Squealing 8W SE

[marquimsp]

it isn't that thick, around 4mm total... can't find specs anywhere.

https://www.tecniforte.com.br/cabos-montados

Ah, those are "pre-assembled cables" (montados), not what I have here.

Thanks!

[Phil_S]

https://www.tecniforte.com.br/mojopath
OK, so here is a picture of the cable you have. I have no Portugese, so I guess at what it says based on the little French and Spanish I know. I don't see any specs, but you can always contact the company and they should tell you what you have.

[marquimsp]

You guys should be proud of me (minus the "buying shitty amp" part), I did almost everything you've suggested:

1) Twisted the input transformer wires
2) replaced the microphonic cap
3) Ordered a 12AT7 (should be here by Thursday).
4) replaced shitty input wires by shielded one

Still squealing
But it's ok, I'm learning a lot in the process and the amp is probably much quieter than before.

Thanks you all for the help!

[Phil_S]

The layout of the tube sockets and transformers is poorly done. If changing the 12AT7 doesn't help, try installing a tube shield if you can find one that works. You might figure a way to make one that screws onto the chassis. It can be a cylinder or box that is open at the top.

I wish the manufacturer had rotated the output transformer 90 degrees so it would not be in the same orientation as the power transformer, but I'm doubtful that is causing the squeal. That would more likely be a source of hum.

[bepone]

You guys should be proud of me (minus the "buying shitty amp" part), I did almost everything you've suggested:

1) Twisted the input transformer wires
2) replaced the microphonic cap
3) Ordered a 12AT7 (should be here by Thursday).
4) replaced shitty input wires by shielded one

Still squealing
But it's ok, I'm learning a lot in the process and the amp is probably much quieter than before.

Thanks you all for the help!

dont worry, you will finish with hard modifiying this thing and the constructor will ask you for help!

if you are not familiar , every gain/volume pot has 3 pins, you can solder 500k 0.25W-1W resistor directly on pins 1-3 (end pins) below on the pcb this would also help, i have some concerns that theese pots are also faulty

[Stevem]

Just how would his pots be faulty if they are not scratchy or producing drop outs?

[bepone]

check the videos can be

[Phil_S]

Now that you've made a number of changes, can you post another sound clip? Just a short clip. Dial in the setting with the most noise. No instrument plugged in. That's all we need. I hear a lot of hiss and I wonder if that is contributing to one or more other problems. You say the amp is much quieter, so it might suggest to us another direction.

I don't know if this is worth pursuing to reduce hiss. This amp is supposed to have 2 12AX7 preamp tubes. I want to suggest replacing the plate load resistors with 1W rated or 1/2W if 1W won't fit. I'm assuming the amp has 1/4W resistors. But I can't see or can't find the plate load resistors. These would be on pins 1 and 6 of V1 and V2. I am thinking these are on the other side of the board.

[Stevem]

To check for the max level of hiss you should have your guitar plugged in, this is done to open the shorting switch on the input jack and then have the guitars volume fully down.

[marquimsp]

Helloooo the 12at7 was delivered today! I thought it would kill the gain, so I put it in v2 (left a 12ax7 electro harmonix in v1)... there is definitely more bottom end and just a little less gain, not much of a difference (still squealing at max gain and 50% master volume). So I changed the 12at7 to v1, now it's a beautiful sound, lots of bottom end, beautiful mids, more than enough gain for rhythm. I guess if I add the 500k resistor to the gain pot I'll be able to use the 12ax7 in v1, since I'll have twice the resistance? I'll make videos as soon as I can.

Thanks!

[bepone]

great,
now is a job also to reduce anode resistors from 100k to 68k where is 12at7 , for even lower gain and warmer sound, but this is level 2

[Phil_S]

The lower gain tube that works well with the 12AX7 configuration is the 5751. Before you go changing the plate load resistor (which I think is underneath) try a 5751. Or just leave it the way it is and use the 12AT7. Nothing bad will happen.