Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: mechtonia on January 23, 2019, 02:26:15 pm

Title: MOV or capacitor in Egnater rectifier section
Post by: mechtonia on January 23, 2019, 02:26:15 pm
My Egnater Tweaker 40 started blowing fuses and in the process of tracing the circuit, I came across a what I think is a capacitor across the input of the rectifier. Is this indeed a capacitor and if so what is it's purpose? Filtering? I have limited experience but I haven't seen a capacitor across the input of a rectifier.

Schematic of rectifier section of circuit:
(https://imgur.com/B2DapUh.png)

Image of rectifier components:
(https://i.imgur.com/ezramOV.png)


Also, can anyone with Egnater experience confirm if this is stock/typical? This is on the bottom of the power board opposite a relay.
(https://i.imgur.com/bi6D3QG.png)

Title: Re: MOV or capacitor in Egnater rectifier section
Post by: PRR on January 23, 2019, 02:36:56 pm
Welcome.

What is the component designator under the blue lump? (Like C41, D9, R69...)

In general, either a cap or a MOV here would be a just-in-case protection against different crap coming from the power line. (I do have doubt about how they implemented it.)

The other mod might be a poor factory change or a later owner's hack-work.
Title: Re: MOV or capacitor in Egnater rectifier section
Post by: mechtonia on January 23, 2019, 02:52:59 pm
The component designation is C46. All other capacitors have a"Cxx" designation too.
Title: Re: MOV or capacitor in Egnater rectifier section
Post by: PRR on January 23, 2019, 02:58:35 pm
Pull the handy HV fuses. Feed a 9V battery through a 1K resistor, each side one at a time, see if you get 7.8V (9V - two diode drops) at the other end, and if the 9V leaks from one side to the other
Title: Re: MOV or capacitor in Egnater rectifier section
Post by: mechtonia on January 28, 2019, 08:54:21 am
Quote from: PRR on January 23, 2019, 02:58:35 pm
Pull the handy HV fuses. Feed a 9V battery through a 1K resistor, each side one at a time, see if you get 7.8V (9V - two diode drops) at the other end, and if the 9V leaks from one side to the other

Winner winner chicken dinner.

I performed the test as described and it failed. So I replaced the cap and everything looks good on the power front. Except the amp has no output. I made a new thread about it here https://el34world.com/Forum/index.php?topic=24246.0 (https://el34world.com/Forum/index.php?topic=24246.0).
Title: Re: MOV or capacitor in Egnater rectifier section
Post by: jojokeo on February 02, 2019, 10:45:22 am
Quote from: mechtonia on January 23, 2019, 02:26:15 pm
I came across a what I think is a capacitor across the input of the rectifier. Is this indeed a capacitor and if so what is it's purpose? Filtering? I have limited experience but I haven't seen a capacitor across the input of a rectifier.

Yes - the capacitors help filter out any possible rectifier switching noise that can be created. There's other things like transformer ringing and/or oscillation prevention as well.