Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: roelrdz11 on July 21, 2013, 02:02:15 pm

Title: Help with 5F2a build!
Post by: roelrdz11 on July 21, 2013, 02:02:15 pm: Hey guys, this is my first amp build. After some research, I decided to buy the Mojotone Tweed Princeton clone as my first amp build. I have built a good amount of pedals and decided to move up. After powering it up with no tubes there was no oscillation or hum (Great!). But after the tubes were installed then the problems occurred. There is constant oscillation and hum from volume 1 t0 11 and then it dies off a tad at 12. My guitar signal is going through but VERY distorted (ala ZVEX Fuzz Factory) and the oscillation occurs mere seconds after I strum a note. What could be the problem (Sorry, I am a complete newbie)
Thanks in advance!

-Roel
Title: Re: Help with 5F2a build!
Post by: roelrdz11 on July 21, 2013, 02:08:20 pm: amp problem (http://www.youtube.com/watch?v=tbE-Kh8gPKw#ws)
Title: Re: Help with 5F2a build!
Post by: stratele52 on July 21, 2013, 02:15:36 pm: Congrat for the fist amp buid . This is lots of work but don't be discouraged . Its happenned of all of us.

1- Take you time an look if you have put all wire and capacitor and resistor at the rignt place . Good chance you miss something.

2- Be sure all solder are good

3- Send us some photo from inside the amp AND some clos up too . Good wiring dress is not esy
Title: Re: Help with 5F2a build!
Post by: stratele52 on July 21, 2013, 02:18:52 pm: Send a video with sound from the amp only ; NO guitar plug.

With volume to 0 , and volume in the midle
Title: Re: Help with 5F2a build!
Post by: roelrdz11 on July 21, 2013, 02:30:57 pm: http://s1273.photobucket.com/user/Roel_Rodriguez/media/CAM00398-1_zpsc1f55501.jpg.html?sort=3&o=2 (http://s1273.photobucket.com/user/Roel_Rodriguez/media/CAM00398-1_zpsc1f55501.jpg.html?sort=3&o=2)

http://s1273.photobucket.com/user/Roel_Rodriguez/media/CAM00399-1_zps04cdca0e.jpg.html?sort=3&o=1 (http://s1273.photobucket.com/user/Roel_Rodriguez/media/CAM00399-1_zps04cdca0e.jpg.html?sort=3&o=1)

http://s1273.photobucket.com/user/Roel_Rodriguez/media/CAM00401-1_zps8009c1e9.jpg.html?sort=3&o=0 (http://s1273.photobucket.com/user/Roel_Rodriguez/media/CAM00401-1_zps8009c1e9.jpg.html?sort=3&o=0)
Title: Re: Help with 5F2a build!
Post by: stratele52 on July 21, 2013, 02:51:32 pm: Thank's for pictures.

IMO there many wire are not seated well close the chassis and are too close from other one . These wire could act like an antenna . Hard to explain here what you have to do . Look at any Fender blackface inside the chassis , wiring .

First of all, with NO guitar .

1- Vol to 0 do you hear some noise , hum buzz ?
If Yes , remove tube V1. Vol at 0 , you hear noise ?
Title: Re: Help with 5F2a build!
Post by: sluckey on July 21, 2013, 02:52:44 pm: Some things to look for first...

1. Wiring error. Compare actual wiring to layout diagram.
2. Missing jumper under board.
3. Missing ground, especially from board to chassis or ground buss.
Title: Re: Help with 5F2a build!
Post by: stratele52 on July 21, 2013, 02:53:38 pm: Is this amp schematic is like any 5F2-a Fender amp ? Like princeton 5F2-a ?

or can you show me schematic ?
Title: Re: Help with 5F2a build!
Post by: roelrdz11 on July 21, 2013, 03:04:09 pm: http://s1273.photobucket.com/user/Roel_Rodriguez/media/CAM00406_zps0e5b2a89.jpg.html?sort=3&o=0 (http://s1273.photobucket.com/user/Roel_Rodriguez/media/CAM00406_zps0e5b2a89.jpg.html?sort=3&o=0)

http://s1273.photobucket.com/user/Roel_Rodriguez/media/CAM00405_zpsd3430c4e.jpg.html?sort=3&o=1 (http://s1273.photobucket.com/user/Roel_Rodriguez/media/CAM00405_zpsd3430c4e.jpg.html?sort=3&o=1)

The video is uploading at the moment..
Title: Re: Help with 5F2a build!
Post by: roelrdz11 on July 21, 2013, 03:10:29 pm: Fire up with no guitar (http://www.youtube.com/watch?v=zBMFEmK2fck#ws)
Title: Re: Help with 5F2a build!
Post by: roelrdz11 on July 21, 2013, 03:16:02 pm: The oscillation doesnt occur when the 6v6 tube is taken out
Title: Re: Help with 5F2a build!
Post by: stratele52 on July 21, 2013, 03:19:27 pm: Thank's for the video. IMO if everything is at the right place ( do you check all your work ? ) you have problem with wiring dress . Many wire act like antenna .

But check carefully your work before
Title: Re: Help with 5F2a build!
Post by: stratele52 on July 21, 2013, 03:20:50 pm: Quote from: roelrdz11 on July 21, 2013, 03:16:02 pm
The oscillation doesnt occur when the 6v6 tube is taken out

I'm sure of that and no oscillation with no speaker I guess :laugh:
Title: Re: Help with 5F2a build!
Post by: roelrdz11 on July 21, 2013, 03:24:31 pm: lool I misread your v1 to be 6v6... the amp doesn't oscillate when the ECC83 is out. How would i go about dressing the wires appropriately?
Title: Re: Help with 5F2a build!
Post by: stratele52 on July 21, 2013, 03:37:29 pm: Thank's for shematic , same as a Fender Princeton I have .

A very sensitve wire is the one comming from the volume and going to 12AX7 pin 7 . This wire must be short as you can and follow the chassi close to metal . Best is to use a shielded wire , shield solder to ground at one end only.

Heater wires must be tight twisted and must be far from any other wire .

Another sensitive wire is the one coming from the input jack ; must be short and along chassis metal too.
Title: Re: Help with 5F2a build!
Post by: stratele52 on July 21, 2013, 03:40:21 pm: Quote from: roelrdz11 on July 21, 2013, 03:24:31 pm
lool I misread your v1 to be 6v6... the amp doesn't oscillate when the ECC83 is out. How would i go about dressing the wires appropriately?

Problem is aroud this ECC83 , check what I just send you . Sensitive wire .

Now I should go out . Take your time, you'll find it ; )
Title: Re: Help with 5F2a build!
Post by: nandrewjackson on July 21, 2013, 10:50:54 pm: Triple check EVERYTHING.

A good friend of mine is a woodworker. He said the first thing they learn is "measure twice, cut once" Very good advice.

It will probably be an "A-ha" moment when you find the offending mistake/component.

What kind of pedals do you do?
Title: Re: Help with 5F2a build!
Post by: roelrdz11 on July 22, 2013, 09:42:06 am: I have built a couple fuzz factories, a tube screamer clone, and a wah. I am checking everything out today, hopefully I find the offender x)
Title: Re: Help with 5F2a build!
Post by: roelrdz11 on July 22, 2013, 10:04:20 am: So it turns out, I misread the schematic. When i checked with the actual circuit I noticed I sent my negative resistance wire to my 6v6! (Doh!)
I will make those corrections and let you know what happens

-Roel
Title: Re: Help with 5F2a build!
Post by: stratele52 on July 22, 2013, 10:35:13 am: Quote from: roelrdz11 on July 22, 2013, 10:04:20 am
I noticed I sent my negative resistance wire to my 6v6! (Doh!)

Great !

Wich resistance ( resistor ? Are you french speaking ? ) and where on 6V6 ?
Title: Re: Help with 5F2a build!
Post by: Willabe on July 22, 2013, 10:50:26 am: I think he might mean negative feedback?

http://www.el34world.com/charts/Schematics/files/fender/PRINCETON_5F2A.pdf (http://www.el34world.com/charts/Schematics/files/fender/PRINCETON_5F2A.pdf)

Brad :dontknow:
Title: Re: Help with 5F2a build!
Post by: sluckey on July 22, 2013, 10:52:01 am: Negative resistance wire is negative feedback wire. The black wire that should connect from the speaker jack to the 22K on the board is actually connected from the 22K to the 6V6. Looks like pin 8, cathode. I can't tell if the 500Ω/25µF that should connect to pin 8 is even connected to anything.
Title: Re: Help with 5F2a build!
Post by: stratele52 on July 22, 2013, 11:01:04 am: This make sense Willabe and sluckey,

Thank's
Title: Re: Help with 5F2a build!
Post by: roelrdz11 on July 22, 2013, 11:26:29 am: Yeah at the time it wasnt connected to anything, which would explain why the power section was being driven so hard, as well as the oscillation. I fired it up just now and...
It sounds great!
No hum, no oscillation just clean Fender goodness. However, at about volume 10 (out of 12) I experienced some arcing!... But after i dressed the wires more appropriately and cleaned up some solder joints, I have yet to experience this again.
Thank you guys so much for everything!

-Roel
Title: Re: Help with 5F2a build!
Post by: sluckey on July 22, 2013, 11:36:55 am: I hope you cleaned up the 6V6 socket. Your pic shows pin 2 and 3 to be very close together, maybe even touching. That would be a very bad thing if they do actually contact each other.
Title: Re: Help with 5F2a build!
Post by: roelrdz11 on July 22, 2013, 11:41:52 am: That's exactly where the arcing was happening so I cleaned all the pins up (I guess I shouldn't have been soldering while studying for a physics test simultaneously :laugh: )
Title: Re: Help with 5F2a build!
Post by: stratele52 on July 22, 2013, 12:44:45 pm: Great , enjoy it now
Title: Re: Help with 5F2a build!
Post by: Willabe on July 22, 2013, 05:13:35 pm: Quote from: roelrdz11 on July 22, 2013, 11:41:52 am
(I guess I shouldn't have been soldering while studying for a physics test simultaneously :laugh: )

No you shouldn't. :w2: Maybe while making a sandwich or cooking an easy dinner, but not with a hot soldering iron. I'd bet if you would have focused just on 1 or the other at a time you would have done better on both.

Would have saved you the time to debug the amp so how much time did you really save, if any?

Some mistakes you can get away with but others are costly and will take out your PT and or OT.

Glad you got her running and all in all considering you didn't give it your full attention you did pretty good for a first build. It will be interesting to see how much better your next build will look when you give it your full focus.

Brad :laugh:
Title: Re: Help with 5F2a build!
Post by: stratele52 on July 23, 2013, 03:54:17 am: +1 Willabe

Next amp project ; remember NEVER power ON until triple check wiring . You can burn / damage expensive parts.
Title: Re: Help with 5F2a build!
Post by: Ed_Chambley on July 23, 2013, 06:13:29 am: Quote from: Willabe on July 22, 2013, 05:13:35 pm
Quote from: roelrdz11 on July 22, 2013, 11:41:52 am
(I guess I shouldn't have been soldering while studying for a physics test simultaneously :laugh: )

No you shouldn't. :w2: Maybe while making a sandwich or cooking an easy dinner, but not with a hot soldering iron. I'd bet if you would have focused just on 1 or the other at a time you would have done better on both.

Would have saved you the time to debug the amp so how much time did you really save, if any?

Some mistakes you can get away with but others are costly and will take out your PT and or OT.

Glad you got her running and all in all considering you didn't give it your full attention you did pretty good for a first build. It will be interesting to see how much better your next build will look when you give it your full focus.

Brad :laugh:
With me and my ADD, I have done this many times. That is, until I had a bassman grab me one day and I thought I would never let go of the thing. Some people listen and others learn from experience, and I have lots of experience. :BangHead:
Title: Re: Help with 5F2a build!
Post by: roelrdz11 on July 23, 2013, 09:14:35 pm: Yeah I apologize for the absent-mindedness x) getting ready for college and stress does weird stuff to your attention span x)
well here is a video of the finished product!

Fender Princeton Tweed Amp build test (http://www.youtube.com/watch?v=Ov4o49EWUlE#ws)
Title: Re: Help with 5F2a build!
Post by: tubeswell on July 26, 2013, 11:34:00 am: You must be pretty happy with that Roel. Smooth playin' BTW. Pink Floyd was one of my favourite bands when I was a teenager.