Silvertone 1448

[lowell]

I have installed a 3 prong cord in this. It's an amp in a guitar case dealy. I also recapped it. When installing the 3 prong cord I rewired these items. The bottom of the filament transformer only goes to the power switch now. I jumpered across the 68k/cap so all ground are earth grounded to the 3rd prong. The thing is blowing my circuit breaker, but only after being on for about 10 seconds. What did I miss? Yes I know it should have an iso transformer for safety, but I'd like to fix this issue first.

http://elektrotanya.com/PREVIEWS/634..._sch.pdf_1.png

[nickb]

It sounds like you have neutral and earth shorted with the result that some of the neutral current is returning via earth so tripping the RCD.

[DrGonz78]

Adding a ground wire to that amp design will not add any safety factor. That amp need needs isolation from the mains voltage, isolation transformer.

Edit: If there is added safety adding a ground wire to amp design like this then I could be wrong. My first instinct looking at that schematic is what I wrote. I would be curious to know the advantages of adding a safety ground in this situation though.

[lowell]

There is added safety. If anything shorts to ground internally, it shorts to earth...and the circuit breaker will blow before the current shorts thru YOU thru your guitar. I understand that adding an iso transformer is ideal...as in my original post.

Nickb I don't see anything shorted via neutral to earth. If you dont see anything wrong with the way I wired it then maybe a tube is faulty. But the tubes were fine before the mod.

Again, it takes about 10 seconds before it blows the breaker. And even with my light bulb limiter, it takes a while longer, but blows the circuit breaker.

[lowell]

Here's how it's wired. I do not have the output transformer connected as it's mounted directly on the speaker and I have the thing out of the case on the bench. Wondering if this is why it's blowing the breaker.

[Jazz P Bass]

Why are you screwing around with this?

It's a "Widow Maker'.
Plain & simple.

Get an iso.

[oc disorder]

Meanwhile in Australia we didn't have department stores encouraging us to become Rock & Roll delinquents ,
nor did we have women with the intensity and allure of Nancy inviting us to be walked on!

Seriously these are interesting to us who didn't experience this kind of marketing.

Sorry for interjecting.

Back to the safety issues where an isolation transformer is mandatory for our younger readers
who don't know who Nancy is and have a few years ahead of them unlike us !

Wikipedia - Danelectro Amp in case.
https://en.wikipedia.org/wiki/Danelectro_Amp-in-case

[nickb]

Here's how it's wired. I do not have the output transformer connected as it's mounted directly on the speaker and I have the thing out of the case on the bench. Wondering if this is why it's blowing the breaker.

The HT current is returning via the safety earth (not shown and which I presume is connected to the chassis).

[Jazz P Bass]

Meanwhile in Australia we didn't have department stores encouraging us to become Rock & Roll delinquents ,
nor did we have women with the intensity and allure of Nancy inviting us to be walked on!



Back to the safety issues where an isolation transformer is mandatory for our younger readers
who don't know who Nancy is and have a few years ahead of them unlike us !

[/url]

Nancy (Legs) Sinatra


https://www.youtube.com/watch?featur...&v=SbyAZQ45uww

[52 Bill]

You are asking for trouble here. I can understand you wanting to try this, but you should rethink it before you kill yourself or the owner, if it isn't yours.

My guess is that it takes time for the fuse to blow, because the filaments need to warm up before the current begins to flow. Why did you connect the original separated grounds together?

How do you have the Hot (black) and Neutral (white) wires connected to the amp?

[nickb]

The point is this. You cannot fix your RCD issue with removing the safety earth. Therefore you are no further forward than where you started. So you might as well get the isolating transformer now and be safe. Also, you should add a full wave rectifier after the heater transformer but before the 35W4 to prevent the iso transformer from saturating.

$50 or your life? ITR300: JAMECO VALUEPRO: Power Supplies & Wall Adapters

[J M Fahey]

Yes I know it should have an iso transformer for safety, but I'd like to fix this issue first.

YOU DO NOT UNDERSTAND:
FIRST YOU ADD THE ISO TRANSFORMER
SECOND: you find your problem magically DISAPPEARED

[eschertron]

Here's how it's wired. I do not have the output transformer connected as it's mounted directly on the speaker and I have the thing out of the case on the bench. Wondering if this is why it's blowing the breaker.

As Nickb says, the HV side of the rectifier is connected directly to the chassis via the hand-drawn path. With the rectifier out, and the amp unplugged, verify continuity to see that it is so.

[lowell]

Ok I get it guys. Haha I had a feeling I'd get the ruler on the wrist for even trying this. Thank you for the concern and insisting. So, in my drawing, I see no direct connection of the HT to safety earth. Are you saying that the main filter caps should NOT be grounded to earth? Is this why the breaker is blowing? I think I'm missing a basic electronic rule here. Which is embarrassing honestly, been working on amps for about 16 years. There's something I'm missing about this amp having the GROUND be the neutral of the mains, and not earth ground. And I'm guessing this is because there is no ISOLATION transformer. Final question here: This customer may or may not want to pay for the iso and labor. If so, should I convince him because of the "widow maker" issue? And if so, how could they manufacture amps like this back in the day with the risk of killing people??

[52 Bill]

Final question here: This customer may or may not want to pay for the iso and labor. If so, should I convince him because of the "widow maker" issue? And if so, how could they manufacture amps like this back in the day with the risk of killing people??

If the owner does not want to pay for the repair to be done correctly, you should turn down the job.

This version at least has an isolation transformer to separate the input stage and ground from the ac line.