1965 Fender Vibro Champ Amp, low volume, What are some people thinking when they mod an amp????

 

This was a repair amongst many I did for Southside Guitars last month over a marathon 2 day period. Simple amp, somehow it took up more bench time than the rest!

You're looking at a run of the mill used 1965 "Fender Electric Instrument Company" pre-CBS Vibro Champ. Lovely little buggers. The first time I ever played one was at this guys apartment in the 80's in Boston. He used a TS9 Tube Screamer into it to record my guitar tracks when I was a Berklee student. I was pretty floored at how good it sounded. I think he had a reel to reel or one of those cassette 4 track machines we all had in those days, the Fostex X15 or Tascam something or another. 

Anyway. This one had very little volume. I popped the chassis and, well, you tell me what you see:

Yeah. Seriously. What the eff? That nice bit of lamp cord poorly soldered between the input of the volume knob directly to the 15k midrange resistor which goes to ground. So where you want to see up to 250k between you and ground, you get 15k maximum. I just don't understand what they were trying to achieve here! Did they put it together and say "Yeah, now that's the ticket to Hollywood baby?" 

Why didn't they just undo it? Ugh......

That was the first thing to take care of and while it helped tremendously, there were plenty of other bugs.

Always start from the back and go forward. The speaker was an old alnico full range 8 ohm job with a whizzer cone. That wasn't helping any so I just threw in what we had that day, a reissue 4 ohm used Jensen Alnico speaker. That helped but still, meh.... blah.... lackluster. No bass at all.

They had replaced every single signal capacitor with used / leaky weak caps that were also the wrong values. I used Mallory 150s and if you notice, I grounded the amp and used the .047 "Death Cap" at the midrange capacitor cuz, why not? Reduce reuse recycle! And those never go bad and have a special sound. 

I also replaced the tremolo caps with fresh ones as that was super weak and they had some weird stuff going on in there too. 

But still, no bass and pretty sad tremolo.

Cathode caps..... no bass, sad tremolo. Tremolo is just an LFO right? Better have fresh cathode caps to get it strong. In fact, just replace them already! This amp is 56 years old now.

After that I still wasn't happy though. Tremolo was working albeit, just not awesome, and the bass would vanish when you turned the treble up. Weird......

So upon closer inspection I noticed the tremolo intensity pot was dated 1966, but no indication of the ohms. They always say 25K RA. So I pulled it and measured the thing. 500k. WRONG! 

I dropped in a 50k pot since that was all I had on the shelf. Those 25K reverse audio pots are hard to find. The 50k pot isn't correct but it did make the tremolo work better. With the 500k pot there was almost no tremolo until you got up to about 8. So, while not satisfied this would work. I could also bypass it with a 47k resistor to make a fake 25k pot. I don't like doing this but in a pinch it does work and only the rabid amp fanatic can usually tell.

But that treble control bit was really driving me bananas. The amp still seemed weak too. So I then figured if the Bozo that modded this amp changed that tremolo pot to something so wack, maybe they changed a tone pot.

They didn't. The tone pots are the original 250kA pots dated 1965. 

So I checked the volume pot. Lo and behold, it was the 25K RA Intensity pot I needed! Captain "Wha? TechNo No No" used the 25k pot and scrapped the 1Meg pot that was in there. I took that 25kRA pot and put it where it belonged and threw in a new CTS 1 Meg volume pot. 

Now we're cooking with grease...... GREAT tremolo and GREAT tone!

The power transformer was replaced sometime in the 70's with the correct part. I did clean up the wiring there too. Come on folks, twist those AC lines already!!

In conclusion. I do not know what this person was trying to achieve with the mods they did. If they were trying to make the amp play with little volume, why not just turn the volume knob down? I imagine they may have been trying to get more tremolo so they used that 500k pot. Nope! 

If you do not know what you are doing then please consult someone! Otherwise a fella like myself can spend hours undoing your ill conceived ideas. Seriously, ask. Most of us are happy to share information....

J

1964 Fender Deluxe Reverb. Re-capped but still too much hum. What can I do?

 Here's the desert island amp for many of us and I think after all these years I'm one to be on that island myself. A really clean 1964 Fender Deluxe Reverb. 

About the amp: Transformers are original, speaker was replaced with a Celestion G12M greenback 30 watt. I'm a fan.... Amp was re-capped well enough. All of the electrolytic caps were top shelf expensive Sprague Atoms. Some of the work wasn't exactly tidy but done well enough.

But, I just didn't like the amount of hum I was still getting. I right away saw some things to improve. First is the bias supply cap:

Whoever re-capped this amp went with the original value. I mean, why wouldn't you. That's what Fender used in 1964 so.... 

Nah. When I worked for Jeff Bober in 1994 he just told me to upgrade it to 100@100v rather than 25@50v. I've been doing it ever since. Better regulation and less hum. I do not detect any change to the sound of the amp and I have well trained ears. And for what it's worth Fender upped it later to 70uf then 100uf cause they could. Caps got a little better. So just do it. If you think that's blasphemy try it anyway and put the old value back in if it freaks you out.

Yup, being dramatic here but I'll share a story. I once had a client who paid me to convert an AB165 Bassman to an AA864. That's no small task. Big job. I made one mistake and one executive decision. He took the amp home and inspected the work under a microscope. The next day I had an irate customer who brought his amp back and he (understandably) expressed his trust had been burnt. So I gladly changed the one pot value that I missed to the correct one. But he was really upset about my little executive choice: using a 100@100v for the bias supply. I explained to him why I did this: with a 25@50v cap it will hum. He didn't believe me one bit and I could tell I was losing his business.

So we gave it a listen, I then replaced it with a 25uf cap.... HUM! And not a teeny tiny difference. It was significant enough that he heard it and looked a bit embarrassed. He asked me if it would make a tonal difference and I said no but if he thinks it does bring it back in a week. I put my little 100uf cap back in, fired it up and he was happy with the quiet. I never saw him again. All is well that ends well!

So here ya go. Use a pretty blue Philips Vishay cap if you will! I like them cause they look nice and European:

But wait! We're not done yet. Amp was much improved but I still wasn't 100% satisfied. This next part involves the signal caps.

If you have been inside as many old Fender and other high quality amps you'll notice even the signal caps have a direction. No they're technically not polarized like an electrolytic cap is, but there is a direction you want them to go in. The have an inside foil and an outside foil. Some old caps like my favorite Ajax blue capacitors you find in Fender amps even tell you which side is the outside foil.

Rule of thumb: always have the outside foil closer to ground. In other words, if one side of the cap is on the 100k plate load resistor and the other is connected to the 1Meg volume pot, outside foil goes on the 100k resistor. Fender almost always got that right! I've only seen a few exceptions. 

Another example is the tone stack. The .1 bass cap goes to a 250k pot and the .047 mid cap goes to a 6.8k resistor. On the other side is the 100k slope resistor then the 100k plate load resistor for a total of 200k. So the bass cap should have the outside foil attached to that slope resistor and the mid cap should be going the opposite direction with the outside foil connected to the 6.8k resistor on the bass cap. Like this:

The phase inverter has three .1 caps. Two are connected to the plates of the 12AT7 while the third is connected to the grid. On the plate load side you have a 100k and an 82k resistor going to each plate. On the other side you have two 220k resistors going to the bias supply. So the outside foil goes to the plates, inside to those 220k resistors. The third cap however is connected to a 1meg resistor on one side and a 47 ohm resistor going right to ground on the other side. So that cap goes in the opposite direction. In this case the previous owner used my least favorite cap, the Sprague 715P. No indication for inside or outside foil so you just read it from left to right. It will look like this:

Notice how the print is going in the opposite direction.........

Here's the dry channel tone stack. I had a spare old polyester orange drop cap that has a stripe on it for outside foil. The mid cap you'll notice reads left to right with the left going to the 6.8k resistor. If you are experienced you'll notice the .047 600v blue Ajax cap for the final stage. Sadly entire channel was orange dropped. But I have a bag of .047 Fender "Death Caps" from the AC balance. I never throw these out when I ground an amp. I save them for classy amps like this one!

One cap backwards will not make all that much of a difference but in this case I counted 5. It adds up. In the hundreds of old Gibson and Fender guitars I've seen over the years, the tone caps are almost always done in this arrangement: outside foil to ground. If the good people at those companies were sticklers for such a detail on the treble bleed cap, there's something to it.

So there you have it. The amp behaves like my own '69 model now. Quiet! Of course it's not possible to eliminate all hum and noise but it is possible to reduce it using these little steps. And the less noise the more music dig?!

Thanks for reading, hope this was helpful and feel free to leave a comment of ask a question below! J

1979 Fender Vibrolux Reverb with tremolo issues. Should I charge more for silver panel amps???

 Here was a mess.......

Fender 2x10" Vibrolux Reverb circa 1979. When it came across my bench it had your typical noise issues and one nasty "bumpity bump" from the tremolo circuit. 

Once I opened it up the first thing I noticed was someone had done a rather half assed job at a black panel conversion (AA964 circuit.) So I figured I may as well complete the job. I changed all the elecrolytic caps first which helped but there was still that tremolo issue. Curiously enough it  was far worse when you turn the reverb up! So I started by eliminating that boost circuit, which takes away a length of wire that is about 8" long traveling from the reverb transformer output to a switch on the back of the volume pot. That made a little bit of difference, less wire generally equals less issues. But that didn't knock out the problem. 

Sometimes this problem is as simple as changing the tremolo tube or the "bug" network (the photo cell neon bulb thing) or just putting a .1 cap across the bug from the 10M resistor to ground. This was already standard factory goodness by then and the amp had that, though they used a .01. I upped it to a .1.....

Next I noticed the 2.7k cathode resistor and the 820 ohm resistor were opposite of where they were on a black panel amp. The 2k7 resistor should be on the left closer to the tremolo tube and the 820 ohm resistor should be on the right closer to the reverb recovery / mixer tube. That made a sizable difference. And it came that way from the factory. I next changed the cathode cap on the 100k resistor on the tremolo tube to a 4.7uf. That helped too.....

But, I like things to be close to perfect. When you turn up the reverb it still did the bump like my parents did in 1978 at the disco in Germany. Cool for the dance floor though they were told to "get a room" by an English fellow.

So what to do next? 

The silver panel amps can be cantankerous. They're just not that well made. The foundation is there: great transformers, hand wired, this one retained the 5u4 tube rectifier, but they just used things like cheaper wire. I've had noisy silver amps that I literally needed to change the wire to get the noise level down.

In this case it became clear to me they just used too much wire! Lead dress is important. 

I mean, look at this jive:

An experienced tech can see the problem. The wires on the tremolo tube are way too long and crossing the wires on the reverb recovery tube! This is factory wiring folks from the CBS days. So I proceeded to shorten the wires and move them away from one another....

That knocked out the problem. I wound up shortening the leads throughout the amp. Overall, it lost about a foot + of wire!

I cannot imagine this isn't a problem that developed with time. The wiring was all factory and the amp has been played hard for the last 40 years. I'm stunned to see that no one attempted to correct this issue before, or maybe the previous owners never used the tremolo circuit. That's plausible. Tremolo isn't for everybody.

So now this amp is ready for proper use. It's got a great sound and I feel good about it going to a new home. When I had my own shop I'd roll my eyes whenever a 70's Fender came in. Most were okay, straightforward, but many were challengers. 

So hopefully this post will help another tech out. Do look at the lead dress. There was a good amount of haste in those days at Fender. I mean look at a 1979 Stratocaster. My first guitar was one and it was terrible. Seriously a sad, heavy, careless piece of corporate lack. This amp is better than that guitar, they were just five dollars away from making both well but chose to cut corners. Fortunately this amp is now terrific cause amps are easier to transform! My poor old guitar will never be good. I didn't feel bad giving that one away years ago!

JB

1965 Fender Showman amplifier. Killer bass or guitar head.

When I was in high school I had a cousin named Bryan. He had issues with telling the truth. But while I didn't trust him I loved the cat anyway. He wasn't a blood relative, just my god brother.

One day he showed up to my house with a Fender Showman, property of the Baltimore City Public School system. Yeah, he stole it.

But whatever. I'm sure they didn't notice it. The amp was missing tubes, badly neglected much like Bryan and that school system. It just needed help.

I was fascinated with the thing. I just wanted to get it working. I opened it up and shocked the hell out of myself on the still charged filter caps. It had power just no sound.

So I found a few tubes for it at Radio Shack and got some resistors that matched. I'm not sure if I even knew what a resistor was in those days. One just was burnt so I had to match it. Yes, Radio Shack in the Columbia Mall sold tubes! Good tubes. Not the crap made today.

I got it working. I remember it sounding like it was underwater, not in a bad way, it was just so warm.

Thus started my fascination with tube amps. And my fascination with the Fender Showman. I think I traded that chassis in on something I bought at Angela Instruments a couple years later. Early on when Steve had his shop in Savage Mill, or maybe in his house. Those were the days!

I did buy a working one when I was in Berklee. I used it for a while. I think I was fascinated as well cause a Marshall Plexi was intimidating to me. A Marshall seemed like an exotic nuclear power source. Yet, when I watched Jimi play Monterrey in the film, he had his Marshall and a glorious Showman amp too. Seemed more manageable to me.

So this one was from Indigo Ranch and had been sitting neglected for a couple or more decades. Simple re-cap, re-tube and there you go. I replace the (either 500pf or .1000pf) cap that feeds the phase inverter with a .002-.005. We're using the amp for a clean 80 watt bass amp. The Showman is 8 ohms, whereas the dual Showman is 4. I prefer these.

Such a beautiful sound......










Old caps. It's dumb but on an amp like this I re-use the sleeves cause they have the dates on them. But folks, do change the filter caps. It's just stupid not to!




Did the usual. New grounded cable yadda yadda..... Transformers are all original and this amp is no longer sad and neglected, its cutting tracks once again at Sonic Circus in Vermont!

J

'65 Deluxe Reverb Re-issue. This offends me!

 Today we have what I consider to be one of the best values on the marketplace today: a good ol' Fender '65 Deluxe Reverb reissue. Classic design, perfect club amp for those who like the black panel Fender sound. 22 watts of power through a pair of 6V6 tubes. There was a time when if I had a dozen original ones in my store they would be gone in a month. Everyone seemed to want one about 15 years ago. Now the watts war is in reverse and that honor goes to the Princeton Reverb. Those sell effortlessly enough that Fender made a re-issue of those as well. I prefer the Deluxe myself.

  So hopefully my headline got your attention. These are great amps but there are a few things about modern construction that just bum me out. This one was dead, no big deal, just had a burnt 6V6 tube. The fuse didn't pop so the 470 ohm 1 watt screen grid resistor burned up. Again, no big deal.

  In the old amps Fender put the 470 ohm screen resistors on the tube sockets along with the 1.5k grid stop resistors. To cut cost they put these on the circuit board. When one burns up, and it is a dramatic burn, it makes a mess. Here is the socket:

And here are the burnt resistors on the board:

So first step is to cut those resistors out and clean up the board with sandpaper and compressed air. Get as much of that carbon out as you can.

  Next I bypass where the old resistors were. I also bypass R60 & R61, the grid stops. I will be moving those to the sockets as well. Why? They should be on the sockets. They don't always work when they aren't. Why risk that? I've seen it happen before, having them on the board doesn't prevent oscillation at high volumes. Simple fix.

  Now admittedly, I'm cutting a corner here too. The proper way to do this is to remove the board and remove the resistors, then replace them with a solid piece of wire. Do as I say, not as I do. This does add time to the job but we are on a budget and this works just fine.

  Here are the re-wired sockets:

  Notice I moved the orange from pin 4 to 6 and put the 470 ohm, now 2 watt resistor between 4 and 6. I also moved the green wire from 5 to 1 and put nice sounding carbon composition 1.5k 1/2 watt resistors between 1 and 5. This is how they did it in the glory days of amp building.

  Now if a tube blows again, there is less mess to clean. I feel better about the whole thing. Not to mention, if we were to put those screen resistors back there they were, the next time they burn, they will burn a whole through the board most likely, then we'll have a real mess! Prevention is easy on these amps. Do this and save yourself trouble down the road!

JB