Lap Amp

 


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This is a little unknown make and model Lap Amp.  It has 2) 6V6, 6N7 and 5Z3 in a push pull configuration.  The owner ask me for a little help in reconnecting the re-coned speaker with the output transformer attached.  We figured that out.  Now like any good vintage tube project the concerns are to be prepared for the eventuality of restoration.   The wax/paper caps are original.  The carbon Dog Bone resistors are original too.  

I always replace the waxed paper caps and those dog bone resistors.  The paper in the caps does not last.  It will leak (electrically) and perhaps short circuit.  The dog Bone resistors are 20% tolerance.  They should read with in 20% of the indicated value.  But I often find them bad.  

How to read a dog bone resistor

We have been covering what is needed to do a test power up.  One thing is to first, get the speaker re-connected.  Second is replace and get the AC bypass cap off of the Hot side of the replaced line cord.  Line cords from this vintage were not polarized.  If that cap is leaky or shorted the guitar player probably will get shocked through the lips from a grounded mic.  

I am personally from the school of restoration (replace all the caps, replace all the resistors).  The amp will then meet the factory design specifications and reflects the original intentions of the amp designer.  And, BTW, restored is what is sounded like when it was new.  

Now for some pictures:

IMG_9624.JPG (1643056 bytes) Looks nice.  The owner nicely cleaned up this vintage Lap Amp. IMG_9622.JPG (1138804 bytes) IMG_9619.JPG (1166091 bytes) IMG_9612.JPG (1283674 bytes)I could not see the value of the black cap in the lower right secured to the chassis.  IMG_9638.JPG (98086 bytes)I could not see the value of the waxed/paper cap in the lower right against the chassis.  
IMG_9642.JPG (269717 bytes) IMG_9645.JPG (274194 bytes) IMG_9647.JPG (256343 bytes) IMG_9649.JPG (269301 bytes) There is a cathode resistor from V1-8 to ground.  I could not see the colors.  IMG_9651.JPG (249644 bytes)
IMG_9652.JPG (258862 bytes)That bypass cap (orange) is connected from Hot to chassis.  It should be connected from Neutral to chassis.   IMG_9655.JPG (275085 bytes)      

 

scan0005.jpg (1328685 bytes) This is the current revision of the unchecked schematic.  It need to be traced against the actual circuit.  I am working from pictures.   Green Line (pencil) the correct connections and components.  Put corrections in red.  Correct part values in red.  

 

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