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Vintage amp info and power cord?

Started by cerealport, May 14, 2015, 06:33:36 AM

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cerealport

I just acquired this vintage amp and I'm trying to see if anyone might know anything about it...  It has a model number DV112 etched into it.

I'm also trying to find a suitable power cord to use with it... It's a three prong ac connector.  Would any extension cord work?  Anyone seen anything similar? This is my first vintage amp so any help would be amazing!





Roly

Hi cerealport, welcome.


The power board looks like it has had a couple of caps removed, and a fine blue wire kluged in there for some reason.  I would certainly investigate this before I applied power.

With an amp like this that is a total unknown quantity it's a good idea to initially power up via a limiting lamp.
If you say theory and practice don't agree you haven't applied enough theory.

Enzo

And on the power amp I see two TO39 transistors.  Each has a rectangle drawn around it on the board, leading me to think it originally had a heat sink for each.  Probably RCA 40409 and 40410 types.  If those were replaced without heat sinks, they would likely overheat.   But all that is just an assumption.


yes, the power cord would be a plain old three-wire extension cord.

tonyharker

Da Vinci amplifiers were made by Magnatone and they just re-badged their standard models.
The transistor versions were build between 1967 & 1968. 
You may be lucky and find a schematic.
This site may be able to help you www.magnatoneamps.com




Roly

Quote from: EnzoProbably RCA 40409 and 40410 types.

I agree, but with one reservation.  These transistors also had downward lugs to attach the heatsink portion to the board, and I don't see matching holes in the board for these lugs, but it certainly looks like somebody intended the drivers to have heatsinks that aren't there.

I'd approach this one with considerable caution and suspicion because it looks like it has been badly messed about at some stage in its long life.  Until you get it going you are going to need to be in constant reality-check mode.

Here is an account of my own bruising encounter with a messed about Gibson amp.
If you say theory and practice don't agree you haven't applied enough theory.

cerealport

Thank you all so much for your responses... I got an extension cord and powered up but there's definitely an issue.  As soon as it's powered on it has a hum that alternates loud every second like a square wave. None of the knobs or switches have any effect on the noise and no input is heard.  Any ideas on what could cause this? 

Roly

Quote from: RolyI'd approach this one with considerable caution

Just plugging it directly into the mains without a limiting lamp isn't "considerable caution" - it's an invitation to smoke something.

I hope you wouldn't try to drive a car that obviously had a wheel missing - this amp is obviously missing bits it needs to operate properly.  Two highly experienced amp techs have told you that they can see that this amp has problems, and that they need to be investigated before you do anything else.  We can only advise but if you ignore vital advice/warnings we aren't going to get very far.  You have tapped into hundreds of years of collective professional bench experience here, make wise use of it.   ;)

To do;
Until a circuit turns up we need well lit crisp and clear pix of the main power board, both sides.

Disconnect the speakers at the amplifier end (if you value them).

What is the actual value of the fuse fitted to the "2 amp" holder?

Until we get a circuit or pix you can remove the output transistors and test them.  Be careful not to mix them up as they may be different (mark as you remove).  Post their type numbers.

You can also make up a limiting lamp which you are going to need down the track.


To be crystal clear - this amp shows signs of being hacked by somebody who is clueless, and who has abandoned it in a mess.  This doesn't mean it's unrecoverable, only that there may be several introduced faults apart from the original failure that was being chased, so we need to proceed very carefully.
If you say theory and practice don't agree you haven't applied enough theory.