Cyrus 1 refurb information and questions

[atriptothemoon]

Evening all,

After 30 years + of use, a mains inlet failure has finally promted me to refurb my beloved mission cyrus one. With the help of this fabulous forum and others I have gathered the following info :

Schematics : attached

Video : YouTube (a cyrus two but still relevent I hope)

The most used and recommended replacement caps appear to be Nichicon ES non-polar (the green ones)

The caps I plan to replace (left channel/right channel), their values and Nichicon ES replacements are :

C41/C42 - 6.3V 470uF - UES0J471MPM
C33/C34 - 50V 2.2uF - UES1H2R2MDM
C39/C40 - 25V 22uF - UES1E220MEM
C49/C50 - 25V 22uF - UES1E220MEM

I note that the values of C33/C34, C49/C59 on my board differ from the attached schematic

The mains inlet is a Bulgin PF0011/15/63

While I am at it, I am replacing some dodgy phono input sockets with a gold plated variely (Lumberg 1552 02 V BLACK). Not a perfect fit but a little work should sort that out.

My questions are :

1. Is my amp with its different capacitor values to the attached schematic just a varient ?

2. There are a number of other capacitors on the power stages. Is it worth replacing these as well ?

3. I have read that the two power supply capacitors - 50V 6800uF - are of the slit foil type and are usually ok. I will test. But, if I decide to replace, What would you recommend ?
I can find plenty of 50V 6800uF - but not slit foil type.

I have found these slit foil type:

ST2-010: 10000uF 80V Supertech 2T Slit Foil Capacitor | Hifi Collective

but they are 80v 10000uF - would they be better or worse than the original spec ?



Thanks for your time reading this and for any suggestions.

I hope this thread will help others with relatively little expertise to refurb their cyrus one

krgds

Atttm

 

[jaycee]

Get the full service manual from here:
Cyrus 1 - Stereo Integrated Amplifier - HiFi Engine

There were 3 revisions of the amp. You'll probably find the big caps are fine, but there is a
little red circular capacitor marked "ROE" which is notorious for going bad. Make sure you definitely replace those ones.

 

[atriptothemoon]

Thanks for the info Jaycee - and I've jsut noticed that by one of the big capacitors the board is marked "Cyrus by Henry Azima issue 03" .
The red capacitors marked "ROE" on my board are C41/C42 - 6V 470uF - replaceing them with UES0J471MPM .
Cheers

 

[AndrewT]

Looks like C31, C43 & C57 are all Bi-Polar.
The other electrolytics are shown as polar.

 

[traderbam]

Hi. If you are going to replace any, you might as well replace all electrolytic caps, polarized and non-polarized alike. Note that you can use non-polarized in place of polarized if that saves you money. But don't replace any non-polarized with polarized. 🙂

 

[atriptothemoon]

thanks AndrewT and traderbam - yes I see what you mean, guess I was jsut wondering which caps were most critical. So yes it makes sence to change everything else while I'm at it. Should I go with NP all round or is polarity critical to the circuit design ?

 

[AndrewT]

Bi-Polar are generally larger and more expensive than the same value of Polar.
Bi-Polar are not available in high values.

That size/availability may force you to using Polar where Polar are already specified.

 

[atriptothemoon]

Cheers AT - I get it - any thoughts on suitable replacement for the two 50V 6800uF's ?

 

[Konzentr8]

While you are replacing the phono sockets have a close look for hairline cracks in the board under them, as repeated pressure from plugging interconnects in and out from
above tends to put more stress on it than a more conventional design .
Took ages to trace this as the reason i kept losing a channel on my mk 1 .

 

[atriptothemoon]

thanks Konzentr - have it on my bench at the moment and have jsut checked - all seems fine /// phew - cheers for the heads up. Thankfully the amp was in place for about 20 years in its first home 🙂

 

[ej25awd]

Bi-polar capacitors are different from non-polar capacitors. Just sayin'

 

[atriptothemoon]

Bi-polar capacitors are different from non-polar capacitors. Just sayin'

Thanks EJ25, whats the difference? and what nomenclature should I be using ?

 

[ej25awd]

Below is an excerpt of Nichicon's electrolytic capacitor guide

"( 4 ) Aluminum electrolytic capacitors are polarized.
Make sure that no reverse voltage or AC voltage is
applied to the capacitors. Please use bi-polar
capacitors for a circuit that can possibly see reversed
polarity.
Note: Even bi-polar capacitors can not be used for
AC voltage application."

Panasonic has exactly the same guideline.

Non-polar electrolytic are usually found in cheaper speaker crossover networks and in the days of CRT displays used them for AC coupling the horizontal deflection coils. Non-polar electrolytics usually have "NP" printed on their sleeve as opposed to "BP".

Non-polar electrolytic are much bigger than bi-polar electrolytic for the same capacitance and voltage rating. This might not be true anymore.

 

[atriptothemoon]

thanks ej25 🙂 - that has prompted a good 4 hour charge.. into reading about capacitors. I'd never heard of Leyden jars, 1745! amazing. And I see the distinction you make.
The voltage rating marked on the side of a capacitor - does that always refer to DC?
Anyone have thoughts on replacements for my (slit foil) 50V 6800uF resevoir/smoothing capacitors ?

 

[AndrewT]

Measure your PSU voltage and the mains voltage at the same time.
You can then estimate the maximum voltage your PSU will output.
If that worst case maximum is (well ?) below 40Vdc, then you can use 40V 6800uF slit foil.

 

[atriptothemoon]

sorry AndrewT I think we may be at cross purposes - what is there originally are two ELNA 50V 6800uF black caps that I read somewhere wer of the slit foil type, I cant find a liek for like replacement online. Bur I found these: ST2-010: 10000uF 80V Supertech 2T Slit Foil Capacitor | Hifi Collective and was wondering if they might be ok. I have since read that it may not be a good thing to go messing around with these cap values .. open to opinions - but now thinking i should just go for a good quality (whatever that means) 50V 6800uF -again open to opinions.
cheers
Rob

 

[jaycee]

I think the originals are DNM Slit Foil manufactured by BHC. I would agree with just going for good quality 50V 6800uF capacitors though, as capacitor manufacturing technology has come a long way in 20 years

 

[traderbam]

Your choices will be narrowed by the physical dimensions and termination type of the originals. I suspect they are snap-in or screw terminals. Making sure the replacements fit nicely is important.
50V and any values between 6800 and 10000 will be fine. Vishay, Nichicon have plenty of choices in this range. If you still have several perfect fits to choose from buy an above average priced one.

 

[02GF74]

I've never heard of slit foil capacitor must Google that.

From what I have read about denon amp upgrade is the power supply capacitor value can be I creased to the next value up obviously the same or slightly higher voltage as long as there is space.

 

[Mark Whitney]

BHC is now owned by KEMET. Look for ALC10S (S = Split foil) for the closest replacement.