Please help - Peavey classic 30 transformer buzz/vibrate

[jase128]

Hi, ive had quite a bit of trouble with this amp, mainly down to excessive noise. its been in pieces many times - all caps replaced, some resistors, diodes. many dry joints and a tube socket replacement and the tubes themselves.

now the issue im left with is buzzing from the transformer.... ive taken the transformer out and yes there were loose lamination which have been reflown with varnish and tightened etc and the buzz on the workbench was eliminated  but i have just reinstalled the transformer back in to the chassis and its buzzing quite loudly  I disconnected all outputs and  also (from the primary side) switch and lamp,  so all that is connected is mains - fuse to transformer and its still buzzing!!!

The transformer is bolted tight? what else can i do? extra washers, rubber mounts.....help   

all help appreciated


Jason

[sluckey]

replace it

[jase128]

the amp or the tranny   

im suprised you say that as it works fine, its been insulation resistance tested  and the the outputs are spot on?

I will price it up!

thanks

Jason

[kagliostro]

The last chance

Try to submerge your tranny in shellac or, may be better, paint for transformers

Shellac was used for fixing inductor, motor, generator and transformer windings. It was applied directly to single-layer windings in an alcohol solution. For multi-layer windings, the whole coil was submerged in shellac solution, then drained and placed in a warm place to allow the alcohol to evaporate. The shellac locked the wire turns in place, provided extra insulation, prevented movement and vibration and reduced buzz and hum. In motors and generators it also helps transfer force generated by magnetic attraction and repulsion from the windings to the rotor or armature. In more recent times, shellac has been replaced in these applications by synthetic resins such as polyester resin. Some applications use shellac mixed with other natural or synthetic resins, such as pine resin or phenol-formaldehyde resin, of which Bakelite is the best known, for electrical use. Mixed with other resins, barium sulfate, calcium carbonate, zinc sulfide, aluminium oxide and/or cuprous carbonate (malachite), shellac forms a component of heat-cured capping cement used to fasten the caps or bases to the bulbs of electric lamps.

https://en.wikipedia.org/wiki/Shellac

if you have no good feedback ..... I think you must replace it, as previously told

Franco

[jase128]

thanks for the reply,
 i will look at submerging it or ask a local motor rewinder to do it for me?
 worth a try as they are not cheap to replace in these parts!

I just find it strange that its fine on the bench no hum/buzz whatsoever but as soon as its mounted on the chassis its noisey even though no secondary connected.

thanks again gents


Jason

[shooter]

but as soon as its mounted on the chassis

maybe the chassis is harmonic 

what happens when you wire it to the chassis AC, don't bolt it down to the chassis but insert cardboard under the tranny, does it buzzz

[jase128]

shooter, thats what Im gonna try next but i just got in from a long night shift and i need some zzzzzs first

thanks  again all for replying


Jason

[Leevi]

Rubber between the chassis and transformer contacts damps the noise but does not prevent the vibration.
/Leevi

[jase128]

ok quick update...

I have unbolted tx from chassis,  powered up and the noise dissapears, i have opened the holes slightly as it was a little squeeze but im not happy with the vibrating so I have just ordered some insulating varnish and im going to dip the transformer coil in to this when it arrives.
 when reinstalling i will put some rubber under each mount to try and dampen whats left of the vibration!

fingers crossed, i will get back upon completion!

thanks all


Jason

[jase128]

Ok so , the insulating varnish arrived. I made a little tight fitting tub so as not to use too much varnish. I left it to soak overnight.
It has taken forever to dry and still feels tacky.
I put a supply on it and it has reduced the hum significantly although there is still a little vibration.
I have reinstalled  the tx into the chassis and included four small rubber washers to stop the thin tin chassis exaggerating the vibrations! ..hopefully.

the big switch on is tomorrow! 

fingers crossed

Jason

[jase128]

The majority of the hum has gone now BUT there is noise when using reverb .....

if the reverb is at 0 there is no humming the more you turn up the reverb the more prominent the noise???

any ideas anyone?

Jason

[shooter]

isolate drive side or recovery side, or wiring or grounding or roll in a bunch of tubes or play without verb 

[Leevi]

Verify first if the noise is coming from the tank or from the recovery stage.
Try to short the recovery stage input (or tank output) to ground in order to check that.

/Leevi

[jase128]

do i actually put a wire link from the centre of the tank output connector to a ground?

I have tried a few different tubes but it makes no difference!


Jason

[Leevi]

do i actually put a wire link from the centre of the tank output connector to a ground?

Yes, either shortcut the cable from tank output or the RCA socket on the amp.
/Leevi

[jase128]

I removed the tank - no difference , noisier the more i turn up the reverb pot
shorted out the tank output - no difference , as above!

if i touch the lead that connects to the output on the  tank i get a very loud amplified hum

the reverb does work but its just very hummy?


    oh how i prefer point to point wiring!!


thanks gents


Jason

[jase128]

maybe a step forward?

Ive just tried a different speaker in, it was an 8ohm, i know it should be 16ohm but just for tests sake i tried it in  and the hum never appeared????

its the original 16ohm blue marvel speaker installed and it works ok and tests ok    but does this look like the obvious remaining issue??

do some speaker pickup more hum than others ?? or is the speaker damaged internally?


looks promising either way


Jason

[Leevi]

I don't think the speaker change has  solved the issue. Rather something else has happend when changing the speaker like cables, position of reverb tank, have you maybe turned it 180 degrees?


Leevi

[jase128]

reverb tank it outide of chassis cables have been moved and speaker was at 90degrees so yes there are changes!!!

i will investigate further....cables 1st

thanks

Jason

[Leevi]

It seems that the hum goes via transformers most likely power transformer.


Try to find an optimal position for the tank. Normally the output socket must be as far as possible from the power transformer.


If there is no good place inside the cabinet place the tank outside.


/Leevi

[sluckey]

Another thing to consider with the speaker change/ hum reduction... maybe there really was no hum reduction. Maybe the speaker just doesn't reproduce low frequencies as well as the other speaker.

[jase128]

Another thing to consider with the speaker change/ hum reduction... maybe there really was no hum reduction. Maybe the speaker just doesn't reproduce low frequencies as well as the other speaker.

noted: i would never have thought that, but yes it was a small 8"  cheap speaker so presumably ,exactly what you said sluckey

its never ending .......

Jason

[Soulfetish]

Just to be clear; so, with the reverb tank disconnected and the reverb return shorted, you still get noise?
have you tried another tank?

[jase128]

yes it still has noise with the output shorted.

the amp has been re put together again (a major pain with the horrible 3pcb design)  taking note to reroute the cables as much as possible away from mains tx also remounted the tank (testing the amp before final fixing) and the amp has settled to an acceptable level of noise, not great but much better than it was. the mains tx needs replacing as it does vibrate but the reverb squeel has now stopped (for now). I didnt do anything that I can say resolved this issue but it is ok.

thanks for the help everyone, im just going to call this done

I need to build a small amp from scratch.

Jason