Fender 1961 Concert Brown face 6g12a re-cap time, need input

[Enzo]

There are USA made electrolytic caps?

[km6xz]

Did the customer want the original sound? If so, just add a buck transformer to lower the mains to 110 volts which it was designed for and not have to worry about higher rated caps and changing the bias and screen circuits.

[MWJB]

I would hate to change the character of the amp to much for the man wish they made 550v caps as I have seen marshalls with the same 550v cap rating is this not America where we have the best of everything..health care good paying jobs pretty girls awesome Fender amps Telecaster guitars....plenty of food for the country, cheap gas BUT NO 550v caps, My god. Maybe Ill hop on my private jet and shoot over the pond and get me those caps they seem to have but we cant get th over sized cap pan is starting to look good to me Ha ha. I am going to go do some voltage readings and would like to post some pics of this totally cool amp.. mojo factor priceless

The amp won't sound right if it doesn't work properly. The "uf" rating of the caps will affect tone/mojo, but not the voltage rating unless underrated/underperforming/unreliable.

Sprague atom 20uf 600v caps will not fit in the cap pan & will look like a bodge job if you clutter up the main chassis with them.

Good tubes, speakers & biasing to taste will give that amp plenty of "mojo" (as long as the power supply is up to snuff), it'll probably sound better now than when when it was built.

Note that the higher voltage blackface amps all went with the totem pole main filter stage within a couple of years of the Concert & other brown/blonde Fenders...the BFs still have "mojo"! ;-)

[Smitty02]

Yes he is picky about not altering the sound "to much" as I was told, I tried to explain that even new ones would change is a little before I new there were 550v caps in it Thanks for all the suggestions guys. it does have a hole for a jack drilled in it and another where a toggle had been mounted. I want to run a bias pot to one of the holes, this morning I started on it a compiling a shopping list. It does have a good hum going but I got it to play without popping a fuse it needs new octal sockets and keepers, going with the bakelite old school quality better solder lugs on them also, but expensive i know. I like em used them in several vintage re-store jobs.. I took some measurements this morn and the plates are at 498 respectively down from the other day and the bias voltage AFTER the divider is down to -62v I did measure it before the divider at the 10k series on standby the caps are riding at 525v but my house current is down a couple volts from 120.9 to 118 and change from the other day.. Ive never heard of a Buck transformer are those only available in Russia and Europe heh heh How does the buck trasformer work and what do they cost ?? Yes the 600v spragues are crazy expensive. I like the F&T's I ran across a posting awhile back the sprague and been bought out by a chineese company so Ive been sticking with F&T lately I will check out the webers but the size is the killer as well as the price and I know webers are china but wonder what actual brand ?? Thanks ya'll.... Ill be back and put some pics up for all..........I just scoped out the Webers they are almost a 1" X 2.062.... Anybody try these out before ??? Looks promising but too good to be true.... what gives ?? I'm such a pessimist I see somehting that looks like it would work and automatically suspect the worst....2 dollars ! ?? 2 good to be true...quality??? and If I went and ordered them they would be out of stock or dropshipped from ching chong cha china.. and take 8 weeks to get LOL

[jpfamps]

F&T make 550V caps (with a 600V tempory over load rating).

The 22uF/550V F&T caps will fit in doghouse.

These are quite hard to find, but Ask Jan First (Frag Jan zuerst --- Ask Jan First) in Germany sell the these under their own brand.

In my view in that amp all the filter caps should be rated for the unloaded voltage as this is what the caps will experience with a SS rectifier if the amps is turned on without employing the standby switch, which will happen at some stage.

[Smitty02]

+1 on the amp getting switched on jp. I seen Jan First but was lookin into them and there is customs and shipping and ....probably a long wait I just pulled the trigger on the Webers and got my fingers crossed, I have built a couple Weber amps actually there caps seemed alright.. So in the best interest of the owners tone instructions and need to get this job done for him asap I am taking a shot with the Webers n hope they are in stock cause you cant get them on the phone..I already emailed them to find ou ifthey are n stock. If all goes smooth I want to use the extra $ for tolex and recover the amp for him make it adjustable bias too get him a good quality leather handle really surprise him turn this turd into a looker and it will increase its value a lot, I got to get a pic up of this amp, you'll see what I mean.. and if Im lucky buy the time the Weber caps wear out they will be selling 550volt caps in America

[bob p]

Sprague atom 20uf 600v caps will not fit in the cap pan & will look like a bodge job if you clutter up the main chassis with them.

Yes -- with voltages climbing it becomes harder to find a single cap that's rated for the voltage, and when you can find it it will be too big to fit where you want it to go. I honestly don't understand why Atoms have to be so big. All of the rest of the caps in the world are shrinking, but they continue to make Atoms as big as ever as if doing that is a marketing gimmick for people who want caps to be as big as they were 50 years ago.

The really good news is that other brands of caps have shrunken in size by incredible amounts, making it possible to fit a totem pole arrangement inside of an amp without any real trouble. On high voltage Fenders I've had no problem fitting a totem pole arrangement inside of the doghouse.I honestly think that the totem pole arrangement is a great way to go -- caps are small and easy to locate and the risk of over-voltage is minimized.

At the risk of speaking heresy: I like snap-in caps. It's easy to find high quality name-brand snap-ins that have plenty of voltage rating, ripple rating, low ESR, compact size and low price. There's no doubt that axial caps are going to be harder and harder to find in the future, so why not embrace high quality parts that are readily available? Companies like CDE, Nichicon and Panasonic make some great quality snap-ins that are very easy to source.

[km6xz]

Boost or Buck transformers or coils are used commonly to adjust a mains voltage to another standard voltage. They are used less now in non-industrial applications but still are used in heavier applications where, for example a 208v device can efficiently be run on 230volt mains. It goes back to the first uses of transformers in the 1800s. If a coil shares the same flux field, putting an inductor in series, depending on wiring, boost the out put from the secondary or drop it without generating heat or losses much.
If you have variac, run the amp at a lower voltage(110 VAC) and see if the schematic and readings don't match.

[bob p]

google for "vintage voltage adapter"

[Smitty02]

61 Brownface Concert rehab

Ive finally got a gut shot and am starting thhttp://music-electronics-forum.com/images/attach/jpg.gifis project I wanted to post some pics for all so here we go Notice the blue jumper wire that is missing the 220k resistor, does anyone now why some one would pull the resistor ? You can see it was modded there is a 1/4 inch jack and a switch that was added at some point and then disconnected ??? the switch is shot I dont know what they would have done this for. Any ideas people ?

[Dave Curtis, dB AudioTech]

I will have to agree that placing 512 volts on a 500 volt cap is asking for trouble.

I did that (closer to 520v) with a Xicon for almost a year; it didn't explode. YMMV ;o)

I'll add that it was not in a customer's amp...

[MWJB]

The black/blue? wire appears to be stock, just connected direct to the PI coupling cap & 220K omitted (more gain/clarity). The yellow wire from the Vibrato channel appears to be grounded out and the vibrato function bypassed?

Edit: On closer inspection the yellow wire is connected as expected (to a 220K at top of board), parallax in the photo made it look like it went to the ground point. Both channels should function properly, as well as the vibrato, just less series resistance on the Normal channel and a change in bleed through from one channel to the other due to mixer resistor imbalance.

As I suspected, your filter caps are 525vdc rated...many folk who resist the use of caps less than "600vdc" rating, due to an anticipated loss of "mojo" are mistaken/deluded/uninformed, as Fenders of this era often never had 600vdc rated filter caps!

[Bruce / Mission Amps]

If you're thinking about doing the totem pole cap arrangement, you could always take a look at the Super Twin Reverb schematic for reference. The STR has a B+ of about 530 VDC on modern 125VAC supply voltages and It uses the same totem pole cap configuration that MWJB is describing.

Many people like to strap bleeder resistors across capacitors, but I'm not one of them. I don't even like to put them inside of the doghouse. Whenever possible I prefer to locate bleeder resistors, cathode resistors, Pi filter resistors, etc., as far as practicable from their associated capacitors. Resistors generate heat, and heat is one of a capacitor's worst enemies. If you take a look at the attached gut shot of a stock Super Twin Reverb chassis, you'll see that Fender mounted the bleeder resistors for the totem pole caps as far away from the caps as possible. Instead of putting the bleeders in the doghouse, which would retain all of the heat in an enclosed space and threaten capacitor life, Fender put the bleeders on the terminal strips that I've circled on the attached photo. Then they just run wires from the caps in the doghouse to the terminal strips.

[ATTACH=CONFIG]22774[/ATTACH]
[ATTACH=CONFIG]22775[/ATTACH]

IMHO... of course do what you want but ... really?

530v across two series 220K resistors for a total of 440K... 530v/440,000 ohms = 1.2ma 1.2ma^2 * 220,000 ohms = .32 watts each resistor.
It would be a pretty cheap piece of crap capacitor to be effected by that tiny amount of heat an 1/8' away and exposed to such a large area of the cap body.
I'd just stick them across the capacitor somewhere and close the lid for 20 years.

[Smitty02]

Well I posted some pics but they seem to have disappeared, they were there ?? Any how.. I talked with the owner and he said the #2 vibrato channel was much weaker and had a noisey hiss to it, he had to pump it up to 8 to get any volume and tone from it. I will be going through it and checking all the resisitors soon but I want to finish the upgrades and cap job first I went with the Weber 20uf 600v they are the only game in the USA with 600v caps small enough to fit in the doghouse and I dont see any red flags in useing them seeing everything is from china now pretty much I am making this amp stock original no totem pole wiring I am putting the missing 220k resistor back in and see where we will go from there I am also making the bias adjustable and hope to eventually re cover the cabinet for him, but we are on a tight budget so I have 140 in parts already another 50-60 bucks will get the cabinet done. its going smooth so far I will be documenting the process for him and will have plenty of pics.

[bob p]

> ...really?

Is it worth doing it just for the bleeders? sure.
Is it worth doing it for the Pi filter resistors? sure.
It is worth doing it for all of them? sure.
I'm talking about a 180W amp, not a 40W amp.

> 530v across two series 220K resistors for a total of 440K... 530v/440,000 ohms = 1.2ma 1.2ma^2 * 220,000 ohms = .32 watts each resistor.

Maybe you didn't notice that the amp I was referring to didn't have 220k resistors, so those calculations won't apply.
The photo I posted shows that the color bands on the bleeders are orange-white-orange, or 39k. Schematic says the same thing.
530v/78,000 ohms = 6.8mA; 6.8mA^2 * 39,000 ohms = 1.8 watts each resistor.
So far we've got 3.6 watts being dissipated just by the 2 bleeders.
Looking at the first stage of the Pi filter, over 100V is being dropped across a 2k7 10W resistor; that's 100^2/2700 = 3.7 watts.
So just the bleeders and the first Pi resistor are dissipating over 7 watts.

Fender was smart to move these resistors out of the doghouse.

Some people think it's important to buy 105*C caps rather than 85*C caps because they think that it's worth spending the extra money for a cap that will have a longer lifespan. If the cap is never subjected to that extra 20*C of temperature then the more expensive cap is a waste of money. We all know that thermal de-rating is one of the main determinants of cap life. Although one or two 220k bleeder resistors may not put out a lot of heat, 39k resistors like those that Fender chose for the big amps like the Super Twins and the Studio Bass certainly will.

If all of those resistors were in the cap can they'd dissipate a significant number of watts into a sealed/non-ventilated space. The heat is trapped and it can't go anywhere, just as if you stuck an incandescent bulb in there. Temperature is going to rise, and nothing good will come from it. I think that most people would agree that it would be a bad idea to put a 10W incandescent lamp in your cap can to keep your caps warm, but the resistors would provide the same net result. Personally, I think putting heat sources in a sealed cap can is a bad design that shouldn't have been done in the first place. Most amps made in the Golden Era have some form of chassis ventilation, but not Fenders. Leo made simple designs that were cost effective to mass produce and people just accept those designs as classics without bothering to think about how to improve them.

It doesn't bother me to take a few extra steps in an effort to prolong the lifespan of the components in my amps. My objective is to do a little extra work up front when overhauling my amps, putting in features that hopefully will prevent me from ever having to go back inside and having to repeat doing the same work twice in my lifetime. Getting rid of bad ideas like trapped heat is just common sense. It's good engineering practice too. Little things like this can help to prevent failures over the long haul, so why not use them? I think it's a good idea to think outside the box and build amps smarter so that you don't have to maintain them as often.

I have to admit, I'm looking at this problem from the perspective of an engineer/hobbyist, not from the perspective of a professional repair technician. Whenever my amp goes up on the bench for repairs, it's a total loss for me. My amp is down, my time gets consumed, and I have to spin my wheels to get it back in action. Contrast that to a professional tech who gets paid for benchwork. For him, an amp going onto the bench is a good thing. I don't don't get paid for bench time, so having an amp go back on the bench is a losing situation that I'd prefer to avoid if at all possible.