new d-lite blowing fuses on power up

[pinkmarkos]

hello everyone- Just completed my first d-lite build (after a couple successful TW builds) and it is blowing fuses instantly when trying to power it up with the bulb limiter. I am using the brown note layout with chassis, Edcor trannies, and boards from RJ. I am using the progressive off-stby-on switch for my power and I suspect I may have wired it incorrectly. All grounds are good as far as I can tell. Included are some pics of the power supply area and wiring diagram for the switch. Any diagnostic help would be highly appreciated. Thanks!

[rock_mumbles]

I can't tell from your pictures what's what ...

What you need to do is connect one power transformer primary lead to the AC common on the IEC connector (or AC supply cord), also connect one lead of the indicator lamp to this connection as well.

The the other power transformer primary lead and the AC line from the IEC connector will connect to the 'AC' switch lugs on the switch. Connect the other lead of the indicator lamp to the same switch lug as the power transformer primary is connected to ...

The standby is connected just like a normal standby switch.

[pinkmarkos]

thanks for looking- I know the pics are hard to discern what is going where. I believe I have it wired how you are suggesting already. One side of the switch has the hot (through the fuse) to one lug connected with one side of the indicator light and one leg of PT primary, and the other side of the switch has the neutral connected to the other indicator lead and the other PT primary. Other side of the switch is standby (red leads). Far as I can tell, this should work. Guess I'll give it a rest and put some fresh eyes on it tomorrow. Thanks again for your input

[Guitarman18]

Hi pinkmarkos,

It's not going to sort out your issues but you have wired your presence pot the D'lite way instead of the D*mble (correct) method. Check out the sticky layouts in the files section for the correct method.

Hope that helps,

Paul.

[ToneMerc]

Personally, I would reconfigure that hybrid bias supply while you're at it. Looks like you will need more resistance anyway.

TM

[Structo]

Which power tranny did you get?

So you are taking the bias supply from the HT?

What wattage light bulb are you using in your limiter?

[amplifiednation]

I would move the earth ground on the IEC to it's own dedicated screw, lug, and toothed washer, closer to the IEC switch.

That is the most important solder joint in the entire amp (safety-wise). I'm not sure it's why your blowing fuses, but you have the PT and also the 1R bias resistor current flowing to that same grounding point. Too many variables. (actually do you have the 1R resistor...i can't see it?)

[M Fowler]

You could temporarily change to a power switch only with no standby switching to test. If that gets the amp fired up then I would go back and see why the amp blows fuses at start up.

Mark

[amplifiednation]

Did you test continuity on the switch

[pinkmarkos]

OK- have had a chance to check replies (thanks to all the input BTW). I have moved the IEC ground to its own dedicated spot, and moved the center taps to their own dedicated ground. Looking back, I should have realized that grounding almost everything to the same point was not a great idea.

I checked continuity on the switch. It seems the switch is closed in all three positions on the power side. This isn't consistent with the wiring diagram. Standby side seems OK.

In regards to the presence pot, my boards are made to work with the D-Lite layout, thats why I wired it that way. (I also realize the capacitance and voltage is incorrect, waiting on the correct cap to arrive). Also, no room on my board for the cap/resistor. I'm still trying to understand to understand to nuances of NFB circuits... hopefully once I get this thing powered up correctly

PT is an Edcor. 300-0-300, 250mA. 6.3VAC CT. 4.8 A. No bias tap, hence my bias scheme. I had considered that my bias voltage will need to be adjusted, I just wanted to get it powered up first. I do have the 1R resistors in place, just can't see it from the angle of my pics. Tone Merc- how would you reconfigure the bias supply? Just add more resistance?

So, I tried another power up with the new grounding scheme. Using a 28W bulb, I still get no dimming to the the bulb, so something is still wrong. However, this time my indicator light stays on until I go to the middle position on my switch (which should be standby) and the fuse blows right away. So I am still stumped. I am considering implementing M Fowler's idea to do the power switch only with no standby. Is it wise to let B+ to the rest of the amp if I'm still blowing fuses? Thanks again for everyone's help.

Mark

[ToneMerc]

Tone Merc- how would you reconfigure the bias supply? Just add more resistance?

So, I tried another power up with the new grounding scheme. Using a 28W bulb, I still get no dimming to the the bulb, so something is still wrong. However, this time my indicator light stays on until I go to the middle position on my switch (which should be standby) and the fuse blows right away. So I am still stumped. I am considering implementing M Fowler's idea to do the power switch only with no standby. Is it wise to let B+ to the rest of the amp if I'm still blowing fuses? Thanks again for everyone's help.

Mark

Pres- some of the D'Lite layouts floating have the Pres control wired wrong. You can circle the wagon on this later.

Bias- you can just leave it as is. Actually you might have to decrease the first resistor to around 180k. I think I see, 220K >10k pot>27K correct?

Short-( divide and conquer)- like Mark said remove that PSS. If the fuse still blows, start disconnecting feeds off the PT secondary until the short goes away.

Tm

[Structo]

I see 220K-10K pot-22K

With the 28w light bulb which is a weird value, you are only supplying about 280ma current.

Try a 40 or 60w light bulb.

If you wired your amp like a stock D'lite, the reservoir filter (B+cap) isn't supplied until the standby switch is thrown so there won't be the typical flash of the light at first.

I would disconnect that power switch and temporarily at least, wire two switches.



With your bias supply wired to the HT, you are not getting a bias voltage until the standby switch is thrown.
Usually you want that bias voltage before the B+ is supplied.


Are first trying the power up with no tubes? (you should)


And just to be certain did you wire your limiter like the diagram?

[rock_mumbles]

...
(a) One side of the switch has the hot (through the fuse) to one lug connected with one side of the indicator light and one leg of PT primary,
(b) and the other side of the switch has the neutral connected to the other indicator lead and the other PT primary.
(c) Other side of the switch is standby (red leads). Far as I can tell, this should work. ...

I've edited your quote to be able to identify your statements
(a) and (b) are not right ...
(a) one lug of the AC side of the switch will have the AC line from the fuse nothing else, the other lug on the AC side of the switch will have the PT primary and one of the the indicator leads.
(b) these wires do NOT connect to the switch they are simple connected together and insulated.
(c) sounds correct

......

The way you have it wired when you switch the amp ON you are connecting the AC line to the AC neutral and therefore blowing the fuse

[pinkmarkos]

To rock mumbles- Thank you! I rewired the switch per your instruction and it now works correctly with no blown fuses. I made it through the rest of the power up successfully without any problem. Next up is to refine my bias supply to get some more negative voltage to the grids. I'm at max negative 18V or so and my tubes (using 5881s) are redplating. But I am getting sound, which is awesome. Thanks again to the Amp garage community for all the help.

Mark

[rock_mumbles]

Cool!!!