So Fender has been doing this in their RI amps....

[rooster]

I don't work on too many DRRI Fender amps, but I ran into something that caused me pause.

Typically, in the original BF and SF amps, Fender used two 70uf/350VDC electrolytics in series for a resultant 35uf/700VDC primary power supply cap. But here in the DRRI, they used a 220uf/100VDC cap in series with a 47uf/500VDC cap. Technically, this would equal 40uf/600VDC. This use of misbalanced caps had never occurred to me. I find it interesting and something worth sharing. Amazing to me how the bean counters and the circuit designers can get together on something like this. Does it alter the sonics of the original design I dunno.

[JazzGuitarGimp]

Now that's "thinking outside the box"!

[tony hunt]

Intruiging. Did you take a voltage resding at the junction of the two caps?
Are the balancing resistors different too?

[lovetone]

Sorry which amp is the DR?

[pdf64]

'65 Deluxe Reverb http://support.fender.com/schematics/gu ... ematic.pdf

[Stevem]

Like all things big company's do its for ćost effectiveness not nessasarily betterment !
They changed the circuit board layout with the HRD to have all the output circuit components on the main board and now when a output shorts out the circiut traces arc over near every time !

[gui_tarzan]

Not to mention bias caps that are only half soldered in.

I wondered about the 220s myself, I worked on one a few months ago and found that very strange. The one I worked on had a pair of 220/285 though, not a mis-matched set.

[The Ballzz]

Well Hey,
"It's well within our standard +/-20% tolerance and it's what we had available that day!"
Just Sayin'
Gene

[rp]

This use of misbalanced caps had never occurred to me.

Not only did it not occur to me but for some reason I'm not sure of I thought they had to be matched for capacitance and voltage rating. Maybe that they should have resistors across them to balance them was the reason I thought this. I wouldn't even hazard to use unmatched brands of the same value out of fear of some construction imbalance causing one to work harder and fail sooner.

No one here has mentioned this and Fender engineers can't be all that misguided so I guess it's fine. I still wouldn't do it just because it looks like a parts box kluge, or has that low budget "good enough" aspect.

[martin manning]

As long as you don't need to have the junction of the two caps at half of the total voltage for some reason, it works fine.

Presumably the combination of a low voltage high capacitance part and a high voltage low capacitance part (220u/100V + 47u/500V) is cheaper than two identical medium voltage, medium capacitance parts (2x 100u/300V). It's probably not worth the time to figure it out unless you are making a large production run of amps.

[tony hunt]

There are unequal balancing resistors in the schematic that pdf64 posted. I reckon there would be 70V across the 220uF/100V, maybe as high as 80V on start up.

My gut reaction would have been that the cost of stocking two more different components would have outweighed any economic advantage. But that 220uF/110V has to be about 1/4 the cost of the 47uF/500V. These days, it just has to make it past warranty anyway.