Stephen1966 wrote: ↑Mon Aug 30, 2021 9:49 pm
Thanks, I have a variac. Current limiting lightbulbs as well if called for. Given an unknown time since their manufacture, is there any rule of thumb for the voltages and/or current dissipation we should be looking for with "new" caps? Having just finished building them into the amp's circuit I don't really want to start disassembling it. This power design will discharge itself when switched off though... Slow? Fast? I don't know, my other amp discharges through a snubbing resistor in about 30 seconds.
ok variac to 0, power and stby switches ON. attach multimeter with clamps to the first C in the bank..slow raise to +50VDC on first C with variac - and return to 0.. wait the caps to be discharged..after, start the new cycle, slow raise to +75V..wait to be discharged..slow raise to 150V..wait to be disch.. and so on.. after 10 times and reach 450VDC on cap. i think you will awake the electrolyte so you can start directly there would me minimum chance for explosion or smoke. if the cap is dry and not good in operation, you will heard t-r-t-r-t sound from the speaker and maybe also a smoke / you'll get some visual effects
Richard1001 wrote: ↑Tue Aug 31, 2021 2:36 pm
Why would someone want to form new electrolytic caps.
I guess It does not hurt them, but it is not necessary either.
I thought the same thing, this is only for old dryed out electrolytics if you MUST keep using them instead of doing the right thing and just replacing them.
New caps are fine with a power on so long as it's below their max operating value... I found that out the hard way ... on my tweedle dee build, I didn't realize I had about 515 VDC before the tubes conducted and my caps were 500 V rated... it took a few power ons before it blew, but it did
A good friend of mine and Vintage guitar amp dealer was good personal friends with Ken Fisher so I had an indirect pipeline to the man if we needed it and one of the questions we had for Ken was do you think it's a good idea to form new capacitor's? He said he thought it was gave his reason behind it, much of it I didn't understand at the time,but said he always brings up a new amp with fresh caps slowly and on a variac (as this was around 2000 or so)..Somewhere in my notes I have his procedure. I will see if I can dig those out from my old Maxtors and share it.
You never realize how much energy is in DC current until it hits you
Tony
" The psychics on my bench is the same as Dumble'"
talbany wrote: ↑Wed Sep 01, 2021 1:21 am
A good friend of mine and Vintage guitar amp dealer was good personal friends with Ken Fisher so I had an indirect pipeline to the man if we needed it and one of the questions we had for Ken was do you think it's a good idea to form new capacitor's? He said he thought it was gave his reason behind it, much of it I didn't understand at the time,but said he always brings up a new amp with fresh caps slowly and on a variac (as this was around 2000 or so)..Somewhere in my notes I have his procedure. I will see if I can dig those out from my old Maxtors and share it.
You never realize how much energy is in DC current until it hits you
Tony
I have always brought up any new amp (or newly capped amp) in 10V 30 min increments. I have no idea if it does anything good but it does extend the excitement of listening to a new amp
pompeiisneaks wrote: ↑Wed Sep 01, 2021 2:22 am
Interesting.
I've never heard negative issues with it... What is the impact theoretically to powering them on at full voltage?
"dry" cap can explode or go into open loop (i have seen reseistance of 47k-100k) so cap is without the function.. about "new" cap , nobody knows how many years el.cap spent on some shelf, 2-5 years maybe? so "new" is variable .
ESR with reforming is coming downto normal values and cap starz to behave normally. in use, electrolytic cap can last 10-20 years without problem. on the shelf? not so..is killing it slowly
often explosions occurs at transistor amps and high uF values.. per example from 12 electrolytic of 10.000 63V in parallel for some transistor amp (Aleph-Pass), directly powered /bought from mouser/ make 2 of them exploded immediately
talbany wrote: ↑Wed Sep 01, 2021 1:21 am
A good friend of mine and Vintage guitar amp dealer was good personal friends with Ken Fisher so I had an indirect pipeline to the man if we needed it and one of the questions we had for Ken was do you think it's a good idea to form new capacitor's? He said he thought it was gave his reason behind it, much of it I didn't understand at the time,but said he always brings up a new amp with fresh caps slowly and on a variac (as this was around 2000 or so)..Somewhere in my notes I have his procedure. I will see if I can dig those out from my old Maxtors and share it.
You never realize how much energy is in DC current until it hits you
Tony
I think given the unknown amount of time the electrolytics have been sitting on a shelf somewhere, it's a good idea for that reason if none other, too. As it isn't burned in your memory in letters of fire, I gather you don't use Ken Fisher's method either. But am I correct in assuming we form the caps with the tubes in (and so hooked up to a dummy load/speaker)? Given the interest in Fisher's work it would be great if you could find those notes and if you can, I will be the crash test dummy (it wouldn't be the first time ). As the power section is a bit of unknown quantity if I gradually increase the voltage it will give me a chance to measure the voltages at the nodes in a perhaps more controlled manner.
Here are a couple pictures of the amp to be going on with.
SAM_7699.JPG
SAM_7620.JPG
The interior shot was just before the final stage of build - adding the power transformer and so on. It's all ready now, just waiting for the first power up.
Stephen
You do not have the required permissions to view the files attached to this post.
Stephen1966 wrote: ↑Wed Sep 01, 2021 11:41 am
The interior shot was just before the final stage of build - adding the power transformer and so on. It's all ready now, just waiting for the first power up.
impressive! i can see all the options , reverb, dumbleator integrated!
allready i know what i will do with that amp, clean + reverb for one great sound, and OD + some delay in the loop for the other great sound! no need more reverb and fx loop would be relay switchable!
I have to disappoint you I think, the FX loop is entirely passive. We talked about adding a Dumbleator/active FX loop early on but in the end, and even with one good design out there (Normster's) the reverb consumes so much space there wasn't room for the extra tube. That and several builders had had problems of interference with their experiments. This passive loop (the schematic is earlier in the post) offers serial or parallel switching and a bypass if that's what you want with the effect's jacks left plugged in. Pull them out to get bypass automatically. A Dumbleator is one of my next projects and with a 24" head and cab all weighing about two metric tonnes I've given up the idea of carrying a pint in one hand and the amp in the other. One more piece of kit isn't a big issue and this will be small enough so that I CAN hold that pint. It's all very experimental so the passive loop might not end up being that impressive - I've put a 250K mixing pot in there for the parallel signal for a start which will attenuate the clean signal but leave the signal out to the effect unattenuated. So, for unity gain for instance, it comes down to whatever the pedal/effect can manage. It could end up being quite noisy compared to the gain stages and filtering of the Dumbleator.
Here's a picture of the loop. I will offer a barrel of Brexit fish to anyone who can spot where the missing wire should be
SAM_7645.JPG
The reverb is real enough though. I have a three spring long delay tank waiting for me to get my woodworking head on and build the head.
Stephen
You do not have the required permissions to view the files attached to this post.
This power design will discharge itself when switched off though... Slow? Fast? I don't know, my other amp discharges through a snubbing resistor in about 30 seconds.
smoke and visual effects 
