st- 35 shorting out somewhere.

[Shannon Parks]

HI...

I checked the power transformer's secondary outputs and suprisingly , I got 6.9Vac out of the brown & brown /white pairings. I got ~0 Vac out of the green & green/white, and also ~0Vac between the red & red/yellow (both sides).

I have a 2A slow blow fuse in the circuit. I guess I got a bad power transformer? Should I just return this to Ned @ Triode?

Thanks,
JG

Sure thing. I'd email him first, of course.

Shannon

[EWBrown]

I'd say, let Ned know about the bad trannie, in all likelihood, he'll replace it, from what I've heard.

I was going to go with AC right to the LED, but figuring that I might replace it with a blue or white one later on, I stuck in the resistor.
The panel mount lamp already has the "sissy bar" resistor inside.

The ten pin "bidirectional" LEDs are pretty cool, red one way, green the other and yellow with AC.

For a really "sci-fi" look, I'm considering mounting a couple of the blue 1 watt Luxeon Star LEDs under the chassis on the DIY35 mounted in the black par-metal chassis. The blue glow streaming out the vent slots and the socket holes should look pretty eerie...

/ed

[merlin2049er]

I called Ned up and he told me to check the primary side for ~4ohm. I got that and the seconday side (red pairs) for ~150 ohms. I got that too.

I'm going to have to test this transformer again, maybe it's just a loose connection. argggh.

:x

[EWBrown]

One possibility, is that the two separate 6.3VAC filament windings, connected in parallel, were"bucking" each other. Normally green goes to brown, and green/white goes to brown/white. If all is well, they are in phase and will add their currents. If they are out of phase, then they will "buck" each other and will blow the fuse (hopefully).

Refer to the topic "Ned's PA774 Power Transformer" here:
http://www.diytube.com/phpBB2/viewtopic.php?t=31

Tne simple way to check this is to disconnect all the transformer secondary leads from the terminal strip, and be sure that the two red (HV) ones are in a safe location, or tape them up for now.

Place a 120VAC 40-60 watt light bulb in series wiith the primary, this acts as a current limiter, and a short circuit indicator. With no loading on the transformer, the bulb should light only dimly, or not at all. Power off, then connect the two filament windings as described in the instructiions (no tubes installed on the board) and try again. If the bulb lights up bright, then the 6.3 VAC windings are out of phase, reverse one and try again. the unloaded AC voltage will be around 6.8 to 7VAC. Next, connect the two red HV leads to their assigned terminal strip lications. If all is well, the light bulb will light up brightly, then slowly dim down. as the capacitors charge up.

If all seems OK, remove the light bulb "protector" and then plug it in and power it up (no tubes installed, yet). The unloaded AC voltage from each red secondary wire to ground will be 330-350 VAC (approx) measure this with caution, as hazardous voltages are now present. The caps should charge up to around 400VDC, maybe a little more. Don't leave it powered up for too long without the tubes, as the DC voltage will be higher than normal operating levels and is close to the caps' maximum voltage rating.

Before proceeding to the next "power up" test, make sure that the output transformers are wired properly, the red (CT) leads to the B+ terminals on the strip, and that the plate and screen (UL) leads are properly connected to their respective tubes through the terminal strips.

If all seems OK, then let it sit turned off for a few minutes, in order to let the caps discharge, then install all of the tubes and then power it up again.

If the fuse pops now, pull out the EL84s, then try again. Then insert 2 EL84s in one channel, try again. If OK, then put in the last 2 EL84s. This will help isolate a bad or shorted EL84 tube.

If the cathode bias pots were pre-set to 400-430 ohms, then the bias current on each EL84 should be around 30-40 mA after warm-up. In most cases, I find that the bias is pretty close to 35 mA with a matched quad of EL84s.

I hope this is 1: clear, and 2: helpful information.

/ed brown in NH

[merlin2049er]

I got it working !!! I think?

I wired it back up and put the tubes in place, and turned it on. I got a nice glow from the tubes (I left it on for ~ 2 minutes).

I didn't adjust the bias while it was powered on. I'll get to that, and I'll have to wire up the binding posts.

I got 1 question regarding wiring. I'm using some radio shack wire, and some stranded copper wire. Just wondering if I should be concerned with the quality of the wire I use to hook up the inputs and various connections.

Thanks,
JG

[Shannon Parks]

I got 1 question regarding wiring. I'm using some radio shack wire, and some stranded copper wire. Just wondering if I should be concerned with the quality of the wire I use to hook up the inputs and various connections.

JG,

I would suggest using 20GA or better wire for transformer connections. I would focus on well insulated wire for other connections. The inputs can benefit from different types of shielded cable and such, but I'm not an expert here. I would just suggest keeping those cables as short as possible.

Shannon