Volume / Voltage Issues with Bassman 6g6B

[Willabe]

Not trying to frustrate anyone

Your fine, no problems.   

[Willabe]

(bass channel white wire ground lug to bus)

Your saying it backwards with respect to the flow.

Your talking about a ground buss and it's ground point. So it flows from > pots ground lug to > ground buss to > jack ground lug to > chassis ground point connection, in this case through the jacks ground lug which is connected to the jacks frame that connects to the chassis when bolted in.

You can connect the shield to any 1 of the 4 jacks ground lugs.


                      Brad     

[HommeMarrBuckley]

If you want it to work like the 6G6B hi/lo jacks you'll have to wire it IAW the schematic. You must use one 1MΩ and two 68KΩ.

 
Ok,  If I want to use coaxial I need to remove the resistor on the tube and put the (2) 68k at the jacks as per schematic/diagram.  I will run wire from jack ground lug to my bus bar and cut ground off of RG74 (and perhaps heatshrink the end there connecting to resistors)


I have some mogami cable left over from making guitar cables.  Can I use that or is it best just to use the RG74?

[Willabe]

Ok,  If I want to use coaxial I need to remove the resistor on the tube and put the (2) 68k at the jacks as per schematic/diagram. 

No you can use shielded cable and leave the 2x68K R's on the tube socket.


                  Brad   

[sluckey]

Ok,  If I want to use coaxial I need to remove the resistor on the tube and put the (2) 68k at the jacks as per schematic/diagram.

Yes yes yes. Do it that way. That's the simplest. The center conductor of the coax connects to the junction of the two 68Ks. The outer shield of the coax connects to to the ground buss OR the ground lug on one of the jacks. The center conductor at other end of the coax connects directly to the tube socket. Outer shield at the other end of the coax connects to NOTHING.
 

No you can use shielded cable and leave the 2x68K R's on the tube socket.

If you do this you will need two coax cables.

[Willabe]

No you can use shielded cable and leave the 2x68K R's on the tube socket.

If you do this you will need two coax cables.

I use a dual coax shielded cable for this.


               Brad   

[HommeMarrBuckley]

Yes yes yes. Do it that way. That's the simplest. The center conductor of the coax connects to the junction of the two 68Ks. The outer shield of the coax connects to to the ground buss OR the ground lug on one of the jacks. The center conductor at other end of the coax connects directly to the tube socket. Outer shield at the other end of the coax connects to NOTHING.
 

Crystal clear.
Now, for normal channel.  Everything wired the same BUT outershield of coax connects to nothing and ground lugs of jacks connect to nothing.

[sluckey]

Wire the normal input jacks EXACTLY like the bass input jacks.

[HommeMarrBuckley]

Great and understood.


Will post results Monday/Tuesday.  Hopefully have some coax remaining.
Thanks for the patience.


Cheers

[Willabe]

I use a single coax, but I never use a low input.  On Bassman setups, jumping channels works better for me to have 4, high inputs,

I don't understand.

On a stock 4x input amp if you plug into both the Hi and Low jack on 1 channel the way their wired up they will both be like plugging into the Hi jack alone. Right?

So what are you doing differently?

                   Brad   

[sluckey]

I may be wrong, but it seems like there is a drop in signal on my 6G6 Bassman when I jump from the high on the Bass channel to the low on the normal.

Duh! The bass channel has 3 inverting gain stages. The normal channel has 2 inverting gain stages. That means when you combine the two channels just prior to the PI the signals will be 180º out of phase and there will be major cancellation going on.

Jumping normal and bass channels on the 5xx bassman amps works but it should sound like crap on the 6G9B.

[Willabe]

Can't be too wrong because it sound great.

If it sounds great then it can't be wrong.


          Brad     

[sluckey]

Can't be too wrong because it sound great.

If you like the sound of two jumpered channels cancelling each other then it must be a good thing.

[sluckey]

The brittle highs is a result of the phase cancellation. Some people just say it sounds thin. I'd like to see the mod you are doing that results in no phase cancellation. Can you post a schematic?

The bass channel goes thru three 180º phase inversions prior to the mixing resistors. The normal channel only goes thru two 180º phase inversions prior to the mixing resistors. When you mix these two out of phase signals back together THERE ABSOLUTELY WILL BE PHASE CANCELLATION! Please try to convince me otherwise.

[sluckey]

The cap in question is a .002 capacitor inline with a 100k resister that leads to pin six on the second preamp tube. This capacitor acts as a treble bleed.

The cap is not in line. It's parallel to the 100K. Yes, it will bleed some treble. IT IS A BASS AMP. That channel was voiced for bass. Treble was not part of the bass sound back then.

I am saying the Bass Channel Stock is useless.

It was pretty useful FOR A BASS back in it's day. Leo made other stuff that sounded pretty good for a guitar.

Google the 6G6B Ness Mess.

Nope. I'm waiting for you to try to convince me there is no phase cancellation going on when you jump the channels of your 6G6B. You say when you jump the channels there is a loss of volume and the highs sound brittle, but in the same breath you say there is no phase cancellation. Those are two classic symptoms of phase cancellation due to jumping channels when one has an even number of gain stages and the other has an odd number of gain stages.

Steve, I swear I can count.

At least to 3!    Your math skills are not being challenged here.

[sluckey]

It was not in the same breath that I wrote where I stated it sounded Brittle.

It was certainly in the same sentence. Oh, maybe you took a breath during the comma? Or was that a coma?   

     These amps have a simple known mod and there is no known cancellation, but it does cause the highs to be brittle as hell 

however I have not modified my Brown Bassman since it is original.

Mind you, this amp is completely stock.

I did say it was stock, but it is not.  The Bass channel does not sound good stock to me so I had to revise it some.

I consider an amp stock if the modifications are easily reversed.

Tell us what you really got? It's either stock or it ain't.

You're doing a lot of backpedaling buddy, but you're only driving deeper into the ditch. And just think... All because I said jumping the channels would sound like crap. You've made my point. 

[shooter]

Still can't figure out the smilies, but sluckey gets a +2.  The build I have going are 2 channels jumped together, i made the mistake of counting a CF as an inverting stage, it sounded like S&*T, n my scope confirmed the ugly sound.  Made the CF common n sounds nice n full.

[sluckey]

I am not arguing with Sluckey that the 6G6B's channels are not in-phase.

That's exactly what we've been debating!

I am arguing with Sluckey that it is possible to easily mod the Bass Channel to be in-phase and he keeps saying it prove it.

The only way you will ever mod that Bass channel to be in phase with the normal channel is to add an inverting stage or remove an inverting stage. Since the normal channel has an even number of INVERTING gain stages you must have an even number of inverting stages in the Bass channel. Otherwise when you mix the two together with simple mixing resistors THE CHANNELS WILL BE OUT OF PHASE WITH EACH OTHER AND THERE WILL BE CANCELLATION.

I mean all you have to do is wire it like a AA-864

Guess what? The Bass and Normal channels are out of phase on that amp too.

You can believe what you wanna believe, but you already made my point. And I'm satisfied that you cannot convince me otherwise.

[sluckey]

So you are saying if you revise the Bass channel of the 6G6B ond only the bass channel to an AA864 leaving the normal channel you will get phase cancellation when jumped.

Careful, you're twisting my words.

This is exactly what I said...

     "Guess what? The Bass and Normal channels are out of phase on that amp too."

Nothing more, nothing less. You can twist that however you want, but then it becomes YOUR words.

[Ed_Chambley]

It is impossible to rework a 6G6 Bassman to not have phase cancellation when jumpered.

You twisted mine as you KNOW i was only speaking of the Bass Channel.  You are the winner tho.  And when you were young playing in bands you know the majority of bassmans were used for guitar.

Also Sluckey,  don't back off.  Really you are not bothering me.  Don't let your one feeling make you feel bad for debating me.  You finally learned you can run heater wires without twisting.  BTW, you lost that debate.

What is next, are you getting a little self conscience picking on a hobbyist when you have an extensive background in electronics.  You can do much better if you try.

[Ed_Chambley]

Remember, I am sensitive.

Your words, well maybe the words from Icehouse.

[sluckey]

It is impossible to rework a 6G6 Bassman to not have phase cancellation when jumpered.

Not true. I told you exactly what you must do to avoid phase cancellation.

And when you were young playing in bands you know the majority of bassmans were used for guitar.

Not so either. Back then EVERY Fender Bassman I ever saw had a Bass plugged into it, usually a Fender bass.

You finally learned you can run heater wires without twisting.  BTW, you lost that debate.

Actually, I didn't start twisting filament wires until I started hanging out in amp forums. I don't recall any such debate. Can you post a link?

What is next, are you getting a little self conscience picking on a hobbyist when you have an extensive background in electronics.  You can do much better if you try.

Hey, I'm a hobbyist too! And I'm currently between projects with plenty of time on hand. So watch what you say buddy.   

 

Your words, well maybe the words from Icehouse.

Alright! You finally got one right! But Icehouse speaks the truth and you should know it. Now I've got to make a beer run, but I'll be back. See ya buddy! 

[SILVERGUN]

So, the beauty of all of this is that we are slowly prying out the super secret non-stock, stock Bassman schematic from the great Ed Chambley..
 
The world has been waiting.

So,, I'm assuming that an imaginary schematic would look something like this?

Channel jumper has been omitted but is implied. 

[Willabe]

Of all people to mod an amp by taking OUT a 12AX7 I never thought it would be you SG!



               Brad     

[SILVERGUN]

Of all people to mod an amp by taking OUT a 12AX7 I never thought it would be you SG!

Being around all of you senior gents, I can't help but grow up a little... 

But this is Ed's amp. I like the bass channel on the 6G6B, and used it recently.
If I were building it, I'dve added a triode to the normal channel. (so, you got me pegg'd)

But since he did these mods years ago, I'm just trying to get a working schematic going.
It must be SUPER DOOPER special since he's protecting it with all of these verbal gymnastics.

It must sound  2x as good as Brian Setzer's amp, because he only uses one normal channel and Ed uses 2 at the same time.
 

[Ed_Chambley]

Of all people to mod an amp by taking OUT a 12AX7 I never thought it would be you SG!

Being around all of you senior gents, I can't help but grow up a little... 

But this is Ed's amp. I like the bass channel on the 6G6B, and used it recently.
If I were building it, I'dve added a triode to the normal channel. (so, you got me pegg'd)

But since he did these mods years ago, I'm just trying to get a working schematic going.
It must be SUPER DOOPER special since he's protecting it with all of these verbal gymnastics.

It must sound  2x as good as Brian Setzer's amp, because he only uses one normal channel and Ed uses 2 at the same time.
 

No, I use both channels on a Fender amp most of the time.  When I cannot use 2 amps, one wet and one dry, I use the 2 channels on a fender, one wet and one dry.  Usually I use the normal channel for my Dry signal except on this Bassman I use the Bass channel now.

I do mods and dont revise a schematic.  I did a mod from Dave Funk on one of my Super reverbs last weekend and love it.  It involves changing it to CF design.

You will not find a schematic for it, so

"IF IT IS NOT ON A SCHEMATIC IT DOES NOT EXIST".
...........................................................Sluckey, esq.

[Ed_Chambley]

Of all people to mod an amp by taking OUT a 12AX7 I never thought it would be you SG!

Being around all of you senior gents, I can't help but grow up a little... 

But this is Ed's amp. I like the bass channel on the 6G6B, and used it recently.
If I were building it, I'dve added a triode to the normal channel. (so, you got me pegg'd)

But since he did these mods years ago, I'm just trying to get a working schematic going.
It must be SUPER DOOPER special since he's protecting it with all of these verbal gymnastics.

It must sound  2x as good as Brian Setzer's amp, because he only uses one normal channel and Ed uses 2 at the same time.
 

I did the mod about a year ago.
http://archive.ampage.org/threads/6/gagd/323798/6g6_bassman-1.html

The above link is a discussion and I have searched the metro forum, but I cannot find the step by step.

[sluckey]

I did the mod about a year ago.
http://archive.ampage.org/threads/6/gagd/323798/6g6_bassman-1.html

That's nice. But it has absolutely nothing to do with jumping channels on a Bassman 6g6B and the resulting phase cancellation.

I'd say you're out of bullets. Besides, you quit already.

[sluckey]

I won't swap personal insults with you. I'm done.

[Ed_Chambley]

I won't swap personal insults with you. I'm done.

Sorry, intended as a joke.  I meant nothing personal.

[HommeMarrBuckley]

Almost finished the jacks.  Underestimated the time needed and didn't have a good time with the RG-74.  Really easy to break that outershield wire when cutting in.
Anyway, concerned with ground loop and before I put stuff away, I wanted to see if this was in unison.
My coaxial hot is going to the resistors and coaxial ground is going to the bus.  Now, for the ground (Hi Jack) coming off of 1M resistor?  Is it ok if I put that to the ground bus too?
SL, I read in the scrapbook about hi lo jacks and it makes sense.  This ground I am asking about will help shunt when I plug into the Lo.

[sluckey]

Now, for the ground (Hi Jack) coming off of 1M resistor?  Is it ok if I put that to the ground bus too?

Yes. I like to connect that ground buss to the input jack ground lug. I also connect a short wire from the buss to a ground lug bolted to the chassis right near the input jack(s). Here are a couple pics...

     http://home.comcast.net/~seluckey/amps/VAC15/big_guts.jpg

     http://home.comcast.net/~seluckey/amps/revibe/revibe_07.jpg

[mresistor]

Sluckey - in the pictures on the board you have a couple turrets that have three leads into the top hole; did you drill the turret out a little to fit them in?

[sluckey]

There's one turret with 4 leads in it. The turrets are stock and came from Doug. No drilling. And the leads on those 1/2 watt metal film resistors are skinny. You could probably even get 5 in one if you had to.

[HommeMarrBuckley]

Well, in brief, got the jacks rewired and now all four jacks are working--Hi and Lo on both channels.  So, good news there, however, still got that buzz/hum just like in vid when I turn it on.  Can understand now how this can test somebody. Frustrating in that I went with the coax and ground bus to keep it dead quiet only to have this result.  But maybe it's not there--I dunno--perhaps just to leave this issue and see if tech in area with more experience can pinpoint the problem.  Overall, pleased with how the amp sounds.  Sounds exactly of what I have heard of the originals.  Little smirk when I could hear the windows rattle. 


2 Hammond AO-43s are en route here.  Supposed to have all working parts except the tubes--@$50 each--hoping it was a good deal.  That along with weather kinda got me sidetracked.  Been thinking about trying the DR AB763 with them.  That along with Supro should keep me busy.  Haven't given up but just need to take a break from this one cuz it got me brooding.  So just wanted to update.


So I gots a working amp...but it still needs to get quiet.

[Willabe]

Well, in brief, got the jacks rewired and now all four jacks are working--Hi and Lo on both channels.  So, good news there, however, still got that buzz/hum just like in vid when I turn it on. 

So I gots a working amp...but it still needs to get quiet.

Glad you have the 4x jacks and the amp working now.   

I listened to your sound clip and I was looking at the picture you posted at the beginning of your thread.

One thing I see is the blue and brown OT plate fly leads and the red OT CT fly lead look like they were not trimmed/cut to length? Looks like you left all 3 in a long loop? If so they need to be shortened up. The blue and red wire look like when shortened they would be only around 3" or so. They're at least 8" to 10" long now.

Also the OT secondary wires, yellow and black, that go to the output jacks need to be shortened up too. When you shorten them twist the 2 together like you did with the 6.3 heater wires.

You might need to use shielded wire for the power tube grid wires, brown and green, that go from the PI's .1 coupling caps to the power tube grid. Just like with the shielded cable on the input jacks, only ground the shield at 1 end. Wire the shields ground wire to the PI's ground.

Can you post some more good quality pictures of the amps inside? Someone might see something a miss.



                     Brad     

[HommeMarrBuckley]

My ground bus bar is attached near input jacks and runs to end of normal channel by presence pot (not attached to chassis).  Should it be one bar like that running whole way down for both channels?  Or should I have two bars--1 for each channel?  Probably grabbing straws here.

[tubeswell]

My ground bus bar is attached near input jacks and runs to end of normal channel by presence pot (not attached to chassis).  Should it be one bar like that running whole way down for both channels?  Or should I have two bars--1 for each channel?  Probably grabbing straws here.

I just finished a '6G6B' build with EL34s at high voltage (616V and 380 on the screens).  I used one (the same) ground buss for both channels. This is 'mirrored' with a single HT supply dropping rail for the whole amp. (rectifier -50uF reservoir - 15k screen dropper (because of the high voltages) - 50uF screen filter cap, 4k7 dropper to PI node, 22uF PI filter cap, 4k7 dropper to normal channel node, 22uF normal channel filter cap, 27k dropper to bass channel node, 22uF bass channel filter cap). The voltages for the PI, normal channel and bass channel nodes have all ended up being approximately what is shown in the 6G6B schematic.




The ground returns are galactically-grounded at each respective filter cap ground. The ground buss attaches to the chassis at the bass channel's 'hi-input' jack sleeve terminal only. The normal channel's 1M grid resistor is grounded at the normal channel jack's sleeve terminal (and is not connected to the buss bar). The output stage ground returns, heater elevation ground return, bias ground return, and screen filter node ground return are all connected to the reservoir cap ground return. This is then connected by a single wire to the end of the buss bar where the PI ground return is connected (at the other end of the ground buss bar to the input chassis grounding point). The normal channel's ground returns are connected to the buss bar at the same point as the normal channel's filter cap ground return, and the bass channel's ground returns are connected to the buss bar at the same point as the bass channel's filter cap ground return. The heaters are balanced with a humdinger pot. There is absolutely no hum whatsoever in my amp.

[mresistor]

Tubeswell - looks like you have 10uf extra reservoir and 30uf extra screen filter capacitance. This will certainly help with smoothing and reducing 120hz hum. Still would like to see pics the big capacitors and wiring on this bassman.

[tubeswell]

Tubeswell - looks like you have 10uf extra reservoir and 30uf extra screen filter capacitance. This will certainly help with smoothing and reducing 120hz hum. Still would like to see pics the big capacitors and wiring on this bassman.

This is the most recent gutshot. (I made a couple of subsequent minor changes - minor change to the location of the presence control circuitry and insertion of a 22nF coupling cap after the CF in the bass channel and the insertion of 15k screen supply dropper (where the 4k7 wire-wound is.) and wiring the suppressors to one of the points in the bias voltage divider. You'll note that this has 12VAc heaters and voltage doublers for the B+ and for the Bias supply, which was what the original Jansen Bassman 50 had because this uses the original PT which was salvaged from the old carcass). I also use series filtering for the screen and PI nodes because I wasn't sure when I was putting it together how high the voltages would be when I first flicked the switch. It really only needed the 2 case in eh voltage doubler, The rest i could've gotten away with single 600V caps (which I have plenty of).


Sorry for the hijack. Didn't intend to (but it was by way of explanation about the grounding scheme). 

[HommeMarrBuckley]

Hey Tubeswell, nice build.  If only you lived on my street. 
Wish someone with experience could just take a look and point the way.
I thought it might be something in the home considering the age.  Got an unsure answer in terms of grounded outlets so took it downstairs and got same result but not as loud. 
Took Silvergun's help and measured hum.  It's 60 HZ.
Will take Willabee's advice to cut the lengths because they are needlessly long.  Although, I did chopstick it and moved wires with it on and didn't notice any difference in hum volume, perhaps this doesn't matter.
Lastly, good method for screwing jacks?  Should I put toothed washer on inside and outside of chassis?  Will look at speaker outs as well.
Will post some pics next week.  Thanks.
Matt

[shooter]

60HZ indicates filaments.  1 toothed washer should hold in a hurricane.

[tubeswell]

...
Lastly, good method for screwing jacks?  Should I put toothed washer on inside and outside of chassis?  ...

Yes - inside chassis

[HommeMarrBuckley]

I have 4 Tung-Sol reissue 12ax7s in this and have just read online about others having issues with them and hum.  Might not be it but who knows.  Don't think if I interchange positions with the four, will it matter?, considering they're all the same brand.   I have the tube shields, as well, but dunno if that makes a difference.

[Willabe]

I have 4 Tung-Sol reissue 12ax7s in this and have just read online about others having issues with them and hum. 

I have a few I'm using that sound very good to me. But I did buy them several years ago. Sometimes they get bad batches. The batch before could be just fine so you think you like the tube and bam new stuff is a bad batch. Or some tube seller got a large order, tested them, kept the quite 1's for re-sale and either returned the noisy 1's and the tube manufacture re-sold them or the guy who tested them sold them to some other tube dealer. 

I have the tube shields, as well, but dunno if that makes a difference.

Yes, sometimes it can make a difference. Put them on and see.


                  Brad   

[HommeMarrBuckley]

Again, been searching "Tung-sol 12ax7 reissue hum/cathode follower amp" and keep reading about this.  Without any experience in doing this, it's hard for me to believe that it's the source of the hum but I dunno.  Seems to be something about cathode follower amps and internal design of filaments inside tube.  Could it just be in V2? 


Brad, what amp(s) are you using them in?  I don't know enough about voltages there and tube design and CF amps.

[Willabe]

Don't think if I interchange positions with the four, will it matter?, considering they're all the same brand.

It might be just 1 tube that is noisy.

The 1st input preamp tubes noise, along with it's signal, gets amplified/re-amplified the most because it goes through the most stages.

This is where a small Champ type amp comes in handy to test for a noisy preamp tube. It only uses 1 12AX7. If the amp is quite you can try different 12AX7's in it to see if their noisy.

I need to build 1.


                        Brad   

[Willabe]

Without any experience in doing this, it's hard for me to believe that it's the source of the hum but I dunno.  Seems to be something about cathode follower amps and internal design of filaments inside tube.

It's heater to cathode leakage their talking about. Some tubes can have it and others are just fine. I think that the stress from the high voltage on the cathode of a cathode follower can make it worse or bring it out in a tube that wouldn't have a problem with it in a standard common cathode set up, preamp gain stage?

Brad, what amp(s) are you using them in?  I don't know enough about voltages there and tube design and CF amps.

I'm using them in my 5E3 (Fender tweed Deluxe), 5G9 (Fender tweed Tremolux) and my new build a Gibson GA77, which has a CF for the TS (tone stack).

I don't think their noisy amps but there is some hiss because I'm using CC R's for the plate R's. As soon as I start to play I can't hear it, so it doesn't bother me.   

But I do use a dcv stand off of 70 to 80dcv on the heaters to help keep them quite. Fender never used them and their amps weren't noisy, but than again Fender had USA made tubes from the golden age of tubes.

I can post the circuit for you but probably best to try and figure out if it's just a noisy tube 1st. (Be easy enough to try on your bread board and see if it helps?)


                    Brad   

[Willabe]

Don't think if I interchange positions with the four, will it matter?, considering they're all the same brand.

You can get a lemon from the same batch coming of the production line. Quality control and materials aren't what they used to be like in the golden years of tubes and even then they had bad tubes come off the line, but probable way less % wise.

You can try this, take out the 1st preamp tube from the channel without the CF and leave it out for now. Then 1 by 1 swap tubes in the CF position, each time putting the tube shields back on.

You might find a tube that doesn't like being in the CF socket.   

Worth a try.


                       Brad   

[Willabe]

Did you shorten up the OT leads like I suggested in reply #85?

I'm suspicious of them causing a noise problem. The red CT wire loops around the -bias pot and all the others are way too long too.

You saw/heard what it was doing on your bread board with long hook up wires.

If you shorten them up they might fix it but if not at least you'll take them out as a possibility.


                   Brad