Troubleshooting Sluckey Dual Marshall Build

[pompeiisneaks]

So per sluckey's request, I'm moving the troubleshooting from my video series thread to here. 

The earlier parts are readable here on the thread if you're interested.

https://el34world.com/Forum/index.php?topic=23799.0

So from sluckeys' last comment:

Quote from: pompeiisneaks on April 01, 2019, 06:51:27 pm
I wasn't planning on it, just asked the question.  What I'm not sure I understand, is 'if the transformer has a center tap for the B+ side, why couldn't it be used with a FWB"?  What am I not understanding about the transformer being designed for FWBR?  I'm sure it's something stupid I'm missing.  Just that the voltages would come out too low in non FWBR ?
It's just that simple. That PT puts out 500VDC with a bridge and that's pretty typical for a 100W amp. That same PT would only put out 250VDC with a conventional rectifier. That would make a real wimpy 100W amp.

There is a proper way to use a CT with a FWB. But you don't connect it to ground. Instead you connect it to the junction of two series stacked filter caps to force the voltage to split equally across them. Like this...

     https://el34world.com/charts/Schematics/files/Marshall/Marshall_2203_jmp_master_volume_lead_100watt.gif

Are you sure the Plexi preamp has low output? The 2204 preamp has one more gain stage than the Plexi so it will naturally sound louder. Remember, the 2204 is a big hair screamer. The Plexi is just a crunchy sounding amp.

Can you move text discussions about this amp to a new thread? It's really a drag to wait on those seven videos to load just to read a text message.
 

So here we are.  That's possible, I get it, I'll check it out.  I had the plexi at max volume on both channels and it comes out clean, with a touch of hum and 0 crunch, I thought at max it should be pushing some gain.  I understand the 2204 has an extra gain stage, but expected more than just 'weak clean' out of the plexi.  I'll get out the scope and trace signals today.  (I hope).

~Phil

[sluckey]

I had the plexi at max volume on both channels and it comes out clean, with a touch of hum and 0 crunch, I thought at max it should be pushing some gain.  I understand the 2204 has an extra gain stage, but expected more than just 'weak clean' out of the plexi.  I'll get out the scope and trace signals today.  (I hope).

You should have plenty of crunch way before you hit max on the plexi volume controls. I'd say something is not right with V1 circuit or switch. Post some voltage readings for V1 and the B+ rail and some hi-rez pics of the V1 circuit and your switch. Also of the B+ caps and dropping resistors. Did you do any mods in the V1 area? Or in the B+ filter area? Is your Plexi preamp B+ 10K?

[pompeiisneaks]

I had the plexi at max volume on both channels and it comes out clean, with a touch of hum and 0 crunch, I thought at max it should be pushing some gain.  I understand the 2204 has an extra gain stage, but expected more than just 'weak clean' out of the plexi.  I'll get out the scope and trace signals today.  (I hope).

You should have plenty of crunch way before you hit max on the plexi volume controls. I'd say something is not right with V1 circuit or switch. Post some voltage readings for V1 and the B+ rail and some hi-rez pics of the V1 circuit and your switch. Also of the B+ caps and dropping resistors. Did you do any mods in the V1 area? Or in the B+ filter area? Is your Plexi preamp B+ 10K?

I'll get some numbers.  I seem to recall getting about 140VDC on the anode of the plexi stage and like 1.1vdc on the cathode.  I will get the rest later from home. 

~Phil

[pompeiisneaks]

First I'll post voltages, then I'll get the pics cropped down to tiny size so I can upload :D

B+
A 495 B 487 C 387 D 318 E 308 F 297.7

Power Tubes:

493 anode
486 screen
-45.5 grid

V1a
A 161.3
C 1.15

V1b
A 225
C 1.97

V2a
A 225
C 2.25

V2b
A 274
C 3.2

V3a
A 179
C 1.179

V3b
A 318
C 180

V4a
A (gah apparently I don't know how to write these down, the PI seems fine and balanced, my problem seems solely with V1, V2 sends out good signal to the PI etc.)
C

V4b
A  238.8
C  49.6

~Phil

[pompeiisneaks]

Eh I'll just share the full rez google photos:

https://photos.app.goo.gl/UqZ6iryJ8FUpC7nDA

the output of the right coupling cap  has continuity to the left pot, and the output of the left has continuity to the left pot in the second image.

Here's where things are odd.  If I have the v1a channel volume set to 0, I get strong output from that side.  at the exit of the coupling cap, but when I dial it up, it drops to 0.  Like the pot, at max is sending all to ground.

Now that I just typed that, I think I know why, and it's nothing unexpected.  When the channel is not selected, it's going to earth, after the 470k mixer resistors right?  but oddly it seems like channel V1b doesn't do that? 

At any rate, I seem to have identical signal coming out of V1A as I get out of V2a.  so the first stage is doing it's job, something is getting lost after that, maybe some unexpected interaction between the channels?

The only deviation I have from the standard here is that I've added 'bright' switches to both V1b and V2a so I can toggle the bright cap in/out.  You can see the bright cap on the center pot in the picture. 

I also get a decent amount of hum when I engage the relay.  (it seems like when the relay is 'off' I have JCM800, and when on, I get Plexi, doesn't matter much to me, but due to the hum appearing with plexi engaged, it makes me think the signal wires for the 5V add it somehow due to being 'on' at that point.

Ideas?

~Phil

[SILVERGUN]

I would suugest posting your schematic so troubleshooting instructions can be given.
I found myself saying "what relay?"


Divide and conquer...you got this

[pompeiisneaks]

I would suugest posting your schematic so troubleshooting instructions can be given.
I found myself saying "what relay?"


Divide and conquer...you got this

Sorry it's in my original post but sluckey wanted me to bring the troubleshooting side here.  It's his dual marshall the relay switches between the plexi preamp and the JCM800 preamp. 

[sluckey]

Right now I suspect you just have a simple wiring error in the plexi circuit or the relay. When the relay is energized what voltage do you measure directly across the diode on the relay board?

Do you feel like the 2204 circuit is alright? If so, let's just work on the plexi channel.

I want you to bypass the relay and feed the plexi channel directly to V3-2. Ie, remove the wire from the relay that goes to the plexi 470K mixing resistors and remove the wire that goes to V3-2. Tack solder those two wires together. Does plexi work now?

I can't relate your pics to my schematic so I'm working from the schematic only.

[pompeiisneaks]

Ok.  I'll check those.  I will get a layout up again after getting that for you as well.  I did check across the diode and when not engaged I get 0 volts and when engaged I get 5 volts.

The 2204 side seems to only have a bit of hiss, but otherwise seems to perform perfectly.

I'll test and get back to you on the 'removing of the relay' steps.

Since I don't have a dropper for the 2204 channel (it's just switched) do I need to also desolder it from the relay so it's not in the mix at all?

~Phil

[sluckey]

Since I don't have a dropper for the 2204 channel (it's just switched) do I need to also desolder it from the relay so it's not in the mix at all?

No need. Once you lift the wire from V3-2 everything is out of the mix. And when you lift the wire from the plexi preamp and connect the two dangling wires together, the plexi will be the only thing connected to the rest of the amp. The 2204 will just be sitting on the relay doing nothing.

I want to see if the problem is with the relay wiring or the plexi preamp wiring. Starting at the relay seems like a good place to start troubleshooting. If bypassing the relay doesn't fix the plexi problem I still want you to leave the relay bypassed until we get the plexi to be as loud as it should be.

[pompeiisneaks]

sounds good will do, I misunderstood the first post but now that you say it again, I get it.  But then I was woken at 2:30 am for a work issue so my brain's a bit behind the curve today.

~Phil

[shooter]

I was woken at 2:30 am for a work issue

I don't miss those 15 calls a week

[pompeiisneaks]

Okay so fixed one issue.  Jumpering Plexi straight into V3a grid made it sound great on one of the two channels only, the other was messed up, weak at low volumes and gone at high.  I found that somehow the grounding wire was pressed so hard against that side that it was almost earthing it.  I removed the connection and connected from on top, and both sound nice now.

Now, when I re-connect to the relay, I still get good behavior with the 2204 side but when I engage the relay, I get a horrid hum, and I actually get weak output from ALL THREE channels, i.e. plexi a and b as well as the 2204 side.  So it seems like a wiring issue with the relay. 

Here's how I have it connected, see my crude ms paint drawing:

One other thing of note.  There are definitely 0VDC when not engaged and the 2204 side is working, and 5.05VDC when I've flipped the switch across the terminals of the diode on the relay board.   

Also when I engage the relay I get a lot of 60 cycle hum it seems.  I think it is anyway, and it goes away when I remove it.

This hum didn't exist when I was directly jumpered from Plexi to V3a

~Phil

[Willabe]

Okay so fixed one issue.  Jumpering Plexi straight into V3a grid made it sound great on one of the two channels only, the other was messed up, weak at low volumes and gone at high.  I found that somehow the grounding wire was pressed so hard against that side that it was almost earthing it.  I removed the connection and connected from on top, and both sound nice now.

 

[pompeiisneaks]

heh,

yeah dumb one

One other thing I'm debating is taht maybe the relay itself is hosed.  I'm debating just pulling it out of the socket, and manually jumpering things with those perf board style pins in the socket to see what I get.  If that makes things work, it's the relay or the power supply for the relay. 

~Phil

[shooter]

I get a horrid hum

is it possible that because your "top" channel is 180
and your "bottom" ch is 0
that it's causing phasing issue with the OT? 

[SILVERGUN]

Just throwin this out there...
How do you have the ground for the relay power circuit wired? You don't want to have it shared with the signal ground....it should be floating.

Sorry if this was covered. I didn't read all of the other posts leading up to this.

[sluckey]

Yeah, the relay is the issue but I think it's simply wired incorrectly. Wire it exactly as shown in the attached pic and it will work properly. Plexi mode is relay not energized. 2204 mode is relay energized.

The ground connection to relay pin 13 (com2) refers to chassis ground (preamp ground buss).

THIS IS VERY IMPORTANT!!!

If you are using the PT's filament winding as a 6.3VAC source for the relay power supply board...

DO NOT CONNECT THE GRND LUG OF THE RELAY PS BOARD TO CHASSIS!
DO NOT CONNECT THE GRND LUG OF THE RELAY PS BOARD TO CHASSIS!
DO NOT CONNECT THE GRND LUG OF THE RELAY PS BOARD TO CHASSIS!
DO NOT CONNECT THE GRND LUG OF THE RELAY PS BOARD TO CHASSIS!
DO NOT CONNECT THE GRND LUG OF THE RELAY PS BOARD TO CHASSIS!
DO NOT CONNECT THE GRND LUG OF THE RELAY PS BOARD TO CHASSIS!
DO NOT CONNECT THE GRND LUG OF THE RELAY PS BOARD TO CHASSIS!
DO NOT CONNECT THE GRND LUG OF THE RELAY PS BOARD TO CHASSIS!
DO NOT CONNECT THE GRND LUG OF THE RELAY PS BOARD TO CHASSIS!
DO NOT CONNECT THE GRND LUG OF THE RELAY PS BOARD TO CHASSIS!
DO NOT CONNECT THE GRND LUG OF THE RELAY PS BOARD TO CHASSIS!
DO NOT CONNECT THE GRND LUG OF THE RELAY PS BOARD TO CHASSIS!
DO NOT CONNECT THE GRND LUG OF THE RELAY PS BOARD TO CHASSIS!
DO NOT CONNECT THE GRND LUG OF THE RELAY PS BOARD TO CHASSIS!
DO NOT CONNECT THE GRND LUG OF THE RELAY PS BOARD TO CHASSIS!
DO NOT CONNECT THE GRND LUG OF THE RELAY PS BOARD TO CHASSIS!

[pompeiisneaks]

Yeah, the relay is the issue but I think it's simply wired incorrectly. Wire it exactly as shown in the attached pic and it will work properly. Plexi mode is relay not energized. 2204 mode is relay energized.

The ground connection to relay pin 13 (com2) refers to chassis ground (preamp ground buss).

THIS IS VERY IMPORTANT!!!

If you are using the PT's filament winding as a 6.3VAC source for the relay power supply board...

DO NOT CONNECT THE GRND LUG OF THE RELAY PS BOARD TO CHASSIS!
DO NOT CONNECT THE GRND LUG OF THE RELAY PS BOARD TO CHASSIS!
DO NOT CONNECT THE GRND LUG OF THE RELAY PS BOARD TO CHASSIS!
DO NOT CONNECT THE GRND LUG OF THE RELAY PS BOARD TO CHASSIS!
DO NOT CONNECT THE GRND LUG OF THE RELAY PS BOARD TO CHASSIS!
DO NOT CONNECT THE GRND LUG OF THE RELAY PS BOARD TO CHASSIS!
DO NOT CONNECT THE GRND LUG OF THE RELAY PS BOARD TO CHASSIS!
DO NOT CONNECT THE GRND LUG OF THE RELAY PS BOARD TO CHASSIS!
DO NOT CONNECT THE GRND LUG OF THE RELAY PS BOARD TO CHASSIS!
DO NOT CONNECT THE GRND LUG OF THE RELAY PS BOARD TO CHASSIS!
DO NOT CONNECT THE GRND LUG OF THE RELAY PS BOARD TO CHASSIS!
DO NOT CONNECT THE GRND LUG OF THE RELAY PS BOARD TO CHASSIS!
DO NOT CONNECT THE GRND LUG OF THE RELAY PS BOARD TO CHASSIS!
DO NOT CONNECT THE GRND LUG OF THE RELAY PS BOARD TO CHASSIS!
DO NOT CONNECT THE GRND LUG OF THE RELAY PS BOARD TO CHASSIS!
DO NOT CONNECT THE GRND LUG OF THE RELAY PS BOARD TO CHASSIS!

But I am using my 6.3V center tap to earth so if I understand it, I should connect the relay PS ground to chassis right?

I KID I KID :) It's floating already,   Don't beat me.

I'll lift the relay board again and look at it and see if I did something stupid.

I may also try to do the physical wiring tests as I mentioned with jumpers to see if removing the relay itself proves its either the ps supply for relays or the relay itself.

~Phil

[pompeiisneaks]

We have a solution.

The relay itself is defective.

If I manually jumper the socket pins it works perfectly (i.e. jumper both sides manually between center pin and top or center and bottom I get both working)

So I took an external 5v supply and tested the relay.  I hear the coil clicking.  I tested when NC and I get connectivity and when not engaged no connectivity.  I then setup my DMM to connect to NO and get nothing, engage the coil, hear click do NOT get continuity beep.  On either side.  So I'm guessing that something internally is blocking the relay from sweeping the switch over to the NO side on engaging it.  Ugh.

I'll get another.

~Phil

[sluckey]

I've never seen one of those OMRONs fail. I'm stubborn. Show me exactly how you tested that relay, which pins you had your meter connected to, etc. A hi rez pic would really be worth a thousand words.

[shooter]

OMRONs fail

nope they are pretty bullet proof, but to be honest, the 5v ones don't like being powered from a 28v circuit 

[pompeiisneaks]

DOH!  I'm a mutton head. 

I somehow didn't get your image loaded at all when I was reviewing it last time, not sure why, but I thought you were referring to my wiring drawing being right.

Then I made a video, that's now moot, because I realized I had it wired wrong.  My drawing is wrong.  It's how a DPDT switch would be wired, but not a relay. 

the common terminal is the first pin!  I had it the middle pin!

 

That fixed it.

Now, the only remaining real issue seems to be the 2204 channel has a ton of hiss.  Very noisy, but still sounds great.  Now, maybe that's just expected with that much gain, not sure. but what could be causing that hiss?  Sounds a lot like white noise. 

~Phil

[pompeiisneaks]

Ok I think I mostly fixed that as well, not 100% gone but mostly gone, and I think it's more just noise in my shop now due to the higher gain.

Basically, the .001uF cap on the bright switch was noisy as hell touching it etc.  when I disengaged the bright switch then noise was gone.

I had a CDE mica .001 that I thought I didn't whne I first installed it, and this solved the bulk of that w hite noise,  I still seem to have a decnet amount at high volumes but at lower it's fine, and again, I think that may be related to being in the shop under LED lights etc. with no cabinet around to block that noise etc.

~Phil