Bad case of GHOSTING...tried everything...but to no avail.

[bmwfreq]

To begin with. Thanks to everyone that replies. Everyone's input is most appreciated.

So, out of the blue and with no warning signs. My amp, a 1984 horizontal input JCM 800 2203 exhibits a bad case of ghosting. It's not as bad on the lower strings as it is on the G string on up. I also cannot turn the MV past 8 without the amp going into a low frequency feedback (like a kind of low rumble.) With the PA on 1, and the MV on 2, the amp should be nice and clean. It is not. I have a mild distortion with these low settings when I shouldn't. I am also getting this 'reverb' type of effect as part of the ghosting.

I have done the following to remedy the issue, but to absolutely no avail:
New 50uF/50uF filter caps x 5
New 10uF 100v bias caps x2
New resistors everywhere - entire PCB
New PRE-AMP tubes
New power tubes
all new coupling caps -5x.022uF/2x.1uF/1x.68uF
all new pots
New input jacks
Tried different speaker cords, instrument cords, guitars, speaker cabs, power cables, wall outlets
Addressed lead dress till I'm blue in the face
Changed the balancing resistors on the screen filters from 56K to 220K and even 470K (even tried NO resistors)
Checked for bad solder joints and reflowed solder almost everywhere
Change the OT (40-18026)
Tried a different choke
Even tried some alternate grounding schemes

None of these changes made any difference in my ghosting/reverb/feedback issue. Needless to say...I'm at a total loss at this point.

Any suggestions with the exception of the things I've already tried would be greatly appreciated.

 

[marshallmellowed]

To begin with. Thanks to everyone that replies. Everyone's input is most appreciated.

So, out of the blue and with no warning signs. My amp, a 1984 horizontal input JCM 800 2203 exhibits a bad case of ghosting. It's not as bad on the lower strings as it is on the G string on up. I also cannot turn the MV past 8 without the amp going into a low frequency feedback (like a kind of low rumble.) With the PA on 1, and the MV on 2, the amp should be nice and clean. It is not. I have a mild distortion with these low settings when I shouldn't.

I have done the following to remedy the issue, but to absolutely no avail:
New 50uF/50uF filter caps x 5
New 10uF 100v bias caps x2
New resistors everywhere - entire PCB
New PRE-AMP tubes
New power tubes
all new coupling caps -5x.022uF/2x.1uF/1x.68uF
all new pots
Tried different speaker cords, instrument cords, guitars, speaker cabs, power cables, wall outlets
Addressed lead dress till I'm blue in the face
Changed the balancing resistors on the screen filters from 56K to 220K and even 470K (even tried NO resistors)
Checked for bad solder joints and reflowed solder almost everywhere
Change the OT (40-18026)
Tried a different choke
Even tried some alternate grounding schemes

None of these changes made any difference in my ghosting or feedback issue. Needless to say...I'm at a total loss at this point.

Any suggestions with the exception of the things I've already tried would be greatly appreciated.

Have you checked the low input contacts? The input signal to the high input is routed through the contacts of the low input when nothing is plugged into the low input.

 

[bmwfreq]

Yeah. I forgot to add that to my list. I actually took the low input socket out of the circuit altogether by soldering the wires together in place of the low input jack. Before that I actually replaced both input sockets with new ones.

Good idea though...

 

[guitarbilly74]

Check the PI plate resistors, if they drifted it would cause ghosting.

 

[bmwfreq]

Check the PI plate resistors, if they drifted it would cause ghosting.

I did. They're both right where they should be...82K/100K.

 

[ElvisNixon]

To begin with. Thanks to everyone that replies. Everyone's input is most appreciated.

So, out of the blue and with no warning signs. My amp, a 1984 horizontal input JCM 800 2203 exhibits a bad case of ghosting. It's not as bad on the lower strings as it is on the G string on up. I also cannot turn the MV past 8 without the amp going into a low frequency feedback (like a kind of low rumble.) With the PA on 1, and the MV on 2, the amp should be nice and clean. It is not. I have a mild distortion with these low settings when I shouldn't. I am also getting this 'reverb' type of effect as part of the ghosting.

I have done the following to remedy the issue, but to absolutely no avail:
New 50uF/50uF filter caps x 5
New 10uF 100v bias caps x2
New resistors everywhere - entire PCB
New PRE-AMP tubes
New power tubes
all new coupling caps -5x.022uF/2x.1uF/1x.68uF
all new pots
New input jacks
Tried different speaker cords, instrument cords, guitars, speaker cabs, power cables, wall outlets
Addressed lead dress till I'm blue in the face
Changed the balancing resistors on the screen filters from 56K to 220K and even 470K (even tried NO resistors)
Checked for bad solder joints and reflowed solder almost everywhere
Change the OT (40-18026)
Tried a different choke
Even tried some alternate grounding schemes

None of these changes made any difference in my ghosting/reverb/feedback issue. Needless to say...I'm at a total loss at this point.

Any suggestions with the exception of the things I've already tried would be greatly appreciated.

Are you 100% positive the speakers in whatever cab you are using are wired in phase?

You can check with a 9V battery on each speaker. The speaker will briefly move in or push out (excursion). Out of phase speakers can cause some weird sounds.

 

[bmwfreq]

Are you 100% positive the speakers in whatever cab you are using are wired in phase?

You can check with a 9V battery on each speaker. The speaker will briefly move in or push out (excursion). Out of phase speakers can cause some weird sounds.

Good idea, but, I'm using a single 12" V-30 extension cab during the testing phase...

 

[anitoli]

.

 

[Tatzmann]

Stby-Switch.

 

[bmwfreq]

Stby-Switch.

Hmmm...why do you question the standby switch?

 

[dtier]

Did you check the power tube grid stopper resistors that are fly mounted off the power tube sockets as well? This problem could be an oscillation in the power amp. Have you had a scope on this?

 

[FleshOnGear]

I’m not an expert, but it seems like the only things you haven’t changed are sockets. Also, have you checked ground connections? Have you done a voltage chart? Just thinking out loud here. In my mind the rumble indicates some kind of problem with the PI, or some kind of phase shift somewhere. The bad distortion at low settings might be from oscillation. Do you have a scope?

 

[knulp]

I’m not an expert, but it seems like the only things you haven’t changed are sockets. Also, have you checked ground connections? Have you done a voltage chart? Just thinking out loud here. In my mind the rumble indicates some kind of problem with the PI, or some kind of phase shift somewhere. The bad distortion at low settings might be from oscillation. Do you have a scope?

In such cases a scope is necessary,having a tech look at the amp too even if you’re tech savy

That could have saved lot of money but above all plenty of time,plenty of playtime and some headaches..

 

[knulp]

it could really be useful to check everything related to the pt..heaters?
But really everything voltage related should be verified
and a scope

 

[bmwfreq]

Did you check the power tube grid stopper resistors that are fly mounted off the power tube sockets as well? This problem could be an oscillation in the power amp. Have you had a scope on this?

I changed all four of em with brand new value matched 1 watt 5K6 carbon film resistors.

 

[bmwfreq]

I’m not an expert, but it seems like the only things you haven’t changed are sockets. Also, have you checked ground connections? Have you done a voltage chart? Just thinking out loud here. In my mind the rumble indicates some kind of problem with the PI, or some kind of phase shift somewhere. The bad distortion at low settings might be from oscillation. Do you have a scope?

I didn't change the power tube sockets, but I did tighten each pin of each socket for a snug fit on the power tubes pins. I checked as well as tried a number of different grounding schemes. All voltages were as expected. I suspect an oscillation somewhere as well.

Unfortunately, I do not own a scope or signal generator.

 

[anitoli]

Scopes are cheap for what you need it for:

https://www.ebay.com/sch/i.html?_fr....m570.l1311&_nkw=oscilloscope+analog&_sacat=0

 

[bmwfreq]

it could really be useful to check everything related to the pt..heaters?
But really everything voltage related should be verified
and a scope

What are your concerns with regard to the PT heaters?

 

[bmwfreq]

Scopes are cheap for what you need it for:

https://www.ebay.com/sch/i.html?_fr....m570.l1311&_nkw=oscilloscope+analog&_sacat=0

Wow! That is a great price for a scope. Unfortunately, after paying the state and feds just days ago. I'll be lucky to get pork 'n beans for dinner for the next six months in the least, if I had the money, I would snatch that up in a second.

 

[dtier]

Do you get the rumble over 8 on the MV without an instrument plugged in? You could remove V1 to rule out instability in the first stage while maxing out MV.