Marshall 8080 "80v" problems im trying to solve

[jigibao]

Hallo. Im still newby to this forum but i do have hughe expiriance with vacuum tube amps and electronics in general. Now lets get to point. Few days ago i have bought for small money broken Marshall valvestate 80v guitaar amp. From first moment i new that main problems were end transistors and i solve this with new TIP142 and TIP147.. NPN transistor goes on positive and PNP on negative voltage. First before i started i check that bias components were not damadged . I brouht it up slowly with variak to working power and eind amp is running good BUT twoo problems, NO INPUT and buzz coming from speaker "quiet but there".. i looked up the board and found that heating from tube 12volt connected over 4-5pins is strait conected from transformer without rectification and filtering??? I mean who did this mistake by Marshall?? this is BIG NO NO.. If someone wants to know "50-60Hz buz in tubes damadge the sound".. and for dead input tomorrow i will take some time and check what is else nocked down in amp.. Do i must say that im litle bit tempted to pull electronics out and build a tube amp as chassis is perfect for it !!! this much for now !!

[jigibao]

compleet print

[jigibao]

Tube is chineze and is NOT WERY GOOD FOR AUDIO.. i prefeer more EI Nis from Yougoslavia oor old Philips-Adzam tubes !!! LIKE !

[xtian]

i looked up the board and found that heating from tube 12volt connected over 4-5pins is strait conected from transformer without rectification and filtering???

Not sure I follow you. It's very common to power tube heaters directly with 6.3vAC coil from power transformer, no filtering, obviously, because it's AC.

[Stevem]

I have found on my hybrid amps that if the board traces that bring the AC filament to the tube run passed preamp sections ,that AC heater noise can be greatly reduced on many amps by running twisted wires to the tube and unpowering the traces on the board.
In the same vein and dependant on the board layout if you remove the rectifier bridge section and run the filtered D.C. Output to the board that this too helps with 60 hz noise!

You can convert that tube to D.C. Power with this simple circuit.

A side note , the new B series of Zino / China made preamp tubes on average sound better then any Russian / EH made tube, they just don't last as long in high current needs like PI sections, this being said , stay away from there 12AT7s as I have yet to test a new one that does better then 75% on my Hickok tester!

[jigibao]

i looked up the board and found that heating from tube 12volt connected over 4-5pins is strait conected from transformer without rectification and filtering???

Not sure I follow you. It's very common to power tube heaters directly with 6.3vAC coil from power transformer, no filtering, obviously, because it's AC.

Hallo, when tubes are in preamp schematics and specialy in HYGH GAIN ones than is dezirable to dc filter the 6,3v for heating to avoid hummm.. Oor to inject thru resistor litle bit HV so the oscilation in AC wil match each other.. This is my expiriance..

[jigibao]

I have found on my hybrid amps that if the board traces that bring the AC filament to the tube run passed preamp sections ,that AC heater noise can be greatly reduced on many amps by running twisted wires to the tube and unpowering the traces on the board.
In the same vein and dependant on the board layout if you remove the rectifier bridge section and run the filtered D.C. Output to the board that this too helps with 60 hz noise!

You can convert that tube to D.C. Power with this simple circuit.

A side note , the new B series of Zino / China made preamp tubes on average sound better then any Russian / EH made tube, they just don't last as long in high current needs like PI sections, this being said , stay away from there 12AT7s as I have yet to test a new one that does better then 75% on my Hickok tester!

Hallo, and yess, the DC is the solution to filter humm, but i just today relize that many people complain on this amp because of hars sound ?! After just few minutes looking at schematics"wich are fine" u realize that damn thing is full of ceramic capacitors? ! EEEUHHH .. I dont know what Marshall was thinking of BUT this is only if you want to cloze the door of your buziness !!! THIS IS BIG NO NO NO ... now when im done reparing i must recap everithing with normal capacitors..EUHHH bad bad Marshall..

[Cameron]

I have found on my hybrid amps that if the board traces that bring the AC filament to the tube run passed preamp sections ,that AC heater noise can be greatly reduced on many amps by running twisted wires to the tube and unpowering the traces on the board.
In the same vein and dependant on the board layout if you remove the rectifier bridge section and run the filtered D.C. Output to the board that this too helps with 60 hz noise!

You can convert that tube to D.C. Power with this simple circuit.

A side note , the new B series of Zino / China made preamp tubes on average sound better then any Russian / EH made tube, they just don't last as long in high current needs like PI sections, this being said , stay away from there 12AT7s as I have yet to test a new one that does better then 75% on my Hickok tester!

Hallo, and yess, the DC is the solution to filter humm, but i just today relize that many people complain on this amp because of hars sound ?! After just few minutes looking at schematics"wich are fine" u realize that damn thing is full of ceramic capacitors? ! EEEUHHH .. I dont know what Marshall was thinking of BUT this is only if you want to cloze the door of your buziness !!! THIS IS BIG NO NO NO ... now when im done reparing i must recap everithing with normal capacitors..EUHHH bad bad Marshall..

You have filled your head with a lot of nonsense....Chinese preamp tubes can sound great ...and ceramic disk caps can also sound great in amps with distortion or gain. I'm not sure what your background is but don't always believe that hi-fi things should be applied to guitar amps....

[jigibao]

Hmmm, im speaking from expiriance that ceramic caps are bad for audio path. When compared with Fender im reparing FM212r all the capacitors in audio path are poly oor mylar,mkp oor mks.. And i know what im talking abouth. Now back to topic, the IC's ar partial repaired because someone try to repair the amp and made more damadge then good. I did use sockets for IC's opamps for easy acces and now i have clear channel running. Overdrive not working yet but will come to there. Litle test with old nos tube from ADZAM advanced the sound. Im still waiting for other components to arive . Rest will follow..

[Cameron]

Hmmm, im speaking from expiriance that ceramic caps are bad for audio path. When compared with Fender im reparing FM212r all the capacitors in audio path are poly oor mylar,mkp oor mks.. And i know what im talking abouth. Now back to topic, the IC's ar partial repaired because someone try to repair the amp and made more damadge then good. I did use sockets for IC's opamps for easy acces and now i have clear channel running. Overdrive not working yet but will come to there. Litle test with old nos tube from ADZAM advanced the sound. Im still waiting for other components to arive . Rest will follow..

What is so bad about them? There are other reasons that amp has a tone people consider fizzy or harsh....and it's not those caps. Either way..have fun!!

[Stevem]

All caps are microphonic to one degree or another , and Ciramic disc are the worst!
If you want your gave some fun get your hands on a large .02 uf Ciramic cap ( like a 800 volt one) hook it actoss the end of your guitar cable , Crank the volume up and you can accually talk into the sucker !

Ciramic and mica caps should always be silicone glued down to the board or chassis!

[roberto]

Woah, what a thread.

In my amps I always use ceramic caps because I like their sound.
Yes, they are (more) microphonics (than others), it's just a matter of how you install them.

In my amps I always use (elevated) AC supply for the heaters.
Never had noise issues.

In my amps I always use chinese tubes because I like their sound.
Way better than (most of the) russians.

Thanks