Physical capactor sizing 1

[tapiochre]

Hello,

I have acquired a vintage (1970s) transistor amp (Sinclair Project Stereo 60). Its a 50W stereo amp kit for general use.

Docs say it needs an output capacitor on the line out of each amp and the cap specified is 1000uf 63V "anything less may cause a reduction in bass".

The artwork shows a mighty large 1000uf cap (appx 100mm x 35mm, with axial leads). I'm a bit new to this but can I not just use a physically smaller 1000uf/63V capacitor, modern technology being able to scale size down over the last 30 years or so?

If its a ripple current thing, I have NO idea what ripple current is applicable on this unit.

Any help anyone?

Chris

 

[VEBill]

If there is a 'ripple' current going through the output capacitor (presumably in series with the speaker), then it would also be going through the speaker and causing a loud hum. So hopefully not...

If your question is about the current handling capabilities of the capacitors for the audio, then - yes, it is worth checking the specs for each capacitor.

I wonder why these necessary parts weren't included in the box in the first place?

 

[felixc]

Ripple current here is referred to the ripple current that the capacitor has to pass, as an AC coupling device. Do you have the specs or the part number of the original capacitor? It's almost sure that any modern capacitor will have similar if not better specs. The ESR (equivalent series resistance) is an issue here, and the ripple current capability is a direct consequence of the ESR. Try to pick up a high-quality grade of capacitor. The lowest ESR the best. For 50 watts into 8 ohms, P=RI2 so the current will be around 2.5 amps. The more current the cap can handle the less likely it is going to heat.

 

[tapiochre]

Thanks VE1BLL,

You are right - its in series with the speaker!

The big cap has no "markings" so I have little to go on when I'm looking at specs.

The parts were not included "since it is a bulky component and inclsing it in the Z50 [the amp] would substantially increase its size, In addition the output can be selecetd for the loudspeaker chosen and there are certain applications where an output cap is not required..."

Not a lot of help I guess!

Chris

 

[tapiochre]

Felix,

Thanks for the maths! That may help a lot, partic the 50W into 8ohms part. I'll have a look to see what caps I can get that are dinky, good quality and can handle that current rating.

Chris

 

[Comcokid]

Check to see if the cap or circuit board has a polarity marking. Some audio electrolytic capacitors are nonpolar (sometimes called bipolar). If so, you will want to replace it with another of the same type. (With a 1000uF/63V rating, it sounds a little large to be this type, but check anyway.)

The most available electrolytic types today are radial lead. You can replace your axial electrolytic with a radial electrolytic as long as you observe polarity, insulate the longer lead, and secure it mechanically. You can also use a capacitor with a higher voltage rating.

 

[tapiochre]

Thanks -

This is an electrolytic, most definitely, as polarity is marked on the cap in the diagram with axial leads...

 

[cbarn24050]

Hi, it's been a long long time since I saw 1 of those. I hope your not expecting too much in the way of quality out of it, the 50W rating is very optimistic as well. A standard cap will do although I would increase it to 2200uF. Cap physical sizes are about half what they were in the 70s.

 

[ScottyUK]

The larger the capacitance value, the lower the frequency at which the LF rolloff will begin. It is improbable that the cap needs to be as big as 10000uF unless you are driveing a particularly low impedance load and are trying to achieve the full 20Hz - 20kHz bandwidth as well. As a point of reference, the old Leak Delta 70 used a 2200uF coupling capactior on its output stage, and it had a pretty good performance for its day.

Higher ripple current ratings tend to come with two other factors: lower ESR and ESL, and larger physical size. If you can accomodate 2200uF or 4700uF in the same space, do so. Modern capacitors have a far better capacitance per unit volume, so it should not be a problem.

If you are looking for excellent quality capacitors, Evox-Rifa's PEH 169 and PEH 200 series are both very good industrial grade types which we use as standard fitment for equipment on severe service duty.



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If we learn from our mistakes,
I'm getting a great education!

 

[tapiochre]

Thanks to both cbarn24050 and ScottyUK...

I ceratinly have no great expecttaions on quality from this vintage amp - though when I used one through the 70's as a guitaer practice amp, it was the dog's nuts!

The cap (ScottyUK) was a 1000uf, not 10,000uf, so I'll be heading on a 1000-2200uf flavour based on current remarks.

Evox-Rifa ... is there a UK distributor/retailer for these? RS Components, Farnell?

Thanks all

Chris

 

[ScottyUK]

Chris,

RS Components P/N's & approx. can sizes for the PEH200 series screw terminal industrial capacitors:

4700uF 63V, RS189-765, 35mm dia x 51mm high
2200uF 100V, RS189-822, 35mm dia x 60mm high
4700uF 100V, RS189-838, 35mm dia x 95mm high

There is a datasheet available on the RS website.

My reference to a 10,000uF cap was just my opinion on the suggestion in your original post that this size was required for decent bass response. I think that a 10,000uF cap is excessively large for the output of a 50W amp, but it is not going to have a detrimental effect if it can be physically accomodated. It will just cost more and in all probability will not give any discernable benefit.

Hope this helps,



----------------------------------

If we learn from our mistakes,
I'm getting a great education!