Phatt - i have played 4 guitars ( 2 stock new ) through it . I doubt its a pickup . Also i have a peavey vyper combo and small fender combo - no microphonic feedback from guitars in that amp. And as far as potting , that specific pickup - Jackson j-50b had problems years ago 1994 to be exact . Went bad on stage . I potted it the next day . It had been in and out of multiple guitars , played through loud amps etc , bounced around in a box and was fine . My stupid move was exchanging back plates just because i didnt want to get longer screws to mount it . I think when i soldiered the ground from the plate , or took the screws out it loosened a coil again. But after potting that feedback went away . I can tell pickup microphonics from other feed back . Very screechy and you can stop it temporarily by tapping the pickup or pushing down on it . And it wouldnt explain why the amp feeds back with the cord unplugged from the guitar .  Oh and when i pot , i do it right . I put a can inside a pan of water on jar lids as not to get the pickup too hot and warp it , bring water to boil ,i hold the pup in the wax with pliers moving it around until i see no bubbles come out , take it out put it in a small glass with wax , let the wax cool a little bit so it coagulates in the pup .Let it dry, Scrape wax off top with emery cloth. Wire back up.   

Anyway , didnt call the amp guy yet . Ill call tomorrow . 

Im convinced that the high microphonic squeal did something inside . The amp was fine - amazingly fine for a solid state not feeding back when gain is dimed . Then after the pup squeal - problems.

So ill just leave the problem at that and have the tech fix it .

Any ideas why the amp is a bit muddy sounding ? Related to main problem ? Cheap marshall MG cab ? It sounded good in the pawn shop . The only guitars they had to test were crap . I stupidly brought my dark sounding guitar back to test it. Lots of gain and good dynamics , figured the warmness was my guitar .

So im curious if say the tone of the amp is normal , can the amp be modified for a reasonable price ? I know tube amp modding can be spendy because of transformers , tube sockets, point to point wiring etc but with these things parts seem cheap . The output diodes are like $2 !

And the reason im going through all of this is ive been slumming with gear for a while . It seems pointless to fix this , sell it and get something else with maybe another problem or that i wont be happy with in the long run . Ive done that too much in my life. If he can fix and tweak it to my liking ill stick with it. If i had the dough id have a Granger m 100 or a Engl invader 150 but until i win the lotto , ill slum it with this gear .

         

Cleaned it to no avail . Still squeals .

Ill call the guitar amp guy today but if you guys have more ideas and suggestions , post em. And thanks for the help so far. I appreciate it. 

Thanx for the help by the way . Its kind of the same . When i play the squeal stops ( or is covered by the sound ) but when i stop and even mute the strings it squeals . Then if i unplug from the guitar side ( still plugged into the amp ) it still squeals . If i unplug the cord completely it stops or if i short the jack like you suggested , it stops.

Ill try cleaning the input with electrical cleaner on a q tip.

The other problem, which may be related , is the sound has no edge to it at all . Even when i crank the high. It could be the marshall mg cab i bought with it. I know they arent the greatest . Its a good saturated sound but its a little too rounded/warm . Even if you have the voicing switch disengaged to get that old RG sound , its still not that bright . The sound overall is good and with the voicing switch on it is very tube like. But its missing some clarity . I have heard clips on youtube where its very clear and almost shrill on the non voiced setting.  Like i said i put a different pup in my main guitar and played two other brighter guitars through it . Same deal. Any ideas on what that could be ?

If its normal can i have it tweaked for more clarity ?       

Thats it ! I shorted it and it stopped . So how do i fix that ? Or should i have someone do it ?

Quote from: galaxiex on August 09, 2016, 11:02:16 AM
He means a switch that is part of the input jack. It's internal so you won't see it.

ok, i get it. Ill try it

phatt- It has a ground lift switch near the speaker outputs . Ill try that . But i dont see one near the input .

New to this forum . Pre History - have played guitar for almost 30 years and getting back into it more seriously. Im buying new/used gear. I have owned ( and sold ) many nice amps over the years Soldano , Peavey 5150 , Marshall etc .  Im Mostly a blues, hard rock, classic metal guy.

So my question - I purchased a used Randall rh ( not rg ) 100 g2 head last week . I gave it a workout in the pawn shop, they gave me a grace period of a day to try it . It put it through its paces and it did fine . I used a guitar with high output passives and surprisingly you could crank the high gain and treble all the way dimed and get 0 feedback . The reason i dimed the treble is because my guitar is dark sounding , and the amp seems a tad bit on the warmer side to me. For a solid state this is usually a good thing but its a bit warmer than id like . So i figured id slap an old brighter lower output pup in my guitar . Turns out the pup was microphonic . I messed with it for a while but the guitar screamed . If i switched to the neck pup it went away so i know it was the bridge pup. So i wax potted the pup, plugged it in and no more pup squeal , But now when i dime the gain and treble the amp squealed . Even if i unplugged the guitar .

I tried other guitars , cords , speaker cables , etc to no avail . Its still playable at lower volumes but when i first got it i could crank it with no problem .

So im wondering if the high frequency squeal at high volumes damaged or changed something in the amp ? I know ultra high frequency at high volumes can actually heat things up .  I took the chassis out and everthing looks clean and no burn spots.

Also the cab is not great - its a marshall mg 4x12 but its in good shape .

So i am going to call a guy that repairs SS amps in the morning .

My other questions are , if the problem can be/is fixed , can the amp be modified more to my liking ? I know the reverb is terrible ( i think the amp took a tumble once from the outside damage ) can they replace a spring with a digital reverb circuit ?  Also if the amp is voiced as warm as it is , can it be modified to have more control over the high end ?

I dont mind spending some dough on fixing it because i got it for very cheap .

So any ideas and suggestions would be greatly appreciated .