1966 Blackface Vibrochamp rescue

[mresistor]

HBP could inform on the why..  the primary 117VAC side is larger wire and it is a step-up tx where the secondary side winding wire is much smaller I think.

[mresistor]

Here are photos of my 1965 Vibro Champ that may or may not assist you in your endeavor. I bought this in an estate batch with more than one C and VC. I was told the old man that owned them had recently died.
Some parts were replaced. It also came with a brown frame 10" Jensen 4 ohm speaker. I have never looked to see how hacked up the baffle might be - seems ok to me.

[mresistor]

This amp is free of hum  and as you can see the filaments are still wired stock.

[jeff_free69]

SWEET!  - hard to believe how something almost 60 years old looks so new, especially compared to my rust bucket.

Looks like you have a resistor hanging on your 6V6 that i dont have.   something new/old?

Do you recall what value you used for the bypass cap on the preamp second stage ?   The layout posted on this thread shows 2 uF, but my unit has a 10 uF, which matches the AA764  schematic.  My understanding is that this affects the   bass cutoff frequency   ( eg 2uF = 100Hz;  10uF = 20hz;   4.7uF = 40 Hz)

General question
- any  preferred brands for these caps (I haven't done any shopping for several years and dont know the current state of affairs)

[pdf64]

... i am perplexed by the HT secondary reading (red wires) being so high = 380 ohm
Is that normal??  With the Rectifier tube out of the circuit, shouldn't the impedance through the windings be pretty low? 
 ...

It's fine, valve rectifiers require >100ohms of 'protecting resistance'.
The HT secondary will have more than 650/120 = 5.5 times the number of turns used for the primary.
The use of thin wire allows the protecting resistance to be built into the transformer.
That avoids the amp builder needing to use external resistors.
And allows the transformer builder to save on copper etc.
>180ohms per rectifier anode is probably more than the minimum necessary, but that's the designer's choice, it won't cause a problem per se.

[mresistor]

Looks like you have a resistor hanging on your 6V6 that i dont have.   something new/old?

Do you recall what value you used for the bypass cap on the preamp second stage ?   The layout posted on this thread shows 2 uF, but my unit has a 10 uF, which matches the AA764  schematic.  My understanding is that this affects the   bass cutoff frequency   ( eg 2uF = 100Hz;  10uF = 20hz;   4.7uF = 40 Hz)

General question
- any  preferred brands for these caps (I haven't done any shopping for several years and dont know the current state of affairs)

That is a 470R screen resistor.  I haven't been in this amp for a few years, and should probably pull tha amp out and implement HBPs recommendations.
The cap for the second stage is 10uf as seen in this photo blown up some.
I think axial caps would be best but you could use Orange Drops, Mallory poly caps, but since there are so few maybe get some Sozo or Dougs Jupiter caps which a lot of people like.
For electrolytics you could use Sprague or the new Mod caps. 

Doug has all you need here in his store.

[jeff_free69]

Parts are on the way!

I lifted the legs on a bunch of components and took measurements.   The other Mallorys are out of spec by 40-50%  and there's a one suspect resistor.
Of course no 1 vendor had everything, but hopefully everything will be in place next week

Have a great weekend!

[jeff_free69]

Latest update -
Got my parts and installed them.  Of course some complications to keep things interesting

Quickly discovered i really need the bigass iron for chassis grounds.

Found a Switchcraft slider switch rated for 3A  that fit perfectly  (original Carlson was 4A).  But of course the mounting holes on the wings are not threaded like the original, making a major pain to get a nut&washer onto the screw.  but at least i was able to keep the original screw.

The screws that secure the boards to the chassis were completely rusted, and one completely rounded out, and it was really bugging me..   Plus i had the nagging feeling that a washer may have disappeared underneath (see above).    I ordered a screw extractor kit and got them out  - BTW anybody know exactly what a replacement would be?

I was then able to lift the board a little and take a partial peak underneath.  I discovered that I was actually  able to completely slide out the insulator board, since the filter cap can was still not wired.  I was then able to give it a fiberoptic colonoscopy, underneath the main board, without unwiring anything.     Wasn't pretty , but relieved that there was no sign of any stray metal parts. 

The insulator board needed some real cleaning, especially the rust on the bottom side.   I've tried cleaning it a couple times, most recently resorting to 60 grit sandpaper.  I figure its the bottom of the insulator board so no need to worry about patina.  But I still can't get all the rust stains out, and i know how  conductivity can be such a sneaky problem.

Anyway here's the current state.  I'm debating if its ready to give it shot
 

[Willabe]

It's your amp, but there's no way I'd re-use that eyelet board. Too much work to re-wire/solder that all up and then run into trouble. And if not right away, it's coming. 

And I would not use a new eyelet board made of that same material. I'd go with a fiberglass board. Our host has them in his store as do other on line stores.
 

[HotBluePlates]

1) Transformer:  removed tubes and took a bunch of measurements for shorts etc   around the transformer:
...
Red p4 - Red p6  380 ohm
...
... i am perplexed by the HT secondary reading (red wires) being so high = 380 ohm
Is that normal??  ...

Hammond Champ Replacement PT ---> 277Ω
Hammond has lower winding resistance than vintage power transformers (as you see with yours).

... the high value had me concerned. 
Pure ignorance on my part and  not terribly important,  but if the measurement is just through the windings, i wondered why not something lower ...

High Voltage winding is many-many turns of Skinny Wire  --->  Big Volts step-up (120v up to 650v), but small current (only 0.1A for Hammond's part)

Low Voltage winding is a few turns of Very Fat Wire ---> Big Volts step-down (120v down to 5v or 6.3v), big current (2-3A for Hammond's part)


Primary has to have some goodly number of turns for Inductance (40x the resistance of the low-volt windings in Hammond's part), and carries a moderate current (about 0.775A to 0.8A for Hammond's part).

   - Gotta have fatter wire for higher current.
   - Gotta have many-turns for big step-up.
   - Skinnier wire is higher Resistance per unit-of-length.

   - Add It Up: High Voltage (B+) winding is typically high-resistance.

[jeff_free69]

It's your amp, but there's no way I'd re-use that eyelet board. Too much work to re-wire/solder that all up and then run into trouble. And if not right away, it's coming. 

And I would not use a new eyelet board made of that same material. I'd go with a fiberglass board. Our host has them in his store as do other on line stores.

Thanks, I hear ya - I have to acknowledge that the board may be more trouble than its worth.

But with that in mind, i dont see any reason not to reinstall  the insulator board (after i  take another crack at cleaning and removing mositure) to see what's what.   The new caps are already installed (i just have to wire up the filter can).   

Hopefully will see  some improvement and then can start chasing down what other gremlins there are.   

[angelodp]

Maybe try Evaporust on the board, then alcohol and finally acetone. Did that on my Champ board and got all the DC off. It is true these boards will absorb grit it time and then might go conductive again. Oh, and stick it in the sun to get it real dry, with a weight on it.

[jeff_free69]

Thinking about the condition of the insulator board and what i saw peeking under the main board made me realize there's a lot more to be done here.  A deeper cleaning is called for.

To get underneath the main board I thought I'd have to unsolder at least a few things ,  like the but the 4 grounds on the brass plate.    But I figured out  a way to get complete access without unsoldering anything else at all.    By unbolting the front panel pots and jacks I was able to flip out the whole harness along with the brass plate.   

Gently folding it all back revealed the loveliness lurking beneath. 

Using dozens of Qtips I did a couple of  passes with copious amounts of isopropyl.  On the last one I hit with a heat gun (at a low setting)

Also did another drenching of the insulator board  and hit that with  the heat gun.  Put it under a weight while it felt a little more pliable.

I'll give it another pass and focus on the rust on the chassis bottom...

[angelodp]

Yikes, that's a bunch of rust....not good. You can get that all out in time.

[mresistor]

Yikes, that's a bunch of rust....not good. You can get that all out in time.

After its down to bare metal again it has to be treated properly ..  or it will rust again when exposed to humidity.  I would suggest Por-15 or something similar.

[Platefire]

Hey I been watching this one. I thought I had a lot of cleanup on my highly neglected and abused 1974 Pro Reverb head but your really going the extra mile to bring this back. The guy that sold it to me told me it would never work again unless you replace the board, but I guess I was determined to prove him wrong. So I hope this one works well for you after you finish the cleanup process

[mresistor]

Hey the solder joints for the cap can and other joints to the chassis requires a lot of heat, you'll need an 80W to 120W iron to get those done properly.   I use and great big old 80w Wall pencil iron. Also take care not to melt or damage components and wire around the joint when applying heat. I usually use some heavy duty tin foil doubled over and then create a heat barrier around those areas to solder.

[jeff_free69]

Hey the solder joints for the cap can and other joints to the chassis requires a lot of heat, you'll need an 80W to 120W iron to get those done properly.   I use and great big old 80w Wall pencil iron. Also take care not to melt or damage components and wire around the joint when applying heat. I usually use some heavy duty tin foil doubled over and then create a heat barrier around those areas to solder.

Yes, thanks.  just realized i wasn't completely clear in that i had already picked up the Weller 80W  (WLIRPK8012A).  Even together, my old 100W Radio Shack gun + modern 80W digital workstation dialed up 900 degrees  weren't hacking it.   
The Weller has the big fat tip for stained glass work, plus a screwdriver tip which is perfect for prying up the tabs once you get the solder flowing.  Worked like a charm.   I just haven't gotten around to soldering in the new can yet.   
I learned to keep some teflon oven sheets handy ( because i tend to focus on the tip and loose track of everything else )


I'll be making a few more passes of WD40 soakings and various scraping tools sporadically over the weekend.


I think i  have some silver Rustoleum on the shelf...

[mresistor]

Consider applying some rust converter prior to topcoating.  Here's some on the cheaper end of the spectrum


https://www.amazon.com/Rust-Oleum-Automotive-248658-10-25-Ounce-Reformer/dp/B003HG48AC/ref=sr_1_5

[jeff_free69]

scraping/cleaning is coming along very well, just about done

The Rust Reformer  looks like an excellent option.    But just to be clear, is this going to be appropriate only in the completely stripped areas?  Seems like its not suitable for galvanized steel (needs alkyd paint?)   and isn't that what the chassis is, except where the zinc coating completely rusted off?

I was originally thinking of taping off and spraying the whole area under the boards, but maybe i need to be more precise.

Now that i think about it, i recently redid my metal fence using Rustoleum "rusty metal" primer ( thick redish brown stuff)  its oil based and also not suitable for galvanized metal, but it would be  easy to paint in the affected areas,  then use  the silver paint.

Thanks for the metallurgy lesson

[jeff_free69]

Here's how she's looking down to bare metal.  Scratched the heck out of it , but patina under the board took a back seat to getting it clean.
I expected to see more damage, but it looks like there's just some pitting.

not sure how this affects my previous comments above ...

[angelodp]

Moving along. What's your next step? This amp is for you yes? On rusted machinery I have sandblasted to remove all rust then use a primer and then paint. Clear primer may be the ticket to seal it up as is and get back to making music. A labor of love.

[AlNewman]

You should be able to polish the nasty scratches out...  The patina is definitely gone, but there's no reason you can't get it shiny again.
Some sort of a preserver may be a good idea?  But it looks like you'd have to paint the chassis, which...  on the outside is fine, but the inside?  I dunno.
Normally amps aren't subject to that much moisture. 
Maybe just wiping it down with oil or something would suffice.

[angelodp]

Agree, maybe just a bit of polish and light wipe of anti-rust (WD or light oil). Less is more. It's not gonna get abused now so it should stay clean for ages. Looking forward to a sound take.

[jeff_free69]

thanks for confirming that any rustoleum paint is pure overkill at this point.

The more i look at the chassis here the less worried I am about it.    i  now realize all that rust which accumulated underneath likely dripped down from above over time.  And the pitting on the bottom is relatively minor.    Here's one of the original photos of the cabinet top with the rusty screen stapled to it.    of course  these conditions will never happen again.   Check out the rust stalactites!
   
I have a product called Everbrite that is a clear coating for metal.  I used it a few months ago on a brass mailbox and some door hardware, and its held up very nicely.    I thought about just coating it with wd40, but as long as i have this  think it is the way to go. 

 I did a couple more passes trying to polish with some higher grits of sandpaper.    IF the project is a success, no human being is likely to ever look underneath the insulator board again.    If not then a new board is probably needed, and a few scuffs wont matter.

[angelodp]

Crank that baby up.... but first. bulb limiter

[jeff_free69]

Got her all back together, all cleaned up (or at least as clean this poor old girl is going to get for now) 
 
After all the jostling i thought it'd be a good idea to reflow all the solder joints on the tube sockets and pots.

The tube sockets were tightened up and cleaned.

The boards are temporarily secured with some #4 bolts & nut (because they slide through without stripping the threads) .  The 2 original machine screws are rusty trash, so I'd appreciate it if somebody knows exactly what they are (and where to get them if they're unique/hard to find).  They seem to have a tapered tip and I'm guessing #6 , but with a low thread/inch.

Here's how the chassis bottom looks with the clearcoat .

Also took some closeups of the pots while they were dangling.  those 2 weird ones  ( Vol, Bass)  are hard to make out).     They've  all been DEOXIT-5ed several times over the past couple of weeks.

Tomorrow I'll do the powerup and test...

[DummyLoad]

https://darrenriley.com/homepage/fender-screw-php-zi-6-32-x-14-0038900000/

https://www.mojotone.com/Self-Tapping-Stainless-Steel-Screws-BF-Chassis-Fiberboards

Either is a source for the 6/32 screws.

--Pete

[angelodp]

Good sources - or just stock up

https://www.amazon.com/1000Pcs-Nickel-Plated-Phillips-Self-Tapping-Electronic/dp/B07HF46Q4R/ref=asc_df_B07HF46Q4R/?tag=hyprod-20&linkCode=df0&hvadid=693675560295&hvpos=&hvnetw=g&hvrand=9113095291155701964&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9061105&hvtargid=pla-571118526895&psc=1&mcid=7c908a653d9339e5af567711be3c135c&gad_source=1

[mresistor]

I usually use a tap to chase the treads then any screw will work, no need for self-tapping.

[bmccowan]

I think Doug has those screws right here in the parts catalog.

[jeff_free69]

Looks like I have a good update for you - Its actually making music ! (though  my playing is  rustier  than the chassis was).

I rigged up  my 2x12, 4 ohm TwinReverb cabinet and was happily surprised when the Strat rang out , loud and clear.
But there is that nagging hum, even with all the controls set to 0.  Maybe its just what's inherent to the design, and with 2 12's right in your face you're going to hear it

Miraculously the Volume and tone pots are quiet.

The only issue is the tremolo intensity seems to go full on  by the time you get to 2 .   Sounds really good , and the speed control is good.  But  its practically on / off .

Also kinda feels like there's a lot of gain.  I'm not familiar with the VC, but it seems to break up a little early.   not complaining, just assumed it would be on the polite / clean side
 

~~~~~~~~~~~~~~
The Bias is coming in at 12W  / 85% dissipation.   
I still have the original cathode resistor in there, and it measured  650 ohms (instead of 470)
Voltage across it is 22.5
Plate to cathode  measured 368V 

~~~~~~~~~~~~
Most of the other voltages are looking much more robust.  Before the cap update they were all pretty low.  Now they are higher than the  design calls for.    But considering the higher AC coming out of the transformer (line in  is 120VAC), i guess this could still be acceptable (?)

The exception would be the Tremolo 12ax7, which are actually lower than expected. so this is something that needs to be looked into.   I can try swapping some tubes - any other ideas?

For reference here are the latest

             Expected  /  MEASURED   
5Y3 
p4,6 red   315 AC  /   356 AC
p2,8 yel   355 DC   /  405 DC


FILTER CAPS       
320  /  375
340  /  395
355  /  405

6V6     
p3     342  /  390
p4     340  /  394
p8       21  /    22

12AX7  preamp
p1      205  / 224
p3      1.6   /  2.0
p6      200  /  240
p8      1.5  /   2.1

12AX7  vibrato (OFF)   ***
p1     210    /    180
p2       ?        /   1.6
p3        2     /  ?
p6      410   /    390
p7        210     /  180
p8        215      / 186
***EDIT : The expected values on the vibrato tube shown here are wrong; see below

[Lectroid]

...  But there is that nagging hum, even with all the controls set to 0.  Maybe its just what's inherent to the design, and with 2 12's right in your face you're going to hear it

The only issue is the tremolo intensity seems to go full on  by the time you get to 2 .   Sounds really good , and the speed control is good.  But  its practically on / off .

Also kinda feels like there's a lot of gain.  I'm not familiar with the VC, but it seems to break up a little early.   not complaining, just assumed it would be on the polite / clean side

As far as the hum goes, how's your lead dress?  Audio wires routed away from any AC voltages and HT DC.  Don't route near the heaters.  Do wires cross at right angles if they must cross?  Try a chopstick pushing on B+ wires. wires here and there to see if the hum level changes.

Tremolo intensity sounds like your intensity pot is a log taper.  If so, you might get a better range of control if you swap in a linear taper pot of the same value.

I wouldn't have expected a too-much-gain problem with that circuit.  Interesting.  One easy thing to try is to swap in a 12A_7 cousin for the 12AX7 in the gain stage.  This trick worked to tame a Marshall 1975 clone I built.  I currently have a 12AU7 in the first gain stage, and the range of overdrive vs. clean is much more manageable than it was with a 12AX7. 

12 AT7    µ = 70
12AY7     µ = 40
12AU7     µ = 17

Try a 12AT7 in the first position.  Play some.  You may find you like a different tube so you can adjust µ to your taste.

[dude]

That filament circuit in the VC is prone to hum, unless you convert it to layer BF circuit filament wiring, getting rid of using the chassis as the ground, the hum probably isn’t going away.

[HotBluePlates]

... But there is that nagging hum, even with all the controls set to 0.  Maybe its just what's inherent to the design ...

The hum is normal; it's not heaters or lead dress.

Look up the 5E1 Champ, and compares its power supply to your Vibro Champ.  You will see the reason for the hum in the Vibro Champ.

[AlNewman]

If your 470R cathode resistor reads 650R, try changing it out for a new part within spec.
That will bring down your voltages. 
I've had good luck with higher wall voltages by using a small value dropping resistor after the rectifier.  I've found if I can get voltages at the front end to line up with the schematic, the rest of the amp falls into place.

[dude]

The hum is normal; it's not heaters or lead dress.
Look up the 5E1 Champ, and compares its power supply to your Vibro Champ.  You will see the reason for the hum in the Vibro Champ.

I have a 67 VC, with a different SE OT (vintage 10 watt paper wound) and 10" alnico spk, only differences but I have rewired the filaments not using the chassis ground and have "no hum". OK, I did reverse the two dropping R's. Is the choke what your talking about in the 5E1, or the 8uf filters..?  You have 100 times more experience than I have, maybe it's the different OT I installed..? Or maybe the the 4th filter off the 5Y3, I installed..?

[Willabe]

Is the choke what your talking about in the 5E1, or the 8uf filters..? 

It's the choke BEFORE that feeds the OT CT.

Push/Pull power stages have natural noise cancellation that SE amps don't have.

So for a long time now, here and at other forums, guys add at least another filter cap and a low value B+ dropping R before what's already there. It works great. On new SE builds a choke works even better.

I built a Princeton 5F2a, Champ with single tone control. I used a Fender choke for a PP 6L6GC Fender amp for a pi filter before what's already there; filter cap/choke/filter. Amp is very quite.

The Fender PP 6L6GC choke can supply enough current for a SE 6V6 amp and it's preamp tubes. IIRC it has enough to use a 6L6GC SE and it's preamp tubes.

A Fender Deluxe PP 6V6 amp's choke is fine if you want to also add a 2nd choke for the screen supply node on a SE amp. It could be smaller but where do you find it easily?     

And a choke fro the screen supply. 

[jeff_free69]

Thanks All!
I'm going to try to live with the hum for a little while and get used to how she sounds.  When playing it wasn't noticeable.   I'm going to hook up the original speaker ( haven't tested it at all)

The hum reducing suggestions are still cooking in my mind, as I have the extra 20uF element in the can...  And I will also review the bias.


But I was thinking about the Tremolo situation. 

1) the voltages seemed lower than expected:   I realized I had wrong expected values , as i must've been looking at the AB version for that.   With the trem OFF, the values are now slightly above expected. 
 I also wanted to try measurements with the Trem ON   (which of course will vary  on certain pins) . When ON they go way higher .   So I guess this is a bit more consistent


12AX7  TREMOLO
        Exp  /   OFF  / ON
p1     170    /    180       /   10-260
p2       ?      /   1.6
p3       2     /  ?
p6      340   /    390       /  390
p7      170   /  180         /  10-260v
p8      175   / 186          /   10-260

2) Intensity.     I haven't swapped  in another tube yet, so will do that next session.  Any other thoughts on what to check ?  The obvious culprit looks to be the pot

[shooter]

When playing it wasn't noticeable.

I've built a handful of xSE amps, my "hum test";


IF it does away when I move the guitar volume from 0 to 1, it's not a problem

[HotBluePlates]

But I was thinking about the Tremolo situation. 

1) the voltages seemed lower than expected

If you hear trem when you turn up the Intensity knob, you're good.  The trem works fine.

The amp won't sound better when you exactly-match the numbers on the schematic (which weren't what I measured in a 100% stock 1965 Vibro Champ, either).

[Platefire]

be looking forward to the finish pixs

[mresistor]

Concerning the cabinet..  that shield screen is hideous..  time for some staple pulling.. also have to remove the carry hanlde IIRC.


Its also obvious that Leos bean counters had their eyes on staple usage - they sure didn't waste any securing the grill cloth.

[jeff_free69]

Concerning the cabinet..  that shield screen is hideous..  time for some staple pulling.. also have to remove the carry hanlde IIRC.


Its also obvious that Leos bean counters had their eyes on staple usage - they sure didn't waste any securing the grill cloth.

OH yeah, that rust collector is long gone!   Along with hundreds of staples   

Washed it down good, and only getting around to thinking about what to do about replacing it. 
Foil tape?
Would it even make a difference , considreing the internal  hum thats already in there?

[mresistor]

I've used and some manufacturers use the 3M foil tape and it seems to work well. Not very expensive and easy to try.
It's really up to you.

[Willabe]

Here's my Princeton 5F2a schematic drawing showing how I did the power supply and dc standoff voltage.