Hello everyone,
I just got a Quad 405 that I want to refresh parts.
It is with the board ISS9 so I was wondering what are you guys replacing obsolete parts with ?
This is what I got so far.
1) All electrolytic capacitors were replaced by Nichicon 105C electrolytic.
2) Both 10000µF were replaced by Nichicon LKG1K103MKZ 80V instead of 63V to fit original size mounting ring (50WX80H) with soldering lugs like the originals.
3) Output transistors have already been replaced on one side, they are toshiba on both side but different year, I'd like to replace them with all the same version and year.
Original output transistor are 2SD424 and can be directly replaced by MJ15001 if I am not mistaken. If you have other suggestions, I'd be happy to see what you guys did.
4) Op map are missed match and one have been replaced (on the side where the output transistors have been replaced).
On the side that has already been repaired, the op amp is UA301ATC from 1977.
On the side that looks original, op amp is LM301AN from 1975.
I'd like to have both of these replaced but I have a hard time finding the right component. If you guys could tell me what you use on your 405s that are using the stock boards, I'd appreicated it !
Here are all the cross-reference I've found so far but not sure which one to pick at this point.
LM318, OP07, OPA134 and OPA277 all seem to match pinout but I am not sure about the rest of the specs.
5) The 40872 pre drive are originals from 1978. I think they can be direct replaced by TIP42C if I am not mistaken.
6) R30 and specially R31 have got a lot of heat, the circuit board has change color, I have redone soldering but the leads of R31 look oxidated. The value reading is spot on at 570ohms, they are 5% tolerance as the orignal schematic state for 10%. Not sure it is worth replacing them because of the heat stress they got...
Other than that, it's pretty much it. If you guys have any thoughts, I'd like to hear about it ! I tried to find information on the threads in here about the 405 but it seems many of you guys are having newer revisions and parts were not matching what I had here.
Again, I just want to refresh the components and that they be identical on both side and put the cover back on.
Thanks for all the input !
I just got a Quad 405 that I want to refresh parts.
It is with the board ISS9 so I was wondering what are you guys replacing obsolete parts with ?
This is what I got so far.
1) All electrolytic capacitors were replaced by Nichicon 105C electrolytic.
2) Both 10000µF were replaced by Nichicon LKG1K103MKZ 80V instead of 63V to fit original size mounting ring (50WX80H) with soldering lugs like the originals.
3) Output transistors have already been replaced on one side, they are toshiba on both side but different year, I'd like to replace them with all the same version and year.
Original output transistor are 2SD424 and can be directly replaced by MJ15001 if I am not mistaken. If you have other suggestions, I'd be happy to see what you guys did.
4) Op map are missed match and one have been replaced (on the side where the output transistors have been replaced).
On the side that has already been repaired, the op amp is UA301ATC from 1977.
On the side that looks original, op amp is LM301AN from 1975.
I'd like to have both of these replaced but I have a hard time finding the right component. If you guys could tell me what you use on your 405s that are using the stock boards, I'd appreicated it !
Here are all the cross-reference I've found so far but not sure which one to pick at this point.
LM318, OP07, OPA134 and OPA277 all seem to match pinout but I am not sure about the rest of the specs.
5) The 40872 pre drive are originals from 1978. I think they can be direct replaced by TIP42C if I am not mistaken.
6) R30 and specially R31 have got a lot of heat, the circuit board has change color, I have redone soldering but the leads of R31 look oxidated. The value reading is spot on at 570ohms, they are 5% tolerance as the orignal schematic state for 10%. Not sure it is worth replacing them because of the heat stress they got...
Other than that, it's pretty much it. If you guys have any thoughts, I'd like to hear about it ! I tried to find information on the threads in here about the 405 but it seems many of you guys are having newer revisions and parts were not matching what I had here.
Again, I just want to refresh the components and that they be identical on both side and put the cover back on.
Thanks for all the input !
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Check and/or replace Zener supply resistors R7 and R8.
These are also different on the boards shown.
These are also different on the boards shown.
Out of interest before you start you can do a null test to evaluate the difference between the 2 channels by feeding the same audio to each channel and connecting the speaker between the 2 red outputs.
OPA134s work very well but there is no need to change the drivers. I also replace C8 with a 1% film type, it is also worth reducing the gain. Once finished if you test again there should be almost no difference between the 2 channels. The 2 560R resistors do run hot and can be placed on the rear of the board but it does not look very original.
Stuart
OPA134s work very well but there is no need to change the drivers. I also replace C8 with a 1% film type, it is also worth reducing the gain. Once finished if you test again there should be almost no difference between the 2 channels. The 2 560R resistors do run hot and can be placed on the rear of the board but it does not look very original.
Stuart
The original first generation op amps were hissy. I have personal knowledge of the competitor uA741. I'm unfamiliar with your suggested replacements, but one of them might have a noise voltage spec. Look for something with a microvolt noise spec <.5 uv or a bandwidth spec <7nv/hz. The replacement has to be pin compatible with 301 IMHO plus bipolar input instead of fet would match the circuit better.Edit it appears you have DIP op amps. In that case OPA604 may be pin compatible, it is with 741.
I don't know why you are changing transistors. Are yours blown? I have tried TIP41c/42c as drivers in the AX6 circuit, and they were inadequate to reproduce tinkly bells & top octave grand piano. I have hearing to 14 khz. The original RCA 2n5320/22 had Ft of 50 mhz versus the TIP42c/42c of 6 mhz and the surviving pair 5320/22 I had sounded much better than the TIP's. I can't find Ft data on 40872 but you might be taking a giant step backwards by replacing them. If you must replace, I found MJE15028/29 with ft 30 mhz adequate to reproduce high frequency source material.
Metal film resistors above 100 kohm tend to have less hiss than carbon comp resistors from the seventies. Be sure the ones you buy have higher wattage rating. Recently vishay has reduced size of metal film resistors with a new plastic that will withstand hundreds of degrees of heat. Your board will not withstand that; buy resistors that are physically larger than original.
Zeners by contrast with driver transistors, do tend to age.
It was stated that 400 khz Ft homotaxial output transistors limited the high frequency response of my ST120 amp too. I don't have any of those but any epitaxial TO3 transistor will have Ft>2mhz and should sound as good as the TIP3055 the simulator operator tested. I have found MJ15003 adequate.
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hello 405man, thank you for the comments and suggestions !
Will do the null test and see how it goes before/after.
Thanks for confirming that you got good results with the OPA134. I will swap both of them so they are the same, currently they don't match exact part and date code.
I'll try to find a 1% 120pF film cap, schematic states 120pF 5% no voltage rating stated on the ISS9 part list I have for C8. Any particular reason that cap should be replaced ? Just out of curitosity...
As for the drivers, if you think it is not worth to replace them, I'll leave it. I had not expected that it was already repaired when I got it because many parts don't match with each other channels. That is the only reason I wanted to do a overall refresh of the parts so they all be the same.
I really appreciate your time and ideas. Can't wait to complete the project !
Hello indianajo, thanks for all the detail reply.
after verifying the uA741 and OPA604 you are talking about, they do not seem to match pinout so I think I'll go with the OPA134 exact pinout match and seems to be an excellent audio component. I will review the spec sheet with your suggestions see if they match but I am pretty sure they will as they are high grade audio op amps.
As for the transistors, no they are not blown, just missmatch on both boards. Driver are identical on both side but date 1978. I just wanted to refresh all of them with modern components but reading your comment and previous ones, it seems it is not necessary to replace any of these transistor if they are good. I though it would have been a good idea, this is why I posted question here to get the exact type of answer you guys are providing so I am grateful for that !
Thank you for all the detail information you provided about the transistors and resistors. I will carefully chose the right components !
I really appreciate all the input you guys are providing ! Thanks a lot !
I remembered this thread from a few years back:
Quad 405-2 Overheating on right channel.
It is worth reading as it highlights subtle issues caused by incorrect parts (as in modern semiconductors replacements)
Quad 405-2 Overheating on right channel.
It is worth reading as it highlights subtle issues caused by incorrect parts (as in modern semiconductors replacements)
Hi Mooly, interesting stuff there... I had been ingnoring 405-2 thread because they did not match the model I have currently have so thanks for pointing that out.
After three comments counting yours, I think I will leave the original transistors in place even though they do not quite match on each side. They are not blown so I won't replace I think.
Thank you for pointing this thread out.
After three comments counting yours, I think I will leave the original transistors in place even though they do not quite match on each side. They are not blown so I won't replace I think.
Thank you for pointing this thread out.
I don't know what all this stuff about opamp pinouts was about. All opamps have the same basic pinout, and the 405 doesn't use any special pins. Specificially OPA604 and OPA134 willl both work in a 405.