18Watt.com

This is a new problem for me, but maybe one of you had experienced it before. So I completed a 36/TMB. When I let a note ring it fades w/what seems to be blocking distortion or parasitic oscil. after a few seconds and then stops all together as if I were using a gate. If I turn the volume pot on the TMB side full throttle it pops then squeels at 80% and shuts down at 100%(Not on normal channel though)I'm pretty sure thats because of the difference in gain between channels. Keep in mind both channels are having the other problem though. I am not a complete Newbie(around 2.5 years in) but most of what I've always done was mods and rebuilds. This is the first time I've built a kit. Also my voltages are a little lower than whats posted here for a 36w. Especially on V1, so I suspect this could be the issue as well. Copper cap SS rect. by the way. You can probably guess now which Kit I purchased(oops). I'm sure I will figure it out eventually, but it takes a lot longer than if someone has a suggestion from their experience. Thanks in advance.

P.S. I would love to put up pics but my kids broke my digital. I can tell you that my lead dress is not horrible so I doubt its that. Plus I've alread moved wires around everyway possible to find the lowest noise floor.

By the way.When I said I'm not a complete newbie I didn't mean to imply that I don't want responses from newbies, cause I am one as well. I just didn't want anyone to waste their time on asking me if I checked for cold solder joints/bad tubes etc....I've done all the obvious, believe me I can be a bonehead sometimes, so I make sure to check things over many times. I even measured readings from all my POTS to make sure they are all in spec.
Keith

I had a ceriatone 36w and using shielded wire on the volume pots, input jacks and pin2 and 7 of the first preamp tube removed all the squealing I was getting.

Ground 1 end of shield.

Hope this helps...

Chubsman wrote:I had a ceriatone 36w and using shielded wire on the pots, input jacks and pin2 and 7 of the first preamp tube removed all the squealing I was getting.

Ground 1 end of shield.

Hope this helps...

Yes that does help, because I was thinking the same thing for the squeeling and you re-affirmed that. There is still the other issue however.
How does your Ceriatone sound?

Sounds killer. Dead quiet. AC/DC when pushed hard with an LP. I sold it and bought a KIller 1990 LP Classic. I am finishing up a Marshall Silver Jubilee for a trader for a Ken Lawrence explorer... and Will rebuild my 1987X clone as soon as I am done that......

kedsinger wrote:

Chubsman wrote:I had a ceriatone 36w and using shielded wire on the pots, input jacks and pin2 and 7 of the first preamp tube removed all the squealing I was getting.

Ground 1 end of shield.

Hope this helps...

Yes that does help, because I was thinking the same thing for the squeeling and you re-affirmed that. There is still the other issue however.
How does your Ceriatone sound?

Your two issues may be the same issue. The sound cutting out may just be the amp breaking into super-sonic oscillation, i.e., squealing at a high enough frequency that you can't hear it.

I'll replace w/ shielded tonight and let everyone know how I make out. I'm gonna do inputs and volume pots.

That sounds like the best thing to try...

Sometimes swapping the primary leads of the OT cures the problem. This trick did wonders for me in the past.

HTH,
Gabi.

Holy crap!!! I just fell off my chair. Was that a post from Gabi??? Where you been, man?

Stop Phil - heheheheh

I am soldering wire not like you geeks waisting time on this board - hehehehehe.

You know I sometimes become melancholic...

Anyway - seriously - the swapping of the two primary leads did wonders to me.

G

Guys, anybody can explain the "the swapping of the two primary leads " thing.
Long time ago i tried this thing and solved my problem (50W plexi), but anybody understand why happening this...

Simple case of positive versus negative feedback. Swapping leads changes phase 180 degrees. Often not sure how the output is feeding back (unless you install negative feedback), but I believe that is what is happening when this fix works and you don't have negative feedback intentionally installed.

Michael wrote:Simple case of positive versus negative feedback. Swapping leads changes phase 180 degrees. Often not sure how the output is feeding back (unless you install negative feedback), but I believe that is what is happening when this fix works and you don't have negative feedback intentionally installed.

Thank you Michael

I just about soiled myself when I saw the Gabster...too... only place we see him now is in Guitar World... or Guitar Player... Good job Gab!

Swaping primary wires...well...although two primary windings are of same number of turns(likely ) their capacitance(or wire length) is not because of nature of stack winding.
((Measuring CT and each side (DMM ohm position) will get you the picture.))
Which leads us to swaping wires,ballancing/unbalancing PI experiments,I suppose...

When you try everything with shield cables,chopsticks,ground,tubes....and you cant seem to find fix for months it's time to consider OT causing the troubles.
Sometimes poor vacum varnish is causing oscilation,microphonic...when dimed or earlier.
Poting transformer in hot wax (double boiling) is solution to consider.
Of course wait until air bubles stop.

Also try running the amp out of the chassis and upside down. I found on my 36W build that the amp would go into oscillations when anything got near the master pot. Sitting there it would be quiet, move your hand close and it would start squealing. Once my hand actually touched the metal chassis, it stopped. I set another chassis right on top with the two chassis touching and the amp would squeal until the two chassis touched. I ended up placing an aluminum in the headbox for the chassis to lay on and hasn't squealed since.