AO-28 C5 & C11 capacitors

[sdemers]

In my A-100 AO-28 amp, I want to replace capacitors C5 & C11, to hopefully get rid of the popping sound that occurs when switching the vibrato/chorus tabs. Mouser part numbers: C5, 75-715P200V0.01 & C11, 75-715P600V0.0047. Mouser says these are no longer available. Any suggestions on where to get these?

[David Anderson]

Just search 715P and 0.01uF or 0.0047uF on Mouser's site. The numbers you have are obsolete because that line of capacitors is now owned and manufactured by Cornell Dubilier, not SBE (formerly part of Sprague). All SBE's product lines were sold to CDE in 2012.

Or use Mojotone's Dijon line of capacitors.

That said, by the time A-100s were made, the capacitors Hammond was using in their preamps were pretty reliable. You might try swapping 6AU6s first with known-good ones. They can develop a problem known as grid emission that will act like a leaky capacitor even though it isn't.

The world of electronic components is constantly changing. Product lines are sold or discontinued all the time.

[sdemers]

Thank you David. These two seem to be the closest options on Mouser.
https://www.mouser.com/ProductDetail/598-715P47256JA3 (Specs seem to match original part info?)
https://www.mouser.com/ProductDetail/598-715P10354JA3 The voltage is 400v vs. the 200v listed on the original part info. Is this ok?

[enor]

The voltage on the original part is a maximum voltage. In other words - your replacement can have the same voltage or higher; but not lower.

[sdemers]

Thank you. The voltages listed on the parts AO-28 parts list, http://hammondb3organ.net/a028parts.php, are those AC or DC?

[Jaim]

DC Voltage

Jim

[sdemers]

I have read that in amplifiers, the polarity/orientation of the 715P orange Drop capacitors makes a difference. Looking for an answer on this. The caps I have do not have any markings showing polarity, just labeling for values.

[David Anderson]

Paper and film capacitors are rolled up, creating an outer foil layer. The idea is that it's best to orient the outer foil towards the lowest impedance to ground because having this more exposed foil at a lower impedance may reduce the tendency to noise pickup or interaction with other nearby components. This is usually, but not always, with the lead connected to the outer foil connected to the source.

How much this is a benefit is a matter of question. It may help in circuits that are less stable and prone to oscillation, particularly at the input to the output stages of some Fender guitar amps.

Some capacitors used to have the outer foil marked, but this is not done anymore. To determine the outer foil, you have to test each capacitor. I can do it with my oscilloscope. Some people will tell you something about it tracking with the printing on the capacitor, but I have found that this is nonsense.

Bottom line: Unless you have the equipment necessary to test for outer foil, there's no point in worrying about it. The vast majority of people install these capacitors without even thinking about it. I don't think the capacitors Hammond used were generally marked for outer foil. These are non-polar capacitors.

[sdemers]

I replaced the C5 and C11 capacitors in the AO-28 pre-amp. The popping noise still happens when switching the vibrato/chorus tabs. David Anderson mentioned that some 6AU6 tubes could cause grid emission, creating a similar popping noise. I would need to know which 6AU6s specifically?

[David Anderson]

6AU6s do not "cause" grid emission. Worn-out or damaged tubes of any type can exhibit grid emission. I've seen it in worn-out 12BH7s, too, not to mention damaged 6L6s,

[sdemers]

Thank you David. Which 6AU6 tubes specifically should I try replacing?, V#?

[sdemers]

Actually, I have read There are only two 6AU6 tubes, so that answers that.