Weirdorama From The House Of National Dobro

We give you, without comment, the National Dobro Model 31.

Saving Money The Old Fashioned Way

Ever since my last Ampeg fiasco I've been looking for an amp-any amp-with a line in line out feature that was cheap. Did I say cheap? Above all cheap.

The Ampeg mess began with a VT22 that was bought on the cheap by a local fellow, I suspect because nobody could repair it down where he got it from. After fielding the numerous curves it threw my way-no filament voltage on the phase inverter, bad tubes, one of which died on the operating table, a number of burned resistors, sick electrolytics etc, and testing every god damned component on the preamp and power supply boards, I was in the 9th inning and wondering how I could declare defeat gracefully.

By the by, there are four different schematics for the VT22, they're all somewhat different so if you are working on one, it is best that you figure out whether you have the right one for your project.

In a last desperate bid I decided I needed to test the preamp and power amp sections separately and I borrowed an amp-a Blackstar head-which had a line in/line out feature. This allows you to take the preamp signal of one amp and run it into the power amp of the other, and vice versa-thus isolating a problem to one section or the other of the corpse on your workbench.

As it happened both sections worked well enough but they were not talking to each other, and the problem that caused all this emotion and wailing was a bad ground on one of the line out jacks.

So much for the Ampeg. It's gone.

Now the quest began for an amp-any amp, but cheap, with line in line out, with no results. On a whim I strolled back to where I keep my junkers and found a Randall RH50 tube head that I'd bought for spare change a few years ago, the kid said the volume was low, and there were the line in line out jacks that I'd wanted. I'd stripped the tubes out of it and had tried with no luck to dump it as a project amp and then forgot I had it.

A set of tubes later, and I had no filament voltage-which was a good thing because it took me right to the filament fuse inside. One fuse and a plateful of junk tubes from my stash of pulls  later I was in business with a functioning piece of test equipment that doesn't sound half bad.

Of course the volume was low. It never worked at all.

Kid, it woulda cost you ten bucks to fix and if you want to buy it back you know where to find me.

How To Profit From Planned Obsolescence In The Computer Age.

I've got an elderly Dell desktop workstation named Edgar in the shop that I use for schematics and some basic internet browsing, and lately it has been running painfully (excruciating, really) slowly.

So I decided to reload the operating system, not without a few hiccups, so here's the score on how to avoid paying Microsoft-again. In my case I did not want to cough up a hundred bucks or so for a copy of Windows 7. In a philosophical sense, calling something a "workstation" when it's used in the office for fooling around on the internet is something of a puzzle but nevermind,

As a point of information Microsoft says it no longer supports XP but there are ways, my friend. Inside many cash registers and ATM machines resides a computer running XP, and there is a registry hack that is supposed to convince Microsoft that your computer is a cash register in a bar or an ATM at a casino. Either way I haven't bothered monkeying with it yet.

When Microsoft comes up with the message that says "You're screwed. Buy a new computer with Windows 8 and stop with the whining willya?" just ignore it. Let google be your accomplice.

The only caveat here is availability of drivers for equally elderly devices. The update to Windows 7 compelled me to obtain a new scanner to replace an equally good one for which drivers could not be obtained. Thanks again for adding to the growing mountain of e-waste, Acer and Microsoft. 

As it happens I'm ahead of the game all over this because we already got a couple of hundred dollars in a class action settlement here in Iowa-didn't you know it, Microsoft was overcharging us all?

In any event this computer started out with parts from my Dell computer that went to Goodwill a few years ago (memory sticks) parts harvested from a defunct TiVO recorder (hard drive and DVD drive), parts from Newegg and the now defunct CompUSA chain (internal hard drive, Western Digital standalone hard drive and DVD drive) a case with a motherboard, power supply, Pentium IV 2.8 processor and a floppy disc drive from Iowa State University surplus sales, and a Viewsonic 21 inch CRT monitor, all of which got me to about $150 over the course of six or 7 years. I still retained the OS disk from my Dell that went to Goodwill.

I also have a large box where I store all my spare cables, parts, software and miscellaneous stuff I've acquired over the years. It pays to save the stuff.

So, I redid the boot sequence as required, started a clean reload and all went well. They didn't even ask me for a product code so maybe they think I'm Iowa State University or maybe they don't care anymore. Either way you take your pleasure as you find it.  Installing the Linksys software for the wireless receiver took a couple of tries with different CDs before it took hold when I used an earlier version 4.0 of the software.

The big problem was that my OS disk was a very primitive installation, and I had to next install service pack 3. To make a very long story very short, you can get it from Microsoft for free (it's the version for network administrators) and put it on a DVD yourself. No other third party source will work properly as I found out.

Once you get a good working copy of service pack three, you can load it and then proceed with retrieving at least 133 updates, which took a couple of hours. I loaded the usual stuff for viewing images and documents-Adobe Acrobat reader and MS Office 2003 complete with product code, thanks to a former employer who shall remain nameless because they're world class asshats.

This morning I installed a nice flat panel display courtesy of Kevin Neal's studio, which predates USB ports but I did have an RGB cable ready to go-remember that big box of obsolete crap?

I may see if I can up the memory some more. Right now it's 2gb but it is cheap because it's obsolete.

Cheap and Cheerful: The Peavey Delta Blues 115

Those who know me know my weakness for anything with a fifteen inch speaker and a nice set of tubes. So I had a Delta Blues 2x10 here for some repairs last week and when repairs -of which more anon-were completed I liked the sound enough to go and hunt one down in the fifteen inch configuration, which arrived today. The idea of spring reverb, vibrato, and a 15 inch speaker was one I couldn't pass up for $380 all told including shipping. Quite a value considering that they're about six hundred or so new.

A little more experimenting with it should tell me whether it's a keeper or not.

The Delta Blues has the same chassis more or less as the Classic 30, and thereby hangs a tale. They're known for needing to have the tube socket pins resoldered because they're kind of weak. This is a bit tedious because of the way that the three (yes, three) circuit boards are connected with bare wire and folded into a U-shaped configuration. Here's what I mean.

As I recall this one had some problems with filament voltage not getting to the right place, and a little rework because the solder joints with the connecting links getting loose because of the amount of flexing I had to do to make the needed repairs.

The new-ish 1x15 amp arrived in very clean condition with a cover and some unnecessarily heavy duty casters which I will save for another project. Some of these amps are known for acoustic feedback through the reverb tank, but this is not one of them. It does have a very slight hum, and if I ever get the notion to take it apart it'll get some nice new F&T electrolytics. In the meantime I shall try some different preamp glassware.

Stay tuned.

UPDATE: The date of manufacture of this amp appears to be circa 2004, and the background hum was accountable to a brand new preamp tube. Mr. Hickok said no, so in the trash it went. . If you're so inclined, give homage to one Job Barnart, who patented the Hickok tube tester mutual conductance circuit in 1935 and founded an industry.

UPDATE 2: Wouldn't you know it? A week after this arrived I stumbled over a 1971 non master volume Twin Reverb for a great price so the Peavey is gone-at a profit too.

The Panther Tank And The Engl 530

From the fine folks that brought you the Panther tank-a great gun and frontal armor but cursed with a bad transmission, a gas guzzling engine that had the life span of a mayfly, and final drives that would puke if you looked at them crosseyed-where was I?

Oh. I remember. A friend of mine brought in an inoperative Engl 530 tube preamp-a nice piece of gear, but one in which the product support borders somewhere between weak and nonexistent.

The power transformer looks like a brick, but without all the endearing qualities of the said brick. The 6.3v filament circuit that runs the two 12AX7s is defunct. No voltage is forthcoming.

Over the last few weeks I have emailed Engl, the Weiss transformer people in Germany, and the alleged distributor of Engl parts in the US and what's uniform about all of these is that they do not respond to their email or phone calls. In fact they've treated the owner the same way.

A week or so later I managed to reach someone  at Weiss and they said no, they didn't have one in stock and they were having a hard time getting anyone over at Engl to respond to them. A (former) Engl repair center in California informed me that they'd stopped dealing with Engl because of similar parts hassles and the owner had two Engl amps deadlined for parts. Thanks for the good words, Jens. Velvet Distribution has not returned calls or emails at this date.

Maybe Engl could build a nicely designed product like the Panther, but it's no wonder why they couldn't move the ball across the goal line.

Donald Douglas said it best. When one of his design engineers came up with some super spiffy design for something, Douglas would impatiently say "Yes, yes, that's all very well. But how will it do in Peoria?"

That's something the Engl people ought to consider if they want to sell more than the odd amp or two here in the colonies.

From the Compression Ignition Department: Biasing a Diezel Hagen

It's rare that I have an amplifier in the shop that is more expensive than my 2002 Ford Ranger pickup, but this one arrived for a bias reset the other day.
Diezel is a smallish German builder of high end guitar amplifiers, and the Hagen is a 120w, 4 channel number with high gain characteristics that endear it to the metal crowd. That's not exactly my cup of tea (or stein of lager, for that matter).
The Hagen is often criticized for its numerous pots, but it's rather simple when you think it over-each channel has its own EQ, master volume and gain controls. Do your chosen setup on all four channels, flip the small toggle switch and you're right where you want to be.
Did I say it's well built? Everything about it is precise and well fitted, and the layout of components and wiring is organized with Teutonic thoroughness and attention to detail.
Unlike a lot of gear out there from various builders that's built down to a price, this amp is built up to a standard and it is user friendly. Top grade components abound, and the chassis is made of folded .060 steel with resistance welded end caps.

Setting the bias is a simple affair, if a little time consuming.

The KT77 power tubes are numbered T1, T2, T3 and T4. The fuses for the power tubes are  T1 and T4, and T2 and T3.
The instructions for setting the bias level are printed on the circuit board in English no less. So here goes.
Power up the amp with a suitable connected speaker load and let it warm up for fifteen or twenty minutes.  The volume and gain should be set at minimum. Then shut it down between steps of biasing
1. Remove the tube fuse for T1 and T4 on the back panel.
You will see the two bias adjust pots and three test points as shown above.
2. Using the pot, adjust to 70 ma between the MPA and MPG test points.
3. Shut down, replace the fuse, remove the T2 and T3 fuse and power up. After the amp stabilizes set to 70 ma between the MPB and MPG test points.
4. Repeat this procedure three times.

As you can see it takes a little time to let the amp stabilize and to get everything warmed up properly. There is a tendency for new tubes to drift a little.

I checked the plate voltage which measured out at 476v, and consulting the Weber bias calculator, 70 per cent dissipation looks like a few ma more than the factory limits called out, which means it's conservatively rated.

Remember, this information is purely informational and there's no warranty express or implied by you misusing it. If you don't know what you're doing here take your amp to a qualified technician for any adjustments.

Burned Up With Cement Resistors

One of the less endearing features of Fender's Deville and Deluxe series amps is the low voltage supply. Let me explain.
In order to operate the solid state devices these amps contain, it is necessary to supply -15 and +15 volts. Fender did, of course use a dedicated winding which is good because some amps like the Valveking piggy back their low voltage supply off the filament winding, and a shorted tube can wreak havoc on those solid state devices if it burps and backfires.
However, Fender chose a brute force solution to reduce the voltage down to the required level and that was the pair of cement resistors you see. In many cases such as this HR Deluxe, the circuit board can get some significant burning and in some cases the solder can melt.
I got this fix from Andy Fuchs, the New Jersey Amp Wizard, including the picture of the Arcol resistors.
It consists of getting a couple 15w 470 ohm Arcol resistors at about $3 each from Mouser. They are then mounted to the chassis with 4-40 screws and nuts, the original cement resistors are carefully removed so as not to damage the pads (easy to do), and the resistors are wired up as if they were on the circuit board.
After reassembling, these resistors transfer any heat generated right in the handy dandy heat sink of the chassis, and are barely warm to the touch.