Soundcity replacement caps - where to buy ?

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Re: Soundcity replacement caps - where to buy ?

Postby Papa Dog on Thu Nov 06, 2014 4:36 pm

jaywalker wrote:Am I seeing 220 and 220K being used here in reference to the same resistors? Maybe just a typo.


nope...2k2 on pre-amp cathodes...220k plate and grid leak on pres as well. also 220 k attenuated input...

recommended power cathode resistors are: 22 ohm 5 watt right side (with power tubes facing away from you) and 68 ohm 5 watt (wirewound) on the left 3 (power tubes facing away from you).
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Re: Soundcity replacement caps - where to buy ?

Postby jaywalker on Fri Nov 07, 2014 3:02 pm

pdf64 wrote:
If I where to use the 470uF caps @ 450v What value would I change the parallel resistors to? The 220 ohms would now not be of much use

The 220k balancing resistors should be fine. There purpose is to ensure that the voltage is evenly divided between the two series caps, and their value should be somewhat smaller than the expected leakage current, which won't be linearly related to the cap value.
Pete

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Re: Soundcity replacement caps - where to buy ?

Postby Papa Dog on Fri Nov 07, 2014 4:26 pm

jaywalker wrote:
pdf64 wrote:
If I where to use the 470uF caps @ 450v What value would I change the parallel resistors to? The 220 ohms would now not be of much use

The 220k balancing resistors should be fine. There purpose is to ensure that the voltage is evenly divided between the two series caps, and their value should be somewhat smaller than the expected leakage current, which won't be linearly related to the cap value.
Pete

here

oh...ok then...the schematics on [url=soundcitysite.com]The Sound City site[/url]which I reveued all seem to show 220k resistors in the power supply.
I might have missed something, but I do not recall ever seeing one as 220R...they all seem to be consistently 220K.
AND i would think that metal film and not carbon comp would be the way to go, moving forward.
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Re: Soundcity replacement caps - where to buy ?

Postby jbmdisco on Sat Nov 15, 2014 10:47 pm

jaywalker wrote:Am I seeing 220 and 220K being used here in reference to the same resistors? Maybe just a typo.


Now, having submitted the above (220 + 220k) reference to resistors I read my post to keep myself right for the components I had removed. Today I fitted new caps, as in replaced the ones I hadn't already and then re-replaced the ones I had already changed - as I got a good deal on rubycons. I made a quick reference to my post, as above, and fitted 2 x 220 !!!!!! resistors, completed the job and switched on quickly followed by 2 flashes and 2 rather loud pops :roll: Yes I fitted 2 x 220 ohm as opposed to the 220K I removed :sleepy:
However, having done this only a few weeks ago also, having switched the amp on again the sound from it is first class and so far the restoration has been reasonably successful as well as educational. The simplicity, or apparent, of the valve amps is amazing compared to the SS amps I am used to poking about at. Having tried my best to keep the Sound City as original as possible I found the 2 10k trimmer pots to be u/s and replaced these with a slightly more modern equiv with plastic adjusters which are a bit more on the safe side than fiddling with a small screwdriver to adjust.

I have another little problem which I am sure will be simple to resolve. With Volume at max, treb,mid + bass also at max, when I adjust the presence I get a high frequency oscillation which I am hoping to confirm with your kind selves as a pre-amp valve 'singing' as the pots are all good, clean and smooth.

:not_worthy:
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Re: Soundcity replacement caps - where to buy ?

Postby Papa Dog on Sat Nov 15, 2014 11:38 pm

what you have there is an oscillation. Freq controlled by the caps in the circuit.
there is one cap on either side of the control pot. the one going to ground should be .022 mfd and the one from the plate to the pot is, I believe, 1000 pfd. if you changed out that 100k pot and did not wire it back correctly that is the usual result. Id either of the caps is leaky you can get an oscillation centred on the freq of the cap. I know that is not a technically correct description, but it is close enough for amateurs like me.
Make sure that the wiper on that pot goes to ground.
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