Seems every build has a glitch and this 1959 100 watt super lead is no exception !

[Phoenix1]

This build was much easier than the JTM45+ with much more room inside the chassis. All moved very smoothly and double checked everything which seemed fine. I did find a couple mistakes that I corrected. With no testing process in print I referred to the testing section of the JTM45 which seems to be basically the same. So I powered it up with LBL in line checked out great. Installed the preamp tubes and did the tests on several turrets and voltages were right down the line perfect. Except V1 the tube would not go in i rocked the amp up and pin 7 was blocked off and I checked the back or under side thinking solder might have gone inside and that did not happen it was just defective. I had an extra new one so replaced it. The tube while out, I did drop on the floor but did not break or look like anything was wrong. So installed it. Then on to power tubes under V4 and V7 I installed the Bias Meter sockets. Powered up no sparks or smells and bias meter seemed backwards as the needles went upwards so I backed it down counterclockwise to 37mA and let it sit for a few minutes and all seemed great. At this point I was getting pretty pumped up. I had one of my Marshall cabs plugged in impedance selector was set on 16 ohms to match the cabinet.
SO time to plug in and see what it does. With nothing plugged in it was very quiet but when I plugged into channel 1 or 2, i got a hum like the jack cord had no guitar and a thumb or finger on the tip. No sound from the guitar being strummed at all. It cant be serious as the amp lights up and all seem fine.
I am wondering if the V1 tube got damaged or if the input jacks have a problem as it is not really clear on the layout which is the front or open end.

 

[PelliX]

I am wondering if the V1 tube got damaged or if the input jacks have a problem as it is not really clear on the layout which is the front or open end.

I doubt the valve is faulty, as you're hearing buzz/hum, but no harm in trying another one to rule it out. Not sure what you mean by the front and open ends?

Same on all input sockets? Check your grounding strarting from an input jack. Do you have a scope or signal probe?

 

[Phoenix1]

I doubt the valve is faulty, as you're hearing buzz/hum, but no harm in trying another one to rule it out. Not sure what you mean by the front and open ends?

Same on all input sockets? Check your grounding strarting from an input jack. Do you have a scope or signal probe?

Front or open end is the one you see from the outside where yo put the jack cord in. Iam pretty sure I have them correct as on of the puctures is looking at the input jacks. The one thing that does not make sense is if you look at the layout at the bottom of the input jacks they are jumped from the sleeve to the tip end basically just shorted out ! I am tempted to reach in and clip that bare steel jumper unless I hear from the tech @Mojotone tomorrow

 

[PelliX]

Iam pretty sure I have them correct as on of the puctures is looking at the input jacks

If those are standard jack sockets, yes.

Try pulling V1 and see what happens. If the buzz/hum clears up, you know where to look.

 

[Phoenix1]

I wanted to pull that Valve but did not know if I could ! It did hit that cross leg pretty hard ! I am on my way down to do that right now !

 

[Phoenix1]

It IS an ac hum ! The valve is fine no change ! I made a 10 second video to let it be listened to but cant figure out how to add it !

 

[Gunner64]

Are they Electro harmonix 12ax7s?

In my Mojo JMP2204 v2 took a shit immediately almost. Apparently the EH tubes don't like the v2 position in my amp.

 

[dtier]

I believe your input jacks are transposed from the layout picture. The green input leads to the 68k resistors are on the switch terminal of the jacks so they are floating when you plug in. The layout picture intends for them to be facing the other way.

 

[Phoenix1]

I believe your input jacks are transposed from the layout picture. The green input leads to the 68k resistors are on the switch terminal of the jacks so they are floating when you plug in. The layout picture intends for them to be facing the other way.

I was wondering that ! I actually sent that quiry to Tech at Mojotone and he said as far as he could see it was ok BUT he doesnt take much time to reall look ! I actually found a problem on their Schematic as the had the green wire from the OT as 4 ohm and it is black on the Heyboer trannys. I will go down and take it all apart and start clean and see if it fixes that I faced them the other way just because it was more open that way !

 

[Gunner64]

Did you swap v2? The russian tubes dont like that position apparently. My mojo build took that kit suppied EH tube out almost immediately. It Did nothing but buzz.

All my voltages were within spec, my wiring spot on, so I swapped tubes and that brand new v2 was the issue. I did a little searching and it turns out these EH tubes don't last in the cf position.

 

[Phoenix1]

Did you swap v2? The russian tubes dont like that position apparently. My mojo build took that kit suppied EH tube out almost immediately. It Did nothing but buzz.

All my voltages were within spec, my wiring spot on, so I swapped tubes and that brand new v2 was the issue. I did a little searching and it turns out these EH tubes don't last in the cf position.

Yes I tried that and no difference ! Put it back in !

 

[Gunner64]

Something to be aware of either way.

 

[Pete Farrington]

I believe your input jacks are transposed from the layout picture

Me too, it matches the symptoms.
You can't swap wires from the tip lug to the switch lug and expect it to work.

 

[Trouble Free]

I agree with these guys input jacks are wired wrong, if you plug into the hi jack your signal is going straight to ground.
(Might still work if you plug into the low input.)

I would rewire them the way Marshall does but this way would work if you wire them correctly.

 

[Phoenix1]

Wil

Something to be aware of either way.

l keep in mind ! These are not EH they are JJ

 

[Phoenix1]

View attachment 147782View attachment 147783Me too, it matches the symptoms.
You can't swap wires from the tip lug to the switch lug and expect it to work.

I didnt ! I took all components apart cleaned them and started over on all four inputs from scratch. Pretty sure its right now. Turned it back on and still have AC hum and no sound with jack cord plugged into input jacks

 

[rtcook]

Not that any of this is the cause for no sound, but I noticed a few discrepancies in some component values.

The 5.1k resistors on the EL34 tubes should be 5.6k.
The tone stack for SL is 33k/500pf
The tone stack for SB is 56k/250pf.
Their layout is a mixture of both.

 

[Phoenix1]

Me too, it matches the symptoms.
You can't swap wires from the tip lug to the switch lug and expect it to work.

Hello Pete, as I said above yes I took it all apart cleaned and reassembled as shown on the layout ! There was so much room on the other side of the input jacks I thought it would be ok to turn them over, turns out it turned me around ! I got them right now but AC hum is still there amp turns on, tubes are biased at 37mA and will sit there looking like its ready to go until I turn the standby to on and hum is there. No difference if a jack cord is plugged in no sound from it just a hum Through the speakers.

 

[Phoenix1]

Not that any of this is the cause for no sound, but I noticed a few discrepancies in some component values.

The 5.1k resistors on the EL34 tubes should be 5.6k.
The tone stack for SL is 33k/500pf
The tone stack for SB is 56k/250pf.
Their layout is a mixture of both.

It is assembled with what I got in the small parts and I have nothing left . As far as I know it is assembled to the layout and schematic. I am not doubting you but this is what I went by from Mojotone. They might have modified it.

 

[rtcook]

Yep. A little different from an original schematic. Not even sure how much of a difference it would make. Just wanted to point it out.