Egnater Renegade

[lowell]

I just replaced a blown PT in this amp with a Mercury Magnetics.

Powered it up on my limiter and bulb was very dim so it locked good. Then put EL34 in there...still looked good. Voltages looked low but good for limiter.

Took it off the limiter and got good plate and screen voltages around 400v+. Cant remember exact figure as its the weekend and I'm out of the shop but wanted to get some feedback before Monday if possible. At least I thought the voltages were correct. Played the amp for about 1 minute and BANG a capacitor exploded. Was literally like an M80 lol!!

So C8 in the PA exploded. As far as I know there are 2 reasons a cap will explode... over voltage, and reverse polarity. Neither of which seem likely. Its the only cap that exploded... and the amp still works albeit there's noise now.

I suspect I'll need to investigate further on some voltages in the power supply as this cap feeds the PI. But what are your thoughts on the matter?

[g1]

Maybe C8 was going bad and took out the PT, now it just blew?

[drewl]

Sounds right.
Had a Vibrolux last week with bad filter cap.
It would redplate the rectifier tube.

[lowell]

Thanks guys. I'll replace C8, strap safety goggles, and check voltages.

[lowell]

OMG I just wrote this whole post and it was deleted.

So... C8 is in and working great. Amp sounds good. Howvwer Main 2 master volume isnt working. When using the front panel channel switch SW1, Channel 2 controls all work except the Main stays on Main 1.

schematic whereabouts:
SW1 is top left of input jack
Main 1/2 board is far bottom right
IC5 TC4069 and Q6 are next jack J6

Q6 Vb stays at zero on both channels. It needs to rise to +2v or more to pull down the relay coil and supply.

IC5 Pin1 stays at +11v on both channels

IC5 Pin2 stays at 0v

What I dont understand... is where Q6 Base is going to be pulled up to turn it on. ?? Isn't IC5 supposed to put Pin2 at 0v or -12v since it's an inverter?

Also... Unless J6 ring is grounded... I don't see voltage on Pin1 changing. It will stay at +12v.

Finally... Q6 Vb is +1.3v if I ground J6 ring. This makes both Main1 and 2 function simultaneously.

Help!

[lowell]

Well I read the manual... I am not crazy lol. Main 2 ONLY WORKS with the footpedal. And it supplements Main 1... which always is functional. Problem solved. But hey had a good exercise in troubleshooting switching circuits. Still odd that IC5 output puts out +1.3v when it's input is 0v.

Anyone care to enlighten me?

[Enzo]

IC5 is a hex inverter - six independent LOGIC inverters. Not voltage inverters. The power to the IC is 0 and +12v. IC5-1 stays at +11 until a FS grounds it to zero. The logic inverter changes a high to a low and vice versa. SO +11 in means 0 out. Ground the input and pin 2 will rise to +12. And that +12 is what would turn on the transistor.

It is not an op amp, it is a logic gate.

[lowell]

Thank you sir!