Need to reform caps - help buying variac

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sreiter
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Need to reform caps - help buying variac

Post by sreiter »

My Original 18w has been in storage for 7 years and I'm afraid to just plug it in. MOST of the caps are original. I've seen chinese variac's for sale on amazon, not crazy about that option. I've also seen various online posts about using them, but they all seem like a lower amperage. Theres a site that has usa made variacs (prob vintage) but its putting out 10 amps. I dont know if that make a difference or not.

Anyone with experience/knowledge who can steer my purchase I'd be most grateful to.

thanks in advance, steve
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Re: Need to reform caps - help buying variac

Post by JMPGuitars »

Hey Steve,

I'm not sure what your concern is, but keep in mind in the US the mains fuse should be 2A slow blow, so anything above that for a variac should be fine. You could also build a dim bulb tester. In either case, I'm curious why you're worried about it. If the filter caps are past their prime, then the amp will be noisy. It shouldn't explode. YMMV ;)

Thanks,
Josh
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Re: Need to reform caps - help buying variac

Post by geoff 1965 »

8EB57CA1-3A3A-4074-9875-2A21F97D6370.jpeg
I used this 8 amp variac for my power supply/limiter and it will run all day powering guitar amps,you can have problems with power on surge popping/tripping fuses with the big variacs but if you fit a thermistor it acts as a soft start and cures that problem.
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Re: Need to reform caps - help buying variac

Post by Daviedawg »

While I understand your concerns, I agree with Josh a bulb limiter will provide the protection you need for start up to see how it is responding.

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Re: Need to reform caps - help buying variac

Post by geoff 1965 »

You could build a unit with switchable direct fused/bulb limiter supply,use the limiter for initial power on to check for leakage etc then switch to direct fused supply for full voltage “depending on what size bulb you use you get a voltage drop through the bulb limiter,mine has a 150W bulb and drops around 10 volts”
If you just want a variable power supply get one with a voltage/current meter then you can watch the current when bringing the voltage up.
8C7F6359-9447-4BFA-98C0-198ED2CD2B34.jpeg
Hope this helps
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Re: Need to reform caps - help buying variac

Post by sreiter »

geoff 1965 wrote:
Wed 10/27/21 8:49 pm
8EB57CA1-3A3A-4074-9875-2A21F97D6370.jpeg
I used this 8 amp variac for my power supply/limiter and it will run all day powering guitar amps,you can have problems with power on surge popping/tripping fuses with the big variacs but if you fit a thermistor it acts as a soft start and cures that problem.
can you give me more info or a link to installing a thermistor please?

Using a higher amperage variac is what my concern is

thanks
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Re: Need to reform caps - help buying variac

Post by sreiter »

JMPGuitars wrote:
Wed 10/27/21 7:23 pm
Hey Steve,

I'm not sure what your concern is, but keep in mind in the US the mains fuse should be 2A slow blow, so anything above that for a variac should be fine. You could also build a dim bulb tester. In either case, I'm curious why you're worried about it. If the filter caps are past their prime, then the amp will be noisy. It shouldn't explode. YMMV ;)

Thanks,
Josh
My '67 18w is from the UK running on 220v - i use a step up /down transformer to run it.

what do you mean by the amp will be "noisy"? Its always been noisy. i figured that was 60 cycle hum.
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Re: Need to reform caps - help buying variac

Post by JMPGuitars »

sreiter wrote:
Thu 10/28/21 9:49 am
JMPGuitars wrote:
Wed 10/27/21 7:23 pm
Hey Steve,

I'm not sure what your concern is, but keep in mind in the US the mains fuse should be 2A slow blow, so anything above that for a variac should be fine. You could also build a dim bulb tester. In either case, I'm curious why you're worried about it. If the filter caps are past their prime, then the amp will be noisy. It shouldn't explode. YMMV ;)

Thanks,
Josh
My '67 18w is from the UK running on 220v - i use a step up /down transformer to run it.

what do you mean by the amp will be "noisy"? Its always been noisy. i figured that was 60 cycle hum.
The amp shouldn't be so noisy if all is well. I guess you could say it will be "noisier" if the caps aren't doing their job.

Have you checked the transformer for a US voltage tap inside the amp? Most of the popular iron has options for 110ish or 220ish.

Thanks,
Josh
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Re: Need to reform caps - help buying variac

Post by sreiter »

geoff 1965 wrote:
Thu 10/28/21 8:01 am
You could build a unit with switchable direct fused/bulb limiter supply,use the limiter for initial power on to check for leakage etc then switch to direct fused supply for full voltage “depending on what size bulb you use you get a voltage drop through the bulb limiter,mine has a 150W bulb and drops around 10 volts”
If you just want a variable power supply get one with a voltage/current meter then you can watch the current when bringing the voltage up.
8C7F6359-9447-4BFA-98C0-198ED2CD2B34.jpeg
Hope this helps
pretty neat looking device you built. Only saw bulb limiters that were very rudimentary

Are you using variable power supply and variable transformer interchangeably?

Curious why you're using voltage and current as the same thing (its been 40 years since I studied analog electronics). Isnt the standard current 15ohms coming out of the wall of a 110v socket?

Or are you saying the variable power supply will show ohms ala ohms law I = V/R ... (knowing resistance of the power supply i guess would be a must) .. ugh, sorry for all the questions ... I'm not a amp builder per se, i just (a) moved to a new place and dont trust anyone to not steal parts and (b) I called a place with the best rep in nashville and they just want to recap the whole thing. dont even care i want to keep it as original as i can/the fact the value of the amp would decrease.

Lastly, single phase or 3 phase?



anyway, i was planning on using a kill a watt between the amp and step up/down transformer

Image

https://www.amazon.com/dp/B00009MDBU/?c ... _lig_dp_it
Last edited by sreiter on Thu 10/28/21 11:36 am, edited 2 times in total.
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Re: Need to reform caps - help buying variac

Post by sreiter »

JMPGuitars wrote:
Thu 10/28/21 9:54 am
sreiter wrote:
Thu 10/28/21 9:49 am
JMPGuitars wrote:
Wed 10/27/21 7:23 pm
Hey Steve,

I'm not sure what your concern is, but keep in mind in the US the mains fuse should be 2A slow blow, so anything above that for a variac should be fine. You could also build a dim bulb tester. In either case, I'm curious why you're worried about it. If the filter caps are past their prime, then the amp will be noisy. It shouldn't explode. YMMV ;)

Thanks,
Josh
My '67 18w is from the UK running on 220v - i use a step up /down transformer to run it.

what do you mean by the amp will be "noisy"? Its always been noisy. i figured that was 60 cycle hum.
The amp shouldn't be so noisy if all is well. I guess you could say it will be "noisier" if the caps aren't doing their job.

Have you checked the transformer for a US voltage tap inside the amp? Most of the popular iron has options for 110ish or 220ish.

Thanks,
Josh
Hi Josh, thanks for the replies. I didnt ever check..i'm aware there maybe / trannys have lugs / taps, but i ddnt want to F with it.

can you describe what you mean by noisy? still not sure what you mean. I mean, my amp is way noisier than my blues jr for example, but again, i'd expect it to be for a 50+ y/o amp.

not sure what you consider filter cap noisy vs regular noisy

thanks in advance
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Re: Need to reform caps - help buying variac

Post by geoff 1965 »

https://youtu.be/-HDpkn8JT_0
easy to install in series before your fuse on the live"hot" lead,you want a NTC type at around 20-25 amp rating.
the voltage/current meter lets you monitor the current draw of the test amp/appliance.
no its one variac switched to pass through the bulb limiter or a direct "fused" lead to the output socket i also bridge rectified/filtered the ac out to DC volts.
E93E63DD-68A9-40BF-A1D1-FFE3489D4A65.jpeg
Don’t be concerned with the higher amp rating,I would choose the USA built 10 amper over those cheap Chinese ones!
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Re: Need to reform caps - help buying variac

Post by geoff 1965 »

“1967 18W” are you going to treat us with some pics of this amp on a separate post?
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Re: Need to reform caps - help buying variac

Post by sreiter »

geoff 1965 wrote:
Thu 10/28/21 11:02 am
https://youtu.be/-HDpkn8JT_0
easy to install in series before your fuse on the live"hot" lead,you want a NTC type at around 20-25 amp rating.
the voltage/current meter lets you monitor the current draw of the test amp/appliance.
no its one variac switched to pass through the bulb limiter or a direct "fused" lead to the output socket i also bridge rectified/filtered the ac out to DC volts.
E93E63DD-68A9-40BF-A1D1-FFE3489D4A65.jpeg
Don’t be concerned with the higher amp rating,I would choose the USA built 10 amper over those cheap Chinese ones!
thanks - appreciate your replies
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Re: Need to reform caps - help buying variac

Post by sreiter »

geoff 1965 wrote:
Thu 10/28/21 12:15 pm
“1967 18W” are you going to treat us with some pics of this amp on a separate post?
I had a gallery of not only mine, but several of my friends, which included a original reverb model (banker has one, i believe). Site was reloaded several times and my gallery no longer exists.

A little later i'll post ALL the pics I have. i'll post the link here or a pm
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Re: Need to reform caps - help buying variac

Post by sreiter »

geoff 1965 wrote:
Thu 10/28/21 12:15 pm
“1967 18W” are you going to treat us with some pics of this amp on a separate post?
7 albums

galleries/index.php?cat=13045
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