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Altec can capacitor upgrade?

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I'm in the middle ordering stuff for 1569A amps. and need some help deciding on parts.
The two 500v cans are 40+40uf. I'm considering 100+100 for the first. 500uf for the second as it's currently wired together for 80uf.

Will there be any negative effects at these values?
I'm open to any suggestions on these. Thanks in advance!
 

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The rule of thumb is to stick as close to the original values. If you are having trouble finding a 40+40, you could go with 50+50 or the highest I would go is 20+20+20. If you are replacing can capacitors you can get the replacements at www.tubesandmore.com They were who I used when I bought the caps for my Pilot 240. I would recommend putting a 0.1uf @ 600V capacitor in parallel with the first capacitor (80uf). They cut down a lot of the noise I had on my amplifier. P.S. Don't forget to replace the BIAS capacitor, those can usually be bigger and I try to get high temp units for all under chassis capacitors.
 
Many people that rebuild these amps leave the original cans on top disconnected to retain the original looks, and replace the caps under the chassis.

By chance, could you start a thread about rebuilding these amps? I have a pair myself I need to rebuild and I would like to see what you do with yours..
 
Funny. I just rebuilt an Altec 345a. It uses 3 40x40x500v can caps. I found Richey caps that worked perfect. I could have gone with the 50x50, but when I found the exact match, for less... Just be sure to pay for faster shipping, it came from Canada and took 3 weeks!
http://www.justradios.com/DUALsection.html
 
Hi-FiGuy said:
The rule of thumb is to stick as close to the original values. If you are having trouble finding a 40+40, you could go with 50+50 or the highest I would go is 20+20+20. If you are replacing can capacitors you can get the replacements at www.tubesandmore.com They were who I used when I bought the caps for my Pilot 240. I would recommend putting a 0.1uf @ 600V capacitor in parallel with the first capacitor (80uf). They cut down a lot of the noise I had on my amplifier. P.S. Don't forget to replace the BIAS capacitor, those can usually be bigger and I try to get high temp units for all under chassis capacitors.
Click to expand...

This is my line of thinking for working on just about anything. I'm also reading that technology limitations and cost sometimes made the decision on values here. Stock values will definitely keep me out of trouble with this.

Good advice! I have three .1uf bypass caps.(One in each section?) for ONE amp. in the order list.
Changed the bias cap on the list to (100UF 100V ELECT AUDIO).

similost said:
Many people that rebuild these amps leave the original cans on top disconnected to retain the original looks, and replace the caps under the chassis.

By chance, could you start a thread about rebuilding these amps? I have a pair myself I need to rebuild and I would like to see what you do with yours..
Click to expand...

Sure, I will doc. the build and post when done. Hopefully, there will not be anything major along the way. If there is there is no thread, you will know that that one of them turned into flames.:D

Looks like two votes for original values.:scratch2:
 
I'm a big proponet of using original values. These Altec amps are supposedly something magical, so I figure when they built them, they did it right, so why change their work?
 
Yes, I do imagine they were quite expensive in their day being a commercial amp. Make that three votes for stock.

From what I understand they can loose a rectifier and output tube and continue without notice. Maybe this equals some sort of "head room" when everything is working properly.
 
I think the reason you can lose two of the output tubes is because they are PPP amps, and all you would really have happen is you are losing half of your wattage..
 
similost said:
I think the reason you can lose two of the output tubes is because they are PPP amps, and all you would really have happen is you are losing half of your wattage..
Click to expand...
Yes, I do believe you're right. I think I would notice half the wattage missing. After reading the man. again, it explained that it will OPERATE after loosing 3 outputs and one rectifier.

Those richey's sure do look attractive @ $16. I could do four of these (50/50 µF @ 500 VDC, F&T) @ $10 each.
 
sloober said:
Funny. I just rebuilt an Altec 345a. It uses 3 40x40x500v can caps. I found Richey caps that worked perfect. I could have gone with the 50x50, but when I found the exact match, for less... Just be sure to pay for faster shipping, it came from Canada and took 3 weeks!
http://www.justradios.com/DUALsection.html
Click to expand...

I followed Mark in exactly as described, same amp, same Richey caps. Double emphasis on paying the extra buck for air mail for much faster delivery. It took almost a month for my order to travel 1100 miles via Canadian Surfacemail.
 
similost said:
I'm a big proponet of using original values. These Altec amps are supposedly something magical, so I figure when they built them, they did it right, so why change their work?
Click to expand...

They ought to be magical. I recently saw a pair of Altec Peerless pre amp OPT transformers sell for $895., and one of the trannys had an open coil.
 
I vote both ways

I would certainly not change the value of the first capacitance after your tube rectifiers by much, since the spec is 40uf for the 5U4G.

That said, you can up it little, some people increase it a lot, but I think that puts your rectifiers at risk of flashover.

The second capacitor is fair game and I increase that one on every one of my amps to 80uf-120uf. For my ears it tightens up the bass a lot. (But so would just putting in new caps!)

The third position I have seen it done both ways and heard arguments that that last cap filters the whole power supply.

On the other hand, as you can see a lot of people like to keep their old hardware stock values, and you can be certain that is a very very safe thing to do most of the time.

The best part is, you have some wonderful pieces and a very nice dilemma. Picking parts is actually 2/3 of the fun for me!

If you post pics as you go we will all enjoy it more than you know.

Dan
 
I too like to stick with stock values if available. That Altec looks very similar to the 345a I have, looking at the schematic. Should perform very well. John
 
DanO55 said:
Restored a set, sold them, big mistake. Great amps!
Click to expand...

Interesting.. I was having this bad idea the other day of selling mine, but then I talked myself out of it... I decided I would get them up and running and at least 6 months of use before I ever consider it again..
 
similost said:
Interesting.. I was having this bad idea the other day of selling mine, but then I talked myself out of it... I decided I would get them up and running and at least 6 months of use before I ever consider it again..
Click to expand...

Hopefully you won't regret selling your A-7's....:tears:

My pair of 1569A's is in the que for the restore.


CIMG6702.jpg


However, I think a Citation I that's in the mail is going to butt to the front of the line......:nono:
 
No.. no regrets about selling my A7's.. I listened to them for a few years. I knew what they were capable of, and after weighing it all out, I decided I could get a better sound with less real estate... like with my JBL's...

SO, that's why I decided not to sell the amps until I gave them listening time... I did try firing up one of my 1569's on a variac and just a nice loud hum... nothing else.. The caps are all pretty well shot..
 
grey said:
I'm in the middle ordering stuff for 1569A amps. and need some help deciding on parts.

The two 500v cans are 40+40uf. I'm considering 100+100 for the first. 500uf for the second as it's currently wired together for 80uf.

Will there be any negative effects at these values?

I'm open to any suggestions on these. Thanks in advance!
Click to expand...

You can do that just fine with a couple cautions.

First off, the tolerance on the original caps was -10% - +90% (or 50% in a few cases). So the original caps could have been anywhere between 36 uf and 76 uf and been in spec!

Second, you do have to respect the limits of the tube rectifiers. The C11 A and B caps can't go much larger without jeopardizing the 5U4s - so you can use 100 uf total, but no more. In fact, if the original caps were even 25% above spec, they would have had 100 uf of capacitance. 100 uf is fine there - but higher than that is not wise.

On the C6A and C6 B caps - you can use pretty much as large a cap as you want - but the law of diminishing returns applies. Those caps decouple the low level and PI stages from the main B+ along with R10 and R21, so I'd make R10 & R21 2 or 3 watts to be sure they run cool. If it was me I'd use a dual section 100/100 cap. I might even parallel a 4-5 uf film cap with each section. That's a healthy increase, it's easy to install, and will make a nice sonic improvement. 500 uf is likely overkill, 200 uf or so is good.

Don't forget to replace C7 - the bias cap; replace the selenium rectifier too! There you could use 100 uf as well. And the cathode bypass on the 1st 6CG7 (C3) should be replaced too. Use 50 uf at 35 volts or higher for there.

Let me know if you have any questions. I'll try to help if I can.
 
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Jim McShane said:
You can do that just fine with a couple cautions.

First off, the tolerance on the original caps was -10% - +90% (or 50% in a few cases). So the original caps could have been anywhere between 36 uf and 76 uf and been in spec!

Second, you do have to respect the limits of the tube rectifiers. The C11 A and B caps can't go much larger without jeopardizing the 5U4s - so you can use 100 uf total, but no more. In fact, if the original caps were even 25% above spec, they would have had 100 uf of capacitance. 100 uf is fine there - but higher than that is not wise.

On the C6A and C6 B caps - you can use pretty much as large a cap as you want - but the law of diminishing returns applies. Those caps decouple the low level and PI stages from the main B+ along with R10 and R21, so I'd make R10 & R21 2 or 3 watts to be sure they run cool. If it was me I'd use a dual section 100/100 cap. I might even parallel a 4-5 uf film caps with each section. That's a healthy increase, it's easy to install, and will make a nice sonic improvement. 500 uf is likely overkill, 200 uf or so is god.

Don't forget to replace C7 - the bias cap; replace the selenium rectifier too! There you could use 100 uf as well. And the cathode bypass on the 1st 6CG7 (C3) should be replaced too. Use 50 uf at 35 volts or higher for there.

Let me know if you have any questions. I'll try to help if I can.
Click to expand...



As always Jim, YOU DA MAN!....:thmbsp:

(As soon as my new Cit I comes in, I'll need PS supply parts. Can I safely assume you can help me out?....:D )
 
Answering the capacitor question, the first capacitor controls the inrush current. You should stay close to the design value for that one. The next one can be 100uF if you want additional storage. I would get slightly higher voltage ratings than are original. The incoming line voltage is almost 10% higher today than when designed. You can increase the value of the resistor in the Pi filter (is 47k ohms) to shed the higher voltage produced today and bring that closer to the design voltages for the amp.
 
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