Pass Aleph 0s: How to disassemble & assemble it to replace power capacitors?

[KatieandDad]

cheapskate Papa

so , how then to replace them (wires) with some of well known audiophool quality ?



- no need for dismantling outputs assembly from heatsink ....... only in case that visual/tactile inspection reveal that thermal goo is dry/better to replace from whatever reason

The wires are so short that they probably won't be bettered by anything other than stout copper.

 

[Albert Hong]

Thank you, ticktock.

 

[Albert Hong]

Maintenance schedule
Year 2013: replacing all of electrolytic capacitors
Year 2018~2023: renew all of IRF244, optionally IRF610, IRF9620 mounted on heat sink (4 at top-view)

I think I don't need to replace input stage IRFD210. It's most sensitive to pair matching - risky.

Q1) how about renewal of bipolars - NPSA92, NPSA42: (guess, not necessarily)

Q2) In this forum, some people couldn't find IRF244 and discussed IRF240 as alternative.
But, by googling, IRF244 (IR, Harris, Intersil) inventory is available. But I'm not sure after 5~10 years later.
To select matched pair, how many numbers are recommended? 2x number or 3x number?
(Aleph 0s has 12 IRF244's. 2x = 24, 3x = 36)

 

[Zen Mod]

no need for changing active parts , if they're working

 

[Albert Hong]

Progress update; Capacitor kitting complete
Power caps: 31k uF --> 47uF
220uF 50V 105C --> Panasonic FR 220uF 50V 105C
4.7uF 100V 85C --> Rubycon YXJ 4.7uF 100V 105C

Physical dimension difference should be considered for Power Caps;
Original: Mallory W4C; H=105mm / D=63.5mm / Lead Spacing=28.6mm / Screw= No 10-32, 0.375 inch
Nowadays, most of caps follow metric size.
D=64~65mm / Lead Spacing=28.5mm / Screw = M5
- Diameter 64.x mm may be tolerable with original VL10 capacitor bracket (adjustable)
- Lead Spacing 28.6 vs 28.5 may be tolerable.
- Screw type 10-32 vs M5; To use M5 screw is highly recommended.

 

[Max Headroom]

Old World Resistors ?...

Hello Nelson, I notice 0.33 ohm phenolic (bakelite) casing resistors on the TO-3 output boards.
Are these carbon composition, do they drift in value with age in this application, what is their circuit function, and why did you specify these ?.

Dan.

 

[Albert Hong]

Hello Max,
I don't have Aleph0s schematic. Guessing from Aleph0 schematic, 0.33 of Aleph0s corresponds to 0.47 of Aleph 0. Aleph 0 output stage is attached.

 

[Zen Mod]

here it is - output cell of 0s

btw - nice example of SE bias

 

[Max Headroom]

Back To The Future Resistors....

ZM, thanks for that.... it confirms that they are emitter resistors.
Ok, so they look like they are carbon composition resistors to me.
My question to Nelson is, for what reason did he specify CC? resistors..is it for technical reasons, or for subjective reasons ?.
Also, what has been the reliability experience with these CC? resistors in this kind of application ?.

Thanks, Dan.

 

[Zen Mod]

resistor as resistor , as long it's dissipation capacity is enough for particular application

there are myriads of CC resistor still in use , after several decades

be sure that Pa use them as completely non-critical part and he probably bought them in drekload quantity , then .

 

[Albert Hong]

DC offset

Replacement of all of eleclytic caps = successfully done as procedure I described.
One more note: As Zen advised, to take sufficient picture at each step is very helpful.

After recap, I barely recognized the improvement of sound. It seems some aging is needed or the original state was still good.

I have two question;
Q1) DC offset
Right =64mV at power-on / 43mV after warm-up
Left = 43mV at power-on / 8mV after warm-up
Are they normal acceptable range?

Q2 Very small (barely detectable) hum
No hum at power-on
barely detectable (to attach ear to speaker unit) after warm-up
What's reason of hum only after warm-up?

 

[Zen Mod]

q1 - everything OK

q2 - let them settle for week or so ; however - do you hear , by any chance , any mech hum from xformer itself ?

 

[Albert Hong]

My assumption is that DC offset is related to hum.
Right, 43mV DC offset = almost undetectable hum
Left, 8mV DC offset = slightly detectable hum but, at power-on DC offset=43mV, no hum

Humble assumption based on observation

 

[Albert Hong]

At all of chassis closed, I can't hear xformer hum.
After opening bottom cover, I attached my ear to xformer within 10cm distance.
I can detect very-very small noise from xformer and different sound from speaker hum.
Then, what's next action?

 

[Zen Mod]

dunno ; maybe to upload somewhere these pics and let us see how assembling came ;

be sure all screws are tight and all solder joints are well done .

it can be everything - from loose wire somewhere , to dirty ground layout , to tired semiconductor

however , it is not related to DC offset in any way

on the other hand ........ I presume your listening sessions aren't with bass cone glued to your ear .......

so , just chill ....

 

[Albert Hong]

=
I presume your listening sessions aren't with bass cone glued to your ear .......
so , just chill ....
=

You are right. Just cautious inspections at this time but no problem in enjoying music from my Aleph 0s.

 

[Albert Hong]

Dear Zen,
I found the case of hum.
When all input (RCA, XLR) are open (not connected at all), no hum.
When RCA inputs are from pre-amp, very small hum as I wrote before.
When the same RCA output form the same pre-amp to another power-amp, no hum.
What should I do? To connect GND between Aleph and the pre-amp?

 

[Zen Mod]

do you have thermistor between audio gnd and case ( safety gnd) ?

ih earlier series it was 2R7 resistor , later replaced with CL60

 

[Albert Hong]

Two thermisters

When I opened the bottom panel, two thermisters are found.
#1. AC socket: Power-line - Fuse holder
#2. AC socket: Earth-line - somewhere

I think you meant #2 thermister.

 

[Zen Mod]

with ohmmeter - what's reading between case and neg spk output terminal ?