Strange squealing in amp when powered up.

[jelle]

Make sure all pieces of bare wire and solder splatters are out of the amp. I evidence of both on the PS board. If they are anywhere else too...recipy for trouble.

[Matt J]

Here's a layout of the power supply board I'm using. It's done with Microsoft Paint, the quickest thing I could come up with.

I'm going to go over and clean up around the board some more too Jelle, maybe there's a washer or something that's loose in the chassis and causing a screwy connection.

- Matt J.

[Matt J]

Oh, I forgot to add this: all the positive ends of the electrolytic capacitors point towards the bottom of the image!

[Structo]

Looks right to me.

[markr14850]

Keep the grounds and the yellow wire from the HV supply board connected.

Remove all other connections.

Power it up and see what happens.

Check the DC voltage on the yellow wire.

If all is ok, add the next piece - the standby switch wiring. Try it again.

If ok, add the choke, ...

Edit: And *BE CAREFUL*!!! This is the most dangerous part of the amp. It can kill you real fast!

[Matt J]

Thanks for the tips markr14850!

Yes, I'm quite cautious and paranoid when working with the amp on. Safety goggles, standing back from the amp on my workbench and with one hand behind my back. I certainly DO NOT want to get zapped by any of these voltages running through this thing!! It would literally be the last thing I do!!

Ok, I'm doing some tests this morning.

Here's with the limiter turned ON (I'm using a 25w bulb by the way) and no tubes in:
Primaries:
Connection with fuse: 16.08VAC,
Connection with mains switch: 66.8VAC
Secondaries:
Top row of diodes: 235VAC
Botton row of diodes: 219VAC
Heaters: 2.45 VAC
Junction of yellow HV wire and 220uf caps: 628.6VDC

There are no popping or snapping noises of any kind.

How does this look to everyone? Is that too high a voltage on the HV wire even with no tubes in and the limiter on? I'm going to try it later with the limiter off after I get some feedback just to be careful

Thanks everyone!
- Matt J.

[Structo]

The voltages won't be reliable with the light bulb hooked up.

What you want to look for is how it acts when powered up.

When you first throw the power switch the light bulb should flash brightly then quickly go down to a low glow.

The flash is the caps in rush current.
Then as they charge the current demand goes down so you get the low glow.

What usually do on a new build I am unfamiliar with is I'll use a 25w bulb, that keeps the current down around 250ma.
If that test is OK, then I'll do it again with a 60w bulb.

If there isn't any smoke or outrageous voltages I pop the tubes in and remove the bulb limiter from the circuit and try the amp.

Not sure how you are getting 625volts with the limiter on so you might want to look over the power section very carefully before going forward.

Do you have your meter set to DC volts and have the black probe grounded to the bare chassis?

And are probing with the red probe?

[markr14850]

That 628VDC seems pretty high, especially as the limiter is putting your primaries at half of normal.

I'm unclear how you're measuring the VAC of the secondaries. Try taking an AC reading from one end of the secondary to the other - not referencing ground. Also, please take another reading of the primary, end to end, as well - so we have a reference.

Lets see pictures, layout, and schematic for your HV rectifier board. Maybe you have a voltage doubler there?

BTW, don't try powering it up without the bulb limiter for now, as you might go way over voltage on your caps.

--Mark

[Matt J]

I was measuring the secondaries wrong! I had the black probe attached to the chassis.

I remeasured them the other way, with the limiter I'm getting 84.9VAC on the primaries and 470VAC on the secondaries. There is a red/yellow 0v wire I have not attached because I have not seen anything to clearly attach it to. Could this be some type of center tap wire that should be grounded? Because there's already an orange wire that is grounded. Here's a layout of the Hammond 290fx PT I'm using.

Here's two pictures I took of the HV board. The mark on top of the 100uf/100v bias capacitor is where it got bumped by the soldering iron (oops).

I'm using the layout of #102 posted on here and I'm reattaching it:

Thanks again for everyone's help in this!

- Matt J.

The schematic is the same, here's the power supply section:

[rogb]

I was measuring the secondaries wrong! I had the black probe attached to the chassis.

I remeasured them the other way, with the limiter I'm getting 84.9VAC on the primaries and 470VAC on the secondaries. There is a red/yellow 0v wire I have not attached because I have not seen anything to clearly attach it to. Could this be some type of center tap wire that should be grounded? Because there's already an orange wire that is grounded. Here's a layout of the Hammond 290fx PT I'm using.

Here's two pictures I took of the HV board. The mark on top of the 100uf/100v bias capacitor is where it got bumped by the soldering iron (oops).

I'm using the layout of #102 posted on here and I'm reattaching it:

Thanks again for everyone's help in this!

- Matt J.

The schematic is the same, here's the power supply section:

The red/yellow on the Hammond is the HV center tap (as shown in the diagram). It needs to be grounded as per your attached layout. I also fuse mine for some extra protection, 500mA fast blo.

[martin manning]

If it's the HT center tap, that red-yellow has to be grounded or you won't have any B+... don't cut it!

[ToneMerc]

I was measuring the secondaries wrong! I had the black probe attached to the chassis.

I remeasured them the other way, with the limiter I'm getting 84.9VAC on the primaries and 470VAC on the secondaries. There is a red/yellow 0v wire I have not attached because I have not seen anything to clearly attach it to. Could this be some type of center tap wire that should be grounded? Because there's already an orange wire that is grounded. Here's a layout of the Hammond 290fx PT I'm using.

Here's two pictures I took of the HV board. The mark on top of the 100uf/100v bias capacitor is where it got bumped by the soldering iron (oops).

I'm using the layout of #102 posted on here and I'm reattaching it:

Thanks again for everyone's help in this!

- Matt J.

The schematic is the same, here's the power supply section:

The PS schematic is incorrect for that layout and the 102 diagram does have the red/yel HT centertap to ground. Not grounding the HT CT makes a world of difference.

See the schematic for #124, review the PT.

[talbany]

Rogb is correct red/yellow is center tap for HV... That transformer does not have a CT for the filiments so you will need to add the false CT at pins 2/7..Take a Deep breath!!
If you are getting 628 on the sec and on the plate caps (rated 600v) is too high so be careful..I see you had the Powerlytics originally.. Do you know how old those caps are and IMHO should most likley should have been formed first.. Not to say that this is the problem but could have contributed..
You going to have to step back and do some math.. What is the HV B+ rated *1.41 should give you DC voltage after rectification...If you want to do the math on the caps here it is..

the basic formula for caps is Q = C*V, where Q = charge in Coulombs, C = capacitance in Farads and V = voltage in volts. The formula works as-is in DC circuits, and you can use it to analyze your case. When two caps are totem-poled, they will have a common terminal which will force them acquire the same charge. The total voltage applied to the pair, V, will be, using the formula above:

(1) V = V1 + V2 = Q/C1 + Q/C2

diving both sides by Q,

(2) V/Q = 1/C1 + 1/C2 = 1/Ceq

So this is the equivalent capacitance for the series is C eq = 1/[1/C1 + 1/C2] -- same formula as for resistors in parallel; caps in parallel, othe other hand, add up like resistors in series. You can use Equation (1) above to see how bad off your caps are:

Tony

[martin manning]

The 290FX should be wired as a full-wave rectifier not a full wave bridge. You're hitting the power supply with twice the voltage it should have!!

[talbany]

Martian
What am I missing? Using the CT Red Yellow should give him 320 AC and 451.2 DC unloaded.