And now, for something completely different

 

This is a little outside the ballywick of this blog but it may be relevant for someone, and electrons were involved.  I have a 1976 Kawasaki KZ750B1 vertical twin which followed me home one winter day back in 2010.

I didn't work on it at all in 2011 but this year I decided I was going to get it up and running and evaluate its mechanical condition prior to deciding on a modification plan. The battery was completely defunct so I obtained another and found that the starter was very weak.
I got a set of starter brushes and earlier in the week I decided to tackle an overhaul.

To remove the starter one has to remove the alternator cover to access the starter sprocket, remove the two mounting bolts and the battery lead, and slide it out to the right with a little help from a mallet and a soft drift.


But wait! If that's what you do, you'll never unscrew the two long screws that hold the starter together. All you'll do is strip the screw heads. So do this before you unbolt and remove the starter like you should have done in the first place.

So get yourself a proper sized phillips head bit and a socket to hold it, a couple adapters and a half inch breaker bar or a good healthy speed handle. Dab some coarse valve grinding compound on the bit, seat it properly in the screw head so it doesn't slip, lean into it and tighten it a little-that's right, tighten it. It'll break the hold of corrosion and then it can be easily unscrewed.

While you were reading this it should have occurred to you to use this old aircraft mechanic's trick on all the alternator cover screws. Otherwise you'll just wreck the screw heads with that idiotic impact driver you bought. If you've ever had to pull the wing planks on a Falcon 20 you'll never forget this trick, and you'll be glad someone taught it to you.

When disassembling the starter pay particular attention to the illustrated blowup from the Kawasaki manual and where your shims are located and take pictures if necessary. When that little item marked 22 in the picture falls out

DO NOT THROW IT AWAY!!!!

Clean the parts with white gas a/k/a Coleman fuel and blow them dry. Then you can test the armature.  Once you've tested and cleaned it with emery cloth and cleaned out the schmutz from the commutator grooves you can put new brushes in and assemble that end of the starter.

Putting the drive end together is a little dodgy. It only goes together one way, the body and housings are marked with index lines, and number 22 gets inserted in the appropriate place in the proper direction. Make sure and grease the planetary gears and sun gear.

Now, you can reef those screws down because without adequate torque on them the sun gear will slip and spin around. Put a screwdriver through one of the mounting holes on the commutator end housing and position it against something solid like the floor. Then use your disassembly rig to tighten the screws up.

Lastly, test it on a battery, and if it runs install it and be happy. You'll probably find that the starter clutch is shot, too, about which we shall speak more anon.

Late model Twin Reverb bias modification.

Here's some info from my shop notebook. I'm working on a late model Twin Reverb that has an extra tab on the bias control pot with three things attached to it. There's the bias feed through a 3.3k resistor, an electrolytic cap with the positive to ground (it was an 80/75 so I ended up with a 100/160 number) and a lead going off to the vibrato pedal RCA connector center post.

After thinking about converting this to the more desirable level adjust and studying it a bit I went ahead and converted it as you see in the third sketch, the one in ink. Vacate the extra post, connect the supply, capacitor and vibrato pedal lead to the lower pot tab, the center tab now supplies bias voltage to the revised phase inverter setup, and the upper tab is grounded through a 27k resistor.

When you think about it, the extra tab on the bias pot makes it easier to construct the bias balance setup, but if you're only going for a level adjust it is unnecessary.

Major Hassle

Every once in a while something rarely seen shows up and that was the case with this Marshall Major. It's a 200w guitar amp head with a minimum of circuitry, kinda like a one channel Bassman with a 200w power section.

It's quite heavy and most of the weight is concentrated at one end which makes it awkward to move around. As a result I've got tennis elbow and a sore back after jackassing it out to the truck, into the house, out to the truck, back into the house for something I forgot, back in the truck and back to where it came from.

All that was necessary was to remove the so called "death cap" and disable the line reverse switch. The owner wanted it all documented so I took photos all the way along and put them on a CD for him.

It gave me a chance to dig out my AC43-13 aviation manual and brush up on my wire bundle lacing technique which I hadn't done since A&P school back in 1980. I had a spool of waxed lacing cord on my workbench courtesy of McDonnell Douglas, and it was a matter of a few minutes of happy reading to remember how to do the ties and knots. For safety's sake I put a little clear nail polish on each tie that was so tastefully executed.

Rationalizing a 1960 Vibrolux amp

This amp is the second in a trio of estate finds belonging to a friend of mine who owns a music shop. The first through the mill was a 1954 Deluxe about which more anon.

This amp is a May, 1960 5F11 Vibrolux that is in beautiful cosmetic shape but which has been hacked a bit. It's not ready for a clean bill of health yet but the patient did not die on the operating table. It has the original output transformer but the power transformer has been changed for something or other, and a 12" ceramic speaker has been installed in place of the original Jensen P10R.

This is but a preliminary report with pics to satisfy some catcalls from the audience.

After redoing the transformer wiring and removing a couple of feet of excess wiring, it needed an adjustable bias and some oscillator capacitors to get the vibrato working at its best. The sweet spot seemed like about 23 ma per side, and it works better if you control it with a foot switch.

Shit Happens, Don't It?

Folks, just a message from your friendly local neighborhood amp mechanic.

You're doing yourself a disservice if you're looking for a cheapish amp and you buy something for which the manufacturer will not provide support information to the trade.

It may be an orphan you bought on the cheap and you're not out much, but it may be something that looks good on the showroom floor but which the manufacturer does not, or more often, will not support out in the field.

 When it breaks-and what amp doesn't over the course of its life?-if your technician can't access the necessary road map-errrrrrrrr, schematic and list of components-you're faced with a choice of either tossing it in the trash, selling it for salvage parts, or sending it back to the manufacturer and taking what they are ready to give you and liking it.




Yes, I know it may be under warranty, but you've still got the logistics problem and we all don't live in New York, Los Angeles, Dallas, or Atlanta.

If it's not under warranty-a craigslist or ebay buy-and you can't service it locally it is just an expensive and useless piece of luggage.

Of course this rules out Blackstar, Bugera, Line 6 and probably a whole bunch of others. It rules in Fender, Peavey, and Traynor, all of whom are known for product support.

You owe it to yourself to find this out before you spend your hard earned dollars and not after the money's gone.

Retrofitting an Ultralinear Twin Reverb

This formerly ultralinear Twin Reverb belongs to a local fellow who acquired it in a curious way. Seems he's a journeyman steamfitter and he was working at a school in Bode, Iowa a number of years ago. He heard casters being rolled across a cement floor and poked his head out of his work just in time to stop the amp from going into a dumpster.

It seems the scientists at the school decided it had a bad power transformer, removed it, and then decided as it was too expensive to buy one that they'd dump the amp in the trash. So he got it sans power transformer and it sat for a few years until the work picked up and he could afford to get it repaired.

The ultralinear Twin Reverb was an uprated amp capable of producing a rated 135w, and they did it by using an ultralinear output transformer. This uses screen taps at about 70 per cent and the idea is that you can run the plates really hard and still keep the tubes alive. It yields clean, glassy tone that seems a bit sterile. But did I say they're loud?

And thereby hangs a tale. Power transformers for these things are a little unusual because the rectifier setup is different than the older Twin Reverb amps. It delivers more voltage because it is a full wave bridge, with a non center tapped secondary.

According to the good folks at Hammond the previous way of doing things yielded an average DC voltage of about .45 of the AC voltage and the ultralinear amp setup yielded more like .90 of AC voltage. So you can't just drop any old transformer in and hope to have a working combination.

The quest began, and the price for a replacement Mercury Magnetics power transformer was nearly three hundred dollars. Ouch!

I did locate a used one but the fellow first wanted a new Classic Tone (Magnetic Components) Twin Reverb international voltage power transformer and a new Classic Tone output transformer to go along with it in exchange for a used, single ultralinear power transformer.

I thought it was too much, highway robbery really,  and he dropped the demand for the output transformer-no doubt figuring he could use the one he had.

I still don't like the idea of being hosed for parts by strangers so I nixed the deal entirely and decided to find something else more suitable, as I'd seen used ultralinear power transformers on ebay  for around forty to fifty bucks.

Had he merely said at the beginning "I want $120 for my transformer" I would, in all likelihood, have gone for it. But that's the rule of life-ask for too much, try to take advantage of people and you're more than likely to get nothing for your trouble but some unhappy folks.

I then obtained a standard Twin Reverb power transformer used for a Grant and a new choke from Mojo and built a bias-rectifier eyelet board, redid the power supply capacitors and the necessary rewiring, converted the bias to a level set and revised the phase inverter circuit to standard and then......nothing. No output to speak of.

Measuring and reevaluating my voltages I came to suspect the ultralinear output transformer was the source of the original malfunction all along. I had a new Magnetic Components transformer  in house for another project and installed it.

Some minor tweaks to the wiring, relocating the bias control to a safe place, and other minor touches

Volume, lots of volume. Tons of tone and plate voltages right at a steady 450v DC.

Useful Things From the Past

Every once in a while you come across something that's such a good idea that you replicate it.

The item below was a promotional pencil handed out by the Gifford-Brown folks when they were still in the electronic components trade.
What it is, of course, is a tube tapper, although the rubber erasers had long since dried up and gotten as hard as granite. It's good for testing tubes for unwanted noise when installed and running. I guess in a way it proves that the problems in the service trade are not all new.

So I put together my own out of a couple of pieces of hardwood dowel that accept rubber cap erasers of the kind people put on pencils-although even pencils are fast becoming obsolete items that tend to confuse the young folks.

A pencil does not come loaded with high definition content and it will not log you onto facebook or get you in touch with your BFF. It will also not let you send a picture of your tackle to your girlfriend and then have to tell her parents and yours and an army of policemen that it was all in fun.

You're welcome to make your own tube knocker and I commend it to you.

On the subject of pencils, I kinda like them.

When I was a little kid in Miss LaPolla's first grade class I'd always get stuck with the pencil that had a busted up inner lead, and frequent trips to the Boston pencil sharpener were an embarassment.

There and then, I swore a dark and bloody oath-which is a funny thing for kids to do-that when I grew up I would have as many pencils as I wanted, and as many pencil sharpeners as I wanted so that I could have as many well sharpened writing instruments as I pleased.

Well. Here it is, fifty seven years later, and although many opportunities have escaped my grasp since then, this one can be checked off my so called bucket list. I have a lifetime supply of good pencils, cap erasers for the ones that are dried up, and a fine selection of Panasonic electric pencil sharpeners for every mood.

Every now and then I'll sharpen up an older cedar pencil, and the smell is enough to take me back to that classroom.

I showed 'em.