Magnatone Varsity capacitor confusion

[mellotron]

A while ago, I got a "mother of toilet seat" Magnatone Varsity amp. All caps have been replaced (except the death cap, which was simply removed), and I have all the originals in a bag. A three-prong power cord has been installed, correctly from what I can tell.

Attached is the schematic and a couple pictures of the old caps. I am trying to match the markings on the schematic to the old caps, specifically around where they are electrolytic vs. non-polarized. My knowledge of amps goes about as far as my study of the Princeton Reverb reissue that I am rebuilding. Some things on the Magnatone schematic look familiar to me; others do not.

The first thing that jumps out at me as odd is that all of the caps on the schematic share the same symbol, but some are physically easy to tell as electrolytics and some are confusingly labeled.

The two filter caps are and were electrolytics, which makes sense--positive toward the circuit; negative to ground. While shown as a 33uF and a 10uF (which is what is currently installed), the original must have used the large, dual-section 16/16uF 450V cap. No biggy; I guess they just used what they had available. The 6V6 cathode bypass cap would have been the smaller orange 25uf/50V cap. Both of these have the black band and are labeled Positive. Easy peasy.

The red caps are all .05uF/600 Sangamo caps. There is an arrow molded into the body on the side opposite the printed values. Two of them have a + on one end, but at the opposite end to where the arrow points; the third one has no + or -. One would have been between the 6SJ7 plate and the volume pot; another from the 6SJ7 screen to ground; the third was the death cap.

What does the arrow indicate? What does the + indicate? Where would the two with the + have been installed, and in what orientation? What would have caused the third not to require polarity, and where would it have been installed?

The final two are the tan .01uF/600V Sangamo caps. One would have been the coupling cap into the 6SJ7; the other would have been across the output transformer. Neither of these have a + molded into them.

If one were to build this amp from scratch today, solely utilizing the schematic, how would one know where to use electrolytics vs. bipolar caps? Maybe the typical tech back then would have understood this just from placement in the circuit, but it is rather confusing to me. The amp is from 1953, based on date codes on pots. When did they start indicating + and - with the two parallel bars for electrolytics, like I see on the PR AA1164 schematic?

Thanks for your help.

[PRR]

There are NO point-oh electrolytics. Look in any reputable catalog.

The Sangamos are molded, the arrow is in the mold. Why? Rarely, caps are marked for "outside foil" and there are whole schools of thought (and not-thought) around that. Or maybe the mold maker put in an arrow "just in case"--- steel carvers are not cap-experts.

Off-the-point: If this will be a bedroom amp, consider a 10uFd 450V at 5Y3 pin 8 to ground. That adds a little more filtering especially of the high buzz harmonics.

[sluckey]

The two yellow caps are electrolytics and you must observe polarity. The three reds and two tans are NON-POLARIZED and can be installed any way you want.

That's the only important info about those caps.

[mellotron]

Thank you both; that helps a lot.

Off-the-point: If this will be a bedroom amp, consider a 10uFd 450V at 5Y3 pin 8 to ground. That adds a little more filtering especially of the high buzz harmonics.

PRR, "tradition" (again, from my limited research and learning, 40/20/20/20 and all that) seems to be that the first "reservoir" cap should be the largest. If so, would you suggest that I put the 33uF on pin 8, then perhaps two 10uFs after that?

I am definitely interested in reducing the noise that this thing produces. I am adding an On/Off switch in the fuse holder hole, to get that away from the volume pot, where it currently resides. More filtering should help.

[bmccowan]

If one were to build this amp from scratch today, solely utilizing the schematic, how would one know where to use electrolytics vs. bipolar caps?

You might want to take a look at Rob Robinette's site and the How Amps Work pages. I think he describes pretty well what various capacitors do. Basically, electrolytics are used for filtering and cathode bypassing to ground. The capacitance is high for those applications. The other caps by contrast are much lower in capacitance and a whole variety of "signal"/"film" caps are used in the circuit to shape the tone. And some people will argue with a fencepost about which film caps sound this way or that way.

[PRR]

....PRR, "tradition" (again, from my limited research and learning, 40/20/20/20 and all that) seems to be that the first "reservoir" cap should be the largest. If so, would you suggest that I put the 33uF on pin 8, then perhaps two 10uFs after that?...

Do I look like a traditionalist??

THINK!

A too-large first cap makes trouble.

The plan already works with no first-cap. A large (even 30u) first cap will raise the DC voltage significantly.

We normally want the power stage seeing a large cap to hold it steady.

A small first cap will take some of the rasp off the buzz with not much change of DC voltage.

If your calculations say otherwise, go with what you think best.

[mellotron]

That definitely makes sense. I appreciate the instruction. Thanks.