I am restoring a Stromberg AU-42 and I want to keep the original can cap look. I cannot find a 50/40/30 in order to keep the 50uf cap at the cathode side of the 6L6 outputs. The circuit is push/pull (2 6L6’s) and the cathodes are tied together to 50uf/50v parallel to 200 ohm resistor to ground. I believe this is the current source for the 6L6’s. I can find a 70/40/40 and a 80/40/30 can cap. I am wondering if I can increase this 50uf on the 6L6 cathode to 80uf or 70uf. My gut says this will be okay although in the back of my head, more capacitance means more current on demand which my gut says should still be okay. I don’t want to heat up the 6L6’s. Any advice would be helpful. I really do not want to use individual caps but if I have to I will.
Thank, Tom
Epsom Repair Depot
Thank, Tom
Epsom Repair Depot
Increasing the cathode bypass capacitance by a small amount is not a problem in my experience. Obviously it is better to use original values but needs must.
Consider the old capacitor probably has a tolerance of +40 -10% anyway.
I would choose the 70/40/40 if the voltages are within specification. Don't want to stress the rectifier.
Consider the old capacitor probably has a tolerance of +40 -10% anyway.
I would choose the 70/40/40 if the voltages are within specification. Don't want to stress the rectifier.
As JonSnell has mentioned, the values are not critical, and increasing them slightly only benefits things.
The only thing important to adhere to is the original voltage ratings for each section/cap.
Going a bit higher is OK, but not below. - for instance, a 350V rating can be replaced with a 450V.
Cathode bypass sections are usually much lower, AKA 50V, but can be anything higher and be OK.
I usually replace that section with a seperate "under chassis" replacement.
The only thing important to adhere to is the original voltage ratings for each section/cap.
Going a bit higher is OK, but not below. - for instance, a 350V rating can be replaced with a 450V.
Cathode bypass sections are usually much lower, AKA 50V, but can be anything higher and be OK.
I usually replace that section with a seperate "under chassis" replacement.
Thank you for your reply.
I have looked at some of my design books with notes. I believe that going higher with the bias cap from 50uf to even 100uf will not make much of a difference in the way the tube will function. If I go lower than 50uf, from what I can tell, this will start to effect the functioning of the 6L6 responses. I am still doing a little research on this before I actually purchase the parts but I agree that the 70uf would be okay but then again the 80uf would not make much of a difference. Going with the 80/40/30 will give me the exact capacitors I need for the 5Y3 power stage. Your thoughts. My guts was always that it would be okay but it has been a while since my courses in tube theory, like 1982.
I have looked at some of my design books with notes. I believe that going higher with the bias cap from 50uf to even 100uf will not make much of a difference in the way the tube will function. If I go lower than 50uf, from what I can tell, this will start to effect the functioning of the 6L6 responses. I am still doing a little research on this before I actually purchase the parts but I agree that the 70uf would be okay but then again the 80uf would not make much of a difference. Going with the 80/40/30 will give me the exact capacitors I need for the 5Y3 power stage. Your thoughts. My guts was always that it would be okay but it has been a while since my courses in tube theory, like 1982.
That cap is a cathode bypass cap, not a power supply cap. If you do some searches I'm sure you can find technical explanations of its function.
Unless you don't care about cost or the quality of parts, you should just disconnect the existing can, leave it in place for looks, and use individual caps mounted underneath.
Can caps are much more expensive than individual parts and individual caps that have far better specs are easy to find.
From a practical standpoint I would suggest that you replace it with a 47uf 50v, which is the modern equivalent. For the other sections use 47uf and 33uf rated at 450v. You should also plan on replacing all the electrolytic caps - the schematic shows several smaller value ones - and the coupling caps should also be replaced with modern film caps.
Here's some comments I made about this in a post on another forum last year - different cap values since it related to a different amp but the general comparison is still valid:
I'd suggest using caps rated at 105 degrees for 10,000 hours. Can caps are generally rated at only 85 degrees and sometimes less.
Replacing the cans is also a much more expensive option.
A CE can with four 20uf sections, sells for $36.70 plus shipping at Antique. Its heat rating is only 55 degrees, no hour rating listed and tolerance as much as +50%. Shipping costs for small orders can get expensive.
The cost of four individual Nichicons (22uf 450v) is $1.13 each for a total of $4.52. They are rated at 105 degrees for 10,000 hours and have a 20% tolerance. And, if ordered from Digi-Key, there's the free shipping option. Here's how you can get free shipping:
Free Shipping On Parts Orders | Audiokarma Home Audio Stereo Discussion Forums
So the CE can will likely cost about 10 times the price when shipping is factored in.
You can get custom made cans from someplace like Hayseed that use caps with the better specs but they are even more expensive than the CE cans. But, if limited space prevents you from using individual caps, the Hayseed caps are the way to go since the specs are better.
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I realize I can keep the caps for original look and install individual caps but I do not like the extra clutter. I am doing a total recap, using orange drops for most of the caps when I can and sliver mica for pf caps. From my vendor it will cost me $75 for the can caps I need and $42 for individual caps or a savings of $33. I know I could pocket the extra $33 since customer has already paid me for the restore but, when possible, I like to keep the original look with less clutter. My wife says I am thorough which is really being anal but we call it thorough being a better term for me. I really like your comments, you can never stop learning.
$42? Seriously?? I don't know who your vendor is but those prices are outrageous!
The individual caps needed to replace the two cans are:
47uf 450v
33uf 350v
47uf 50v
10uf 350v
10uf 350v *stock is 300v but DigiKey only stocks 350v.
10uf 250v
22uf 50v
I just looked on DigiKey and the individual caps that it would take to replace all the sections of the two cans cost a total of $7.12. And you can get free shipping.
So, less than 10% of the cost of cans, not even considering the shipping, and the caps are better quality.
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FWIW, there is the "trick" of emptying the old cans and restuffing them with new parts. Modern 'lytics are superior in every way, including volumetric efficiency, than the old stuff.
In my business, people want their equipment serviced, safe, - and reliable.
They're not interested in "looks" of the (internal) parts involved, they want the thing to work, and work well.
Those old buzzards that are into re-stuffing the internal caps on things are over-fussy and have tons of Retirement Social Security time on their hands I guess.
I find that rediculous, since under chassis views will never be seen after restorations.
Who the hell cares what it looks like under there?
Who cares about "keeping it original looking" in some place that's never seen?
Case in point - those old 1920's/30's old Philco radios with the "bakelite block" caps under the chassis - the old buzzards go to great lengths to melt out the old tar, install new poly caps, and re-seal them in the old tar.
All nonsense!
Like anybody in the future is ever gonna peek under there and be amazed!
It's plain obsessiveness.
If I had to do that every time, my fees would tripple!
There goes your whole Social Security check!..... right out the window.
Lower capacitance = more your own listening space presence.
Higher capacitance = more of the record's mastering space presence
This is aside from the capacitor coloration which can be more than either of the above with some of the pricier botique capacitors.
All I can say is at least it has "caps" unlike most of the current and slightly past consumer-grade audio gear
Higher capacitance = more of the record's mastering space presence
This is aside from the capacitor coloration which can be more than either of the above with some of the pricier botique capacitors.
All I can say is at least it has "caps" unlike most of the current and slightly past consumer-grade audio gear
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Those "so called" boutique caps are a fools waste of money.
Just like any other snake oil product.
Of course, the deluded crowd will praise them till the cows come home, and you can't convince them otherwise.
Just like burnt toast, once it's burnt, it'll never be unburnt.
Just like any other snake oil product.
Of course, the deluded crowd will praise them till the cows come home, and you can't convince them otherwise.
Just like burnt toast, once it's burnt, it'll never be unburnt.
I do agree that the new caps are better than the old can type caps. I recapped a Gibson GA40 for this guy and it came out really nice and that is probably why it wants me to do his Stromberg. I am a little thorough/Anal with whatever I do and maybe that is why I lean towards original look. With this amp customer really does not care because it is not an expensive amp but I guess I do. I am not going to re-stuff the can because that is a crap shoot how or if it will come out. I am still leaning toward using new cans which will only change one cap value from 50uf to 80uf with still keeping my power supply caps the same. The 50uf is the Cathode bypass for the 6L6's and after much study found that 50uf to 100uf with have a very minor change in the 6L6 functional response. This of course depends on checking out other vendors and if I save a lot more than $33 I might just put in individual caps. Would make the wife happy since I already got paid from the customer. My vendor and ebay, I only will save $33 and that to me is not enough to NOT stay with original look and create more clutter.
Do yourself a favor - don't purchase parts from ebay, use reputable parts sources.
Because once you get a part that fails because of it being "fake", and a customer complains, you're reputation will be affected.
I've been in the service business for 45+ years, and kept my Five Star reputation intact.
Okay I went on Digi-Key per FlaCharlie comment. I found the site to be very cluttered and the search tool lacks in exact search results. I did find everything although they don't have the 30uf, will have to use 33uf which is okay. The total price is $11.49 which will save me $64. This is the price for 20% tolerance and if I go with 10% the price is much higher. Also they have a 13 week lead time. The price of the parts is minor compared to the actual labor that is charged so I am still leaning toward cans. I am getting the parts from a vendor I can trust that specializes in this field of repair. I quoted $115 for the caps and research so I think I am still doing well and within budget but I still welcome all the feedback. Although the time I have taken to decide far exceeds any savings. The price I pay for being thorough/anal.
Huh? Not sure how you're using the Digi-Key site but I find it very easy to work with. Here's an example of how I found the parts I mentioned earlier.
Step 1: once you're on the main site (DigiKey Electronics - Electronic Components Distributor), click on Capacitors in the list on the left
Step 2: then click on Aluminum Electrolytic Capacitors
Step 3: the next page shows a list of brands, specs etc. Click on More Filters. You can choose to have them displayed in "stacked" (vertical) or "scrolling" (horizontal) format.
You do not need to make a choice in each filter, just the ones that are most important to you.
Step 4: Since I didn't want to have to wade through too many choices I checked the following:
Under Brands: Nichicon (if you prefer a different brand check it instead or don't check any to see all the available choices.)
Capacitance: 47uf
Voltage Rated: 450v
Lifetime@Temp: 10,000 hrs @ 105 degrees
Package / Case: Radial Can
Step 5: then scroll down under the list of filters and select "In Stock"
It tells me that I will have 5 choices that meet the above criteria. If it gives you a "lead time" that refers to parts that are not in their stock and the length of time it will take for them to get them. Or, in some cases, they may have some in stock but if you need a huge quantity it tells you how long you'll have to wait.
Step 6: Click "Apply Filters" and scroll down to view the choices. Notice that one choice has a minimum order of 250 so ignore that one. Each of the others list the number of units that are in stock, the price per cap and, if you scroll sideways, all the other specs for that cap.
If you click on a particular cap's part number it will take you to a page that includes a link to the manufacturer's data sheet with technical specs.
If you want to get free shipping, read the thread I linked earlier. If you order online you pay shipping. Other major suppliers' sites are similar but I don't think any of them offer free shipping.
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Yes, exactly Flacharlie. I did your 6 steps and more but still you get to many choices and then you still have to go through all of them. I prefer Sprague but still I found I get more than I bargained/searched for. Only take you 1 step searching the vendors I use, even ebay and I get pictures and data. I just don't find Digi-key that user friendly. I was a Sr. Software Engineer for 5+ years after my Hardware Engineering years, so I am surely not a stranger to various applications and being able to figure them out. You can write an app but you need to make it user friendly and not bury the user with to much information. Just saying.
I really like JJ capacitors, both their axial and radial can types. Their vintage tone is not too overbearing. Plus they look slick as anything.
Sorry to hear that you find the Digi-Key site so challenging.
And I'm not sure how you're coming up with the huge number of choices that seem to be causing you such frustration. Are we even looking at the same website? You obviously didn't follow the same steps which I laid out.
So I just did another search.
I chose Vishay Sprague (the only listing for Sprague) in the Aluminum Electrolytics section. I specified 47uf 450v. Those basic specs were all that I entered.
Only 1 choice came up. Unfortunately, that choice disappeared when I specified "in stock".
Looking closer it would not be a cap I'd want to use anyway.
The Sprague is rated at 1000 hours at 85 degrees and its tolerance is up to 50%. Not only that but the cost is $10.36 each - and that's with a minimum order of 90 caps. No wonder they don't bother to keep them in stock.
My previous suggestions were all caps that are rated for 10,000 hours at 105 degrees with a tolerance of 20%. The Nichicon 47uf 450v I suggested sells for $2.86. And you can get free shipping.
Searching took me less than 1 minute for each cap value.
I'm curious, though, what vendor are you using? Please post a link.
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I used a couple of their can types in a DIY 45 SET amp I built many years ago. That was before I knew anything about cap specs.
Here's a link to data for the JJ. Specs are even worse than the Sprague mentioned above - 1000 hours at only 70 degrees.
https://www.jj-electronic.com/images/stories/product/capacitors/TC_TE_EN_web.pdf
On the plus side, they are cheaper than other cans, some of which are rated at only 55 degrees. So not the worst possible choice.