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Capacitor help

valcoholic57

Member
Messages
534
HI,

I'm getting ready to order some new caps for my blonde bandmaster. I'm having trouble distinushing the values of the orange astron caps on the tag board. When it says "4 25" or "25 25" what does that mean???.... I know that alot of symbols and representations have changed over the years....00025 is 250pf for instance....any help would be apprciated....

 

TweeDLX

Member
Messages
3,756
25/25 means 25uF (microfarads) with a 25 volt limit, likewise with the 4/25. 4uF and 25 volts handling capability. You can sub the same value with a higher volt rating with no problems. Not advisable to go the other way.

Mike
 

WaltC

Member
Messages
2,129
8-150 = 8uF and 150 VDC

20-600 = 20uF and 600VDC

25/25 = 25uF and 25 VDC

etc.

.003 = .003 uF (or 3000pf I think... I get lost in all those decimal places)

.02 = .02 uF

voltage on the last two should be at least 400 to be safe
 

valcoholic57

Member
Messages
534
ok...the last two astron caps on the board (farthest to the right) read 2X 25 - 25 likewise the schematic says there are two caps there 25- 25 caps there rather than one...does this mean i get a 50-50? thanks
 

VaughnC

Silver Supporting Member
Messages
17,914
ok...the last two astron caps on the board (farthest to the right) read 2X 25 - 25 likewise the schematic says there are two caps there 25- 25 caps there rather than one...does this mean i get a 50-50? thanks
Those 2X 25-25 are actually two, 25uf/25v caps in a single package that connect to different parts of the circuit. To replace those, just get two individual 25uf/25v caps and wire them accordingly.

Also, electrolytic caps are polarized so you need to pay close attention to their polarity when installing the new ones.

You sound like a novice....be very careful inside the amp as there could be 500 lethal volts lurking inside the amp even with it turned off and unplugged.

And, if it hasen't already been done, you should replace the 2 wire power cord with a 3 wire cord and remove the .05/600v death cap.
 
Last edited:

valcoholic57

Member
Messages
534
already have the caps drained:AOK...I've built a couple fender reverb units that turned out nice....my roomate is going to do the soldering as hes a little better than me....this will be my first cap job however....I'm excited to get my feet wet ( I've been working my way up...ive built a couple pedals, reverb units etc...now its time for the cap job)...thanks for the help and concern! its much appreciated....

also...i notced there are some places that sell the 2 x 25 - 25 caps....would i be better off to get those or just get two seperate 25uFs?

Also...for the power supply would be i better off to get to 20 Uf rated for 500 or 600 volts?? the caps that are in it (originals) seem to be rated at 525 but the schematic seems to reccomend 600
 

VaughnC

Silver Supporting Member
Messages
17,914
already have the caps drained:AOK...I've built a couple fender reverb units that turned out nice....my roomate is going to do the soldering as hes a little better than me....this will be my first cap job however....I'm excited to get my feet wet ( I've been working my way up...ive built a couple pedals, reverb units etc...now its time for the cap job)...thanks for the help and concern! its much appreciated....

also...i notced there are some places that sell the 2 x 25 - 25 caps....would i be better off to get those or just get two seperate 25uFs?

Also...for the power supply would be i better off to get to 20 Uf rated for 500 or 600 volts?? the caps that are in it (originals) seem to be rated at 525 but the schematic seems to reccomend 600
Personally, I'd use two separate 25/25 caps...otherwise, if one went bad, you'd need to replace both.

20/600v, definitely!
 

gldtp99

Member
Messages
3,861
Two seperate 25uF/25V caps (i buy 25uF/50v caps--- @same size and @same price) are less expensive than the dual 25/25 uF cap cans---- either will work just fine.
Be sure that the 20uF/600V caps will fit under the doghouse lid before you order them----- i've used 20uF/500V Sprauge Atoms in my 6G7-A re-caps--- i have three of these amps and they sound/work great..................gldtp99
 

Structo

Member
Messages
9,556
It's perfectly acceptable to replace all the electrolytic caps on a vintage amp.
But, I would leave all the Astron coupling caps alone unless you find one to be very leaky.
Those are what give those amps a lot of their great tone.
 

donnyjaguar

Member
Messages
4,199
Actually, given a cathode bypass cap on a typical 12AX7 voltage amplifier has less than 2 volts across it you can easily sub in a 9V capacitor. :)

I couldn't resist my pedantic ways here... :)
 

valcoholic57

Member
Messages
534
It's perfectly acceptable to replace all the electrolytic caps on a vintage amp.
But, I would leave all the Astron coupling caps alone unless you find one to be very leaky.
Those are what give those amps a lot of their great tone.
actually it has all blue mallorys



and they are staying....
 

Fretts

Member
Messages
378
Most guys replace those duals with two Mallorys. I like Mallory because they are... black... really. I don't like baby blue or grey for some reason. I've seen those new black dual 25's and they are enormous, I bought some myself and ultimately decided to leave them out and just go with the two Mallorys.
 

valcoholic57

Member
Messages
534
I ended up ordering all my caps from ted weber...I went with two seperate 25uF's from him....now I'm just sitting and waiting for these to come so I can get my amp put back together....its not easy....although...its not bad playin on my roomates 72 super lead......
 




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