JTM45 rectifier question

[SPeter]

Hot switching, where the rectifier cathode is already hot when it is connected to the reservoir, is not a good thing. In the JTM45 schematic the rectifier is always hot switched because the standby is between the rectifier and the reservoir. The rectifier becomes hot when the main power is switched on, and then it sees a big current surge when the standby is switched to play. The reservoir therefore has to be kept small. If the standby is placed after the reservoir, the reservoir charges slowly as the rectifier warms, and it can be larger.

That's what I meant I keep the standby in the on position all the time now.

That cap is 47nF (not pF), and it looks like it’s across one side of the OT primary.

Do you have any idea what is the purpose?

[SPeter]

Hot switching, where the rectifier cathode is already hot when it is connected to the reservoir, is not a good thing. In the JTM45 schematic the rectifier is always hot switched because the standby is between the rectifier and the reservoir. The rectifier becomes hot when the main power is switched on, and then it sees a big current surge when the standby is switched to play. The reservoir therefore has to be kept small. If the standby is placed after the reservoir, the reservoir charges slowly as the rectifier warms, and it can be larger.

That's what I meant I keep the standby in the on position all the time now.

That cap is 47nF (not pF), and it looks like it’s across one side of the OT primary.

Do you have any idea what is the purpose?

BTW the amp did not feel right with the one rail grounding. I can't explain, probably there was something with my soldering job, I don't know. Anyways I cut off the tail end of it. I kept a piece parallel to the circuit board and created a second star down at the 32/32 filter cap:

20190416_202414.jpg

Last night the cabinet arrived from Sourmash. It is an absolute beauty, I can recommend them based on this work:

20190415_163749.jpg

20190415_163824.jpg

I'm loosing faith that the ghost note problem can be solved. I just want to put this thing in the cabinet and rock out

The new high power choke will be here tomorrow and I ordered a matched set of JJ KT66 from Tube Depot. I'll test those things but have no high hopes that anything would help at this point maybe besides replacing power AND output transformers to some different ones ($$$) And I would never know for sure if that even helped.

[xtian]

We're on page 8 of this thread, and I'm too lazy to read it all. Have you tried multiple guitars, to evaluate the ghost note issue?

[SPeter]

We're on page 8 of this thread, and I'm too lazy to read it all. Have you tried multiple guitars, to evaluate the ghost note issue?

Yes, three of them, all with humbuckers. Same problem with all. I think the hotter the pickup the worse it got though.

Here is a not so short list of what I tried so far (thanks for all the tips from the guys trying to help in this thread)...
I tried with a 16ohm celestion 50w egnater edition speaker and replaced it with an eminence 75W maverick. I even tried both connected parallel in an 8 ohm setup at 16 ohm and 8 ohm. No luck.
upped the main filter from 32 to 48 uF (changed it back)
upped the PI filter from 16 to 32uf (changed it back)
tried the recommended 'Larry' star grounding
tried the Metro instruction regular buss grounding
tried true one star grounding
Upped the resistors on the V4 and V5 over pin 4 and 6 from 470 ohm to 1k
Added 1k flying resistor (removed when restoring the Metro layout)
Added 5.6k screen resistors to V4 and V5 pin 5 I think
uninstalled the Larmar PPIMV
then reinstalled the Larmar PPIMV
Switched around a total of 7 12AX7 tubes (I have six, one was retplaced due to bad microphonics)
Removed the circuit board resoldered all the leads reflowed all the turrets, inspected them under magnifying glass for cold solder
I ordered a new 3H, 250 mA choke (there is a 20H 70mA in the amp right now), it will arrive tomorrow. I have zero confidence that it will make any difference.
I have a new set of matched and broken in JJ KT66 on the way to replace the Gold Lion's, again I don't believe these will make any difference

I think that's about it so far. None of these things had improved the ghost note issue.

The kit has
Classictone 40-18033 PT 465V B+
Classictone 40-18039 OT
All other components were sourced through Valvestorm

[xtian]

With all the work you've done, it seems unlikely the cause is inside the amp, doesn't it?

Let me ask whether this ghost note issue is electronic or mechanically induced. What I want to know is, can you reproduce the ghost notes at ZERO acoustic volume. That is, play into a dummy load, and listen on a line out with headphones or something. I would try to reproduce the issue using a simple sine wave generator, rather than a guitar. That way you have a precise a reliable, and hands free, way to trigger the ghost notes. If you cannot recreate the ghost notes with a signal generator, that would be an interesting data point!

If you can reliably create the ghost notes when NOT playing into a live acoustic speaker, we can conclude the problem is electronic, not mechanical (the mechanical possibilities being speaker, cabinet or chassis or component rattle, rattles from every other sympathetically vibrating object within ten feet, etc.).

[Roe]

Swapping output tubes and pi driver is worth an attempt. High voltage may reduce ghosting since you then tend to bias for less current draw

[SPeter]

With all the work you've done, it seems unlikely the cause is inside the amp, doesn't it?

Let me ask whether this ghost note issue is electronic or mechanically induced. What I want to know is, can you reproduce the ghost notes at ZERO acoustic volume. That is, play into a dummy load, and listen on a line out with headphones or something. I would try to reproduce the issue using a simple sine wave generator, rather than a guitar. That way you have a precise a reliable, and hands free, way to trigger the ghost notes. If you cannot recreate the ghost notes with a signal generator, that would be an interesting data point!

If you can reliably create the ghost notes when NOT playing into a live acoustic speaker, we can conclude the problem is electronic, not mechanical (the mechanical possibilities being speaker, cabinet or chassis or component rattle, rattles from every other sympathetically vibrating object within ten feet, etc.).

I was able to reproduce it with a speaker laying on the floor not assembled in a cabinet so that excludes the cabinet.
The 'vibrating object' caused me a headache a few times as I'm in a basement and some stuff in the ceiling can resonate quite badly, but when it happens it always tied to one particular frequency. These ghost notes are all over the fretboard on D, G and B strings. Most pronounced around the 12th fret. I took the amp upstairs in the walk in closet which has carpet and a bunch of clothes and played it out. I could hear the same thing, so it is definitely coming from the amp somehow but logic tells me that nothing I have done seemed to affect it so it must be in either of the transformers or the way they interact.

How can I set up a sine wave generator? I have a laptop and I can connect its headphone-out to one of the inputs of the amp, would that work?

Great idea about the a dummy load with a line out, any recommendations? I really want the Fryette PS-2 but it's pricey...

[SPeter]

Swapping output tubes and pi driver is worth an attempt. High voltage may reduce ghosting since you then tend to bias for less current draw

Sorry, what is the 'PI driver'? Everything has at least three names and I can barely remember one

[Roe]

Sorry phase inverter or driver or v3

[Reeltarded]

Search (line out) here (use google to search site the search here sucks) and make a simple resistive load. Make it 4x the size of any amp you will ever use it with. 4x 100w resistors or whatever. All of those multi hundred dollar loads are a load of whatever. You can make a perfectly EXCELLENT load for under $50 all in and it sounds like what is plugged into it.

[xtian]

+1. Dummy load is critical for testing amps. Adding a line out requires one or two 1w resistors and a pot, so super cheap.

Yes, you can use your laptop or phone as a signal generator.

[martin manning]

So where is the shield in that piece of cable going to the MV connected?

[SPeter]

So where is the shield in that piece of cable going to the MV connected?

Cut it off, it did nothing and looked bad. The second lead is not even shielded I found some shielded cable I will redo both tonight if I have cable left I will do shielded between the pots and the V4-V5 pins... but I already know it is not the problem

[SPeter]

Line out for Bassman, should work for JTM45 right? Or any other resistor values to consider?

Bassman_Line_Out.png

[martin manning]

A JTM45 is a 5F6-A Bassman ;^)

Don’t forget you must have a speaker or a dummy load connected at all times.