Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: mechtonia on January 28, 2019, 08:52:31 am

Title: Egnator Tweaker 40 (40W 6L6) - fixed rectifier but still have no output
Post by: mechtonia on January 28, 2019, 08:52:31 am

The original problem with this amp was a blown fuse at the power entrance. This thread https://el34world.com/Forum/index.php?topic=24211.0 (https://el34world.com/Forum/index.php?topic=24211.0) details efforts to fix that, which appear to have been successful. No more blown fuses and the amp powers up and all votages read as they should. But after putting the amp back together, it produces no sound at all.

Using a 1000 Hz input signal I traced the signal through all preamp tubes to the power tubes and everything checks out until I get to the plates of the 6L6s. There I get no signal.

Specifically these are the readings on the pins of the 6L6s:

2 (heater): 3.3 VAC
3 (Anode): 450 VDC - no signal
4 (Grid 2): 444 VDC
5 (Grid 1): -40.5VDC with input signal superimposed
7 (Heater): 3.3 VAC
8 (Cathode): 49.3VDC


FWIW I'm using an old Tektronix 422 scope.

Also, I hooked up my tone generator to the primary side of the OT and could hear the tone in a speak connected to the secondary of the OT.

Would an issue with the rectifier circuit cause both power tubes to die or visa-versa? What other test should I perform? I strongly suspect this is some sort of 1D10T error but can't pinpoint my mistake.

Currently my plan is to order another set of power tubes (I need a backup set anyway) and swap those but I'm at a loss to explain how or why both output tubes would completely die at the same time.

Title: Re: Egnator Tweaker 40 (40W 6L6) - fixed rectifier but still have no output
Post by: mat janssen on January 28, 2019, 09:21:33 am

Hi If you have - 40 Volts on G1 grid and + 50 volts on the kathode then the tube has in principle - 90 volts on the G1 grid, so it is completly switched off. And than it is normal you will hear nothing.  :smiley:

Title: Re: Egnator Tweaker 40 (40W 6L6) - fixed rectifier but still have no output
Post by: sluckey on January 28, 2019, 10:53:09 am

Quote

8 (Cathode): 49.3VDC

Are you sure the cathode measures 49.3v and not 49.3mV? If so, check the fuse (F1) and that 1Ω cathode resistor (r12).

     https://el34world.com/charts/Schematics/files/Egnater/Egnater_tweaker40_power_section.pdf

Title: Re: Egnator Tweaker 40 (40W 6L6) - fixed rectifier but still have no output
Post by: mechtonia on January 28, 2019, 01:58:51 pm

Quote from: sluckey on January 28, 2019, 10:53:09 am

Are you sure the cathode measures 49.3v and not 49.3mV? If so, check the fuse (F1) and that 1Ω cathode resistor (r12).

     https://el34world.com/charts/Schematics/files/Egnater/Egnater_tweaker40_power_section.pdf

Hmmm...this is very likely the case. I will recheck.

Title: Re: Egnator Tweaker 40 (40W 6L6) - fixed rectifier but still have no output
Post by: mechtonia on January 28, 2019, 07:56:37 pm

Thanks to sluckey for pointing me in the right direction. The tangs on F1 fuse holder we're a bit chowdered causing the male part to stop short in the female part, resulting in the fuse not making contact.

I fenagled it back in place and she's working like a charm. Thanks for the help!