Hum in the st70

[kheper]

My st70 has developed an intermittent hum.
I have traced it to the multi-cap. When I touch
or twist the cap slightly, the hum vanishes,
temporarily.

Could this be a ground problem, speculating
that the metal in the twist-locks are not making
contact with the chassis? There is a lot of play
between the cap and the chassis. Or, could
the cap be on the verge of 'leaving this world'?

[erichayes]

Your first hypothesis is probably correct. When I restore any of the bigger Dynas, I solder the tabs directly to the chassis with an 80 watt Weller iron, and make that my single chassis ground. Fortunately, the other ground points aren't that far away, so "starring" is not a real problem. Just make sure that all your input and output jacks/terminals are individually isolated from chassis ground, and are connected to the star (or bus) instead. PITA, I know, but the results are worth it.

[kheper]

From what I hear about the premature failure
of the recent production of multi-caps and
my hum problem, I am going to discard the
multi-cap and make a cap board from the
550/600V axial caps pictured below.

http://www.die-wuestens.de/kb/KONEL.jpg

The available values are 10, 22, 47, and 100
uf.

47-100-100-100 will make a rather nice
power supply filter.

[EdStiles]

Just as FYI guys, the Dynakit Parts cap is not a CE. I got one and found that it is actually a German F&T. It has a surge rating of 600 vdc, unlike the CE.

If you compare the Dynakit Parts label with the labels on the site below, you'll see the similarities. BTW, the site is in both English, French and German.

http://www.die-wuestens.de/eindex.htm (F&T caps)

http://www.dynakitparts.com/store/product.aspx?id=273

Ed the Solder Slinger

[kheper]

The product #: KTL25 matches the Dynakit
Parts multi-cap. Looks like a winner. But, it
is 50 beans. Though, it may be worth it.

[Bob01605]

Kudos should go to Kevin at Dynakitparts for importing that high voltage 80, 40, 30, 20 quad cap from Germany. It is a boon to Mark III users who had to deal with a marginal 525 volt quad cap.

That CE distribution cap IS, however, just fine for an ST-70 which has a lower voltage surge than the Mark III. I personally have used over 40 CE Distribution 80, 40, 30, 20 quad caps in the Dynaco ST-70. NONE have failed. I guess they had some problems initially with this cap but have worked out any issues with this quad cap.

IMHO this cap is fine for a Dynaco ST-70 but I would opt for the higher voltage version that Dynakitparts sells if I were to replace the quad cap in a Mark III.

Bob Latino