Hiwatt t40 white noise..souffle

[lukatesta]

Hi guys,
I'm luca from Italy..so..excuse me for my english.. I often repair amplifiers ss or ts and when I have a money I built someone of them.. It's my passion!
Yours site is a great place of information where all can growing! thank you!
But..let's get to the point..
I have to repair a hiwatt t40 (I don't find the complete schematic) that has a loud fffffffffff ...a wind souffle (hardly like a white noise) when I increase the master pot.
I found a power schematic, schematic post master and I made a great effort of reverse engeneering to write a part of schematic where the noise is generate.
This latter is generate between t3 and t4, the first two 12ax7, precisely on -+15v.. so, after the signal passes through the opes.
I replaced the two 4558s, all 15v's caps, resistors and zeneres, master pot and valves..the noise is always there..ideas, tips, helpssss????
please! and.. thank you all!

 

[JonSnell Electronic]

Service manual is here; HIWATT CUSTOM-20 TUBE-AMPLIFIER SCH Service Manual download, schematics, eeprom, repair info for electronics experts
The T40 uses 4 X EL84 output valves.
If the noise gets louder when the master vol is increased, the source is before the pot.
Remove VT1 and VT2, does the noise stop? If yes, check the pre amp and effects driver stages. If not V4a may have an issue. Remove V4 and substitute with another ECC83.
Check anode load resistors for breaking up under load, they can become noisy.
Keep a logical note of what you are doing, that stops repeat actions and wasting your time.
The schematic you have posted looks wrong.
Have fun!

 

[lukatesta]

Hi and thank you for your reply!
Hiwatt custom 20 is another amp, T40 and T20 amp are another serie, the schema is not that one, infact there are 3 preamp valve, not 4 and there is a reverb.

the noise is surely before the pot..I follow the signal with probe and surely is not in valves because without T3 (first preamp valve) the noise is off and without T4 is on but with probe I check the noise before the valve T4, there is already on grids (pin 2 and pin 7).
I know that my schematic can have some wrong but is close enough for thinking together.. it's too difficult follow the signal up and down between the two pcb..
I attach the inner pics

 

[lukatesta]

nothing?

 

[Logic800]

But doesn't the main board actually say T40 on it?

 

[lukatesta]

yes it says t40-a and t40-b (pre board)

 

[GoatGuy]

Wish I could help.
Can't understand which is the actual schematic.
The first one (computer graphics drawn) is a bit weird.
Weird values for capacitors nearer to the EL84 output finals.
Weird symbols for valves.
But I get it, basically.

Is this the amplifier in question?

 

[lukatesta]

Hi..these schematics are roughly right, they are no perfects..anyway, I repeat, the issue is not in output section, is between first and second preamp section

 

[lukatesta]

someone can help me?pleeeeeasee!