Marshall Haze 40C Tube 4 turns sign wave into hard very loud sq. wave to early,ideas?

[Andrew58]

Ok so i received a Marshall haze40 and yes i do have the schematics. I believe it to be something to do with the biasing signal circuits for valve 4 but I'm not certain. It came in with a blown fuse which i believe is a high tension fuse because it bright the plate voltage back. But i also noticed that the el34 in the v4 socket had gone gassy because of all the white powder above the getter and on the glass. I at first thought well maybe its some weird tube thats breaking over extremely early because it got damaged or just a weird batch. But no matter what tube i put into that socket it causes that hard loud buzz that for the most part stays in tune with the sign wave generator signal i give it. If i remove valve 4 it sounds fairly good and plays great aside from alittle higher then average noise floor. But if i put both power tubes in or just tube 4 in after about 3 on the gain control it starts that extremely to hard harmonically rich clipping that isn't anything that it should be even for hot breaking over 6ca7 tube signal. SO i ask all you amp-smiths out there what your ingenious suggestions or ideas may be. Any help would be greatly appreciated!!!

[52 Bill]

If there is a white powder inside the glass, that means that he tube has lost its vacuum.

If the problem happens anytime that you install a tube into that specific socket, I'd check the socket for carbon arcs and all components related to that socket such as the grid and screen resistors, etc.

[Andrew58]

Oh sorry i wasnt clear i suppose. I know when it turns white its broken its vacuum thats what i ment by gone gassy. And no sorry for the bad wording it doesnt cause each tube to go gassy and lose its vacuum at all the tube i orignally pulled out was like that. Possibly the amp got banged around or something unrealted. But each tube just breaks over to quick and distorts the sign wave into the hard clipped square wave in that socket. so the sockets or all good i do believe. Thanks for the quick response!

[Corben]

had one with a simliar problem also wish the repair shop could have figured it out. Maybe some one on here is smart enough to know. would help me as well.

[oc disorder]

Check D10 and D8

Possible you have shorted turns in o/p transformer.
Check resistance of CT (W8) to outside terminals (W6,W7).

The tubes fitted in the factory often don't survive the shipping too well !

[Andrew58]

Yeah i thought maybe the uotput transister had some shorted windings but i beleive the distortion and overdriving happens before the tranformer when i was scoping it for a bit. Ill def check out those diodes thanks for the helpfull input, much apreicated

[Andrew58]

OK well it was the output transformer i believe. The center tap to one side of the windings was 150 ohms and then the center tap to the other side of the winding was 75 ohms. I think there are supposed to be equal all though it is kinda odd that its perfectly half of the other esp if some wires shorted together. Unless theres something I'm not thinking about. Its a push pull amp. If you have the schematic from w8-w6 is 150ohm and from w8-w7 is 75 ohm and yes w8 is the center tap on the primary. And i believe any distortion I'm seeing before the output tranny on the scope is symmetrical and typical of overdriven tube amps unlike the signal after the output transformer. I guess ill order another op transformer. Does anyone know of any good sources besides calling korg that would work well in this amp for a good price?

[Prairie Dawg]

Check D10 and D8

Possible you have shorted turns in o/p transformer.
Check resistance of CT (W8) to outside terminals (W6,W7).

The tubes fitted in the factory often don't survive the shipping too well !

These amps are starting to sound like real Edsels. Had a chance to buy one for $400 and glad I kept my money,