Bandmaster Build part 3

I finished the chassis a few days ago and road tested it on the bench while I was setting the bias. I lugged it upstairs and slapped it into my friend's 1955 Super cabinet that was vacant at the time and gave it a whirl. It sounds good, nice and quiet and clear tone. Metal film resistors are good for making a nice quiet running amp I think.

 I won't know how it really sounds until it's run through the three Weber alnico Signatures that were provided with the kit.

It was worth taking all the extra time to double check every connection on the board and each flying lead because I was not going to take the board out again.

Fact is, I'm trading a D'Evil for a Weber 5E3P Proluxe I used to own, and  I've already got a board half built and stuffed for a conversion to octal preamp tubes. Somewhere in this blog there's some information on how to make your own boards and drilling masks, and install and clinch eyelets.

Now, if the weather warms up a bit I have two tweed cabinets to shellac and tone.

Bandmaster part 2: Wiring The Backside Of The Board

Once I had the components dry mounted on the front of the board it was time to do the back side wiring. For the uninitiated this is the wiring that  is sandwiched between the insulation board and the back side of the component board, and there are more than a few wires. They've got to be installed and soldered to the eyelets unless you want to take it all apart again.

But what to do? The Mojotone manual has a picture of what it should look like more or less but I was not really satisfied with it. Then the solution came to me. The Weber layout diagram image was acquired on my computer and reversed so it showed the hatched lines for the back side wiring as if I was looking down on it from above.

Here you can see what I used to run the back side wiring.

Once the wiring was run I finished soldering up the components and the flying leads. At this point I did not know how long they'd have to be so all of them were 12 inches long. It required an order for some more Stewart Macdonald yellow waxed pushback wiring.

Taking the layout diagram and schematic I then made a map of every termination point on the assembled board and checked every lead for continuity and arrival at the proper destination. Some of the wiring came out from under the board but I moved it to the top for ease of maintenance should it ever need repair. Here's one fellow's assembled board which I used as a model.

And here's mine, installed in the chassis. It's not quite as pretty but taking the time to validate every connection for continuity and proper hookup paid dividends because  it worked as advertised when I powered it up. One thing i did not want were screwups that required a disassembly.

Once the board was in place all it required was stitching up the connections that I had tagged according to the map I made. As I had already wired up the controls and power supply previously, once I wired up the inputs and speaker jacks it fired right up.  With a 5R4 rectifier and a pair of 6L6GCs from the House of Ruby, I got a measured 430 plate volts and set the bias at 40 ma.

The next adventure will be when the weather gets warm enough to coat and seal the tweed covering and final install the chassis.

Building A Tweed Bandmaster part 1.

The tax man was berry berry good to me this year so I decided to spring for a Weber amp kit while I still had the dough. To tell the truth I'd been thinking about doing a tweed Pro for a while but scraping up the cash to do it was always something of a problem. So after some looking around and comparing price to speaker area I decided to build the 5E7 Bandmaster clone, mostly because it was the same price as the Super and cheaper than the Pro. It had one extra speaker and a cabinet that can accommodate a fifteen inch JBL if I ever latch onto one.

With shipping the entire kit cost me $661 even and it arrived in about three weeks. Inspection revealed that they'd shipped it with a Heyboer power transformer  ( a nice touch) but that someone at the cabinet shop had jackassed the handle significantly.

Weber doesn't provide any technical information, I guess they figure that if you're not smart enough to figure it out you'll soon learn without a lot of handholding. It's a midwestern point of view which I happen to approve of. All the components looked pretty reasonable except for the pilot light assembly, the octal sockets and the wire. As it happens I had enough good stuff to replace these items. Whaddya gonna do?  It was three hundred bucks less than the competition.

The folks at Mojotone publish their build manual for the tweed Pro which is about the same thing so I was covered there. Weber publishes a nice layout diagram and thereby hangs a tale.

After some thinking about it I proceeded to start by dry mounting the components on the eyelet board. That took a few minutes.

Cool Tool Alert Straight Offa Grandpa's Workbench

Every once in a while you get an itch you just have to scratch.  I saw something in the back of an old electronics magazine circa 1957 which featured, among the cool new products, the By-Buk bending block which is made so that you can take axial leaded components such as capacitors, resistors, diodes and the like, and bend their leads to register accurately to meet the holes that up until then have remained vacant.

I soon found some plastic ones-bending blocks they're called-that cost about $14 from China.

Of course I went to fleabay, the why pay more store, and by searching for By-Buk and bending blocks, came up with a By-Buk number 700 bending block, and this dawg is built for a lifetime of heavy service. No plastic here, no sirree. This is made from two solid blocks of aluminum properly machined-you can barely see the lines from the fly cutter on the angled parts, and two hardened steel guides plus a nice set screw to keep the whole thing organized.

The one in the magazine was something of a deluxe model with what looks like a microstop adjuster for  exact and professional dimensioning.

The cost, shipped, was about $20.00.

The By-Buk Company of 4326 West Pico Boulevard in the City of Angels surrendered its corporate certificate in 1974, and is thus no longer with us.  A little more tooling around the googlesphere reveals that one Homer Buck was one of the partners in the By-Buk operation, and they successfully sued the Printed Cellophane Tape Co. for theft of their trade secrets. It seems that Mr. Buck was something of an inventor as well, as he had several patents to his name. It's likely the same person as appears in the 1940 census living in Los Angeles.

More's the pity, too. It's sad that we can't purchase things like this across the counter these days.

Mr. Buck, wherever you are, you did a good day's work.

SJ12T schematic

Another In A Series of "Close Cover Before Striking" Moments

This is a Weston Model 7145 bench digital multimeter which I obtained as sort of an homage to The Old Man, who'd worked for Weston about thirty years or so before the new owners, Schlumberger,  decided they didn't need him, or anyone else, or the factory and research labs in Newark New Jersey. He never got over it.

The picture, from 1906, didn't look all that different except that some of the slant roof glassed in assembly halls were removed to make way for a new office building in the 1940s I think.

But I digress. This was part of a line of digital test equipment that Weston introduced shortly before it's demise, and when it popped up new in the box on fleabay I had to have it. It was mine for about thirty dollars.

I powered it up the other day and saw in the display what you see-looking like missing parts of numerals. So today I decided to clean up the edge contacts on the LCD display. I took it apart enough to get access to the innards, popped the display out, squirted it full of juice and reinstalled it. It looked exactly the same. Then, some deep seated brain cell inside my head which had been waiting for this moment for years unleashed its voltage load to the mainframe and I stopped. A few minutes was spent looking for the manual-it's in my shop somewhere. At a loss, I turned the device over and there, as you see, are the display notes and rather than being 0009 with missing segments it reads ORNG-for range.

Good thing I was by myself and didn't have to answer to anyone for wasting an hour in another close cover before striking moment.

Straight Outta Yellville-The Ampeg Jet Reissues UPDATED

I've recently acquired two, and disposed of one, of the Diamond Blue series of Ampeg amps produced by St. Louis Music in the mid nineties which, we are told, are part of the URI a/k/a Updated Reissue series-reissues that have the look of older Ampeg amps but have all new circuitry.

There are four models that I know of-the J12R and J12T, and the SJ12R and the SJ12T. The J12R has the standard volume/treble/bass/reverb layout, but the J12T has volume/tone/speed/strength/reverb control setup.The -R series amps cater to the overdrive types but do not interest me much.

It's tube modulated vibrato, so why anyone would not want that is beyond me. I snagged a J12T off of fleabay for a good price, upgraded the reverb tank with a Mod tank from AES, and then passed it on to a happy person to use in church. It's cathode biased, 15w, uses a pair of EL84s and is a pleasant companion to pass the afternoon with.

I decided I had to have its big brother the SJ12T -alleged to be 50w with a couple of EL34s but more like 30-and soon had one here with a few quirks. The  rivet holding the terminal block on the speaker had broken so it was a small job to get rid of  the remains and install a new pop rivet. It's a nice big Ampeg labeled Eminence speaker by the way.

More seriously, the reverb sounded stinky and thin, and the vibrato was an on again, off again proposition. In addition there were random crackles and spits and pops.

The cabinet is wide enough to accommodate a 17 inch reverb pan so in one went, and things got better.

Replacing the plate load resistors is pretty easy because they're all on the tube board and easy to get at. That helped with the spitting but the vibrato was still dodgy, and then it quit altogether.

Studying the schematic led to the indictment of the J112 JFET in the vibrato circuit, after I'd replaced everything else because it was open and I had the parts. Installing the JFET cured most of the vibrato problems but it still crackled when the vibrato strength was turned up. This seemed to be related to the first preamp tube which is also the vibrato oscillator. This morning I tried a 6072 preamp tube which sounded fine but the vibrato failed to function. As I'd just tried a JJ and a Sovtek 12AX7 and still had the crackling in time with the vibrato, I dug into the archives and found an oldish Bugle Boy which had come from my brown Concert.

It was just what the amp doctor ordered. Now, I can get all the vibrato I want without crackling.

UPDATE: This did not solve the problem. In a day or so it was back with intermittent operation and crackling when the depth was turned up past a quarter. What to do?

I pulled off the back cover and removed the molex connector that links the foot switch board from the chassis. I still had the problem but found that monkeying around with the cable could shut the vibrato off completely or induce random crackles. If the foot switch board and foot switch were connected the LEDs on the foot switch could be made to flicker or shut off entirely.

So today I had a few spare moments to dig into it and the molex connector looked like a likely suspect. I removed the main board and resoldered the molex connector to the board. I then gave the board a lookover and resoldered all the joints that looked dodgy-there were a few, particularlyu on the ribbon cables.

I powered it up and all seems to be well, so far.

Internally the amps are simple and easy to work on, the traces on the board seem pretty healthy, and they've got the look. There's no secret sauce, channel switching, high gain doodads and so on. At 400 volts on the plates they'll last forever, and the tone is nice and clean, not buzzy and fizzy, and enough volume for smallish clubs. I got mine for $300 in minty condition, and the Jet II came for $250. The price is right for a nice medium weight amp with a classic look.

One thing I do not like is the small blue pilot light so I figure a regular jewel style pilot light with a green lens will do the Ampeg thing just fine.

And if they ever explode there's plenty of room to build something more traditional.

If you have one and you're wondering where to get a schematic, if you email Loud Technologies-the current owner of the Ampeg name-and give them your serial number and let them know you own the amp, they will send you a schematic.