1979 Fender Vibro Champ Restoration Part One

The Vibro Champ is one of the rare models that didn't change much from the '60s black panel version. This one is getting some love. The waxed boards after '73 pose some problems - this shows how to solve them.
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[@MichaelSmith-rn1qw]

On my 1979 Vibro Champ, the plate dissipation with the stock 470 ohm resistor was 130% of "maximum". I also went with a 1k ohm 5 Watt resistor and a 50 Volt capacitor. My plate dissipation is now 12.29 Watts, or 102.42% of "maximum". The 1k ohm 5 watt resistor does get very hot to the touch.

[@rjprivate]

Great video. I fitted my '75 vibro champ with a bias pot. Added a 1k pot and used the hole of the vibro switch so all can be reversed. Now I have full control of the bias. The chassis doesn't even get hot and the amp sounds best ever

[@luthiervandros]

Awesome video again. Real forensic approach. I also heat the jacks’ joints. You can sometimes see them resettling.

[@trbr1799]

Great, informative video on this champ. Many thanks!

[@mendamp1715]

Very informative video, thanks for posting 😎

[@jonathangramil5014]

Hi. Your videos are incredibly informative. Especially for someone like me at the hobby level. I just wanted to clarify. When you pointed to the filter cap can for MFD ratings, you said 20, 40, 20. I have the same cap can and going in the same direction you did, mine is 20, 20, 40. My question, does it matter which wire goes to the 40 tab?

[@Nobody_Important_Yea]

Good!

[@NudnikShpilkus]

10:27 - [insert George Hamilton 'TOASTY!' meme here] Wow. That's super hot....

[@NudnikShpilkus]

13:45 - looks like that is part of why the output tube was so hot....

[@NudnikShpilkus]

16:34 - voice coil rub?

[@PsionicAudio]

That and/or old paper. New G8C on the way.

[@doubtingthomas1975]

Would you mind posting a link to the filter capacitor you used? Great video. Many thanks!

[@PsionicAudio]

Thanks! I prefer to just Hayseed Hamfest (modern Nichicons with great specs put into the old style can) but for this one I used a CE. www.tubesandmore.com/products/capacitor-ce-mfg-500v-402020-f

[@doubtingthomas1975]

@@PsionicAudio Thanks so much! I was having trouble locating a 40 20 20. I could find the 20 20 20 20 but not the other. I was also interested in the voltage. Thank you again for your great content!

[@PsionicAudio]

Thanks! Please tell your guitar friends - I'm really trying to build the channel, and the YT algorithm works against small channel videos getting seen.

[@doubtingthomas1975]

@@PsionicAudio I gladly will. Thanks again!

[@dpetrzelka]

What's your favorite make for the Cathode Bias Resistor on these Champs? Ohmite 20 series?

[@PsionicAudio]

Ohmite or Vishay.

[@jonathangramil5014]

Great Channel with so much information! I have an original Vibro Champ chassis. I want to upgrader the power cord to a 3 prong cord. However, the chassis cut out for the cord strain relief is much smaller than the bigger Fender amps. It's the same size as the fuse holder cut out. Do you have a recommendation for a strain relief and 3 prong power cord that will fit properly? I would hate to drill the existing cut out to a bigger size. Thanks!

[@PsionicAudio]

Yes, I'll share it later today. Gotta run some errands, back later.

[@jonathangramil5014]

@@PsionicAudio Hi. I hope you are feeling better. I wanted to check back to see if you could provide a strain relief and power cord recommendation for this amp. Thanks!

[@PsionicAudio]

Sorry, nearly dying threw me off my game. ;) www.mouser.com/ProductDetail/Heyco/M3207/?qs=yBEuiSRKJFWR7N6%252BW8%252BXLQ%3D%3D And tubedepot.com/products/3-meter-3-prong-power-cord

[@jonathangramil5014]

@@PsionicAudio Thank you! Much appreciated. I hope the recovery continues to go well!

[@goodun2974]

@@jonathangramil5014 , another option: if the strain relief insert fits the chassis hole but is a little too small for the new power cord, or the new 3-wire grounded power cord is a bit too fat, and you can't compress the strain relief over the cord sufficiently to allow the strain relief to fit into the chassis hole, ream out the inside of the strain relief a little with a Dremel tool to accommodate the additional thickness of the 3-wire power cord.

[@wardackerman]

I've seen a few videos now where you have to clean the wax off the boards. Was there a reason they did the wax/its fine to remove it? Originally intended as better protection from elements?

[@PsionicAudio]

I think it was so the boards wouldn't absorb moisture and warp. It was a very shortsighted "fix."

[@adrianalcantar95]

Hey! Could you post the links to all of the parts you used? Thank you!

[@crazybaldheadz]

Do the primary and the neutral still need to be grounded to the chassis after the capacitor is removed?

[@PsionicAudio]

The hot and neutral should never have any connection to the chassis. That's what the ground wire is for.

[@crazybaldheadz]

@@PsionicAudio Thanks!

[@maxwhitten8376]

Do you have any amps to sell?

[@MichaelSmith-rn1qw]

Sorry to comment again on a 2 year old video, but you are getting new viewers all the time, and this may be helpful. First a question: Isn't the blue .047 Uf 125V AC Film Metalized Polyester Radial cap from the neutral power lead to ground there to filter RF to ground? Secondly, I have come across a YT video suggesting it is NOT a good idea to increase the value of the cathode resistor to cool the bias on a Vibro Champ or Champ. Reasons given, is when signal is applied and the amp cranked, the bias voltage goes way up, plate current almost doubles and screen current goes WAY up. Also plate and screen voltages increase between idle and cranked. Not how class A is intended to operate. The solution was to swap the position of the of the 1K ohm and 10K ohm internodal resistors (or use a 10K and 22K like Fender used in the Tweeds if you want a darker sound). Plate and screen voltages will be lower (especially screen). I'm not an expert, but for those interested the YT video is entitled "Black Face Vibro Champ Repair and Bias Discussion." He was using actual current and voltages measurements to make his argument.

[@PsionicAudio]

That’s not a needed cap and it’s underrated for modern wall voltages. I’m not “cooling” the bias compared to the original operation. I’m changing the bias so it works as designed with higher modern wall voltages. It’s either that or the owner needs a variac to run at 110 with the stock circuit.

[@MichaelSmith-rn1qw]

@@PsionicAudio I did some tests with my Vibro Champ with a 1K ohm cathode resistor, and did not observe any increase in the plate or bias voltage between idle and (near) full volume when signal was applied, like the guy in the video did. The only thing I noticed was a slight sag in the plate voltage when a chord was played, which I guess is to be expected with a tube rectifier. I did not measure plate or screen current. Incidentally, if I run my amp on the same house circuit as my portable room a/c unit, my line voltage on that circuit drops from around 122V to the "schematic" voltage of around 117V, so I have my own "Cajun Variac" 🤣

[@davidsigglekow1349]

Wax on Wax off

[@davidsigglekow1349]

Wax on Wax off