capacitor upgrade question

ICBM

jaskah said:

thanks for your input. i'll definitely keep this in mind if i have any more work done on the amp. but for now, i'm mainly interested in just reducing the background noise a bit through this theoretical cap swap.

It would be better to identify the cause of the problem first. Swapping the cap is pointless if the actual reason is a poor grounding arrangement.

I would temporarily attach a larger value cap first, without soldering it - if the hum doesn't change, you know for sure that it's not the cap. If it does, then you know you need to increase the cap value, or you could try a different brand cap if you're still unsure.

jaskah

thanks again for your replies.

I would temporarily attach a larger value cap first, without soldering it - if the hum doesn't change, you know for sure that it's not the cap. If it does, then you know you need to increase the cap value, or you could try a different brand cap if you're still unsure.

i've actually already brought the amp to a local, well-respected amp tech here where i live. he couldn't find any issues with grounding, etc.

I would temporarily attach a larger value cap first, without soldering it - if the hum doesn't change, you know for sure that it's not the cap. If it does, then you know you need to increase the cap value, or you could try a different brand cap if you're still unsure.

the person who suggested the caps switch actually did up the values of the 10/500 cap to 15/500 and the 10/350 cap to 15/350. he also used f&t caps instead of the stock ic caps. he seemed to think this helped with the hum.

ICBM

jaskah said:

the person who suggested the caps switch actually did up the values of the 10/500 cap to 15/500 and the 10/350 cap to 15/350. he also used f&t caps instead of the stock ic caps. he seemed to think this helped with the hum.

It will be the value increase that matters, not the brand.

jaskah

It will be the value increase that matters, not the brand.

ok, thanks for this clarification. i guess he just happened to have f&t caps available and did the switch with these.

ecc83

Just noticed that the heater arangements are the basic and primitive 'radio' style.

This means that first stage WILL be hummy and it will get worse as VC is advanced.

Look up "humdinger mod"

Dave.

jaskah

Look up "humdinger mod"

Dave.

thanks, i'll look into this. but i imagine this would be getting in over my head, as i've never modified an amp before.

 it will get worse as VC is advanced.

what does VC refer to here? sorry, newbie alert...

ecc83

Sorry, me lazy sod. Volume Control. The mod could be simple to do or quite tricky depending on the build regime. Essentially you lift the earth from chassis on the pre valve's heater pin and fit a 100 Ohm pot across the heater supply with centre 'wiper' to earth. Trim for minumum hum . Decent amps use a centre tapped heater supply (aka 'balanced') Even better, DC. No hum at all.

Dave.

ICBM

jaskah said:

Look up "humdinger mod"

thanks, i'll look into this. but i imagine this would be getting in over my head, as i've never modified an amp before.

http://www.valvewizard.co.uk/heater.html

It's a variation on using the filament winding centre tap to ground it, but with a pot which you can adjust for the minimum hum - although it's very often dead in the centre, so using the centre tap is actually easier and needs no extra components.

I do find it slightly odd that the transformer has been deliberately not used to the best advantage, given that it does have a centre tap - presumably to stick to the 'vintage correct' circuit.

jaskah said:

what does VC refer to hear? sorry, newbie alert...

Volume Control .

jaskah

can anyone recommend a uk or eu source for f&t caps? the place i usually order from https://www.hificollective.co.uk/ is out of stock right now.
thanks.

Keefy

I have bought F&T from www.hotroxuk.com

jaskah

I have bought F&T from www.hotroxuk.com

thanks, but they don't seem to have the values i'm looking for.

i need 22/500, 15/500

ecc83

https://cpc.farnell.com/vishay/mal204225109e3/cap-alu-elec-10uf-350v-axial/dp/CA08482?ost=10Uf+350v+CAPACITORS&pf=110029775,110177705&searchref=searchlookahead&krypto=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&ddkey=https:en-CPC/CPC_United_Kingdom/c/electronic-electrical-components/capacitors

Dave.

jaskah

great, thanks. will plow through these...

jaskah

thanks for this information about the humdinger mod.

for now, i'll just try changing the cap values and see if this gets the amp to a somewhat quieter place.

can anyone suggest a good uk or european source for f&t caps?

i usually order from https://www.hificollective.co.uk/ 

but they're sold out of the caps i need right now.

jaskah

thanks for this info about the humdinger mod. but i think for now, i'll just go with swapping the caps around.

by the way, can anyone recommend a good source for f&t caps in the uk or europe. i normally use https://www.hificollective.co.uk/ but they seem to be out of stock for what i need right now.

jaskah

thanks for this information about the humdinger mod.

for now, i'll just try changing the cap values and see if this gets the amp to a somewhat quieter place.

can anyone suggest a good uk or european source for f&t caps?

i usually order from https://www.hificollective.co.uk/ 

but they're sold out of the caps i need right now.

jaskah

thanks for this info about the humdinger mod. but i think for now, i'll just go with swapping the caps around.

by the way, can anyone recommend a good source for f&t caps in the uk or europe. i normally use https://www.hificollective.co.uk/ but they seem to be out of stock for what i need right now.

ICBM

You sound like you’re unfamiliar with chasing problems like this. You *really* need to identify the cause before you go spending money changing a lot of stuff you don’t need to and which may not fix it.

It could be the cap values, it could be the filament grounding arrangement, it could be both. It will not be the cap brand.

jaskah

thanks for your feedback.

yes, i am unfamiliar with chasing these problems. but i brought the amp to an amp tech and he couldn't find anything out of the usual. however, someone else with the same amp, changed the original caps to caps with slightly higher values (the 10/500 -> 15/500 and the 10/350 -> 15 350) and found that this subdued some of the amp's background noise.

the caps will be around $20. i think this isn't too costly an experiment. if this doesn't change anything i can look into other solutions.

just by posting this here i've already learned a lot more about the amp and the way it works than before. so, if nothing else, this has been a good learning process.

hywelg

jaskah said:

by the way, can anyone recommend a good source for f&t caps in the uk or europe. i normally use https://www.hificollective.co.uk/ but they seem to be out of stock for what i need right now.

https://www.thefretboard.co.uk/discussion/comment/2408519/#Comment_2408519