Retube/Recap considerations for a 74 SF Champ

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aegert
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Re: Retube/Recap considerations for a 74 SF Champ

Post by aegert » Thu Jan 24, 2013 2:18 am

On the bottom of the cap each tab is marked and the label tells you what each tab references the phot doesn't show this. But it is on the label too :-). Make sure that the value you are looking for is the value of the tab you need. . It ha common ground to the case which is the mounting tabs

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aegert
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Re: Retube/Recap considerations for a 74 SF Champ

Post by aegert » Thu Jan 24, 2013 5:15 am

OK forming it up for you :-) Here is one sections you can see you are looking at about 200 microA of leakage on the first 10-20uF section where spec from the can for that section is 385 microA Very nice.. Took about 10 mins to get there with the Tel-ohmike slowly bringing it up to full rated 450Vdc.. :-) 3 more to go . I took the picture and am posting but as I am about to press post that section has settled to 130 microA very very nice!

Image

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aegert
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Re: Retube/Recap considerations for a 74 SF Champ

Post by aegert » Thu Jan 24, 2013 7:58 am

All sections are formed and showing very low leakage.. Packed up and ready to go. Left my Capacitance meter at home. I have to service balance eye on the Tel-ohmike so I couldn't read the Capacitance value for the sections with Power factor.. Sorry. I ordered a new eye tube today so it will be here in the office. I did a cap job on it 6 months ago so the readings on the leakage should be spot on. It took like 20-30 mins per section so its good I did it or the power section woudl have been a little noisy and never woudl have broken in right. For new from the factory non NOS you can get a way with it but these oil filled FP cans after sitting for 30 to 40 years tend to go south and need to be brought back up.. It is great now..

Leakage on teh 20-40 sections was around 230 microA's the 10-20's were roughly 120 microA's at 450vdc :-)

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Re: Retube/Recap considerations for a 74 SF Champ

Post by Langwich » Thu Jan 24, 2013 8:13 am

Image

WTF is this! This is CRAZY COOL!

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aegert
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Re: Retube/Recap considerations for a 74 SF Champ

Post by aegert » Thu Jan 24, 2013 9:14 am

That is a Sprauge to-6 Tel-Ohmike... It is the ultimate Capacitor tester ever made. IMHO It has the capability to measure capacitance in an Analog method at rated Voltages, It can measure Capacitance with Power Factor for Large Cans, It measure leakage current at full voltage. This feature enables you to bring the Cap up to full voltage slowly while reading the Leakage current. Now why is that good... Big cans like the one in this thread can be leaky and being able to test that makes for knowing when to change them out.. OK that's nice but more importantly bringing up the voltage slowly from 0 volts to full rating, in this case 450Vdc, resting on smaller voltages under load in multiple steps up to full rating Forms the capacitor! We can start another thread if you want on Al Electrolytic Cap forming but for old NOS caps that have been sitting as long as these will not perform right out of the box in most cases. Ratings and measurement, real world operation and reliability under load is not an out of the box thing. . You can see this in forming on the T0-6.. When When I attach a cap to the unit and set for Leakage testing. If I go right to full voltage there is a very large amount of leakage. it starts to go down but even after an hour you leakage will not settle low in its operating range. It might go just into spec but you will be burning leakage pathways through the cap and those really don't go away. Now if we form the cap you get much much better than rated leakage and when you spot check at full voltage its ramp time is much better and it goes right back to low leakage ratings. It makes the caps just plane better IMHO... And that is a shared opinion with the manufacturers of caps as well.

You can do this in your amp with a ss rectifier and a variac but the T0-6 is a snap to use...

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Re: Retube/Recap considerations for a 74 SF Champ

Post by Fiddy » Thu Jan 24, 2013 1:43 pm

That tester thing looks awesome.

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aegert
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Re: Retube/Recap considerations for a 74 SF Champ

Post by aegert » Thu Jan 24, 2013 1:51 pm

tribi9 wrote:That tester thing looks awesome.
That it is... Needs a new tube for one function. I think I am going to get 2 new dry matched polarized spragues for it too... going to do more work on it I have a new 6e5 so the eye will be much brighter and a new tube complement 6AB4, 6C4 and 6BL7GTA on the way... Once that is done the Power factor and Capacitance value readings will be spot on again :-)

If you do tube amp work I highly recomend it if for nothing else than leakage readings and forming. It makes it so easy and as I said its at voltage up to 600Vdc

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Re: Retube/Recap considerations for a 74 SF Champ

Post by Fiddy » Thu Jan 24, 2013 3:18 pm

aegert wrote:
tribi9 wrote:That tester thing looks awesome.
That it is... Needs a new tube for one function. I think I am going to get 2 new dry matched polarized spragues for it too... going to do more work on it I have a new 6e5 so the eye will be much brighter and a new tube complement 6AB4, 6C4 and 6BL7GTA on the way... Once that is done the Power factor and Capacitance value readings will be spot on again :-)

If you do tube amp work I highly recomend it if for nothing else than leakage readings and forming. It makes it so easy and as I said its at voltage up to 600Vdc
I don't really do a lot of amp work, im just a hack if anything. I would love to own one of those tho. Was it hard to find or a lucky score or both? ;D

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Re: Retube/Recap considerations for a 74 SF Champ

Post by aegert » Thu Jan 24, 2013 3:23 pm

they pop up on ebat all the time. I would get the t0-6 not an earlier one. If you get it I have the pdf manual ping me and Ill send it to you

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Re: Retube/Recap considerations for a 74 SF Champ

Post by alberto2000 » Fri Jan 25, 2013 12:16 am

For the other electrolytic caps, which type should I go for? I've read most recommend Sprague Atoms/Orange Drops or Mallory. Are there any ready to buy sets of all needed caps for SF Champs? http://vintagefenderamprepair.com/maint ... recap-kits" onclick="window.open(this.href);return false; makes it easy but seems really expensive for just some caps?

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Re: Retube/Recap considerations for a 74 SF Champ

Post by alberto2000 » Sat Feb 02, 2013 2:33 am

It's a perfect fit!

Image

Thanks again aegert! I am using 20/40/20 (as it was before) and it's just fine!

I don't know if it was the can or the bypass caps I replaced with generic 47uf/22uf 63v caps or the cathode resistor which I increased to 1k 5w but everything is super now. No more 6v6 red plating and the sound is amazing. I am now waiting for some sprague caps to replace the temporarily installed generic caps although they seem to work and sound just fine.

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Re: Retube/Recap considerations for a 74 SF Champ

Post by aegert » Sat Feb 02, 2013 4:20 am

Big Happy.... Glad it worked out! :-) It was my pleasure...

Bypass caps? the 25uf/25v? You should really use 25/25's if that is what you ordered. FOr the 6v6 a 50uf works well too. The red plating could have always been the Cathode resistor on the 6v6. Test the spragues when they come. I had some issue with them last year when I last ordered.

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Re: Retube/Recap considerations for a 74 SF Champ

Post by sookwinder » Sat Feb 02, 2013 6:24 am

on two of my 4 VCs I had the 6V6 cathode resistor almost burnt out ... when people play them on 11 the 470k resistor gets far too hot and deteriorates and then c auses red plating which in turn causes the 470k to get worse... in one VC the 470k was cracked and charcoaled like a sausage left on a BBQ too long
relaxing alternative to doing actual work ...

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Re: Retube/Recap considerations for a 74 SF Champ

Post by aegert » Sat Feb 02, 2013 6:29 am

that's why I use Very High watt NOS Ceramic wire wounds....

BUT and a Big BUT.. Champs sound so amazing because they are always teetering on the bring of fire :-)

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