Spin Off of 2015 list (5E9-A) Im gonna build the 5G9 instead

[lego4040]

I emailed Patrick at MM on the PT. I posted a pic here in one of the older replies and will again. My Bias (white/red) wire is 0volts, NOT -50v(is that my problem) Slucky posted a alternative if your pt doesn't have a - bias tap,If that's my problem. It's here in this thread, I'll look back and see. I will pull all tubes tommorow and check your requests, I noticed that when I tried to adjust bias pot I couldn't get voltage to adjust.  I am using the 5u4gb rectifier. On both pins 2&8 I get 10.31vac & 299vdc

[Willabe]

I posted a pic here in one of the older replies and will again. My Bias (white/red) wire is 0volts, NOT -50v(is that my problem)

It's in reply #163. I would disconnect the white/red wire and with all the tubes out, including the rectifier, turn the amp on and carefully measure that W/R bias wire for acv. You might have the bias supply wired wrong and are shorting it to ground. If so maybe you didn't kill it, yet.

My Bias (white/red) wire is 0volts, NOT -50v(is that my problem)

Yes and no. A bias tap should be a positive acv but not 0 acv's. 

(Just checked my Merc. Mag 5G9 PT and it's bias wire is W/R and it's B+ CT is Bl/R same as yours.)

I noticed that when I tried to adjust bias pot I couldn't get voltage to adjust.

Lego, on an amp that's grid bias (not cathode bias) you ALWAYS have to make sure there's -bias at the power tubes grids before you put in the power tubes.

I am using the 5u4gb rectifier. On both pins 2&8 I get 10.31vac & 299vdc.

Is that measured + meter probe to 1 pin at a time and the other meter probe to ground?



                Brad

[lego4040]

Willibe, on the schematic where the -69vac comes in after selenium to 82k resistor I have -51vac. With ground probe to chassis I measured pin 2 and got 10.31vac and then I measured pin 8 and got 10.31. What I noticed on my PT, where the heater wires come out of pt the green 6.3 are a pair together but the yellow 5volts  one comes out on one side of winding and the othe yellow comes out of other side. You can see that on picture

[Willabe]

on the schematic where the -69vac comes in after selenium to 82k resistor I have -51vac.

Well, that's good, means bias tap is good but it also means you have something wired wrong from that point to the power tube grids. I would trace the -bias dcv back from the power tube grid pins. Look at the Fender schematic and layout drawing to figure out what's wrong.
 

With ground probe to chassis I measured pin 2 and got 10.31vac and then I measured pin 8 and got 10.31.

That doesn't make sense to me. I get  ~5.1acv measuring across pins 2 and 8. I get 0acv measuring + meter probe to pin 2 and the other to ground. I get ~5.1acv measuring + meter probe to pin 2 and the other to ground. (I think the last 2 measurements are because the 5v wind is floating and not referenced to ground?)

I don't see how they would wind the 5v for 10v by mistake.

What I noticed on my PT, where the heater wires come out of pt the green 6.3 are a pair together but the yellow 5volts  one comes out on one side of winding and the other yellow comes out of other side.

That doesn't matter, that's just where they brought the fly leads out.


                       Brad     

[sluckey]

...With ground probe to chassis I measured pin 2 and got 10.31vac and then I measured pin 8 and got 10.31.

Your meter is actually measuring the "ripple" voltage of the rectified B+. If your meter can also measure frequency, set it to do so and you'll see that 'AC' is really 120Hz, not 60Hz line freq.

If you want to measure the 5VAC filament voltage, you'll have to put one probe on pin 2 and the other probe on pin 8.

[lego4040]

My fluke can measure frequency, I should measure black to ground and red to B+ for that?

[sluckey]

My fluke can measure frequency, I should measure black to ground and red to B+ for that?

Yes, but I was just presenting an explanation for that seemingly odd voltage reading. It's perfectly OK to have that much ripple straight out of the rectifier. There is nothing wrong with your PT. This is not part of your problem.

Your #1 priority is fixing the bias circuit. There is a good chance that your 6V6s are shot at this point. They have been severely stressed with no negative bias. Hopefully your OT is not damaged.

The good news is that the bias circuit is very simple and should be easy to troubleshoot. You don't need ANY tubes plugged in until you can measure something like 30 to -50vdc on pin 5 of both 6V6s. And this voltage should be adjustable using the bias pot.

[lego4040]

  not my 6v6s. I just got a really good matches Nos pair. Hopefully(pray)! They aren't shot.

[Willabe]

On a new build I use, as do others, inexpensive new production tubes or old tubes that are still good but I don't care so much if something goes wrong until I'm sure the amps working right.


             Brad     

[lego4040]

Ok so look what I found so far. You this picture, I was supposed to hook up white/red to where it says CT. I didn't. I hooked the wire straight to where it shows on schematic totally bypassing rectifier and 3watt 470 ohm resistor making the +53 volts I am reading right now on the bare bias wire.

[lego4040]

Yes that 18k is there, just not on that pic yet. With the rectifir out I get 5.2 vac across pin 2&8. With ground to chassis and lead to pin 2 I get 5.2. With ground lead to chassis and red lead to p8 I get .9

[Willabe]

With the rectifir out I get 5.2 vac across pin 2&8. With ground to chassis and lead to pin 2 I get 5.2. With ground lead to chassis and red lead to p8 I get .9

Your good there.

Like Sluckey and I said 1st fix the -bias.

on the schematic where the -69vac comes in after selenium to 82k resistor I have -51vac.

I hooked the wire straight to where it shows on schematic totally bypassing rectifier and 3watt 470 ohm resistor making the +53 volts I am reading right now on the bare bias wire.

Which is it?


              Brad     

[Willabe]

I can't see what you have wired to what under the board, here;

Edit; It doesn't matter if the pot is 1st or the tail R going to ground. You can put the R 1st then the pot to ground.

[lego4040]

with the red/white wire disconnect from circuit I got +53volts on wire. I was supposed to hook that wire to the 3watt 470resitor which goes into diode which goes to 82k resistor(where original layout has it). You were red/white is hooked up now on board, I got -69vdc. Bias pot doesn't drop it more then that, maybe bigger resistor later or I'll see when I get a load on it. I'm gonna start with 5u4gb now

[sluckey]

Ok so look what I found so far. You this picture, I was supposed to hook up white/red to where it says CT. I didn't. I hooked the wire straight to where it shows on schematic totally bypassing rectifier and 3watt 470 ohm resistor making the +53 volts I am reading right now on the bare bias wire.

Diode is backwards in this pic!

[sluckey]

with the red/white wire disconnect from circuit I got +53volts on wire. I was supposed to hook that wire to the 3watt 470resitor which goes into diode which goes to 82k resistor(where original layout has it). You were red/white is hooked up now on board, I got -69vdc. Bias pot doesn't drop it more then that, maybe bigger resistor later or I'll see when I get a load on it. I'm gonna start with 5u4gb now

Diode is correct in this pic.

[lego4040]

475B+ with From rectifier with no power or oreamp tubes in it

[lego4040]

Cause you the man Sluckey, you made me spin it around

[sluckey]

Where's the wire?

[lego4040]

Under the board, I just verified continuity too. It's in one of the pics further back in the thread. It's the yellow wire underneath. All tubes in and testing again. I set bias pot so I have 370vdcB+ off the rectifier p8. what#'s am I looking for. Both 6v6's have a -20.56ish on pin 5

[lego4040]

So these are the numbers I got. I dialed the bias to 370vdc and my numbers were close all way around I believe. I had some noise and when I moved some leads around on V3(Tremolo) I got it to go away mostly, so I have some wire management to do later. Bright channel is super crisp and clean and normal channel is nice as well. If I were to build another I'd just build it with bright channel. Tremolo, nice, clean and can't wait to try this with a real speaker cab.

[sluckey]

I set bias pot so I have 370vdcB+ off the rectifier p8.

    Say what???

Something ain't right. Bias pot should have nothing to do with voltage at pin 8 of the rectifier.
 

[lego4040]

I have meter set up to read my B+ off pin 8. Black to ground red to pin 8 on 5u4gb. By adjusting the bias Potenteometer i was able to raise and lower B+, I set it to 370vdc. So say dat ain't right, something still wrong

[sluckey]

Changing the bias voltage does affect B+ due to the fact of changing the current thru the output tubes. Set bias voltage to a low negative voltage on pin 5 causes the tubes to pass more current, which causes the B+ to drop due to the increased current demand. Set the negative bias to a greater value does just the opposite.

There may not be anything wrong. But I was alarmed at the 105v difference between absolutely no current load (no tubes) and full load (all tubes in).

475B+ with From rectifier with no power or oreamp tubes in it

I set bias pot so I have 370vdcB+ off the rectifier p8.

370V is probably a good target B+ for that amp.

[lego4040]

I see what your saying, I have another set of matched 6v6's I'll plug in on Monday and see my voltages again. I'm gonna have to do wire management also to deal with crossed wire noises. I dialed in pots to were I was getting that pulse, I went to V3 and carefully moved wires around and and noise went away, I put that back and noise came back. I also wired heater wires over the top since there isn't much room anywhere else with that chassis.  I'll chip away at it next week, this weekend I will work on the cab I got from SG. Things have been stressful at home lately, I have to have a large tumor and right thyroid removed(benign) but it's causing me to stop breathing sometimes when I sleep and looks like I have a frog in my throat. It's also Very close to vocal chords. Wife's health has been not good and she's going through stressful tests lately. So yeah, I'm a little spacey right now. My wife got a chance to help her sister out at a convention and she just landed in Vegas enjoying a much deserved break

[lego4040]

Alright, using this bias method from uncle Doug http://youtu.be/pjKYiSr497w I used the 6v6's I probably fried from my mistake the other day. The first two sets are with those, dissipation way high. Then the last set is with the other pair I had and I got them under the 12 watts for 6v6. I put the possible bad set back in to try and dial in better numbers but I saw a bulb flash, not sure which tube went

[lego4040]

If the spec sheet on a 6v6 says 350 max VDC why does it show 370? And save wattage 12-14? I'm gonna see if I can send my tubes to the place I bought them to have them checked, maybe I can salvage and use as spares for testing. Not sure how much damage was done to them and I sware I saw a flash in one of them yesterday.

[lego4040]

So I got a phone call from Brent Jesse over at audiotubes about my 6v6's and 5u4GB. The tubes are fine and will not cause any issues. He did say that on the curve test they are not as perfectly matched as they were. They were spot on before and now a little less perfect but no problem using them as a matched pair

[lego4040]

Anyone have a good idea on what I can use the usless ground switch for? I'm Having a faceplate made after I measure it all out and I have two choices, just not have hole made for new plate or add a mod and have it labeled for that

[supro66]

A stand by switch for the high voltage shut off save the tubes 

[lego4040]

i already have that.I am using the 5E5A chassis from mojo

[lego4040]

Last night I had to work and assist the signage company with all our FDNY signs and the owner turned out to be a cool dude from my old neighborhood. All his equipment is state of the art CAD, CNC laser, UV.......... You get my point. I started talking about music and told him I was building another amp but needed a faceplate. I showed him the amp, I showed him Sluckey's AC 15 faceplate and the rest is history. I just need to do all measures and give him the drawing, pick my material and if I want engraving or laser jet printing. I'm hoping it turns out nice and maybe give you guys a option on faceplates, if he's willing to do the service

[Willabe]

Cool.   

[lego4040]

Hours spent drawing the layout for the 5G9 faceplate. I need to go over and label holes correctly and make the call to my sign vender. I did email Mojo where I got chassis to see if I can get the faceplate hole dimensions. This way I can verify mine
Mojo doesn't have the cad file so I'll have to really check my accuracy. I think it's done now but pic is choppy from pano shot

[lego4040]

ITS ALIVE!!!!!! I finally got around to retubing the amp after some fixes. The 6v6's tested great and survived my error. I have 400vdc out of rectifier, 397 on the plates, -28.5v on the control grids and tubes are at 14watts disapation. Even thru a crappy speaker and box it has a really nice sound and tone. The tremolo is true to the legend, this needs a combo fast.

[Willabe]

Very nice!

I really like that amp, run a Fender stand alone reverb in the front and it's a keeper.


            Brad   

[lego4040]

It needs of coarse a cab, a head is easiest but it will be big because of the way the tubes are situated. The tremolo nailed the "How Soon is Now" from The Smiths and has that Fogerty vibe +.

[lego4040]

So I bit the bullet and ordered a cabinet from Mergili. After seeing A 5G9 for sale in Reverb I contacted them and after a few emails I said please make me that cabinet exactly, tint, lacquer and all. It should take 10 days to build and then ship from The Great North West. Speaker is my next quest, I have a 8&16ohm option and it's a 12" cutout. The Celestionlue is out now that I dropped some hard cash on a cab..Tone tubbies lower wattage speakers look interesting in the reviews I've read

[lego4040]

Here she is at 98% finished. tons of head room so I might go with a smaller wattage speaker to break up earlier, this on is rated around 60watts. I will put the foot switch in where the ground switch goes, I used two creme chicken heads where the speed & depth are cause I ran out of black ones but I kind a like it. Where can I get those paper tube charts from so I can make it offcial