Resistor Replacement, All Or Some?

[MorePower]

I have an Accuphase E-202 amp that is in need of new caps and possible resistors. I have the service manual and have ordered new capacitors to replace the 30+year old original caps. There are several carbon film resistors that the outer coating is falling off, the power supply board having the most issues. I removed one resistor from the board, it was rated at 7.5k and measured 7.4k, but the outer coating was almost all gone. Should I go through and replace all the resistors (there are a lot) are just the ones that have some issues? :scratch2:

 

[Fred Longworth]

If you're doing a major restoration, I would replace resistors that have begun to decompose due to long-term expansion/contraction (thermal) cycling.

I would also resolder connections to parts that get hot during normal operation.

I prefer the metal film devices from Mouser.

www.mouser.com

Fred

 

[glen65]

Resistor Replacement, All Or Some?

Generally when you do a recap job its not
necessary to replace all of the resistors
Its only really necessary to replace the ones that
would be seen as questionable. Remember resistors
have a tolerance, so the 7.4k reading you measured
on the 7.5k resistor is ok. But if you see some that are
in bad physical shape get rid of them, theyre certainly cheap enough.

 

[EchoWars]

In order to keep the board looking as original as possible (and to keep the original 'sound', if you are of a mind to believe that the resistors affect the overall sound of the amp), replace the rotted resistors with new carbon film resistors.

Note that there are NO 1/4W resistors anywhere in the amp...all resistors in the E-202 are 1/2W and larger.

The resistors I use are Yageo CFR series 1/2W carbon film from Digikey. They look identical to the original resistors used by Accuphase (but are just a tiny bit smaller). Keeps the boards looking nice.

 

[MorePower]

In order to keep the board looking as original as possible (and to keep the original 'sound', if you are of a mind to believe that the resistors affect the overall sound of the amp), replace the rotted resistors with new carbon film resistors.

Note that there are NO 1/4W resistors anywhere in the amp...all resistors in the E-202 are 1/2W and larger.

The resistors I use are Yageo CFR series 1/2W carbon film from Digikey. They look identical to the original resistors used by Accuphase (but are just a tiny bit smaller). Keeps the boards looking nice.

Thanks for the replys, I removed a few more resistors and all have been very close. I magnified the power supply board and found a few solder joints that looked bad, this board sit against the meter lamps, the hot/cold temps and time have caused some weak spots in the solder joints. I agree there are no 1/4 watt resistors in the amp, you must have work on one of these. :thmbsp:

 

[EchoWars]

Generally when you do a recap job its not
necessary to replace all of the resistors
Its only really necessary to replace the ones that
would be seen as questionable. Remember resistors
have a tolerance, so the 7.4k reading you measured
on the 7.5k resistor is ok. But if you see some that are
in bad physical shape get rid of them, theyre certainly cheap enough.

Many old Accuphase amps/preamps suffer from 'resistor rot'...the enamel coating of the resistor flaking off for whatever reason. Carbon resistors with this enamel removed will absorb moisture and deteriorate. Any resistor found to be doing this should be replaced.

Thanks for the replys, I removed a few more resistors and all have been very close. I magnified the power supply board and found a few solder joints that looked bad, this board sit against the meter lamps, the hot/cold temps and time have caused some weak spots in the solder joints. I agree there are no 1/4 watt resistors in the amp, you must have work on one of these. :thmbsp:

Simply examine all the resistors you can find, and make a list of all the resistors you need to replace (any with cracked/flaking enamel).

 

[westend]

EW, is there any sonic benefit to replace with carbon film resistors rather than metal film resistors? I ask this in a general context, not just for this amp.

 

[EchoWars]

Dunno...Accuphase seemed to think carbon film worked pretty good for them. I'd stick with their formula.

Metal film are supposed to be quieter. With most amps, when I replace resistors, I generally use metal film since that's what I have a lot of on hand. But with some gear (like Accuphase) I want to keep my visible repairs 'under the radar', so I'll use what the manufacturer used - and with 70's gear that generally means carbon film.

 

[westend]

Thanks, EW. I'm in the metal film camp but have been reading about boutique resistors and have come to the conclusion that they are parallel to boutique caps. There seems to be a time and place for everything. To me, reliability is more important than a perceived or other, sonic edge.

 

[MorePower]

Another Question

I found two resistors on one of the main drive assembly boards that I would like to replace, but I do not know where to get them. They are in location R28 & R30, the service manual state they are "Cement Coated Metal Plate Resistors 1ohm +-5% 3.16w" they are about 1/2" wide and 3/4" tall with radial leads. Do you know what they are? :scratch2:

 

[EchoWars]

Those are the emitter resistors for the output transistors, and should not be changed unless you find they are burned up.

 

[MorePower]

The reason I was wanting to change two of them is someone combined two together to get the 1ohm rating, it's just under 1ohm and it looks very bad. When these resistors burn up, does it normally take out other things, transistors etc? :scratch2:

 

[MorePower]

I think I Really Screwed Up

I changed all the electrolytic capacitors, replace a few resistors that that coating was falling off and changed the 4 large 10000uf 80v caps. The only good thing, the amp does not hum when powered up, but it has a very bad distortion problem. The only way to get sound out of the speakers is to adjust VR2 all the way clockwise, but sound is distorted. I am not sure what had happend, I double checked each part as I removed and replaced them. What might have happend? :tears:

 

[westend]

Is there any chance that you have installed one or all of the large capacitors with the wrong polarity? Have you measured DC offset at the speaker terminals?

 

[MorePower]

Thanks for the reply, but they are installed correctly according to the markings on the capactors. I have done several peices of equipment over the years, I would replace the capacitors and have my friend that is a good electronics tech do the fine tuning. I have done four peices of equipment, this being the fifth, my friend has always gave me the thumbs up, it saves him time and me money. I have not been able to get a stable DC offset reading, it's like an output transistor is bad. When I powered the unit up after replacing the parts, there was no smoke, pops, sparks, nothing that would show a major problem. If I test the unit using headphones and it seems to work fine, was does that eliminate?:scratch2: