SE EL34 Plexi-verb

[Phil_S]

I'm feeling a bit greedy about having both plexi channels. I had considered freeing that triode. I've been sifting through what I have for that spot and found I've got a Mullard 6EU7, and I'll hope it's not a dud. I may have to use Russian 6n2p for V2. This one is looking like it may turn out to be a bit of a mongrel. I'm still waiting for parts, including the Belton brick (really, the size of a modest chocolate bar.)

Here's a stab at an updated schematic. I'm sure something still isn't right. Also, I know I've got to fix the strip board layout(s) as I've spotted what I think are some errors.

I feel very fortunate to have such capable "helpers." That SL5 schematic, was very useful, but hard to read. With the extra triode, I think I've got a better spot for the reverb and I got to install the Presence control! I've got two supposed NOS 6AQ7-GT, both GE, one labeled RCA, the other Sylvania. I am guessing at how to bias that recovery stage, based on what I see in RC-30.

I still haven't done the B+ ladder calculations. Most of those resistors are still just place-holders.

[martin manning]

Move the OT B+ lead over to the added RC filter node, and expect to lose about 12V.

C21 should not be joined to the plate of the 6AQ7.

Funny thing about the bias point of the driver stage in the SL5- it's really cold!

D3 needs to be reversed, and it goes to ground, flip C24 too, and connect the lower leg of the transformer winding to the top of C24, not to ground.

C26 can be a much smaller film cap, 330nF.

Delete C34.

Make C27 330nF.

Parallel a 100nF with C30.

Both C29 and C30 should be much smaller, 10uF.

See below...

[Meat&Beer]

I'm also following along curiously, as I love these kind of off the path builds...

Phil, I'm pretty sure I've some old 6av6's or other types of single triodes I could kick in if you'd like to keep that configuration. I'll shuffle through what I have tonight if you'd like?

[Phil_S]

Martin,
Thank you very much for the help. Some of it was just bad drawing, but more was just not right. Either way, I might have built it as drawn, so the adjustments are a welcome boost.

The 5/15V power supply was an added bonus. In addition to botching the tripler, I was having difficulty with clarity. The way you separated the 5V from the 15V segments was much clearer, and instructive, too. I thought I was building this: http://www.electronics-tutorials.ws/blo ... rcuit.html (3x-er about half way down) but I found it difficult to "unpack." Yours made much more sense to me. Go figure. Triple thanks for the tripler ;-}

I am still waiting for parts. I've found it is a bad idea to start cutting the chassis until I have everything. That helps a great deal with size and spacing. I'm not too good at undrilling holes and whatnot The revisions have given me a modified parts list, so now I've got to source a small order of odds and ends. I know I've got enough 22uF 450V caps to go around, so I'll probably use those instead of the 10uF caps, but otherwise, there is some new stuff I don't have. I don't really mind the delay as it allows more planning time.

I've got a few questions about the strip boards I bought for the reverb. When I insert the parts into the holes, as you can well envision, the pins extend through and need to be clipped. It may seem like an odd question. Do I clip these before or after soldering, or does it make a difference?

How important is it to use a heat sink clip when soldering? (Not to worry, I did figure out I needed to buy a DIP socket for the op amp.)

On the 7805 amd 7815, these are TO-220 packages. I have proper heat sinks and film insulators for them. Do I solder directly to the board, or do these require sockets?

Meanwhile, I've updated the schematic and renumbered all the C's and R's and P's. From this I'll probably update the turret board.

Regrettably, I have to do some work that pays the bills now. Maybe I can get back to this in the evening or later this week.

Again, thanks very much for the help.

Phil

[xtian]

When I insert the parts into the holes, as you can well envision, the pins extend through and need to be clipped. It may seem like an odd question. Do I clip these before or after soldering, or does it make a difference?

Solder first. Then trim.

How important is it to use a heat sink clip when soldering? (Not to worry, I did figure out I needed to buy a DIP socket for the op amp.)

Don't worry about it. Beginners might toast some components, but you can solder efficiently. Amirite?

On the 7805 amd 7815, these are TO-220 packages. I have proper heat sinks and film insulators for them. Do I solder directly to the board, or do these require sockets?

Directly, no sockets.

[martin manning]

Looks much better. The wire from C22 to C26 does not connect to ground, though. Maybe a MV would be a good idea? You could replace the 220k grid leak on the EL34 with a 250k pot.

[Littlewyan]

C5 is 0.47uF, which is a bit big. You want 470pF there.

Also C9 and R17 can probably be removed. They probably aren't needed for this circuit.

And you may want a bright cap for the bright channel. Even if its just 100pf. Personally I'm not a fan of amps without a bright cap. Everyone has different taste though .

[Phil_S]

Hey, thanks for the proof read, Martin. MV sounds like a good idea. If I counted right, that makes pot #10. That means the front panel will have at least a dozen holes in it. LOL, it will look like heck. I think I'll be using a rocker switch with embedded lamp, so I get to bypass the separate pilot light. The real problem is that I'm not sure I've got 10 knobs that get along with each other. Details...

Aaron, thanks for the pointers. Amirite? Yesur. I've built lots 'o amp stuff, just not with sand. I can't get over how tiny the stuff is, and cheap, too. The most expensive individual piece is the BTDR-3, at about $16 (didn't exactly break the bank) and that dwarfed the cost of all the other sand put together. That little brick has a 10-pin interface, for which I bought a small bag of 10-pin SIP sockets for, Idunno, maybe $1? I probably over paid! So, no solder goes on the brains of the thing. I haven't actually seen it yet, so I hope I got the right kind of socket. I'm hoping it will come in today's mail.

What am I going to do with all the stuff I don't need? I have about 8-10 ea of 7815, 7805, 10-pin SIP, maybe a few other goodies. I also have a bag of about 10 on-on STDP mini-toggle switches. The postage is more than the goods!

[Phil_S]

I know this is rudimentary to many of you, but I am confused, so I'm going to ask how to properly wire this switch so the light goes on when the power is on and the light goes off when the power is off, or did I buy the wrong kind of switch? If the latter, no harm is done and I can use a regular pilot lamp.

It's clear enough that 1A (L1) goes to the fuse. (At least I can read.) When I put a meter on it for continuity check, 1A (L1) + 1 (L2) is on/off. So, I know the switch makes/breaks power between 1A and 1.

That leaves how to make the light go on and off. The continuity check reveals nothing, all open no matter what combination or switch position. (Actually not surprised about this; it's a neon lamp + resistor, without power.) Look at what's printed on the side of the switch in addition to the diagram.

Since the middle lug (1) and the outer lug on the lamp side (1B) are both marked L2 on the diagram, I think that says to simply bridge them, but it doesn't make sense to me to do that. I keep thinking if I bridge terminals 1 and 1B, the lamp has the no return (and I guess it gets toasted.)

What I want to do is bridge 1A and 1B and that makes the middle lug (1) the return which will be connected to the PT primary.

Thanks for any direction you can offer.

Meanwhile, I've been busy. The main board is built but not soldered. I've done a tentative layout/cutting/drilling plan for the chassis. It looks like I need the 3" high one to allow vertical stacking of the pots. Also 3" gives me the wall space for the PC strip boards for the regulated power supply and reverb boards. If I can figure out how to build the PC boards, I should be ready to drill the chassis. I like to see how everything is going to look, so I don't have to undrill any holes, particularly the large one for the laydown PT.

[sluckey]

I used those switches on three projects last year. They really simplify mains wiring. Look at this...

http://sluckeyamps.com/lil_maggie/Magnatone_M2.pdf

Page 2 is the schematic and page 3 is the layout.

[JazzGuitarGimp]

In the diagram, L1 refers to the "hot" wire coming from the wall outlet, and L2 is the neutral wire coming from the wall outlet. The Load is the primary winding of the PT.

[Phil_S]

This is a "d'oh" moment. I see I got 1 out of 3, clearly a failing grade. It never occurred to me the neutral feed goes through the switch or what "load" actually meant. Thanks to both of you for the help. BTW, the drawings were worth a 1000 words. I have it now!

[jjman]

The input to the Belton is grounded in the scheme. Not sure if that was pointed out. It should probably go only to the wiper of the pot.

[Phil_S]

jjman: Many thanks for a good catch. I was intending to solder that board very soon, so the "input" is very timely. I'll eliminate the jumper on the pot.

[Phil_S]

Next question...I've built the BDTR-3 Board and am probing it to see if it the soldering is good. This is my first adventure with PC strip board. I've encountered something that is bothering me, that I am thinking can't be right. R31, R32, R32, and R37 are wired to show about 19KΩ on the meter. The individual 2M resistors are metering at 1M while in circuit. Am I overthinking this or is something wrong? I am wondering if I mishandled pin 4 of the TL072 op amp by connecting R37 to pin 4. If not there, where does it go? Some confirmation here would be very helpful. Thanks.