Measuring Your Voltages: Why To Do It.

A relatively new Blues Junior III came in the other day because it wasn't making any sound....not a peep.

The first thing I did after testing the power tubes was get out my trusty multimeter I got from Horror Freight and started measuring voltages on the power tubes. Lemme see, plate voltage OK. Bias voltage OK...where the hell's the screen voltage?

Dave's not here, man.

It seems that  R47 (I think) the 2.2k 2 watt resistor in the power supply string had failed open kinda like a self activated standby switch.

From there it was a couple of hours work to crack it open, get rid of the Illinois power supply capacitors and replace the suspect resistor.

It powered right up and all is good.

The point is, measuring voltages is the first thing you do. Had I not done so I'd probably still be throwing parts at it in a random fashion hoping that something would stick or give me a clue.

When Vintage Was Vintage part III-Unobtainium Pots

I completed the Peavey Vintage today and surprise of surprises the reverb actually worked with a 4EB tank installed.

But first there was the problem of the pots. The volume, treble, bass and presence pots were all bad enough that the usual methods of cleaning were of no avail. There was a loud thump about half way up on the bass control, the presence control was pretty much jammed up with a bunch of Duco cement or other fine adhesive, and all this would cause some uncomfortable symptoms when monitoring current.

The pots were pretty conventional except for the method of attachment to the circuit board as these were some sort of primitive snap in controls. I thought about it for a while while I was pulling the board and then I had it,

I took a few resistors and cut the leads off them, removed the offending pots, cleaned out the holes, bent a right angle in the wire lead and soldered them to the board. Then, these leads could be inserted into a conventional Alpha pot of the proper value, soldered up, and then the surplus wire was trimmed off.

Perfect!

So if you're working on one of these old bombs, there's your fix.

Here's the rest of the innards with two nice new 6C10s.

How's it sound with a nice fresh set of JJ 6L6GCs?

Clean and loud. The reverb's not as wet and drippy as you might find in a Fender of similar age but it is reasonable enough considering. I think I may locate a set of new jacks and install them to lower the noise a bit-some nice plastic Cliff jacks might just lower the noise threshhold a bit.

Now all that's necessary is to scratch up the cash for a cabinet and this one can go in the Done file.

El Roacho, or, Secret Sauce Debugged.

I've been toying with the idea of rolling my own Fender style vibrato optocoupler devices for a while now, and a suitable test bed arrived the other day.

It's a Deluxe Reverb Reissue of the '68 Custom variety, and I have been trying out a couple of upgrade transformers to see if I could boost the output a modest amount. So I figured it was a suitable candidate for some roach research of the corksniffer variety.

What do I mean by corksniffer? Read on.

A while ago there was a fellow down in Texas who allowed as how he had discovered the secret formula after diligent experimentation and research into the subject.

He called it the "Surf Bug" and sold quite a number of them for about twenty bucks a copy, until he sadly passed away and, so 'tis said, took the secrets to the grave with him. He did business as Tonecraft Amplification.

After that there was the "Black Widow" bug that was being sold by Austin Amplifier, or so 'tis said although I do not have anything current on the situation.

According to the savants on the TDPRI discussion forum both these operations are out of commission-or maybe one, or maybe operating on some astral plane.

You can read all about the alleged secret sauce mojo here.

Well. I am about to rip the lid off this entire subject. The secret sauce dies here.

I autopsied a number of known working vibrato roaches, and did not learn much of great value. The dark resistance is so high that my multimeter couldn't measure it anyway. 

I obtained a number of GL5537 and GL5537-1 photocells.on fleabay the why pay more store, and a number of NE-2 neon bulbs. I made up a couple of test articles and put each one in the package with the relevant photocell. Of course they slipped out of the packages so I don't really know which was which.

They both worked fine, and the results are a slightly smoother and less choppy vibrato that sounds a bit more like a tube modulated vibrato. Attached are a photograph of the first article and a shop sketch.

In addition there is a photograph I found of what are supposed to be five new Surf Bugs.

I can't tell the difference.

I fully expect that I will be lambasted by people who just want to believe the magic sprinkles and the existence of secret sauce.

Perfectly all right says I. Bring on the bashing

When Vintage Was Vintage, Part II

After a thorough recap and some fresh tubes the Peavey Vintage is up to its old tricks-loud and clean.

Power supply capacitors and all the small electrolytics on the board were replaced, as were all the film caps except two tone caps which are pretty low voltage stuff and not excessively overworked.

To get it running and test everything and set the bias all I had in the way of compactrons were a pair of 6K11s which drop in but don't have much gain in the right places. I will have to hunt up a pair of 6C10s or 6AD10s. Also on the shopping list will be a volume control, bass control, and presence control. I may just replace them all if I can find suitable replacement stock.

 I'll post some pics and internals  and an extended commentary as I do not think anyone has written anything about these rarely seen amps.

Tube pin cleaner.

If you take a stainless steel pot scrubber or a copper sponge and stick it to the inside of a plastic cup with a dab of hot melt it makes a fine tube pin cleaner.

Take your tube and jab it into the scrubber a few times and all is good.

Reverb Resuscitation

A friend of mine brought over a nice old Fender 6G15 outboard reverb unit today and as I had my nose slightly out of joint over other matters (social media drama) I hid out in the laboratory.

This friend has a knack for acquiring stuff on the cheap and this was no different. It had a bad habit of blowing fuses, and when it was brought up on the variac it was drawing about three times the normal current.

The fix was simple, and this seems to be my week for dodgy old electrolytics in power supplies.

A refresh of all the consumables and a new power cord and all was well.

I did find that it is susceptible to ground loops as it developed the granddaddy of a hum in the living room. I soon figured out that it was on a different circuit in the house. Plugging it into the same outlet as the Cowpoke quieted things down and it'll go home tomorrow or the next day.

When Vintage Was Vintage.

What you see here is the progress so far of a two or three year quest.

I'd been reading a piece by Hartley Peavey, the Mississippi amp wizard, and in it he discussed the 5F6A Fender Bassman and how he was inspired to cook up an all tube, 100 watt tweed Bassman with reverb.

Here's a page where he discusses that. I do not think he will mind.

"So" says I to me, "What could be better than an all tube 100w tweed Bassman with reverb?" and the search to locate one started.

In between all that I built a high power tweed twin knockoff which I am still not entirely happy with and I will get to it presently.

So I'd been searching on Craigslist and fleabay without ever finding a good all tube Vintage. There were a couple but one was pickup only in the great state of Oregon, and one was a wreck in Tennessee that the owner still wanted a lot of money for. And then there was the Peavey faux tweed, which is something nobody wants.

Anyway....this amp showed up on fleabay as a bare chassis, no tubes, and it seemed to be in pretty decent shape. A deal was made and it arrived here Saturday, no glass, power cord cut off, the whole works.

It's in good enough shape cosmetically although a few of the resistance welds are broken, but that is what me and Mr. Miller are made for.

Mr. Miller is a Miller MiG140 welder that runs on household current and is good enough for everything up to 3/16 steel plate.

But the overarching consideration was to do enough to power it up and see if it held up or whether one of the transformers was finished, and that required a recap with some of the good stuff from the House of Fischer and Tausche in the great nation of Germany.

But never mind that for now.

I just finished that job and installed a new power cord, fuse holder and strain relief and flipped the switch-running through the variac of course.

It held, by G-d. The plate and screen voltage without power tubes was about 525v and the filaments look happy.

So there it is. The plan now is to repair the cracked welds on the chassis, and order up a head cabinet in blond tolex with a wheat grille.

Stay tuned.

UPDATE: I  decided to try repairing the cracked chassis spot welds with JB Weld epoxy. I cleaned everything with alcohol and an emery board, mixed up some JB Weld, spread the chassis where the welds had come apart, fed it in with a cut off zip tine and then clamped it tight. I'm letting it sit for a few days while I attend to other matters such as figuring out what sort of cabinet to order and polishing up the faceplate.

Stay tuned.