Tweed amp hums louder than normal after replacing electrolytic caps and inputs

strato2009

Member
Messages
54
I had all the electrolytic caps replaced and also the four inputs replaced.
Checked the wiring, soldering job and measured the caps, seemed fine. caps were f&t for the 16uf's and sprague for the 25uf's

Here's a clip of the hum
altough might not seem very loud on youtube. It really is unusually loud, bassy hum which wasn't there when the amp had the original 50's electrolytic caps. It also seems like the amp has lost some output, it doesn't sound very loud at volume on "5"

it's a 5e9-a tweed.

Any suggestions on troubleshooting?

Thanks
 

Blue Strat

Member
Messages
30,183
Make sure soldering is solid and all caps are polarized correctly. Test with a guitar plugged into an input and guitar volume turned down.

If that fails, replace them one-by-one with the originals and test for hum for each cap replaced.
 

strato2009

Member
Messages
54
thanks, I double checked the polarity and with guitar plugged

will probably have to resolder, and if that fails, replace the caps maybe

anything else to check?
 

strato2009

Member
Messages
54
Thanks guys, I used switchcraft jacks, will have to check they're properly in contact with the chassis. Once solved will report back.
 

Steppin' Wolfe

Silver Supporting Member
Messages
5,058
You say you 'had' the caps replaced...as well as the 'four inputs'. Did you do the work or did you have the work done? Was there any reason why the four in puts were replaced? WE all want to see pics of the work areas. I would suspect the wiring scheme on the inputs. Was good general service done during this work? Voltage chart? Same tubes? When you pull tubes one by one starting at V1, when if ever does the hum stop?
 

doctorx

Member
Messages
4,472
Assuming the caps were installed correctly, chances are strong there's something screwy with the input jack installation.
 

TD_Madden

KotWF
Platinum Supporting Member
Messages
2,503
I'm sure that the jacks are probably bolted tight to the chassis (check again to make sure), but also look at each to see if the ground-tab touches the input when nothing is inserted into the jack....and that all grounding wires are properly connected as well. ;-)
 

strato2009

Member
Messages
54
Steppin wolfe, it was a simple soldering job so I did it myself with some previous experience.

they're the same tubes. I suppose it's safe to run the amp without without any single tube to do the test(including rectifier)? testing them is a good idea, just in case.
 

jay42

Member
Messages
7,027
fwiw, I would look at the input jacks' lead dress. I've only built one standard '4-holer' and I ended up using coax, with the 1M resistors on the jacks.

[edit] in the video clip, the two jacks don't look new to me. Please explain.
 
Last edited:

strato2009

Member
Messages
54
I doubt it could be caused because I used 25uf/50v caps instead of the stock value 25uf/25v?
Next I think I'll have to re-solder or take it to a pro perhaps
 

Steppin' Wolfe

Silver Supporting Member
Messages
5,058
strato, pull V1...does the hum cease? IF so, your problems are in that area. IF not, pull V3...the trem function...same story. If the hum persists, pull the PI...V2. IF the hum persists, pull the power tubes.
IF the hum persists with the power tubes out, you have a problem in the power supply. I never thought about it before because I don't bother with faking the look of cap covers, but I like to see caps. like to see orientation, I like to be able to see bulging of the ends if and when it happens.
Have you done a voltage chart?
I listened to the noise....V1 area, imho....maybe a tube problem??? Sometimes good, strong voltage reveals other problems. Fwiw, I never think that replacing caps is a simple solder job. I consider it an overhaul of sorts that demands full service and full evaulation afterward,...even if the amp 'sounds good'. I want to know voltages, biasing, etc.
 

Dan40

Silver Supporting Member
Messages
1,387
The higher voltage rating on the bypass caps will not cause any issues. Like the fellas mentioned, it's likely a bad solder joint or an input jack issue. Sometime a solder joint looks great but is still not electrically sound. Did you by chance move any of the wires out of place around the sockets? Wire dress can also play a roll in a noisy amp.
 

strato2009

Member
Messages
54
strato, pull V1...does the hum cease? IF so, your problems are in that area. IF not, pull V3...the trem function...same story. If the hum persists, pull the PI...V2. IF the hum persists, pull the power tubes.
IF the hum persists with the power tubes out, you have a problem in the power supply. I never thought about it before because I don't bother with faking the look of cap covers, but I like to see caps. like to see orientation, I like to be able to see bulging of the ends if and when it happens.
Have you done a voltage chart?
I listened to the noise....V1 area, imho....maybe a tube problem??? Sometimes good, strong voltage reveals other problems. Fwiw, I never think that replacing caps is a simple solder job. I consider it an overhaul of sorts that demands full service and full evaulation afterward,...even if the amp 'sounds good'. I want to know voltages, biasing, etc.
No I haven't charted the voltages, I will for now focus on the areas that were modified and the tubes(thanks for the tip). Gotta see further if it won't be solved.

 

Blue Strat

Member
Messages
30,183
As per my first post, any of your NEW caps could have an issue. Don't discount replacement them, one by one, with the originals before giving up.
 

Steppin' Wolfe

Silver Supporting Member
Messages
5,058
Filter caps tend to yield a hum that is independent of the volume control. Maybe a bypass cap???
I once did a recap on a BF Bassman that resulted in hum...it turned out that one new filter cap was bad, one new bypass cap was bad...and one OEM tone cap was bad.
 




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