Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: rczcustom on November 05, 2019, 02:18:30 pm

Title: Big Problem with AC15C1
Post by: rczcustom on November 05, 2019, 02:18:30 pm

Why it sound like this?? one audio is with all down and the other one is when I turn up a little bit the volume


https://drive.google.com/open?id=1w6gaIoH4uef95IBWgjxBovlIjzvoNbch


https://drive.google.com/open?id=1w8asmeUUDu3zUF9pvmLgQidHs2TLnduw

Title: Re: Big Problem with AC15C1
Post by: shooter on November 05, 2019, 03:13:49 pm

this one of the re-issue amps, build with a pcb?  If so, there's your answer 80%

Title: Re: Big Problem with AC15C1
Post by: rczcustom on November 05, 2019, 04:06:58 pm

Is ac15c1 from 2016

Title: Re: Big Problem with AC15C1
Post by: shooter on November 05, 2019, 04:14:45 pm

Unless you've logged some time troubleshooting pcb circuits, you are probably better off taking it to an amp tech.  I've turned down most of the pcb re-issue amps because they are a PITA, for little satisfaction  :icon_biggrin:

Title: Re: Big Problem with AC15C1
Post by: rczcustom on November 05, 2019, 04:20:13 pm

I think the problem is one EL84 that sound something inside

Title: Re: Big Problem with AC15C1
Post by: shooter on November 05, 2019, 05:28:10 pm

probably, I've fixed 2 ac30c?, both had major smoke damage in the PA section  :icon_biggrin:

Title: Re: Big Problem with AC15C1
Post by: Willabe on November 05, 2019, 05:40:26 pm

Quote from: rczcustom on November 05, 2019, 04:20:13 pm

I think the problem is one EL84 that sound something inside

You said it's a 2016 model? So, 3 year old power tubes, you play a lot? Loud?

Could just be a bad EL84?

It's a cathode bias power section, no bias adjustment needed for new tubes, pop in a new matched set of EL84's and see if that fixes it.

If not, you'll need new tubes some day, so not a waste of money.

 

Title: Re: Big Problem with AC15C1
Post by: shooter on November 05, 2019, 05:41:29 pm

only schematic I've found is here, older than yours

https://el34world.com/charts/Schematics/files/Vox/Vox_ac15_reissue.pdf
look for crispy, discolored, burnt around the PA tubes, especially the connectors, cn2 & 3 in the schematic.  the burnt typically leads to taking out the board, which leads to bad solder joints, cracked foil n such.
before all that a complete list of current VDC's from all the tubes n PS comes in handy

Title: Re: Big Problem with AC15C1
Post by: rczcustom on November 05, 2019, 06:06:14 pm

Now it's sound okey, I move the EL84 a little bit and it's work fine!

It's Weird

Title: Re: Big Problem with AC15C1
Post by: Pietro on November 07, 2019, 12:46:19 pm

well...then it won.t be fine for long.

Title: Re: Big Problem with AC15C1
Post by: texwest on November 07, 2019, 09:06:50 pm

If moving the tube made it work,  then I would replace the tubes and touch up the solder on the tube sockets.  But if you have never been inside a tube amp don't do it yourself.  There are dangerous voltages in there even when it is off and unplugged.  Take it to a qualified amp tech.