Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TerryD on April 18, 2017, 04:40:38 pm

Title: How do you check an output transformer
Post by: TerryD on April 18, 2017, 04:40:38 pm

I just picked up a Super Reverb 1968.  Crazy things are happening.  I bias by taking the ma off of pin 3 and the OT center tap.  All of a sudden I get no reading there but the amp still works.  I've been getting faint crackling and distortion.

Can a faulty OT ruin 6l6s?

How can I check to see if the OT is working properly?  In your answer could you tell me how to tell which wire is which?

Thanks
Terry

Title: Re: How do you check an output transformer
Post by: HotBluePlates on April 18, 2017, 05:12:21 pm

Quote from: TerryD on April 18, 2017, 04:40:38 pm

...  I bias by taking the ma off of pin 3 and the OT center tap.  All of a sudden I get no reading there but the amp still works.  I've been getting faint crackling and distortion. ...

You should not attempt to play an amp while using the OT Shunt method of measuring plate current.  If everything is happening as it should, the plate current is going through the meter instead of through that half of the OT.

Does the amp sound like it should when you're just playing it without a meter hooked up?  If yes, the amp & OT are probably fine.

Title: Re: How do you check an output transformer
Post by: TerryD on April 18, 2017, 08:13:58 pm

I'm sorry.  No, I never played this with the meter hooked up.

Intermittent  steady light distortion and low bacon frying

Title: Re: How do you check an output transformer
Post by: shooter on April 18, 2017, 08:23:42 pm

Quote

Shunt method now and "NO READINGS"???

I'd power down, pull the power tubes and ohm socket to socket, tube side, then wiggle n jiggle the OT wires

Title: Re: How do you check an output transformer
Post by: TerryD on April 18, 2017, 08:31:27 pm

Whoops Using a friends multimeter because mine just bit the dust and had plug in wrong socket.  Whew!

Title: Re: How do you check an output transformer
Post by: shooter on April 18, 2017, 09:04:59 pm

Quote

Whoops Using a friends multimeter

you wanna minimize Whoops with a friends meter :icon_biggrin:

Title: Re: How do you check an output transformer
Post by: HotBluePlates on April 18, 2017, 09:14:31 pm

So the amp is happy?

Title: Re: How do you check an output transformer
Post by: Bluemeany on April 19, 2017, 05:06:47 pm

I've put tape over the sockets used for taking current measurements on my meter. I find another way - place a small known resistance in series and measure the voltage across it.