electrolytic cap for gibson ga5t amp. - diyAudio
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Old 31st January 2011, 06:48 PM   #1
muscmp is offline muscmp  United States
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Default electrolytic cap for gibson ga5t amp.

i need to replace a sprague electrolytic capacitor from my gibson ga5t amplifier. it is a 3x20mfd-300vdc cap. size is 2 1/4 by 1 inch.

i've tried mouser and tubesandmore already. tubesandmore may have the part in april.
thanks in advance.
mikeB.
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Old 31st January 2011, 07:44 PM   #2
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Multi section caps were very popular in that vintage equipment. If you want, you could substitute 3 20mfd caps for the time being and get it running. You might try a place called Nebraska Surpluss
Surplus Sales of Nebraska
The have a ton of stuff. Amazing, and pretty good web site.
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Old 31st January 2011, 08:09 PM   #3
muscmp is offline muscmp  United States
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firechief:
thanks, i'll try them. someone else mentioned putting (3) 20mfd in its place but didn't know whether it would be in series or in parallel. also, they mentioned that it may need a resistor also.
i really didn't think it would be this difficult. i know the amp is old but i figured that the part would still be fairly readily available. i guess not!
thanks again,
mikeB.
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Old 1st February 2011, 01:31 AM   #4
Enzo is online now Enzo  United States
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Can caps like that were common, but that was 50 years ago, come on.

Your old cap was three 20uf caps in one container. The can itself was the negative lead, and the three caps positive leads were the solder terminals on the end of the can.

You can easily replace the thing with three 20uf caps. The negative leads will all go to the ground where the can was grounded. The positive leads will go to wherever the wires soldered to the can go.

SOmetimes it is easier to solder the new cap right to some point in the circuit, rather than run a long wire. But sometimes I mount a terminal strip under a screw and use that to mount the caps and solder the original wires to the terminals.

ANy resistors it might need are already there. For example if there is a resistor between two of the terminals on the can, you will still need it with the separate caps. They were originally separate caps, they just all lived in the same can. SOmetimes it is easier to install a new resistor instead of trying to extricate the old one and re-using it.
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Old 1st February 2011, 01:46 AM   #5
muscmp is offline muscmp  United States
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Quote:
Originally Posted by Enzo View Post
Can caps like that were common, but that was 50 years ago, come on.

Your old cap was three 20uf caps in one container. The can itself was the negative lead, and the three caps positive leads were the solder terminals on the end of the can.

You can easily replace the thing with three 20uf caps. The negative leads will all go to the ground where the can was grounded. The positive leads will go to wherever the wires soldered to the can go.

SOmetimes it is easier to solder the new cap right to some point in the circuit, rather than run a long wire. But sometimes I mount a terminal strip under a screw and use that to mount the caps and solder the original wires to the terminals.

ANy resistors it might need are already there. For example if there is a resistor between two of the terminals on the can, you will still need it with the separate caps. They were originally separate caps, they just all lived in the same can. SOmetimes it is easier to install a new resistor instead of trying to extricate the old one and re-using it.
enzo:
thanks, really appreciate it.
yes, i was wondering how i was going to get three caps in place of one when the distance of wiring was so great to the far pin tube. that will really help me.
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Old 9th February 2011, 06:42 PM   #6
muscmp is offline muscmp  United States
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Default update but need more info on gibson ga5t

after replacing the electrolytic multi-cap with three separate new electrolytics, the gibson ga5t is quieter but still has the "spikey" sound that i was trying to eliminate. it appears to be coming from the tremolo circuitry. when i strike the guitar strings rather hard it emits a "spikey" sound through the speaker as if too much currency is flowing through.

here is the schematic for it. i believe i either need to change the .047 cap or the three small ones attached to the tremolo frequency pot (or all four).

any suggestions?
thanks,
mikeB.
Attached Images
File Type: jpg GA-5T.jpg (160.3 KB, 23 views)
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Old 9th February 2011, 11:33 PM   #7
Enzo is online now Enzo  United States
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The three filters eliminate hum and decouple the preamp, they are not the suspects for spikey. The caps in the trem circuit determine how fast the trem goes, and are not suspects in spikey.

Spikey is a frequency response thing. Try playing the amp through different speakers just to see. Well, to hear, really.

See that 250uuf cap between V1 and V2, top center? Try increasing that to 0.001uf or something. Just tack a larger cap in parallel with the 250 if convenient.

250uuf is an old way of writing 250pf. uuf meant mirco-microfarad, which means picofarad.
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Old 10th February 2011, 12:57 AM   #8
muscmp is offline muscmp  United States
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Quote:
Originally Posted by Enzo View Post
The three filters eliminate hum and decouple the preamp, they are not the suspects for spikey. The caps in the trem circuit determine how fast the trem goes, and are not suspects in spikey.

Spikey is a frequency response thing. Try playing the amp through different speakers just to see. Well, to hear, really.

See that 250uuf cap between V1 and V2, top center? Try increasing that to 0.001uf or something. Just tack a larger cap in parallel with the 250 if convenient.

250uuf is an old way of writing 250pf. uuf meant mirco-microfarad, which means picofarad.
enzo: yes, i not only swapped out the 6eu7 tubes but i ran it through a different speaker and it did the same thing.

sounds like it may be worthwhile to change out all of the caps. or, is this one of those, if it ain't broken, don't fix it?

just out of curiosity, where do you get your parts? i got the new caps at mouser for a decent price but they charge an outrageous amount for shipping the little buggers.
thanks,
mikeB.
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Old 11th February 2011, 12:46 AM   #9
Enzo is online now Enzo  United States
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Try just increasing that one cap I mentioned.



I use Mouser all the time. Others responded to this in your thread about it.

The problem is a couple things. As they mention, there is a added charge of like $5 at UPS for delivery to a home. I receive deliveries here at my business. I save $5 right there.

ANother thing is the order size. A minimal UPS charge is going to be something like $6-7. UPS charges that for three transistors or a hundred of them. I never place an order for a tiny handful of parts, I fill out a order sheet here before placing it. I may pay $8 shipping, but it will be spread over $100 of parts, not $1 of parts.

Mouser doesn't add onto the UPS charge, you pay what they are charged to ship.

For small orders, the US mail is a lot cheaper - USPS.

I also use Allied and Digikey, but don;t expect their UPS to be much different.


And when you go into a "UPS Store" to ship something, it costs more to use the other brands. At those stores, the UPS shipping itself should not be marked up. If you go there with FedEx it will get marked up.
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