[Jukebox-list] wurlitzer amp blowing fuse...

[Don]

Hello Bill,

There seems to be a little confusion here.
Apart from the fact I don't have the schematic to refer to and so, am taking 
certain risks here...

You say you can measure from center tap to each side of the 5U4.
This presumes you have some point say "a" where you can access the center 
tap of the winding.....  Actually you should be picking your ground point at 
the place where the center tap wire is connected to the chassis. This point 
is depicted by "b" in diagram.

-------------------------------- PLATE of 5U4
B
B   coil @ 51 ohms
B
B
>"a"--------C.Tap----- GROUND"b"chassis
B
B
B  coil @ 51 ohms
B
------------------------------- PLATE of 5U4

So, I wonder, how can you get 44 ohms between "a" and GROUND...? Unless the 
wire from "a" to GROUND is corroded or not electrically tied to chassis 
ground due to a loose bolt or cold solder joint or.....
I wonder what point "a" it is that you are calling "center tap"....
I wonder if you are using the same "GROUND" point for all your measurements.

 I suspect your 600 + volts is "floating" that high because something is not 
grounded, either the CT of the power transformer's secondary or something 
else such as the grounds for the electrolytic filter capacitors.

If, you have no other option but to rewind.... I do that. After holidays in 
next weeks.

Cheers,
Don




----- Original Message ----- 
From: "Bill Taylor" <bt_2627 at yahoo.com>
To: "Jukebox mailing list" <jukebox-list at lists.netlojix.com>
Sent: Wednesday, October 04, 2006 6:41 PM
Subject: Re: [Jukebox-list] wurlitzer amp blowing fuse...


> Jay, and everyone...
>
> I'm still looking to find my problem on my amp.  I
> thought it was the 30mfd cap, C35A.  Got it yesterday
> and put it in the circuit.  Ran about 5 seconds,
> charged up to 600V, then blew the fuse.
>
> Hmmm.. ok, not that.. not much left either...
> transformer T1?  Now, I think someone told me to
> ohm-out the transfomer of the output stage, T3 from
> center tap to the 6L6s, and it worked OK.  I didn't
> look at T1, the secondary windings from the primary
> power transformer before (or at least, if someone
> already told me to watch that, I missed it).  So,
> thought I'd ohm from the center tap of the secondary
> winding T1 to both sides of the rectifier 5U4 with
> tube pulled out.  Both sides ohm'd about 51 ohms so I
> guess that's OK.  Just for grins, checked ohm from
> center tap to ground.  That measured about 44 ohms!
> Should have been a complete open, right? (or am I
> missing that too?).  So if that's the case, I guess I
> have a transformer to replace huh?  Maybe that's
> what's been bringing my voltage up to 600V off that
> rectifier, which should have been only 390v.
>
> -- Bill Taylor
>
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