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- Good ESR values for old filter caps?

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- Thread starter handyguy
- Start date

It should be a sobering and calming read.

Living with something that is potentially problematic vs. actual problems is not the same.

The mantra is: if it ain't broke, don't fix it

I have successfully re-e-capped for cause a Fomoco AM radio 1956, Dynaco ST70 amp (4 times), PAS2 preamp (2X), ST120 amp, Hammond A100, H182(2X) organs, Shober Recital Organ amp, Peavey PV-4C amp, CS800s (2x) MMA-875t (2X), MMA-8150t, M-2600 amp,Allen S100 amp (2x) several DC supplies from the Allen 300 organ, Allen switcher supply from a nineties organ, Reader's Digest AM/FM radio 197?, Lenoxx Sound AM/FM radio, Newark Stellar Lsbs HDTV converter (switcher supply), Herald Electronics RA-88a disco mixer.If you think you are going to outlive it, you can replace it, but before you attempt anything, I recommend you browse through all the recapping horror stories on this site (and others).

It should be a sobering and calming read.

I function test my work after every couple of caps. Points my eyes right at any error I made. The H182 took 177 e-caps. After wearing out the ST70 caps 3 times, I quite buying TV parts store shelf caps and started buying long service life (>3000 hours) caps from newark & digikey.

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The BEST measurement is your bogey & tells you about your meter

Anybody measuring 10x bogey --> trash

Anybody measuring 5x bogey --> trash

Anybody measuring 2x bogey --> trash

...pick whichever one of those lines you like ":^)

Also at some point you gotta test your bogey against a different batch of the same value parts to see if the bogey is trash as well.

https://www.diyaudio.com/community/...ut-and-audio-interface-balanced-input.394417/

However, I found that I need to dramatically increase R2 to 180k (from 9.1k for a claimed 20db reduction) to get a decent attenuation around 23db (550mv down to 3mv). Can someone post the calculation for the DB attenuation for a given R2 resistance?

However, I found that I need to dramatically increase R2 to 180k (from 9.1k for a claimed 20db reduction) to get a decent attenuation around 23db (550mv down to 3mv). Can someone post the calculation for the DB attenuation for a given R2 resistance?

You also have to take into account the load you have on the attenuator. The values given are for open circuit loading.

It appears you have somewhere around 1k of actual loading. Check the specs of the sound card.

-23dB = 20 x log ( 10//60 / (R2 + 10//60) )

10^(-23/20) = (10//60) / (R2 + (10//60) )

0.0708 = 8.57 / ( R2 + 8.57 )

R2 + 8.57 = 8.57 / 0.0708

R2 + 8.57 = 121

R2 = ( 121 - 8.57 ) = 112.5k

If the math is right, the difference is probably in the measurement of the 3mV.

Voltage drop (using a 100hz tone to drive the amp) shows 21.4vac (rms) output on the amp drops to .114vac with the attenuator.

Using the formula RV = 20*log(V2 / V1), I get a 45.5db reduction.

I have always thought +10db = 10x the wattage (or +3db = 2x watts), but this calculation doubles that: 10db=20x. Most amplifier meters also show +10db = +10x watts.

What am I missing? Something to do with peak to peak measurement?

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