Amp capacitor replacement

[Twincam]

Decided to re cap my amp myself as they need doing even though the amp works well, some are slightly bulging etc. I can't afford the prices I've been quoted at all.
I have had a look at the caps (safely learned to drain them etc etc) and written down there values and what I want to replace them with. Can someone check my list and make sure im not doing something wrong. I wanted to replace close for like to like.

40 40uf 450v replacement 50 50uf 500v

2x 10uf 400v replacement 2x 10uf 500v

8uf 250v replacement 8uf 450v

Now one is a 64uf 65v and I can't find something close what I can find is a 50uf 50v will this be ok?. Or should I chain a couple together to make a similar value as original?.

[morgano]

Yes, those seem OK apart from the 65V alternative. It isn't safe to go for a lower voltage rating than the original. A higher voltage rating is generally OK, but the capacitors may be bigger and might not fit - it is worth checking the dimensions.

On that note, if these are PCB mounting (radial type) check the lead spacing, as this can vary, and ideally you want to match the spacing of the existing components.

[3below]

You need at least 65V. Higher voltage ratings are OK. Morgano has covered all the bases 68uF or two 33Uf in parallel seems the way to go.

Edited August 10, 2015 by 3below

[rmorris]

[quote name='morgano' timestamp='1439243005' post='2841308']
Yes, those seem OK apart from the 65V alternative. It isn't safe to go for a lower voltage rating than the original. A higher voltage rating is generally OK, but the capacitors may be bigger and might not fit - it is worth checking the dimensions.

On that note, if these are PCB mounting (radial type) check the lead spacing, as this can vary, and ideally you want to match the spacing of the existing components.
[/quote]

+1

The 50uF in place of 40uF might place a higher strain on the psu/transformer depending on the specifics of the power supply but given that most electrolytics start off @ +/- 20% and decrease the capacitance value over time there's not really much to worry about.

As others have stated you shouidn't really replace a 65Vdc cap with a 50Vdc cap. It'll almost certainly work at first but, all other things being equal, it's useful lifetime will be curatailed.. 68uF is a standard value so something like 68uF / 100V would be good.
Capacitor ratings can be confusing but if possible I'd say go for 105 deg C rated caps cf the cheaper 85 deg C versions. Gives longer useful life.
In general a low ESR figure is advantageous and usually equates with an increased ripple current spec'.

[3below]

[quote name='rmorris' timestamp='1439244313' post='2841319']
Capacitor ratings can be confusing but if possible I'd say go for 105 deg C rated caps cf the cheaper 85 deg C versions. Gives longer useful life.
[/quote]

+1 particularly if these are being used with higher powered valve amp with associated heat issues.

[Twincam]

Ok great thanks for the advice. I shall look for another or use two caps to make up the value/voltage.

I also removed the so called death cap.

On another note are old valves worth anything? Even a few quid or should they be retained for future test purpose or binned?

[Phil Starr]

The good news is that capacitors have got smaller so higher rating capacitors still fit, in fact they may b a lot smaller so you'll need to plan for how to physically support them. Always go for higher voltage and look to match the capacitance reasonably closely unless you really know what you are doing and understand exactly what function the cap is performing in the circuit. However as has been said 20% tolerance isn't unusual. The values now usually follow standard E12 or E24 values designed for resistors http://www.logwell.com/tech/components/resistor_values.html. You shouldn't have trouble finding a 39uF for the 40uF.

[rmorris]

[quote name='Twincam' timestamp='1439249317' post='2841351']
Ok great thanks for the advice. I shall look for another or use two caps to make up the value/voltage.

I also removed the so called death cap.

On another note are old valves worth anything? Even a few quid or should they be retained for future test purpose or binned?
[/quote]

[rmorris]

[quote name='Twincam' timestamp='1439249317' post='2841351']
Ok great thanks for the advice. I shall look for another or use two caps to make up the value/voltage.

I also removed the so called death cap.

On another note are old valves worth anything? Even a few quid or should they be retained for future test purpose or binned?


[/quote]

I guess the death cap is a cap across the mains live and neutral which can develop a leakage current over time and pose a hazard ?
What is the amp in question ?

[3below]

[quote name='Twincam' timestamp='1439249317' post='2841351']

On another note are old valves worth anything? Even a few quid or should they be retained for future test purpose or binned?
[/quote]

Oh yes if they are functional. Mullard EL34s seem to fetch good money, ditto Mullard pre amp valves. USA 6L6 GE also seem to fetch money. A quick look at the well known internet auction site is informative.

[Twincam]

[quote name='3below' timestamp='1439330116' post='2842028']


Oh yes if they are functional. Mullard EL34s seem to fetch good money, ditto Mullard pre amp valves. USA 6L6 GE also seem to fetch money. A quick look at the well known internet auction site is informative.
[/quote]

Had a look couldn't find mine, there Philips ( mullards) gt Britain however mine matched up to non online lettering print wise.

[Slipperydick]

You should be able to get 68uf 100V caps easy enough. Likewise 47uf 450V or 400V. increasing the value or the rated voltage a bit wont do any harm, but dont use lower voltage ones.

Try to get 105 degrees ones if you can, heat kills electrolytics before their time.

[3below]

[quote name='Twincam' timestamp='1439338628' post='2842077']
Had a look couldn't find mine, there Philips ( mullards) gt Britain however mine matched up to non online lettering print wise.
[/quote]

What valves are they? You mentioned death cap so I surmise this is an early(ish) Fender amp.

[Twincam]

[quote name='3below' timestamp='1439414798' post='2842758']


What valves are they? You mentioned death cap so I surmise this is an early(ish) Fender amp.
[/quote]

A little 1972 traynor bassmate. All original parts. Works great but I know it won't for long. 2x 12ax7a 2x 6bq5's.