SCA-35 Selector Switch

[dcgillespie]

Hi --

I'm looking to obtain one of the later version selector switches for an SCA-35 I am restoring to original condition for basically a museum/reference piece.

My existing unit has the early type selector switch in it that has a finger installed at terminal #2 on the rear side of both switch wafers. These fingers serve to short the output of the preamps to ground when low level sources are not selected. The problem is -- and as Dynaco also found out -- this causes the preamps to basically become oscillators in the audio band, which can be heard under certain conditions of no signal.

Early versions of the schematic show this finger, which my unit has. Later versions of the schematic have this finger removed, so I'm assuming there was a production change in the switch to remove it, as removing this finger does solve the oscillation problem.

At any rate, if anyone out there has a newer type switch without the finger that they would be willing to let go of, I'd appreciate it! I just thought I'd check before attempting to operate on the one I have.

Dave

[Pyre]

Hello, Do you happen to have a picture of the terminal in question. I have a couple of SCA-35 corpses at home that may have the selectors still attached. I can check for you when I get home from work.

Are you making a Dyanco museum?

[dcgillespie]

Thanks Pyre --

Kind of you to respond and look.

I have no pictures but it is easy enough to describe:

With the selector switch installed in the chassis, and with the chassis right side up, look squarely into the back of the switch so that you are viewing the rear of both wafers. The through bolts holding the switch together will be at the 6 and 12 o'clock positions.

Viewed in this manner, going counter-clockwise from the top (12 o'clock) through bolt on the rear of the wafers, terminal #1 is just to the left of this through bolt. It will not have a finger on the rear of the wafers. Continuing on around in a counter clockwise fashion, the next terminal (#2) is the terminal of interest.

My selector switch has a short finger located on the rear of the wafers at terminal #2, but I believe in newer versions, this finger has been eliminated, and is the switch I seek. Do not confuse this with the finger on the [/i]front side of the wafers at terminal #2, which does and should have a finger located there. Hopefully this is clear enough for you to check rather easily.

Hafler and Laurent were giants in the early audio game to me. Their design innovations, performance goals, and overall accomplishments left a mark that changed audio history, and is lasting to this day. For all the endless modifications that can be done to their equipment -- of which I have done my fair share -- I have always wanted to have pristine original examples of what their original efforts produced as well. If anything, they serve as a wonderful reminder of just how far today's technology has (or has not!) advanced the art. I already have excellent examples of the PAS preamps, MK III power amps, and Stereo 35 & 70. The SCA-35 I'm working on is likely the final piece I'm trying to finish up. Any help you can provide with the switch would be greatly appreciated!

Dave

[Pyre]

Hi Dave,

The selector switch I have does not have a tab at position 2 but does have one at position 3. Is this the switch you want? If so just PM me your address and I will post it to you and any other of the front panel stuff if you want it.



I also am a huge dynaco fan and have been putting together a collection of stock and modified equipment. I also have bucket loads of original parts if you need anything else.

[dcgillespie]

Thanks Pyre --

I've sent you a PM, but am also posting here to say that is exactly the switch I need so that others might be aware of this problem. The lack of a short finger at position #2 on your switch proves that there was in deed a production change to the switch, as mine has a finger there which grounds the preamp outputs when not selected. This causes the preamps to oscillate which can clearly be heard under no signal conditions.

If anyone else has experienced this problem, then seek out a later production selector switch without this finger to solve the problem.

I don't know at what point Dynaco caught this error, but they obviously did. The production date of my unit was the 15th week of 1964, which is the year the SCA-35 was introduced, so it was at least after that. If anything, the date shows how early my unit really is!

Dave