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Dynaco 150 (Van Alstine Mod)

timmage89

timmage89

Member
I picked up a Dynaco 150 from the original owner. He built it from a kit, then had it modded in the 90's by Van Alstine here in Burnsville MN. Well I got it home and hooked it up to my test system, seems to work great.

Popped the cover off and holy cow, MASSIVE capacitors in this thing. I can't find any other Van Alstine examples online with caps of this size - anyone have any info on this type of mod?

I'm considering hooking this up to my main system, but the amp's reliability concerns me. I've read some examples of high voltage shooting to the speakers after powering off the unit. It looks like there are a good amount of fuses in here - think it's safe?
 

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Bring it up on a Dead Bulb Tester (DBT) or a variac. Monitor the output voltage on both speaker connections. If you got a couple of 8 ohm resistors (20-50 watts), those help. Otherwise, I'd not be connecting speakers unless you don't care what happens to them.

Cheers,

David
 
I recently went through my neighbors 120 and had similar fear. I used a 8 ohm load and scope to verify it was working.

I fixed a Van Alstine power amp i think from the *70s* that had huge PS caps. I think it was the thing to do in the 70s-80s. Audio Amateur seemed to promote stiff PS without understanding the affects on the power on/off switch and other concerns.

I might want to add an inrush limiter to protect the switch.

Bring it over and we can through it on the bench for a once through.
 
Well here's what I found:

Set multimeter to lowest voltage (200mv). Plugged into speaker terminals. During operation it reads 0 constantly on both channels (odd?). Hitting the power switch seems to do nothing, as if it is bypassed. When I unplug the amp, after about 10 seconds, I get a bump up to about 5V, and it slowly discharges over 10 seconds.

My intuition tells me this is bad - your thoughts? It seems to sound nice on my test speakers, but I want to make sure it's fine to use on my mains.
 
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