dynaco 525 volt 30/20/20/20 replacement capacitor

[mark45]

Anyone know of a source that would be some what original
.

Mark

[EdBass]

I moved this to DYI because it seemed more appropriate.
This has been discussed here a few times; here's some interesting reading regarding Dynaco's original Mallory filter caps.

http://sunnforum.ampage.org/index.php/topic,5640.0.html

If you search this forum you will find other good references as well. If you are still looking for the under rated (see above) can cap, Triode stocks the original value units;

http://triodeelectronics.com/c-ec30-20x3-525.html

[Oli]

Hi,

here is another one:

http://www.askjanfirst.de/dindex.htm

[Amptech]

You can always try antique electronic supply..  www.tubesandmore.com

[patlaw]

Further to Ed's comment, I have not been able to find a can that can be used to replace the existing one, which was undersized. The B+ voltage is too high. Just replacing the original cap with an identical one will cause the new one to fail.

[EdBass]

Further to Ed's comment, I have not been able to find a can that can be used to replace the existing one, which was undersized. The B+ voltage is too high. Just replacing the original cap with an identical one will cause the new one to fail.

A couple of points about this;
First, although in theory the above statement would seem true, in practice this is not often the case. Myself and others here have examples of the original 525V can caps withstanding the higher voltages, in many cases for decades, even when running at modern wall voltages. I suppose that the original Mallory caps were underrated enough that they could resist the short voltage spikes that they were exposed to.
Not to downplay the fact that the original values are technically insufficient, and IMO a higher rated filter cap solution is preferable.

Which brings me to the second point. The German AuthentiCap unit that Oli mentions is model KTL13, which is rated at 550+V, which has a 600V surge capacity. A much better option I think, I didn't mention the AuthentiCap because the OP was looking for the original cap. 

Hi,

here is another one:

http://www.askjanfirst.de/dindex.htm

[patlaw]

Ed, I am not arguing or disagreeing in any way. You obviously know your stuff. The question I have is whether you would trust this capacitor at or slightly above its rated working voltage. I would not.

[EdBass]

No I wouldn't put that in one of my Sunns, but I think this one is probably pretty close to the OEM can caps Sunn/Dynaco used in the good ol' days;

https://www.tubesandmore.com/products/C-EC4020X2-525

As I said I personally prefer a more stout filter section as well as SS rectifiers on my gigging rigs, but strangely enough, I can't recall hearing of anyone posting about having one of the 525V Mallory's going Chernobyl on start up.

Here's just one relevant post from one of several threads here about the filter cap issue with tube Sunns. This has been an issue also covered by vintage Dynaco users, as it's been an issue with Dynaco (Dynakit) from early in their production.

The pursuit of "the" tube for any particular application can trigger OCD even in the most level headed types. There are myriad threads on this forum alone that would bear that out, but the general consensus is that tubes from "the good ol' days" are overall superior to the eastern European/Asian tubes available nowadays.
Moot point for the most part with KT88's, a matched pair of vintage GECs can easily bring more than an entire nice 200S rig will bring.
Price to value I don't think you can go wrong with a pair of JJ's (try www.eurotubes.com) , but myself and others here have tried just about everything that will plug into those sockets and opinions are as diverse as the individual posters themselves.

This forum is unquestionably the most information laden vintage Sunn specific resource on the 'net; search KT88 and 6550 and settle in for a few hours...

The rectifier filter cap thing has been hashed out here ad infinitum as well, also good search material.
I've personally got fully functional gigging Sunns with the SDS replacement board from Triad, the German 550+VDC Authenticap, and even a magical '68 200S with original everything including the original 30/20/20/20 can capacitor.

Do a little digging and you will get more information than you know what to do with!

If you use the search function you will find a bunch of discussion about solutions to this issue.

Of course I cheat by using the SDS Labs boards, here's one tucked into the chassis of one of my 2000S amps;



But you can build your own, I think Soundmasterg did his 2000S from scratch.

.

[patlaw]

I just finished recapping my Sentura II. The voltage on the first cap after the rectifier is 536 volts. I would not be willing to operate a (new) 525 volt cap at 536 volts. Moreover, if you use the stand-by switch, depending on how it's wired in the circuit, the B+ rises to 604 volts.

For my recap, I used two 50uF/450v caps in series for the first one and a 40uF 600v for the second. I paralleled two sections of the (new) can for the third cap and two sections of it for the fourth cap. The 6.8K resistors between the second and third sections were changed to three-watt resistors since the old ones were getting quite warm. The Sentura II has the tremelo board, so there's no room to mount the board you used, as I understand it. My total capacitor cost was about $15. So far so good.

[Soundmasterg]

As I said I personally prefer a more stout filter section as well as SS rectifiers on my gigging rigs, but strangely enough, I can't recall hearing of anyone posting about having one of the 525V Mallory's going Chernobyl on start up.

When CE first came out with their 30-20-20-20 @ 525V can cap there were a lot of failures. They have since got better but the quality still isn't as good as the vintage ones, and that is saying something since by and large modern caps are usually better in every way to vintage ones. Can caps create grounding compromises anyway...they were used back in the day because they were quicker and cheaper to install, but distributed capacitance is cheaper and performs better too....though in a vintage amp that is already made with a can cap using discrete caps is a little harder to install.

But you can build your own, I think Soundmasterg did his 2000S from scratch.

I actually haven't done my 2000S yet. I will be using polypropylene Solens and tip pin jacks on the back to set the bias in that one so I won't have to open up the amp again, plus I want to see how those will sound in the amp.....the 2000S has lots of room and thats good because those Solens are HUGE!

I did do my old 200S from scratch.....using series connected caps. It worked well though I ended up selling it a couple years ago and am now down to just the 2000S head and cab and the 1x15 cab I made myself. I sold my vintage SVT and cabinet also. I did recently pick up a vintage 1963 B15N but thats another story.

I just refinishing capping my Sentura II. The voltage on the first cap after the rectifier is 536 volts. I would not be willing to operate a (new) 525 volt cap at 536 volts. Moreover, if you use the stand-by switch, depending on how it's wired in the circuit, the B+ rises to 604 volts.

For my recap, I used two 50uF/450v caps in series for the first one and a 40uF 600v for the second. I paralleled two sections of the (new) can for the third cap and two sections of it for the fourth cap. The 6.8K resistors between the second and third sections were changed to three-watt resistors since the old ones were getting quite warm. The Sentura II has the tremelo board, so there's no room to mount the board you used, as I understand it. My total capacitor cost was about $15. So far so good.

The overall B+ voltage will depend on the era of amp. The earlier Dynaco transformer amps had lower voltages than the later Schumacher transformer amps. Its not just the main B+ that changes either as any change at the B+ without other successive changes elsewhere in the amp will result in higher voltages at each stage, and voltage plays a big part in the tone and power of the amp. The Scumacher transformer amps put out more power and are brighter and cleaner, but don't sound as sweet as the Dynaco transformer amps IMHO. My Schumacher equipped 200S that I used to have had a B+ of 560V at idle when biased up to around 70% of the max and it was beyond 620V when in standby. That was with a tube GZ34 too. The voltages were higher with a solid state rectifier in place. I ended up using a Weber Copper Cap WZ34 and series connected 220uF 350V caps in the first stage, series connected 100uF 350V caps in the second stage, and a 20uF 500V cap in the third stage. Fourth stage was a 20uF 450V cap. Whenever connecting caps in series, make sure you put a 220k 1 watt resistor in parallel with each cap, or one cap in the series connected pair will try to hog the voltage and eventually fail prematurely. The only exception to this is if you have a transformer tap at the junction of the two caps.

Also, are you aware patlaw that with your cap setup on the first stage you are now at 25uF 900V for the first cap section? So you have less than the 30uF in the stock Sunn that was already less capacitance than it should have been.....just sayin!

Greg

[patlaw]

Also, are you aware patlaw that with your cap setup on the first stage you are now at 25uF 900V for the first cap section?

Yes

So you have less than the 30uF in the stock Sunn that was already less capacitance than it should have been.....just sayin!

Yes, there is a little bit of a story there. When my brother recapped this amp many years ago, he used high value photocaps for the first and second caps. When the amp turned off, it would oscillate for a second or two. In replacing the caps, I wanted to make sure not to go too high.

The original Sentura II schematic, which matches my amp, has the first cap at 30 uF. The mid-boost version of the Sentura II, which is presumably a subsequent design, has the first cap at 20 uF. Considering that the value may have been lowered for a reason, and after reading a number of recommendations not to put more than 20 uF after a GZ34, I decided to split the difference.

So far the power amp is working perfectly. With capacitor tolerances what they are, I could actually be closer to 30 uF than 20. I didn't measure it. If I need to add more capacitance, such as would be necessary if I changed to a solid state rectifier, there is room to easily add bigger caps. The amp just sits at my house not being used regularly. (My regular amp is a Fender Vibrolux Reverb.) Even then, I don't play a lot.

Does my thought process make sense?

EDITED TO ADD: I just read back through this thread. When I posted a link to the can cap at Tubes and More, I posted the wrong link. My question actually applied to the cap at the link you posted. That's the one I meant. I didn't realize the they even had a 475 volt version.

[Soundmasterg]

Yes, there is a little bit of a story there. When my brother recapped this amp many years ago, he used high value photocaps for the first and second caps. When the amp turned off, it would oscillate for a second or two. In replacing the caps, I wanted to make sure not to go too high.

The original Sentura II schematic, which matches my amp, has the first cap at 30 uF. The mid-boost version of the Sentura II, which is presumably a subsequent design, has the first cap at 20 uF. Considering that the value may have been lowered for a reason, and after reading a number of recommendations not to put more than 20 uF after a GZ34, I decided to split the difference.

So far the power amp is working perfectly. With capacitor tolerances what they are, I could actually be closer to 30 uF than 20. I didn't measure it. If I need to add more capacitance, such as would be necessary if I changed to a solid state rectifier, there is room to easily add bigger caps. The amp just sits at my house not being used regularly. (My regular amp is a Fender Vibrolux Reverb.) Even then, I don't play a lot.

Does my thought process make sense?

EDITED TO ADD: I just read back through this thread. When I posted a link to the can cap at Tubes and More, I posted the wrong link. My question actually applied to the cap at the link you posted. That's the one I meant. I didn't realize the they even had a 475 volt version.

The reason those small values of caps were used back then was because caps were expensive and the designers of the Dynaco gear that the Sunn amp was based on used the smallest value that would get acceptable hum reduction and filtering. Fender was using 35uF at the same time on most of their amps and some other hifi manufacturers were using up around 50-60uF with the GZ34. The max filter on the output of the GZ34 is 60uF according to the old Mullard datasheets, though with today's lousy quality GZ34's for the most part, going with a modern 47uF would be more appropriate. It will reduce the background noise and hum a little. Incidentally the Ruby GZ34 is the best one being made today....and it will handle that filter value after it just fine. The Sovtek and JJ...maybe not.

The oscillation that you had before wasn't due to the filter cap value btw. If you're happy with the amp and how it sounds and works then that is what counts.

Greg

[patlaw]

The oscillation that you had before wasn't due to the filter cap value btw.

What was the cause? When I changed the caps, it went away.

[Oli]

The oscillation that you had before wasn't due to the filter cap value btw.

What was the cause? When I changed the caps, it went away.

I believe you got an LC resonator as you got an coil (L) and a capacitor (C). I had the same problems with an 350B, changed the caps (see twist lock cap from askjanfirst) and the chokes...vola´ the LFO was gone and the amp was dead quiet.

Greetings

Oli