Dynaco ST-35: My experience buying and restoring.

Peter W. wrote:First of all - whereas I may not entirely agree with your means-and-methods - which is more stylistic than of substance - I really have only one quibble (so far, and on Part 2 & 3) which is your advocacy and installation of a 3-wire line cord, with a ground directly to the chassis.

Second I am impressed with the level of detail and care displayed. Many could learn from it.

The entire issue of 2 vs. 3 wire line cords has been discussed to death on other threads herein. As I note, it is a quibble, not a condemnation of the practice. I prefer using a polarized 2-wire cord - or a non-polarized cord, if, like me, you are plugging that amp into another component that does not accommodate polarized plugs. But the PAS does have a polarized plug and I have marked the rear receptacles as to which is hot and which is neutral.

Curious - have you done other equipment since? Not necessarily Dynaco, but other tube stuff? Has your bench evolved?

Thank you for the post and links!

peterh wrote:My experience is that grounding amps together will reduce hum, especially if one can
connect to a real ground.  
AMEN to that! I am blessed to live in a house with a 1930-style hydronic cast-iron radiator system. Code requires a  hard connection to a proven ground - typically the domestic water service. In our case that, and two ground-rods. 4" cast-iron mains filled with inhibitor-laden water are excellent conductors.

What sometimes bites is that there could be several ground(s) , that floats on different potential,
and this will introduce hum. Cable-tv coax is one, using several outlets another.

Absolutely. And why the main Ground must be at the lowest potential in all cases. BUT....

Grounding amps will also reduce the risk for electrocution.

Current will flow 'downhill' and is entirely indiscriminate as to which direction that might be. The main system ground must be verified, or it will increase the potential for shock by raising the chassis above the neutral in some extreme cases. A VERY bad thing.

( a contradiction is servicing, here sitting on a isolated rubber mat, and no real ground for
device under test and instruments ( but all interconnected) reduces the danger if one accidently
touches a live cable) .

A few things: Concrete floors are quite conductive, and basement floors are the worst. After which are reinforced concrete floors in metal-pan subfloor. Any servicing tech must not rely on a rubber mat or any other passive device. And why it is I advocate for an isolation transformer to be used for service work, especially diagnosis.

An ground fault interrupter ( which has nothing to do with ground) is mandatory. But this practice is illegal for employees in sweden. I do it for myself anyway)
The above setup does not prevent danger from B+ however, thus one should not work alone
instead a mate in the neighborhood that knows heart resurrection :-)

A GFIC device, as with an Isolation Transformer, is one more step in general safety. But working with an Iso really does make things safer. Not 100% by any means, but MUCH safer than without. NOTE: Use only a medical-grade or industrial grade device. Cobbling two conventional transformers back-to-back is simply not a good idea. Perhaps better than nothing, but only perhaps.

( ground fault interrupter works by comparing current in one lead with the current in the other. If
any differences , usually by leakage to ground, will cut the power. Sensitivity a few mA !)