr2]

You'll be soldering to the eyelets on the fiberboard.

You don't need to use a variac to bring new filter caps up to voltage.

Josh

[lincolnic]

Really? I was reading one of Gerald Weber's books and he made a point about bringing new filter caps up to voltage over a period of time, as the dielectric needs the slow build to form properly, or something like that. Any other reason why you would/wouldn't do this?

[Clayford]

it's the OLD ones that haven't been powered up in a long time you want to bring up slowly. Or NOS. The dielectric needs to be babied just like you're talking about so they don't blow. New Caps - they've been charged and have their shape and are all ready to go.

[gordo]

+1 on the new caps.  If you already have a variac it certainly can't hurt, but it's not necessary.  I WOULD strongly recommend building a light bulb power-on box though.  It's saved me from costly mistakes.  It's probably paid for itself in fuses alone!

[lincolnic]

Ah, gotcha. That makes sense, thanks!

gordo, I've heard about the light bulb method before, but I haven't had it properly explained to me - how do I do this properly?

[pryde]

Hello there,
Light bulb limiters are very simple and are really a MUST if you are going to work on amps. I built one years ago and use it several times a week when servicing amps. Essentially it limits the amount of power-draw and serves as a visual indicator if the amp is in-fact drawing to much voltage current due to a short or poor component connection. There is all kinds of info online but this one will get you started:

http://www.antiqueradio.org/dimbulb.htm

[lincolnic]

Thanks for the link!