Hey everyone, was wondering if anyone had much experience with replacing the quad capacitor on the st-70 with a capacitor board, specifically this one. http://store.triodestore.com/st70capupgrade.html . If so, what do you think of it in comparison to other choices such as the dynakitparts.com 80uF cap? And of course if you think it was a worthy purchase. Thanks guys! -Ryan
3 posters
Triode Electronics Capacitor Board
scsidude2- Posts : 21
Join date : 2010-03-19
Age : 38
Location : Dekalb, IL
Bob Latino- Admin
- Posts : 3276
Join date : 2008-11-26
Location : Massachusetts
scsidude2 wrote:Hey everyone, was wondering if anyone had much experience with replacing the quad capacitor on the st-70 with a capacitor board, specifically this one. http://store.triodestore.com/st70capupgrade.html . If so, what do you think of it in comparison to other choices such as the dynakitparts.com 80uF cap? And of course if you think it was a worthy purchase. Thanks guys! -Ryan
Hi Ryan,
The Dynakitparts 80, 40, 30, 20 has a higher voltage rating (550 volts) than the Triode Electronics cap board (500 volts), will take high voltage turn on surges better and costs less. The Triode board and parts set is $75 AND you have to put it together while the Dynakitparts quad cap is $53 and fits right into the old quad cap cutout. Using the Dynakitparts quad cap will also keep your ST-70 looking original. If you use the Triode cap board you can just leave the old quad cap there but disconnected. The only advantage of the Triode cap board is more capacitance BUT (from experience over the years with the ST-70) the 170 uF on the Dynakitparts quad cap is more than enough B+ high voltage storage to run the amp.
Bob
wolverine- Posts : 59
Join date : 2010-02-20
I currently have two SDS cap boards and two quad caps in 4 different units I own. I have had two quad caps short out on me over the years personally, which is why I ended up getting the SDS boards. It gave me a complete upgrade on the bias section as well as the replacing the quad caps. The multi stage quad caps I find a bit easier to work with however because it is easier to change the resistors between the 2nd and third, and third and fourth sections to get the correct voltages. The SDS board is more difficult since you have to undo the board and it is cumbersome to work on once installed with all the wiring.
I remember having to change the positioning of the multi stage quad cap several times due to the differences between the original and the newer ones, you can read here on the forum in fact and see the confusion that can develop over different ideas on the correct symbols and where they should go, devil of a time trying to pin down the exact way to position it according to the symbols and all the different things I read about installing them.
I like the SDS boards in another respect, because if one section shorts out on the multi stage quad cap, then you have to replace the whole cap. On the SDS board you simply have to replace one of the caps on the board. It is certainly easy to get new caps for the SDS board. The SDS boards are very easy to populate and install, once you do one then you could do it in 10 minutes with your eyes closed LOL.
I find no difference at all as far as sound quality in the amp between the two in respect to hum. You will however see posts from folks stating that the "main culprit in the Dynaco ST-70 for producing hum is the quad cap". I have read many many posts on that subject. One of the multi stage quad caps I had developed some sort of ground problem inside and shocked the devil out of me when I grabbed it. I mean a good jolt. That was one of the caps I replaced with an SDS board.
wolverine
I remember having to change the positioning of the multi stage quad cap several times due to the differences between the original and the newer ones, you can read here on the forum in fact and see the confusion that can develop over different ideas on the correct symbols and where they should go, devil of a time trying to pin down the exact way to position it according to the symbols and all the different things I read about installing them.
I like the SDS boards in another respect, because if one section shorts out on the multi stage quad cap, then you have to replace the whole cap. On the SDS board you simply have to replace one of the caps on the board. It is certainly easy to get new caps for the SDS board. The SDS boards are very easy to populate and install, once you do one then you could do it in 10 minutes with your eyes closed LOL.
I find no difference at all as far as sound quality in the amp between the two in respect to hum. You will however see posts from folks stating that the "main culprit in the Dynaco ST-70 for producing hum is the quad cap". I have read many many posts on that subject. One of the multi stage quad caps I had developed some sort of ground problem inside and shocked the devil out of me when I grabbed it. I mean a good jolt. That was one of the caps I replaced with an SDS board.
wolverine
Bob Latino- Admin
- Posts : 3276
Join date : 2008-11-26
Location : Massachusetts
wolverine wrote:I currently have two SDS cap boards and two quad caps in 4 different units I own. I have had two quad caps short out on me over the years personally, which is why I ended up getting the SDS boards. It gave me a complete upgrade on the bias section as well as the replacing the quad caps. The multi stage quad caps I find a bit easier to work with however because it is easier to change the resistors between the 2nd and third, and third and fourth sections to get the correct voltages. The SDS board is more difficult since you have to undo the board and it is cumbersome to work on once installed with all the wiring.
I remember having to change the positioning of the multi stage quad cap several times due to the differences between the original and the newer ones, you can read here on the forum in fact and see the confusion that can develop over different ideas on the correct symbols and where they should go, devil of a time trying to pin down the exact way to position it according to the symbols and all the different things I read about installing them.
I like the SDS boards in another respect, because if one section shorts out on the multi stage quad cap, then you have to replace the whole cap. On the SDS board you simply have to replace one of the caps on the board. It is certainly easy to get new caps for the SDS board. The SDS boards are very easy to populate and install, once you do one then you could do it in 10 minutes with your eyes closed LOL.
I find no difference at all as far as sound quality in the amp between the two in respect to hum. You will however see posts from folks stating that the "main culprit in the Dynaco ST-70 for producing hum is the quad cap". I have read many many posts on that subject. One of the multi stage quad caps I had developed some sort of ground problem inside and shocked the devil out of me when I grabbed it. I mean a good jolt. That was one of the caps I replaced with an SDS board.
wolverine
A NEW cap board isn't any more reliable than a NEW quad cap. What happens is that if an ST-70 amp is not used for 10 to 20 years chemical changes occur inside the materials of the quad cap that can make it unreliable or unusable. That doesn't mean that "all quad caps are bad" OR that "quad caps in general are unreliable". A similar situation is the battery in an automobile in which the auto has sat unused for say 5 or 10 years. Chemical changes occur inside the battery and usually it won't hold a charge - SO - you replace the battery. That shouldn't be an indictment against all batteries. "Hmmmm - the battery went bad after sitting there for a few years - maybe I shouldn't use a battery again ... " I think you see what I am getting at ..
Your statement above >"main culprit in the Dynaco ST-70 for producing hum is the quad cap" is true. Understand that some of these quad caps are now 40 to 50 years old and have long since gone beyond their useful life span. Dynaco never thought, when they created the ST-70 in 1959, that some of these amps would still be in use 50 years later. Parts do have life span and they don't last forever.
A quad cap is a simple device and much easier to work on than a cap board. Contrary to what you say, if just one section of a quad cap goes you can bypass that section with individual caps. It is also easier to "add capacitance" to a quad cap than it is to add it to a cap replacement board. All you do is simply use an electrolytic capacitor of the proper voltage and connect the positive end to the quad cap and ground the negative connector to the chassis. This was most often done to the quad cap section that faces the back of the amp and powers the two output transformers.
A cap replacement board is not a magic pill to to alleviate all high voltage DC power storage ills. They are more complicated. The last three sections contain two 250 volt capacitors in series for an effective 500 volt single capacitor. When they do that they add 330K resistors to balance out any inequities in current draw between the two capacitors of the pair. If you want to remove any of the capacitors or balancing resistors for service you have to remove the entire board.
Bob
wolverine- Posts : 59
Join date : 2010-02-20
One thing I found that I mentioned was that it is a lot easier to work on the quad cap then it is the SDS board. Once you get all the wiring hooked up it's real tough to work on the SDS cap board. Personally I don't notice any difference in sound quality in reference to hum etc between the two.
wolverine
wolverine