Magnatone Vibrato/Reverb build Project

[shooter]

IIRC there were some "black" boards floating in the either that were conductive, so I believe he's "making a distinction" 

did you leave enough room to drill standoff holes?
I like to get those outta the way before I start adding wires n parts.

[wsscott]

Thanks.  Yes, I"ve got about 1/2" clearance around the top and bottom edges that I can drill those holes where needed.  Most of the turrets are 1/4" on center between them.  Others have more spacing.  I looked at Sluckey's builds and based on his comments and the information he's shown in the Vox build, it looks like he uses 1/4" on center spacing that works fine.

Question, when you install a resistor or a cap, do you run the leads down through the top of the turret, or do you wrap it around the body?  I've seen it done both ways and didn't know if it matters, or if there's a reasoning behind one way or the other.  Thanks.

[Willabe]

IIRC there were some "black" boards floating in the either that were conductive, so I believe he's "making a distinction" 

Yes, I think Silvergun bought a black epoxy board that was made/designed to be conductive, but he didn't know it was made to be conductive. 

[shooter]

seen it done both ways

dealers choice;
what you want to "think" about, how many times will I un-solder, re-solder, and how will that effect the "other parts" at that turret.

so, cathode bypass caps get tweaked a lot, coupling caps same, power supply dropping R's.  IF they're wrapped around turret, then you put a couple parts down the hole, it's harder to get to the wrapped parts.

[wsscott]

Well, I bit the bullet and after checking my layout 3 times and being "satisfied" I think its correct, I ran the DIY Layout Analyzer for a Hoffman Turret board, sent it up on Wednesday night to Hoffman to make, he mailed it out on Thursday (wow what service!) and I received it today.  It really looks great--see image below.  I've never seen a turret board before and I was really surprised at how small the turrets are.  Really nice job. Now let's hope my layout works!

[shooter]

fwiw;

typically I try n drill the boards standoffs prior to adding pieces parts.
do a few "dry run" layouts, considering what's "above" the board, how it fits with power supply wires, splitting the distance between tubes on one side and pots on the other (If you have tubes in back)

If you put in the same time building as designing, you will do well in the "ah, Sh " phase 

[wsscott]

Do you drill the holes for off-board wiring as you come to a point where you need it, or try to do it before you start loading the board?  Another question, I've seen one amp builder on YouTube who builds his boards in sections, and tests each section before going to the next.  He starts out with the Power Supply, then the Pre-Amp etc.  I was wondering if at least doing the PS first and testing it for the voltages that are needed at the caps would work and be a good idea? I guess the idea would be you can adjust the resistors more easily at this stage of the build to get the DCV that you need at the tube plates. Is there any issue with just running power from the mains, to the PT, then to the bridge rectifier, and then through the 5 caps/resistors that I have in my design?  Thanks.

[shooter]

I do test my PS "ahead of time", but I've been doing electronics ALONG time 
once I ohm check there is no short + to -, I calculate my PA tubes load, I calculate the value of a "DummyLoad" Resistor, INCLUDING watts.  I gator clip the R for the PA tap, hook up a meter, power up n verify I'm in the ballpark.

as to "fly wire" holes, I drill them as I go, (probably NOT recommended).  IF you don't have complete control on drill speed and pressure things can get ugly.

the key to this phase, slow, methodical, double checking after say 5 connections.
my "double-checking", after I do 5 connections, I walk away for 10 minutes, come back, trace out what I did, fix any "oops", If there are 3 oops in 5 connections, go do something else because you mind isn't where it needs to be. 

[sluckey]

Do you drill the holes for off-board wiring as you come to a point where you need it, or try to do it before you start loading the board?

I drill wire pass-thru holes at the same time I drill turret holes. Same for standoff mounting holes. Much easier while there is nothing on the boards.

Since you have a board with turrets installed I suggest you drill any additional holes ***BEFORE*** mounting anything on the board.

[wsscott]

Thanks guys for the input.  As to the PS testing, what I was thinking of doing is this: Nothing would be installed in the aluminum chassis at this stage.  It would be setup on a wooden board, with a grounding lug screwed into the board to receive the grounds from the PT and the turret board.  I connect the power cord to the transformer Primary, through a fuse, using wire nuts.  I then solder the bridge Rectifier to the turret board, and solder the caps and resistors to their places on the turret board.  I then connect the PT Secondary to the input on the bridge rectifier with wire nuts.  I use my Variac to control voltage, and connect it to the light bulb safety board, and plug the power cord into the safety board.  I would then connect a DMM to the ground lug and to the first B+ coming from the rectifier.  Stand back and turn on the power at the Variac.  Then hopefully read the voltage at that stage which should be the 410 DCV shown in the schematic.  And then take the readings at B, C, D, and E.  Does this work?

[shooter]

which should be the 410 DCV shown in the schematic. 

with no load, that voltage will be bigger.

before you turn on power, even with all the safety stuff, ohm across the PS rail + to red lead, PS - to black lead, you should NOT have anything < than thousands of ohms "charging" as your meters battery charges up the caps.   IF you read like 27 ohms solid, STOP and fix.

[wsscott]

I'll definitely be taking this slow.

[wsscott]

I've identified where I should drill holes on the board to take the wiring under the board, and have a question about drilling the board.  I have a small drill press that I'm going to use, and have a new 1/8" drill bit that I was going to use.  Any tips on drilling the holes?  Is the material that Doug Hoffman uses for the turret boards easy to work with or brittle?  Any need to use a center punch first before beginning to drill?  Any issues about staying a minimal distance from the edge of the board?  Etc???  Thanks.  Stephen

[wsscott]

Sluckey-what type of shielded cable is used for the volume pot, and for the input and reverb connections, and for the 470K 3W resistor as shown on the attached file?  Also, which tubes would you use shielded sockets and covers for?  Thanks.  Stephen

[shooter]

fwiw;
I like RG-174 for shielded cable
I shield ALL small signal tubes, including PI, (assuming 9 pin'rs)

[wsscott]

Do you use the RG-174 going from the ground to the 470K resistor too, or is that a different type of wire?

[shooter]

ground to the 470K resistor too

quick glance, are you talking 470 to ground?
the couple 470k's I seen didn't go to ground, but I'm in a hurry 

If it's the 470, any wire works

[wsscott]

Yes its the 470K 3 watt resistor going to chassis ground.  Its just that your VISIO layout showed it with a stripe or something, so I didn't know if it was special or just being pretty.

[Dave]

I'm following this thread with urinary incontinence. Its like one of those movie where you really start rooting for the would-be hero guy. I can't wait to see how it plays out.


Dave

[wsscott]

Well said!  I'm holding my legs together too!

[wsscott]

Sluckey-I'm using the Hammond 269JX PT, and just wanted to confirm the wiring as I plan this thing out.  My mains are reading 122 VAC, so I'm going to use the 125V option and use the black and white wires on the primary to the input power, and tape off the gray.  Then the 2 green wires will go through the power light and then on to the filaments.  The 2 reds will connect to the 2 center terminals on the bridge rectifier, and the red/orange center tap will go to Chassis Ground.  Is this correct?  Thanks.  Stephen

[sluckey]

The 2 reds will connect to the 2 center terminals on the bridge rectifier

DO NOT USE THAT TRANSFORMER WITH A BRIDGE RECTIFIER!!!

[wsscott]

What type of rectifier do you recommend I use?  What I had purchased is a 3N259 bridge rectifier, 1000V 2 amp.  That won't work?

[wsscott]

Sluckey-attached are datasheets for the transformer and for the rectifier if that's useful to you.

[PRR]

500V CT, into FWB and capacitor, is 700V DC.

I'm tempted to let you try. But wear a face-shield.

[PRR]

This will work. But it is poor economy.

[wsscott]

So should I just use 4 of the 1N4007G diodes in series as shown on the schematic? I thought that schematic was for a full wave bridge rectifier.  Is what I should be looking at is a "full wave rectifier" vs. a "full wave bridge rectifer"? I was assuming that the part I had (the 3N259) did the same thing.  Obviously not good to assume!  By using the part I was going to use it seemed like it would be a neat easy fit. 

[wsscott]

PRR--"poor economy" in what respect?  Do you mean $ (the part was about $2.50--I also have the 1N4007G Diodes I can use if that's what's recommended) or an inefficient use of components that would denigrate the result?  Thanks.

[sluckey]

PRR--"poor economy" in what respect?  Do you mean $ (the part was about $2.50--

Yes. 1N4007s can be bought for $0.04 each, so it's a "poor ecomomic" choice. Your bridge will work fine as long as the negative terminal is not connected to anything. In fact, I suggest you cut the negative terminal/lead off flush with the plastic body just so it cannot ever be used.

[wsscott]

Sluckey-so if I wire it like PRR shows in the attached drawing, and cut off the negative lead as you suggest, what capacitor do I use to connect between the red/yellow center tap lead before it goes to ground, and the positive lead before it connects to the Node A power filter cap?  The positive lead doesn't terminate at the cap does it? Thanks.  Stephen

[Willabe]

Sluckey-so if I wire it like PRR shows in the attached drawing, and cut off the negative lead as you suggest, what capacitor do I use to connect between the red/yellow center tap lead before it goes to ground, and the positive lead before it connects to the Node A power filter cap?  The positive lead doesn't terminate at the cap does it?

That IS the A node filter cap PRR is showing you in his drawing.

He is not showing you a 2nd A node filter cap.

[wsscott]

Thanks, I wanted to be sure.

[sluckey]

Sluckey-so if I wire it like PRR shows in the attached drawing, and cut off the negative lead as you suggest, what capacitor do I use to connect between the red/yellow center tap lead before it goes to ground, and the positive lead before it connects to the Node A power filter cap?  The positive lead doesn't terminate at the cap does it? Thanks.  Stephen

Look at the drawing again. The red/yel C/T wire connects directly to chassis ground. And the Node A cap positive lead connects to the positive terminal of your bridge. And the Node A cap negative lead connects to chassis ***AT THE SAME POINT THE RED/YEL C/T CONNECTS TO CHASSIS***.

[wsscott]

Got it.  Thanks again.

[wsscott]

Meant to add this layout for the corrected rectifier wiring using the bridge rectifier with the negative lead removed--at least as I understand it.

[wsscott]

Ok, so I did a test of the rectifier today.  I soldered the bridge rectifier to the turret board after having removed the Negative lead.  I installed the Hammond 269JX transformer by screwing it down on a board.  I grounded the mains green wire to one of the screws holding the transformer to the board, and then wired together the black and white wires on the transformer and the power cord.  I grounded the Red/Yellow center tap wire to a different screw in the same board.  Its just off by itself, with nothing else connected to it. Then I clipped the 2 red leads from the Secondary to the 2 AC connections on the rectifier.  Finally I hooked up my DMM in DCV mode with the red lead to the + leg of the rectifier, and the black lead to the ground screw where the Center Tap wire is grounded.  I didn't install anything else in the circuit, ie. no filter cap/resistors, etc.  I ran all of this through a Variac and a light bulb limiter.  Nothing blew up or smoked!  My reading showed 239 VDC.  I was expecting it to be around 350 VDC.  So my question is whether my readings appear proper, and if not what's wrong.  Thanks.  Stephen

[Willabe]

I didn't install anything else in the circuit, ie. no filter cap/resistors, etc.  I ran all of this through a Variac and a light bulb limiter.  Nothing blew up or smoked!  My reading showed 239 VDC.  I was expecting it to be around 350 VDC.  So my question is whether my readings appear proper, and if not what's wrong. 

You have to hook up the 1st B+ filter cap, A node cap. Then take your reading. Without the filter cap, your reading will be way off. All your reading is the rectifier pulses, it will confuse your meter.

!!!!!!REMEMBER!!!!!! That cap will hold a dcv charge after you unplug the PT!!!!!! You have to drain it with a 220K or 330K or 470K resistor to ground, 1/2w will work or 1w or larger will be better. The R value is not a big deal, what ever you have that's close. The larger values will just take longer for the cap to drain off it's dcv charge. Leave the bleeder R hooked up for a couple minutes, larger R value, leave it a little longer. Then measure it for dcv to make sure all the dcv bled off. 

I wouldn't hook the power cord green wire to the PT. Hook the power cord green wire, the PT B+ mains CT AND the filter cap negative lead together, 3 leads. You can strap the bleeder R across the filter cap when you do this, if so, then 4 leads grounded together. Or just use 2 alligator clip jumper cables to hook up the bleeder R across the filter cap to drain it.     

!!!!!!BE CAREFUL!!!!!! Or it will bite you!

[wsscott]

Thanks this is helpful.  I've got and used a "snuffer stick" before, but its good to be reminded, and keep one hand in your pocket.  I was going to ask if I also need to install the resistor to the A Positive terminal, but I guess that's not necessary?  And I can use the snuffer stick to bleed the charge from the A Node cap?

[shooter]

fwiw
a big R like Willabe suggested can be clipped in when you clip in the cap, it's large R won't have much effect with power on, then when power is off, it's doing it's job - keeps those fun SNAP sounds at bay 

and ya, hum "one hand in my pocket, the other......." 

[wsscott]

So could I just go ahead and install now the A Node 2K 10W Voltage Dropping resistor at the B+ terminal of the A Node cap, and then ground the other end of the resistor to the chassis ground you describe for it to bleed off?  Would that R be large enough?

[sluckey]

Don't connect that 2K/10W resistor to chassis ground!

If you want a bleeder resistor then permanently connect a 220K/3W directly across the Node A cap.

[wsscott]

Thanks Sluckey.

[Willabe]

Like the guys already said, NO!

At least 220K to 470K, 2K is way too low of a resistance. 

[shooter]

to pile one more 
try and keep Mr. ohm close at hand
to drain caps for safety, current can be real low, so low I = biggish vdc/real big R
if R is low, I goes up, and you want the I's in the amp to operate, not providing heat for the house 

[wsscott]

Success!!-I decided not to install a bleeder resistor and just used my snuffer stick to drain the cap.  I checked the stick and it has 110K resistance and it only took a couple of minutes to get it down into the millivolt range.  So it read 367 VDC!  So that's consistent with the theory of the rectifier increasing the DCV to about 1.4 times the secondary voltage of 250.  My question though is that the schematic shows a voltage of 410 VDC at Node A, and I'm at 367.  Agree that I'm not going to be wiring Node A since I eliminated that part of the circuit, but is this an issue for the rest of the circuit. Node B shows 338 VDC, but when I install the 2K 10W voltage dropping resistor between Node A and B it will lower the 367 VDC--but to what value?  I know this is a holiday so I realize you all probably have more interesting things to do.  Thanks again. Stephen

[shooter]

IIRC all the tubes are small bottle NOT PA
so there is no problem with voltage, probably won't drop much under load since each triode only draws a few mA's

[wsscott]

Sorry, but can you translate this phrase for me "IIRC all the tubes are small bottle NOT PA"? Thanks.

[shooter]

IIRC = if I recall

[wsscott]

I thought that was some technical electronic tech speak!!!!  Yes, no Power Tubes, all 9 pins.

[Willabe]

IIRC = if I recall

And/or; if I recall correctly.

PA= power amp. (Here referring to the power amps tubes).

Snuffer sticks 110K is fine for draining the cap. Too small to leave in the B+ power supply.

2K would drop too much dcv across itself and might burn up along with the PT, over working the PT. Unless you went with a very large wattage 2K R, but that would just save the R, not the PT. More wattage=more $$, but no need. And if you left it in, it would drop the B+ dcv, a LOT of waste.