Ceramic Caps?? replacements

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jeffriesa
Junior tube assistant
Posts: 1
(2/1/04 3:12 am)
 Ceramic Caps?? replacements
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 Hi

What should i replace the current ceramic caps in my SFTR with (.01, .1, .002 and .003) Sprague Orange?. As i see theat you cant get ceramic caps of this value! And in replacing them with non ceramic is there a tonal change.

Lastly i am re wiring the bias and changing all the caps, the amp i have has 2x 70/100 on the bias could i replace this with just one 47/100?

regards
AJ
 
GroundhogKen
Forum Moderator
Posts: 2238
(2/1/04 9:37 am)
 Re: Ceramic Caps?? replacements
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 Which Twin circuit is this--AA769, AA270, 100Watt, 135Watt UL?

Have you replaced all the electrolyic caps in the power supply and on the preamp tube cathodes ( pin 3 and 8 )? If not, I suggest you do that before you change any of the signal caps--unless they're defective.

Without seeing the circuit, I'm guessing that your 47uF 100v substitution will be fine.

I suggest getting the electrolytics changed first because old leaky electrolytic caps will make the amp sound bloated and honky. Swapping out the ceramics may alter the tone slightly--although not too many people are ceramic fans. Ceramic works fine for the tremolo oscillator by the way.

For cap values between .001uF and .1uF, most people use polyester caps like Mallory 150 or polypropylene like Sprague 715p orange drops. One problem with swapping a .1 ceramic with an orange drop is the the OD's are somewhat bulky.

For picofarad values most people use mica.

Welcome to the Hoffman board, by the way,
Ken
 
Tiny Daddy
I will work on all amps
Posts: 466
(2/1/04 10:02 am)
 Re: Ceramic Caps?? replacements
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 Ceramic caps are available in those values but are labeled 2200p and 3300p instead of .002uF and .003uF. Usually the creamic caps have not failed electrically. This is not a recommendation of ceramic caps; too many have said that metal film (polyester or polypropylene) and mica caps made a tonal improvement in their amp.
 
bluesbear
Hey get your own solder
Posts: 318
(2/1/04 10:09 am)
 Re: Ceramic Caps?? replacements
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 "What should i replace the current ceramic caps in my SFTR with (.01, .1, .002 and .003) Sprague Orange?"

There seems to be about a half and half split on which is best, Sprague Orange Drops and Mallory 150's. I can't say which is better, they both sound fine to me. I use Mallory's 'cause they're far smaller if you're squeezed for space but that doesn't seem to apply to your situation.
I go with Ken on the ceramics. I've never heard of anyone who likes them anywhere that affects tone. I use Siver Mica's everywhere. They're only $1 each.
Electrolytics = Sprague Atoms. Unless you absolutely can't find the one you need or must use a can cap (Super Champ, Princeton, etc), accept no substitute!
Lastly, be careful! Working on amps can be both dangerous and addictive!
Dave
 
pzung
Junior tube assistant
Posts: 4
(2/1/04 2:34 pm)
 cap substitution
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 are the two 70-100 caps in series or parallel or separated by a resitor to make two stages ? if they are in series then you end up with 35-200V , if parallel you have 140-100V , if they are separated with a resistor than they are two stages of 70-100V which takes out way more DC ripple but has a slight voltage drop from the resistor . check the voltage and make sure that the capacitor voltage value is much more .

i am new to this so i hope that is right .
 
jeffriesa
Junior tube assistant
Posts: 2
(2/1/04 5:59 pm)
 Ceramic Caps
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 Thanks for all the posts.

I am replacing most of the ceramics as some of the legs on them are just about to break and as i am re-doing the hole amp why not.

Replacing the current .01 and .003 with Sprague Orange drop 715 will be ok size wise. Replacing 4 of the .002 which are connected to the 4 diodes parallel will a issue!

The amp is a 135w UL and the 2 x70/100 are in parallel seperated by a resister.


 
GroundhogKen
Forum Moderator
Posts: 2238
(2/1/04 7:13 pm)
 Re: Ceramic Caps
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 The caps on the diodes are 1KV rated. They are only there for spike suppression in the power suply and have no effect on tone. Don't bother using big expensive orange drops there.

I would just replace the 800v 1A diodes with some 1N4007 diodes and skip the capacitors altogether--or keep the ceramics that are already there..

Doug Hoffman stocks 100uF/100v electrolytics to replace the 75uF and 80uF found in silverface bias supplies.

Ken
 
LooseChange
Senior tube assistant
Posts: 198
(2/1/04 10:48 pm)
 Re: Ceramic Caps
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 Just curious... What about those Brown Xicon caps Doug sells?
I use them in my amps all the time.
 
Tiny Daddy
I will work on all amps
Posts: 468
(2/1/04 11:12 pm)
 Re: Ceramic Caps
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 Xicon polypropylene capacitors: For size and performance they seem the best to me and I have been using them too.
 
GroundhogKen
Forum Moderator
Posts: 2238
(2/2/04 12:14 am)
 Re: Ceramic Caps
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 Yep, I think the larger ones are metallized polypropylene film and the smaller ones ( .001 and .0022) are polyprop film and foil.

Ken
 
 
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