Fender 5e3p from Wurlitzer organ amp

[M Fowler]

When using a 5Y3, 5U4 or other directly heated rectifier the circuit will work normally either way.
If using a 5AR4 (indirectly heated cathode) the B+ current will flow through the filaments in parallel with the 5V winding.
When using the SS diode plug the current flows through the 5V winding.

Better to just wire pin 8 for B+.

rdjones

[Zombie_stomp]

I don't think that Proluxe layout is entirely correct, or else you have mis-read it.

Rectifier: Assuming a GZ34 for which the Weber Copper cap is a direct replacement. If using the copper cap, you don't need any filament supply. If using a real tube, you need a 5V supply connected to pins 2 & 8. Traditionally, B+ is taken from pin 8. I don't know why. I'd say follow the prevailing practice of using pin 8. Pin 8 of the rectifier gets connected to the center tap of the output transformer primary. The wire run from pin 8 to the OT CT is interrupted by the standby switch. (You don't really need the standby. Nothing bad will happen if you omit it.)

6L6. The outer legs of the OT primary get connected to pin 3 (one to each socket.)

I'm not sure about a balance pot. Can you elaborate? Hum balance is usually a "humdinger" which is a ~200 ohm pot between the legs of the 6.3V filament supply and the wiper grounded. It allows you to balance the filament supply to eliminate 60Hz hum. Bias should be totally separate. If this is a 6L6 based 5E3 Deluxe, it would be cathode biased, so there'd be no need for a bias pot.

I planned on using a real tube (5u4gb) in place of the WZ34, or Gz34 (real tube) if necessary for this amp design. So if I were to need to supply the real tube with filament voltage at pins 2 and 8, what would happen with the wires already connected to pins 2 and 8 from the power transformer?

Also, your 'hum dinger' circuit sounds like what this used to use, and is currently wired as: the middle of the 3 prongs on the pot (marked 114807 250 [250 ohms?] 304-6004) does go to ground, I'd assume that to be the wiper, while the other two are on the filaments. Yeah, I'd guess that to take care of AC hum, or in my words, bias it. Biasing in terms of tube amps is something different, so I didn't mean to confuse the two. I do see a bias pot in the new plans though, so I thought according to my reading that this meant it was a 'fixed bias' system.

The main thing is 'what do I do with my rectifier' since it is already wired up just as shown in the diagram except that pin 1 is right now tied to pin 2 of my power tube whereas in the layout on the new plans pin 1 on the rectifier is not used. 7 and 2 is fine and clearly marked as the filament pins on the power tubes, but where and how and why on the rectifier is a mystery to me.

[Firestorm]

Just to be clear, 5V rectifier tubes use an entirely different filament supply from the 6.3V supply feeding the rest of the tubes. 5U4, 5AR4, 5Y3, etc. will have their 5VAC connections on pins 2 and 8 and their high VAC connections on pins 4 and 6. This leaves 4 socket terminals unused and some builders may have used some of these as tie points, but the rectifier tube has no connections to anyplace except 2, 8, 4 and 6.

[martin manning]

Picture for Firestorm's and rdjones' words.

In 5U4 the filament and the cathode are one and the same (directly heated cathode), so it doesn't matter which pin (2 or 8) you take the B+ from. In the case of an indirectly heated cathode like 5AR4/GZ34, the cathode is connected to pin 8, so that is the path of least resistance. As you can see, if you take the B+ from pin 2, the HT current has to flow through the 5V winding and the filament in parallel.

[Phil_S]

That's an awful layout drawing. "A" is the output transformer. There are 3 connections on the primary side. Center tap goes to the standby switch. The other two wires, one each to the 6L6 sockets, pin 3, the plate or anode.

The humdinger is nice but not necessary. More commonly, we manage this with an artificial center tap. This is a pair of 100 ohm resistors. Connect both resistors to a single isolated chassis ground point. (Imagine a V shape.) One filament wire goes to each resistor. Because this is a parallel connection, it can be made at any convenient point along the filament string. Typically, I see it done at the pilot light or at the last tube socket. It just depends on where it's easiest. The humdinger (search the forum) is the same thing, but provides the functionality of being able to vary the amount of ohms on each leg of the filament supply. I'd wouldn't use the term "bias" in discussing this as it is confusing. Stick with commonly used terminology to insure clarity. After all, we're not in the room with you and no one wants to give bad advice.

A picture is worth a 1000 words. Thanks to Martin for the rectifier schematic.

For more details on this, download some of the common Fender circuits. The PDF usually contains both a schematic and a layout. The good news is that 6V6 and 6L6 have the same pin out. Watch out for pin out on different rectifiers. Pour over them for a few minutes and I think you'll get improved clarity on how to wire the rectifier and power tubes. If you've got fixed bias, some of these will not show variable fixed bias (with a pot) and that's not a big deal. The variable fixed bias simply swaps a pot+resistor for a resistor in the bias supply circuit.

[Zombie_stomp]

I've got all the resistors figured out now except just one. According to the color chart, it's 1.2k ohms. I don't see where the layout on the 5e3p Proluxe that it should be. See photos for details.

[The Ballzz]

I'm pretty late to the party here, but have read the whole thread. I won't claim to know enough to comment on the technical end of this build, but have built 2 amps from scratch and would like to make just a few suggestions on the nuts & bolts/meat & potatoes side of things to make your life easier, now and in the future:
A - It seems that nobody else spoke up about your mention (I think) of putting input jacks near the power switches, etc. It is my understanding that you would be well served to keep as much of the AC & other power stuff at one end of the chassis and inputs and as much of the early preamp stuff as far away as possible at the opposite end of the chassis.
B - Get yourself something closer to a real "auto ranging" meter, even a cheap $30 Extech will serve you much better than those Harbor Freight units. I have several of those HF's cause i get them when they're free and while they certainly do the job for household and continuity testing, etc, they are just a pain to understand even what may be fairly accurate readings. Not to mention, with no "auto off" function, the likelihood of having to put in a new battery every other time you use it is pretty high! You're a smart, innovative guy and you owe it to yourself to have a nice meter. I won't try to pressure you into spending $150 on an entry level Fluke, but if you did, you'd love it and guard it with your life. Just be careful about the "FLUKE BRANDED" Chinese units. You can thank me later!
C - Regarding resistors. I have terrible eyes so I meter every resistor. I first sort them into wattage groups, and if I'm lucky, they came in labelled bags or such. I then take one of my handy dandy 1" or so thick X 6" or so X 12" or so block of fine grained white styrofoam or other light colored foam and separate it with Sharpie lines into the number of sections matching the different wattages I'll be using. I then meter each component and stick one leg of it into the foam making it stand up straight and mark the value on the foam. Now as I need each piece, I simply grab it. Tape could be used instead of actually writing on the foam , if you prefer. This make things go much more quickly, you don't end up with tape goo on the lead you need to solder and the margin of error is decreased at least a bit. FWIW, if I have any extra components, they stay in the bags or elsewhere, "NOT IN THE FOAM" as this helps in case I use a wrong value some place, I won't have enough of that value when I come to need it and it will cause me to re-check my work! Again, thank me later!

You're making great progress on a fairly ambitious project and you are very fortunate to have all the folks on this forum watching your back!
Just My $.02 & Likely Worth Even Less,
Gene

[Phil_S]

It is best to meter each resistor for two reasons. One is to verify you've read the stripes correctly. It is easy to mistake 1K for 100K , etc. The other reason is to make sure it is actually in-spec.

I don't see a 1.2K on the Proluxe schematic. This is a value that might be used as a cathode resistor on V2A (R13) or as a grid stopper (R19, R20) but both should be the same. It could also work adequately on the cathode of the inverter (R16) if you don't have the 1.5K. The bias supply calls for 1K (R26) and it will probably work there, too.

If you are only building one input AND only using half of the 1st triode, 1.2K will make a reasonable adjustment for R7 (820 ohms), however, the "correct" adjustment is to double that (1.6K).

Provided you don't have any extra parts and need to use it, these are your options. Sometimes, you have leftovers

[Zombie_stomp]

I'll see if I can read them with my cheapo HF meter accurately next time I sit down at the bench.

Meanwhile, any tips on how to lay out a point to point layout drawing for myself? Would you say the tubes are in a good place? I could move the OT outside the chassis relatively easily of you think that would help, I certainly think it would. Then there would be a big rectangle of open space right between all the tubes. Advisable?

[Phil_S]

All bets are off with real PTP. Hang as much as you can on the tube sockets and the pots. Use as little wire as possible. Think very carefully about what you will do with the things that don't fit on the sockets or the pots.

Identify places where you will need terminal strips. Don't allow flying components. They should be anchored at both ends.

The schematic is really a literal PTP layout except that it is linear and your chassis has stuff moving around a circle. Adapt or die ;-}

You may find a dry fitting of components is helpful in clarifying what is possible. Don't solder or cut anything until you are sure about where it will be placed. In a dry fitting it isn't necessary to bend and crimp leads and actually that may prove to be counterproductive.

Good luck.
Phil

[matt h]

(deleted)

[Zombie_stomp]

Should I go for moving the OT tho the outside of the chassis?

[Phil_S]

I would. I like as much space as I can get inside. Given your level of experience, you will need the space.

[Zombie_stomp]

Ok, again, I'm pretty sure I've got the resistors IDed pretty well, but my cheapo meter isn't reading them very solidly. So I need a recommendation for somewhere online to buy a beginner/mid level decent meter. And how to read capacitors or what settings it needs to have to be able to read capacitors.

I made a little progress on the build. I got a grommet and made it to fit one of the holes in the amp to thread the OT wires from the outside to the inside. I labeled the wires and moved it. They all tech their original connection points, although the speaker jack wire will need to be a little longer, but no big deal. What could potentially be a big deal, and I wanted to ask you all about this, is the OT's proximity to the rectifier, and maybe also the power tubes. Being 1/8" away from the recto may cause it to become a bit hot, potentially causing the wax to melt from the paper, potentially shortening the life of the OT. There's another hole next to the socket, but that would put it almost as close to the PT. Another option would be to create some tube socket platform extension(s) for the tubes, allowing them to be vertically distanced from the trannies. Thoughts? How close are tubes to other factory production model amps?

[Phil_S]

Only 2 left at this price, so hurry:
http://www.tequipment.net/AmprobeAM-220.asp?v=54585
4 of these still in stock, a better choice:
http://www.tequipment.net/AmprobeAM-220.asp?v=54585
Another bargain here...
http://www.mcmelectronics.com/product/T ... 0-/72-9280

Remember, you get what you pay for. In time, you'll be upgrading.
Make the stretch for an autoranging meter.

Do you have room to rotate the OT 90 degrees?