Packard Bell DPA30-4 EL84 console amp blows fuses

[linuxslate]

Still check temp of power transformer after it has been in use for a while. Tubes in, playing music it may get warm, but should not be hot.

Tubes out, as others mentioned, it should not get warm at all.

I was going to say that 390 would be about the upper limit that I would want to run the B+ at.

I would try a small value power resistor between the rectifier and the replacement for the "A" capacitor.

That brings up a point -- Why do the 2 replacement filter caps look different? They are both supposed to be 40 uF @ (I recommend) 500V.

I understand if you just happened to have 2 different suitable caps, but if they are not up to the voltage, it could be the cause of the blown fuses.

 

[gadget73]

I'd put a 2 amp slow blow in there honestly. My Magnavox is a pretty similar amp and it runs under 1 amp normally.


Also worth considering what the heater voltage is. If you can get it to 6.3 vac by adjusting the variac, see what the B+ is. If that makes it normal, see if there is an extra 6v heater winding on the transformer that can be re--wired to work as a bucking winding. This did wonders for my Magnavox. I would not add a resistor between the rectifier and the output transformer feed though, it will make performance really go to crap. If voltages beyond the output transformers are high, you may need to tweak things to make up for the missing tuner.

Absolute worst case, try a 5R4 rectifier. They are lossier than a 5U4GB.

 

[rufleruf]

Let’s see...

Power transformer was cool after 30 minutes

The two caps are a 47uf 500v (blue) and 47uf 450v I had on hand. 47 instead of 40 a problem?

There is an extra winding that is unused. How do I use it as bucking?

 

[s-petersen]

Try one of these, i use it all the time.
http://www.audiokarma.org/forums/in...ital-amp-volt-watt-meter.724611/#post-9780581

 

[lordgarth]

Here's some of my photos. BTW your amp is a DPA-20, not 30

 

[gadget73]

There is an extra winding that is unused. How do I use it as bucking?

Basically you wire it between the fuse holder and the current wire going into the transformer. One direction will boost voltage, reversing the wires will reduce it.

I'd dial the variac to 12v for this just to make sure you don't over-volt things.

 

[rufleruf]

Clever gadg I could see how you'd want the voltage low until you know which way it's going. How much does it reduce it? I'm trying to get my head around how this would work. Gotta get a pencil out.

Lordgarth - thanks for the clarification on the model. Where did you get those OPT covers?? I was thinking of doing something like that.

 

[rufleruf]

Side note - If I have an AC amp meter, could I just wire it in series with the hot side on my variac? Is there anything else to it?

 

[rufleruf]

Did some reading on bucking with an unused heater winding.

http://www.ws.binghamton.edu/fowler...Convert from 115V Primary to 120V Primary.pdf

I'll give it a try.

Also read than an inrush limiter CL-80 etc will drop the voltage a few volts. Could give that a try too.

 

[gadget73]

Clever gadg I could see how you'd want the voltage low until you know which way it's going. How much does it reduce it? I'm trying to get my head around how this would work. Gotta get a pencil out.

Depends what the winding voltage is. If its a 6v, it would basically be reducing your line voltage by that much. Figure a ~5% reduction in voltages.

bigclive on youtube has a recent video about this, but basically what you're doing is making the primary winding longer so its wound for a higher input voltage. Instead of the original 117 vac input, it will expect 123 vac, more in line with whats probably coming out of the wall.

 

[lordgarth]

OPT covers came with purchase of amp.

 

[rufleruf]

Took a few weeks to get to it, but I added the extra 6.3V winding in as a bucking transformer and B+ now sits at just over 370V. Good deal! Time to find a use for this or do some more mods to continue learning.

I found mableaudio has output transformer covers - not sure I will get them.