Fender 5e3p from Wurlitzer organ amp

[Phil_S]

The bad news: something is wrong with your gizmo or with the amp.
The good news: it doesn't matter because you are going to gut this thing.
Even better news: it powers up and doesn't crash and burn. Get the readings and make the voltage chart. (Note: skip the filament supply pins; they should all be carrying 6.3VAC and it adds clutter to the voltage chart.)

[Structo]

By the way, those ceramic caps are coated with wax and the heat from the tubes probably made them bubble.

[Zombie_stomp]

Flip it over, power it on, read voltage of wires coming out of the power transformer, anything else I can do while I wait? I've ordered a bunch of near knobs and a handful of Noval tubes sockets that can be riveted to the chassis. I'm forgetting which of the two designs I'll be building with this 6l6 and 12au/ax7 9pin preamp tubes, but if there is a parts list, I'd love to get all the capacitors, pots, and resistors ordered ASAP. There a set of plans floating around here for that amp?

[Zombie_stomp]

Oh right. I need to draft a voltage chart before anything else. I'll try to get right on that tomorrow after work if I have the energy.

[Phil_S]

There is a bill of materials here for the amps they offer. https://taweber.powweb.com/store/kits.htm
Schematic for the 5F6A that goes with the BOM: https://taweber.powweb.com/store/5f6a_schem.jpg

Really, you can just list all the parts from the schematic. It won't take long.

[Zombie_stomp]

I take it weber only sells full kits? Is Mouser electronics still a good place to buy all the semiconductors? They are who I used to buy from. There are a lot of choices of composition of materials there for each value of semiconductor, so if anyone's got any favorites of economy an sound, let me know.

[Structo]

Voltage chart.

[Zombie_stomp]

I got very few readings this time, but did get some solid ones. I'm not sure if I need to plug more control sockets from the organ into the amp to get things to light up, but here's my first attempt at the voltage chart. The preamp tubes are unchartable since there's no socket number visible from the bottom of the primitive PCB. I switched to AC and was able to get a reading out of the 6L6 where I was not able to previously.

[Phil_S]

It looks like you are measuring AC volts. Set your meter for DC volts! Clip the black lead to the chassis or a grounded lug. Probe with the red for DCV. One hand stays in your pocket. (OK, you can hold the pencil and write down your voltage readings but loose hands tend to wander.) The idea is to keep from accidentally allowing a short circuit to flow across your chest and damaging your heart or killing yourself.

The good news is that you have the high voltage secondary, which looks like we'll call it 350-0-350. This suggests DC volts at pin 8 of the rectifier will be around 420. This is a little on the high side for a 5F6, but not so high as to be any sort of problem.

You may want to increase the 4.7K resistor in the power supply ladder to compensate and get preamp voltages closer to spec, but even this isn't necessary. I'm not even sure you'd hear the difference. The slightly higher voltage will probably give you a bit more preamp clean headroom, which could be a good thing if that is your cup o' tea.

Get the voltage readings and post a new chart.

Weber sells components as well as kits. They serve a particular market. Let's say they price aggressively on many components and you get no-name brand. If I were in the business of building and selling amps, I don't think I'd go there for parts. For a one-off amateur build, I don't see the problem. I've bought stuff there and it all works just fine. For example, you'll get generic yellow barrel or brown mylar coupling caps and metal film resistors. These things lack snob appeal. I'd note, that Weber's generic choke is probably perfect for the 5F6 (if that's what you'll be building) and it is at the right price point.

If you are able to do battle with the Mouser catalog and win, please go there and do your best! Remember, when buying resistors, it is sometimes not enough to get 1/2W rated. Check the voltage rating, too, as you may find that you are going to be above that in a guitar amp.

Usually, it doesn't pay to split an order. After you pay both suppliers $10 each for shipping, it takes the wind out of that idea.

[Zombie_stomp]

I DID actually have it set to DC and tried all the different ranges of DC volts. I only tried AC because it seemed to fail to read. I'll try again with my other meter tonight.

[Phil_S]

Try with clips on both the red and the black leads. Sometimes it is really hard to get a stable hand held reading.

[Zombie_stomp]

Not much new news here, other than that gator clips on another pair of tightly connected test leads give the same readings as before. I'm not sure what would change any of this besides maybe hooking up all the original organ plugs. The amp did work, quietly, but it worked. Or I could start desoldering parts until it's stripped down to just transformers and tubes. I haven't ripped the organ apart yet, but might have disconnected a couple pieces near the main power switch prying on it a little to get the switch block out, but probably not. I most likely COULD put this all back together again, but that's not the way this guitar amp conversion should be progressing... What should I do next? I'm clearly on DCv, and I start high and flip through the different ranges of volts.

[matt h]

(deleted)

[Zombie_stomp]

I kept digging the probe into the chassis ground lug, which appears solidly spot-welded to the chassis, and has some nice malleable solder to dig the teeth of the gator clip or the point of the probe into very firmly. I've been going round and round, digging the probes into these points over and over, sometimes using different grounding points, getting the same results with two sets of test leads. I'm considering changing something out if it is of great importance that I get these readings now, with the amp exactly as it is. Maybe a grounded 3-prong power cord?

[Phil_S]

I'm thinking the rectifier tube is bad or the 5V supply is bad. No DC voltage is flowing. Pull the rectifier tube. Check pins 2 & 8 for AC voltage. That's one probe on each pin, not to the chassis. You should have 5, maybe 5.5VAC. If you have filament voltage, then I think it is safe to conclude you need a new rectifier. Anyone else care to weigh in?

You need the 3 prong cord for safety, but that wouldn't be the problem, so hold off on this.