Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: blueznet on August 30, 2011, 12:59:07 pm

Title: Vibro Champ Heater Wiring?
Post by: blueznet on August 30, 2011, 12:59:07 pm

The layout for the blackface Vibro Champ shows to ground to chassis pins 7 (Octal) and pins 9 (preamp). To use one 6.3vac wire out from PT to all heaters (pins 2 and pins 4/5). Can't I just wire the heaters like I would a AB763 Fender amp? Using (2) 100 ohm resistors from pilot lamp to chassis ground, and omitting use of the Center Tap to ground for the 6.3v heater taps?
See 2 pics below. One is stock wiring, other is the way I normally wire from PT to heaters.
Is there a reason Fender wired the heaters the way they did? Should I wire it exactly like the layout says?


Original wiring of heaters.
(http://i612.photobucket.com/albums/tt210/texasamp/Schematic_layouts/champ_vibro_orig_heaters.gif)

Modified wiring of heaters.
(http://i612.photobucket.com/albums/tt210/texasamp/Schematic_layouts/champ_vibro_reroute_heaters.gif)

Title: Re: Vibro Champ Heater Wiring?
Post by: phsyconoodler on August 30, 2011, 01:13:33 pm

mostly all amps of that era were wire the Fender way.They simply didn't know about twisted AC wires or chose not to do it.If you have an original Vibro-Champ then you know they are quite quiet wired the old-school way.
  Either way works just fine.There is no discernable difference between using the 100 ohm virtual center tap method vs using the center tap.
  By all means do it the way you are comfortable doing it.
I would love to see the guts when you are done.

Title: Re: Vibro Champ Heater Wiring?
Post by: blueznet on August 30, 2011, 02:55:10 pm

Quote from: phsyconoodler on August 30, 2011, 01:13:33 pm

mostly all amps of that era were wire the Fender way.They simply didn't know about twisted AC wires or chose not to do it.If you have an original Vibro-Champ then you know they are quite quiet wired the old-school way.
  Either way works just fine.There is no discernable difference between using the 100 ohm virtual center tap method vs using the center tap.
  By all means do it the way you are comfortable doing it.
I would love to see the guts when you are done.

Thanks for your input. I don't have an original Vibro-Champ.
Question: On original wiring, did Fender use the CT plus only one GREEN secondary tap soldered to one leg of the Pilot Lamp? Then they run the second leg of the Pilot Lamp to Ground? I am not getting how they got 6.3vac out of one secondary tap. Did the original PT's only have one 6.3vac secondary tap?

I have the MM PT and it has the 2 green secondary heater taps, and the green & black CT. If those Vibro-Champs were quiet running amps with the old school wiring, it would save about a foot or so of heater wiring. I just have always read that it was better to run (2) 100 ohm resistors (virtual CT) from pilot lamp to ground, and it may save your PT if a filament was to short to the plate. Plus twisted heater wire will cancel hum if you keep all the soldered ends to sockets in correct polarity.
Yea, I will post a pic of this build when finished.

Thanks,

Title: Re: Vibro Champ Heater Wiring?
Post by: jjasilli on August 30, 2011, 03:41:53 pm

On original wiring, did Fender use the CT plus only one GREEN secondary tap soldered to one leg of the Pilot Lamp?  No check the schematic:  http://www.el34world.com/charts/Schematics/files/fender/VIBRO_CHAMP_AA764.pdf (http://www.el34world.com/charts/Schematics/files/fender/VIBRO_CHAMP_AA764.pdf)
Stock, there is no CT in the filament supply, only 2 green wires; one to ground as shown on the layout diagram.  This is a 6-0 tranny.  Hence there is no humbucking for the AC filament supply.  Adding a virtual CT makes the filament secondary 3-0-3.  Now you can run a 2-wire supply which provides humbucking.  Twisting the 2 supply wires together further reduces hum.  

Per Psycho, I agree that my VibroChamp was not noisy to begin with.  But after upgrading the filament supply to virtual CT with twisted pairs, it is dead quiet -- even after boosting gain.  

Title: Re: Vibro Champ Heater Wiring?
Post by: jojokeo on August 30, 2011, 03:49:41 pm

Here's a BF Vibro that came to me earlier this month to show what you're looking for.

Title: Re: Vibro Champ Heater Wiring?
Post by: DummyLoad on August 30, 2011, 04:08:04 pm

single output tube class A1 amps don't have hum-bucking attributes. there is no P-P for hum-bucking. leo knew what he was doing. wire it the leo way. save wire. save time. save 2 resistors. save $$.

--DL

Title: Re: Vibro Champ Heater Wiring?
Post by: HotBluePlates on August 30, 2011, 10:20:13 pm

You can wire it your way, or you can wire it the original way.

Look real close at jojokeo's picture of the chassis wiring. One green filament wire from the PT is soldered to the chassis. Each tube socket has one end of the filament grounded by running a wire from the tube pin to the chassis at the socket. Now, if you look hard at the pilot light assembly, you will see the lug that contacts the bayonet portion of the lamp is spun around and soldered to the frame of the pilot light assembly (obviously before installation).

Spinning that lug is how the earlier Fender amps grounded one side of the pilot light, so that it would actually light up when using the 1-wire method. It's also why you'll blow fuses when you try to rewire a 1-wire system to a 2-wire system, if you fail to unsolder that tab and run a wire to it.

Title: Re: Vibro Champ Heater Wiring?
Post by: jjasilli on August 31, 2011, 06:36:06 am

Quote from: DummyLoad on August 30, 2011, 04:08:04 pm

single output tube class A1 amps don't have hum-bucking attributes. there is no P-P for hum-bucking. leo knew what he was doing. wire it the leo way. save wire. save time. save 2 resistors. save $$. --DL

We're not talking signal humbucking here, which is not present in an SE amp anyway. He're we're talking humbucking of the 60Hz AC filament supply.  By using a 3-0-3 filament tranny, the 60Hz filament hum is bucked in the tube's heaters (or in the cathode of a directly heated tube).  Optimal humbucking is achieved if the 3-0-3 supply is perfectly balanced.  Sometimes a hum balance pot is used for this purpose, in place of a pair of resistors for a virtual CT.

Title: Re: Vibro Champ Heater Wiring?
Post by: xm52 on August 31, 2011, 09:57:39 am

Here are some vibro champ pics before and after modification.

I have a vibro champ that is one of those magic sounding amps. It has an old replacement out transformer and a new Jensen speaker. People stand in line to use and record with this thing. Not being able to let well enough alone, I wanted to try to figure out what made this amp so special. I measured the DC voltages and they were all within spec. I decided to replicate the main board, and make layout changes to make it quieter, I selected components to optimize the sound, and I slowed down the tremolo. The amp turned out sounding even better. In the end, I put the great tone down to the design.

By the way, everything that I did is fully reversible. Otherwise I wouldn't be able to sleep at night.

Here are some before pics.

(http://s3.postimage.org/4b855itid/image.jpg) (http://postimage.org/image/rm7fpqf8/full/)
  (http://www.postimage.org/)

(http://s3.postimage.org/4b8f2qwg8/b2_small.jpg) (http://postimage.org/image/rmhcxtdw/full/)
  (http://www.postimage.org/)

(http://s3.postimage.org/m1aa9xo12/b3_small.jpg) (http://postimage.org/image/rmnz37d0/full/)
  (http://www.postimage.org/)

(http://s3.postimage.org/wo4a1ia3l/b4_small.jpg) (http://postimage.org/image/rmul8lc4/full/)
  (http://www.postimage.org/)

Here are some after pics.

(http://s3.postimage.org/t4inwgmvx/a1_small.jpg) (http://postimage.org/image/rn6600sk/full/)
  (http://www.postimage.org/)

(http://s3.postimage.org/wo4tvyg0o/a2_small.jpg) (http://postimage.org/image/rnefor9g/full/)
  (http://www.postimage.org/)

(http://s3.postimage.org/ey3ij7uf4/a3_small.jpg) (http://postimage.org/image/rnrnzj7o/full/)
  (http://www.postimage.org/)

(http://s3.postimage.org/4b9vzy0a0/a4_small.jpg) (http://postimage.org/image/rnya4x6s/full/)
  (http://www.postimage.org/)

Title: Re: Vibro Champ Heater Wiring?
Post by: jjasilli on August 31, 2011, 10:58:53 am

Wow that's pretty.  My stuff looks like a rat's nest!

EDIT:  http://www.el34world.com/Forum/index.php?topic=6088.0 (http://www.el34world.com/Forum/index.php?topic=6088.0)

Title: Re: Vibro Champ Heater Wiring?
Post by: LooseChange on August 31, 2011, 12:47:42 pm

It looks like the 6.3v CT was cut off near the PT!
Nice work.

Title: Re: Vibro Champ Heater Wiring?
Post by: xm52 on August 31, 2011, 01:11:07 pm

Thanks for the kind comments guys!

For some reason those amps came with a heater center tap and Fender used to cut it off. I always figured that it was faster to build the amps by simply grounding one leg at each tube socket. It also saved on wire. Rather than use the CT, I wanted a pair of resistors so they could act as a fuse if necessary. I was quieter with the twisted heater wires in place.

I usually apply wax or use CA glue on the ends of the braided cloth covers to prevent fraying. I must have been out of both at the time.

I used the colored braided cloth wire that Doug sells. A very good product and it adds a nice look to a vintage amp.