Friday, January 20, 2012

Bustin' Caps With Victor

In my continual quest for better, low priced test equipment I've been using an IRT-2 Insulation tester as described in an earlier post for determining whether capacitors-particularly the wax paper and foil types-are fit for continued use.

It's an important thing particularly in the case of plate coupling caps in the final stage of an amp, where a smallish amount of leakage-measurable in microamps-can shift the bias point of the tube enough to cause it to be seriously overworked-red plating is also part of the mix. The IRT2 has done a workmanlike job but suffers from the problems of analog stuff in that unless you can get the right range, the precision reading will escape you.

I started searching around and found a number of insulation testers on fleaBay, which range in price from inexpensive on the low end to ridiculously priced lab equipment. I didn't feel the need to pay for lab grade precision with lab grade prices.

Enter the Victor.

It's a digital readout insulation tester from the Shenzen Victor Hi-Tech Company with three test voltages and the ability to measure AC voltage up to 750-a nice feature.

For our purposes we're using the 250v, 500v, or 1kv ranges, and with the two position range switch we can read from 0.1 to 20 megohms or 20 to 500 megohms at 250v, 0.1 to 50 megohms and 50 megohms to 1000 megohms at 500v and at 1kv, 0.1 megohms to 100 megohms and 100 megohms to 2000 megohms-a substantial increase in range from my trusty IRT2.

It came in a nice box with a set of batteries (a big plus, in my opinion), test leads and alligator clips, a carrying strap, and a cover for when the device is not in use, and an instruction manual written in Chinese. It took a little bit of head scratching and a trip to the Shenzen Victor website (http://www.china-victor.com) to suss out the connectors and how to use the beast. However, the fit and finish is very good, the display is large and bright, lighting up on test, and the ranges are good for what my purposes are.

It's evident that the Shenzen Victor people put a lot of thought into this tester and did a very nice job at a good price, shipped for around sixty bucks. Rather than the generic QC passed white sticker this one came with a card with the part number and serial number, the date of manufacture, and the inspector's stamp on it in ink.

Here's an old Sangamo capacitor on test, showing a resistance at 250v of about 79 megohms give or take. At higher voltages, of course, the leakage rate is likely to be higher. Some work with my usual poly caps and some Orange Drops will yield a range of useful figures.

It's well worth the price of admission because you can also use an insulation tester to check transformer windings or any sort of circuit for high resistance shorts.

Props to the good folks at Shenzen Victor. They're doing a great job of putting serviceable, modestly priced test equipment in the hands of people like me.

Wednesday, January 18, 2012

More Capacitor Testing Adventures


Having an ESR tester around the shop is a useful thing when it's time to start looking at the electrolytic capacitors in an amp. I had been using my ESR Micro 3.1, made by Radio Devices in beautiful downtown metropolitan Tver, Russia about which more later.
All was going swimmingly until I went to test a capacitor that had an open ground and was thus chock full of juice-the ESR Micro 3.1 popped and although this is supposed to be an easy fix the diodes and 100 ohm resistor that are supposed to protect the innards seem OK so I figure one of the ICs is gone....where was I?

Oh. I remember. ESR, or equivalent series resistance, is a good metric for checking older electrolytics. The idea is that as a capacitor deteriorates over time it will build up internal resistance that can be used as an indicator of condition.

Well. What to do?

I didn't have three weeks to get another from Mike Klykov although I think I may anyway, so I ordered this ESR tester off of Amazon that came for about $50 shipped.

Of course it's made in China, and of course it has the obligatory "QC passed" sticker and of course it didn't work right. It wouldn't zero but occasionally could be persuaded to go full span if the panel was pressed on. I guess that's what passes for QC in China.

So there I was, faced with the prospect of boxing it up, shipping it back, and screwing around for another couple of weeks.

I figured it was worth a try to fix it, so I whipped the back off, removed the circuit board, resoldered the tabs on the zero set trim pot, shot the pot full of contact cleaner, and put it back together.

Now, I can put my own QC Passed sticker on it because it works just fine.

The MAT Electronics MUL3333 ESR tester is an analog meter contained in a substantial case, large enough to hold the 6 AA batteries you're going to need. It comes with test leads which I shall modify with alligator clips. One thing I like about the ESR Micro is that needles are soldered to the alligator clips, making it easy to poke through the lacquer and get into a trace.

The instructions are pretty straightforward even if the translation into English is a little strained at times. It tells us that the internal frequency of this device is 66khz, and from what I read this is an AC ohmmeter with an internal power source.

Electrolytic capacitors ESR tends to increase over time as the electrolyte dries out or the integrity of the seal is compromised. If the ESR value rises, it is the first sign of a capacitor that's on its way to glory. It's a worthwhile test for any shop bench, and if you're like me and can't afford a Sencore LC3, a simple tester like this is the way to go.

We're going to give this tester a run for its money and we'll have a fuller report. And we'll still order another ESR Micro 3.1.

Wednesday, January 4, 2012

Further Adventures in Capacitor Testing: The IRT-2 Insulation Tester.

When you are in the amp repair business on any level you soon progress from slinging a handful of orange drops at whatever strolls in the door to trying to do some real component testing. With non-electrolytic capacitors that usually comes down to figuring out ways of determining whether the leakage level has become unacceptable.

Why should this matter? Leakage in a signal capacitor gets the wrong kind of voltage in the wrong places, and it can shift the bias point of a tube enough to, in some cases, cause a meltdown. I was first introduced to this when rehabilitating a Fisher 500c integrated receiver amplifier a few years ago. One of the four 7591s was getting a sullen red glow in the plates after some time operating, and it was leakage of the blocking capacitor between the plates of the phase inverter/driver and the power tube in question.

Another reason is that in vintage guitar amps we don't want to replace anything that does not need replacement, lest we be accused of not knowing our trade, shotgunning parts because we don't understand the problem that presents, or worse, mining out vintage parts from our customer's amps and reselling them on fleabay-which has happened to my knowledge.

Well, sometimes it's a chore to fire up the Sprague TelOhmike, the special purpose direct reading capacitor leakage tester I built here a while ago, or something spendy like a Sencore LC3 if you should be so lucky.

Enter the IRT-2 insulation tester. Like many of its ilk it is a high resistance tester used by the refrigeration trades that can suss out high resistance shorts in entombed electrical equipment. It does this by a small power supply that can pump out up to 1 kv of ac at very low currents. It's quite enough to test the windings of transformers on the bench for high resistance shorts, but it can also be used, as is shown here, to test capacitors for unacceptable levels of leakage. As a practical matter, anything less than 200 megohms at 1 kv gets rejected here.

Pictured is a red paper Astron showing about 10 megohms resistance-far too low for my comfort and thus it makes a detour into the waste basket.

My IRT2 was obtained for five bucks at an auction of the estate of an old refrigeration and electronics man. A set of batteries and I was in business.

I'd advise against using a crank operated megger for this purpose-too many hands going in too many directions at once even though they do look cool. Good serviceable digital readout insulation testers are available for about fifty bucks shipped from the PRC, brand new with batteries at the usual place and I may get one if I can find a reason.

The Last Mystery: Unraveling The Standel 25L15

One of the last great mysteries of the musical world can be posed as a question: "What's inside the Standel 25L15?".

It's also a question that may soon be answered, although if Bob Crooks, the creator of the 25L15 was anything like Leo Fender, there were a lot of changes made along the road without a whole lot of documentation.

Here's what we know about it:

The 25L15 guitar amplifier was developed and built by Bob Crooks in the early 1950s. It's unusual in that it used 807 output tubes instead of the more commonly available 6L6 variants. As was common in those days, it was probably seen as good practice to put the power supply in the basement and the preamplifier stages upstairs. This arrangement could certainly cut down on crosstalk between the power supply and the preamplifier.

Crooks also used a JBL D-130 speaker, and it was probably the best choice for high volume, distortion free reproduction that could be had in those days.

Probably the mojo's in the preamp and tone circuitry and that's been the subject of much speculation. I've seen at least two schematics that are alleged to be 25L15 clones, but one of them is, according to Ted Weber the Hoosier Electronics Wizard, "not even close." Ted is contemplating releasing what he calls the Pennebaker 25, and if he does, then the cat will be well and truly out of the bag because he is a fellow whose veracity is unquestioned.

A fellow named Bill McKenna has also produced a schematic on DIY audio that you can obtain and read with jschem, a freeware utility.

Much of the speculation centers around the circuitry and its relationship to the Williamson circuit that was popular in the old days of high fidelity. That may well be so, although I cannot vouch for it and nobody who hasn't seen an original 25L15 circuit laid bare on the autopsy table or has an original schematic can.

We also know that production of the 25L15 by Crooks was very limited. There were maybe 100 or so built and they command astronomical prices on the rare occasions when an authentic one appears on the market. According to the list maintained by the good folks who are reissuing the 25L15, most of the originals are unaccounted for.

There are a number of people around who say they've reverse engineered the original 25L15 (as the people in California allege) or that they've reproduced it in some way, but they're bound to silence by a dark and bloody oath.

One thing's for sure. There're some rumblings that may well let this cat out of the bag. Then, and only then will we see where the mojo is hidden.

Further Adventures From The Tonal Fringe: The Baldwin Professional "Willie Nelson" Model

Here's a chunk of vintage solid state gear that followed me home the other day for a rather modest fifty bucks.

It was crusted with the remains of a million Marlboros and Camels, and it stank up the cab of the pickup all the way back home. A couple hours scrubbing, a bottle of 409, and a roll of paper towels later this is what was revealed.

It's a Baldwin D-1 Professional guitar amplifier with-a drum roll, Maestro-Supersound, which consists of five different voicing selections that can be used singly or combined with the standard voicing.

It's an interesting piece of gear, and it dates from the early days of solid state amplifiers. It was hand wired on perforated phenolic boards, which seems to suggest that the production was pretty low. I've never seen another like it.

It was made by the folks who make Baldwin organs when they took a brief flyer in the amplifier field in the heyday of sixties guitar mania.

Tonally, it's smooth and mellow, and getting clear tone requires something with single coil pickups like a Telecaster. No humbuckers need apply. The nonoriginal speaker's nothing to write home to mother about but a Weber Chicago has been obtained from Gregg Levy and will arrive soon. That alone ought to provide a quantum improvement in tone.

The vibrato is lush, but the reverb is a bit of a disappointment. It's adequate, but that's all. Overdriving the preamp with a Tubescreamer is better forgotten about and yields little improvement of the kind that can be gotten with similarly smooth sounding tube guitar amps.

It is said that Willie is enamored of a Baldwin that he is known to use, and I can see why. It's easy to love and makes no great psychic demands.

Output? Allegedly 75w peak, which really means 25 or 30 on a good day when all the planets are in alignment.




Rollin' With Bone


I figured out how to get the CD player working in the Ford Ranger this morning and loaded in T-Bone Walker: The Complete Imperial Recordings from 1954.

I do not think there is much to top tooling down the highway listening to the blues.

What do I mean?

Give ear, o ye multitude.

Koko Taylor

Fixing Stuff, or, How I learned To Stop Worrying And Love The Transistor


A journeyman musician of my acquaintance left a Music Man guitar amplifier here for repairs and I finally got around to digging into it last weekend. After some routine maintenance type repairs that any 30 year old amplifier would need, I figured I couldn't avoid troubleshooting any more.

The procedure for setting the power tube bias voltage level is to measure the voltage developed across the two resistors in the picture and adjust the level with the potentiometer that is in the tip of the picture.

Doing this revealed that there was no voltage being developed on one tube. Releasing the circuit board from captivity revealed that one of the bias transistors had a broken lead.

At least I had the common sense to order up some integrated circuits and bias transistors while I was dithering over what to do.

It works great.

KittyHawk M5 Gut Shots: The Area 51 Report

Seeing as Sean Huston's Blues Deville is going out on the road here, I decided it was time to start refurbishing the Kittyhawk M5 you see here.

This amplifier is some kind of ultimate orphan, as very little is known about them and the German manufacturer is long since out of business, as far as I know. I do have a partial schematic and I can probably figure out the rest. Some voltage mapping will be in order, and then eliminating the patented plastic "DestructoPots".

If the power transformer is capable of it, it might be fun to plug in a couple of the new JJ 6V6S tubes, as we hear they're more robust and capable of delivering an improvement in wattage.

If you've got any information or documentation on this amp, please send me an email.




We Make What We Make When We Make It And We Can Call It Whatever We Like



We are, of course, referring to the newly released Vox AC15C, and thereby hangs a tale.

The star-crossed history of the AC series of amps from what we'll call the Vox people is pretty well documented in several nice coffee table books, the most recent by Jim Elyea for which I've yet to scrape up the C-note that it'll cost to get it here.

When the Jennings empire folded after an ill advised toxic marriage to the Thomas Organ Co. in the US-a classic case of brand dilution that many a business school MBA ought to take note of-the manufacture of the flagship model AC30 passed through several owners with a gradual decline in build quality until it was naught but a shell of its former self.

When the Korg people picked up Vox in the mid nineties, they set about rehabilitating the brand, using the signature AC15 and AC30 as leaders for a line of forgettable modeling amps that are suited for lesser tasks, but the AC15 and AC30 retained much of what people bought them for.

When Korg reached the ultimate decision to move production out of the UK, they moved it to a factory in China owned by something known as the IAG group-a vertically integrated facility that actually makes a lot of the components that were used in the AC15 and AC30 Custom Classics as they were known. Although built on a printed circuit and incorporating solid state reverb drive and vibrato, they held true to the original Dick Denney inspired dual chassis build.

According to Denney and Peterson's "The Vox Story" Denney built the prototype AC15 on a standard box chassis but realized that they couldn't take a pounding on the road. Ordinarily the answer would be to build on a steel chassis but because the amplifier is high gain, that presented a risk of undesired hum and oscillation. Denney's solution was to put the power supply on a steel chassis and the higher gain stages on an aluminum chassis attached at a right angle to the power supply chassis-all of which served to reduce crosstalk and made the resulting chassis robust and easily serviceable. Air circulation and overheating was always a problem however.

Apparently there was some sort of a falling out between Korg and the IAG Group, as evidenced by the departure of Steve Grindrod, the designer of the Custom Classics, to employ with Wharfedale, an arm of the IAG Group, and the departure of AC15 and AC30 production to an as yet undetermined production facility.

The new amps are being made with MDF cabinets rather than the Baltic birch plywood of the IAG built amps, no more Wharfedale speakers (fancy that), but what's notable is the layout and construction of the chassis, which appears to be a much more production oriented, reduced labor setup. The two chassis approach is gone, perhaps for good.

Which brings us to the ultimate question: When is an AC15 not an AC15 even though the people who make it and are entitled to the name call it so?

We haven't yet seen gut shots of the new improved AC30C, but if what we see here is a portent, it's going to be quite different.

Photos courtesy of ampaholics and oddjobpeters, whose PM bounced.

Sorry, man, they said you don't exist.

Big Joe Has Come and Gone




Did you ever have one of those moments when you're looking for something but you don't really know what it is, and then you hear it? Guitarists do this all the time, and they call it looking for the sound inside your head.

Me and Big Joe-we're like that.

Joe Turner was born in Kansas City in 1911, which would figure large in his musical evolution. Kansas City was a juke joint, barbecue, boogie woogie piano town like no other that has ever been.

Folks from Chicago may cavil and protest, but before Chicago was, Kansas City is. Los Angeles and New York City never were, and the only city that compares is New Orleans.

The music reflects the city-and while New Orleans is all weddings, parades, and funerals, Kansas City was all business when it came to music.

Joe was never a singer of country blues as many other bluesmen were, because his roots were urban and fixed in the time of pre war big bands and boogie woogie.

His blues wasn't hip and urbane like T-Bone Walker's was, or tongue in cheek like Louis Jordan, but its grit and power is unmistakable, like the roar of the daily nonstop 747 from Los Angeles to Paris that struggles off the runway, rattling windows for miles around.

A big man at 6'2" and north of 300 pounds, his music projects like some primal, unstoppable force that drags you kicking and screaming to your feet.

By the time rock and roll came around in the fifties, Joe wasn't a teenager any more and although he had some songs that made it onto jukeboxes, other folks like Bill Haley mostly made the money.

Bill was no spring chicken either, but a galvanized cowboy singer and deejay who knew a good thing when he heard it, and ran with it.

Joe was, in the end a product of the prewar era and his time had come and gone-at least for a time, until an new generation of people like me rediscovered him in the back shelves of dusty used record shops in out of the way places.

I have this mental picture of Big Joe leaning against his brand new Hudson Terraplane looking sharp in his suit and snap brim fedora, thirties all the way.


More Judybox Revival






Sometimes you stumble over something, and as you follow the trail, an entire new world is revealed. People who dig quirky guitar amps are no different, and that led me to the Judybox-partially because it's named after my wife. I decided I had to have one.

The story's quirky. The amps were developed by Al Nelson down in Austin, Texas about six years ago or so, and that's where you'll find most of them. A pretty big splash was made at the 2006 NAMM show which was held in Austin that year, and from what I read on TGP and other forums, the wheels started to come off the project soon after. Deposits were taken and whether they were returned or anyone got amps is anyone's guess.

Suffice it to say there were and are a lot of unhappy people in the Austin area who'd ordered amps and didn't get them.

There are stories of illness and mismanagement, a transfer to shadowy investors, some or all of the assembly being done in China, and that's pretty much where the story ends, in 2007.

The registered address of the business, 8804 Chisholm Lane, looks a lot like a residence with a stable out back. It's owned by a gentleman named Stanley Phillips and has been in his hands since 1972 according to the Travis County Assessor.



Entity Information: JUDYBOX, INC.
8804 CHISHOLM LN
AUSTIN, TX 78748-6378
Status: NOT IN GOOD STANDING
Registered Agent: AL NELSON
8804 CHISHOLM LANE
AUSTIN, TX 78748
Registered Agent Resignation Date:
State of Formation: TX
File Number: 0800639464
SOS Registration Date: April 10, 2006
Taxpayer Number: 32019547028

Well. What's the story on this orphan?

It's cathode biased, two channels each with its own volume, bass and treble, and reasonably well equipped although looking like it was done in a bit of a hurry. There are no identifying marks on the transformers which look a bit Asian. There are extra taps on the power transformer that could prove interesting.

The tube layout is conventional: 5AR4, 6L6GC, 6L6GC, 12AX7, 12AX7, 12AX7. The voltages are relatively low, with a B+ of only 369v and 309vAC on the legs of the power transformer. Some of the fitments are a little cheesy-the pilot light and power inlet socket are pretty much low grade schmutz plastic, and shot, but overall it looks pretty decent.

Sound wise, this amp does clean in a big way, and it's got a nice deep bass tone that's right for single coil pickups, particularly P90s. The original speaker's been replaced with a Celestion Super 65 that gets the job done well.

Where the story ends, I don't know. If you've got some information feel free to post a comment.

UPDATE 4-7-11
Since I wrote this piece I've been doing the work required to get this amp in serviceable condition and here's what's been done so far..

I replaced the pilot lamp assembly with a military surplus item that the original looked like it had been copied from, got rid of all the ceramic resistors except the cathode resistor, replaced the electrolytics with suitable replacement values, and went up to the hardware store for enough hardware to cook up proper standoffs. This required modifying a few holes and drilling others, but now the board is level, well supported and not preloaded at all.

When you think about it, the screen resistors and grid stoppers do not need to be 5w ceramics, and the dropping resistors do not need to be 10w. 7w and 5w ceramics. Fender did just fine for the last sixty years without that stuff. Plus, smaller resistors make for a cleaner installation and that's the look I'm going for.

Even as we speak the UPS man is supposed to be bringing me a new power socket to complete the job. Then, I can reassemble it and survey the grounding.

One interesting thing I found was the control pots-they're all linear, made by Cosmos Tokyo and very nice looking stuff. I shall try and find a source.

Judybox Revival





I finished up the Judybox Revival amp and powered it up today. It got topped off with a nice set of vintage Dakaware chicken head knobs I'd been saving for a special occasion.

Here's what I did to it.

Replaced all the ceramic dropping resistors with a 3w metal film, a 2w metal film, and a 2w carbon comp.
Replaced the ceramic 5w screen and grid resistors with 2w Dale metal film and the grid resistors with 1/2 w carbon film from Rat Shack.
Replaced the pilot lamp assembly with a Fender item. This was broken
Replaced the power receptacle. This was broken as well.
Replaced the 40-22-10 e'lytics with 47-22-22 450v items
Replaced the three ceramic octal sockets with bakelite.
Installed 5 standoffs of the proper length to support the board level and not preloaded.
Revised the ground scheme to a star ground setup
Replaced the chassis screws with new stuff from the hardware store.
Installed a smooth plate Tele in the first position.

How's it sound? About the same-bright and sparkly with a lot of depth on the bottom end. Sounds a lot like an AB165 with the bass and treble dimed and the switch on bright.

The builder used Tocos (Tokyo Cosmos) pots-very good stuff-but they're all linear. I may change them out for audio taper, at least the volume controls. All the connects from the pots to the board are shielded wire. I didn't see a nfb resistor but maybe it's there somewhere. I'm thinking that the first two preamp tubes share a common filter capacitor, because if they did not there would be four and there are only three e-lytics. Both preamp tubes have small electrolytics on both cathodes.

I don't know whether I'm qualified as an expert-I'm in the middle of doing a schematic layout and a bill of materials and when I'm done I may be an expert in which case if you find this drop me a line.

I am in a position to make some recommendations in order of importance.
Ditch the power receptacle and pilot light for something good.
Install proper standoffs to support the board and level it out.
Dump all the ceramic resistors except the power tube cathode resistor. They look stupid.
Revise the grounding to a star grounding common-it was strictly from hunger.
Replace the octal sockets with bakelite, Beltons, or military Amphenols

If you've got any questions about this amp, drop me a line.

Sherwood 84-22





I acquired a Sherwood 84-22 a few years ago in a state of disrepair-deshabille might be more like it-and some stinkiness about which more anon, mostly because I liked its looks.

The Sherwood dates from the late forties and was probably sold by Montgomery Wards. It was clear from the beginning that it had been made by Danelectro back when they were in Red Bank and before they'd discovered the uses of Homasote as cabinet material.

The circuit is interesting, as it uses the filament of the first preamp tube as a cathode resistor, in conjunction with a resistance on the ground side-which keeps the filament above ground and dumps the detritus into the center tap of the filament winding. It also runs the 12SJ7 pentode pretty hot which makes for some crunchy sounds-not the typical late forties thing.

Along with the Rola field coil speaker, with modest voltages provided by the iron from the House of Freed, it's got its own groove that owes little to anything else of the era.

The overhaul resulted in some head scratching because the stinkiness got worse and finished up with a cloud of evil smelling smoke and lots of distortion. After puzzling over it I realized I had a similar amp in the collection and on opening it up, it was easy to see where the last owner had bodged the circuit which accounted for the stinkiness and lousy vibrato.

Of course, experimenting with odd circuit ideas was something that happened a lot in the House of Nat Daniel. I've seen several variations on this theme, including one which uses a power tube to modulate the field coil current for a Leslie type vibrato effect, and one that uses a potentiometer to adjust the preamp tube filament voltage for yet more cool Danelectro edginess.

The circuit is the same as the Silvertone 1303, and I've seen it in amps from Wabash, Noble, and Danelectro. As part of a cooperative project I dug up an original copy of the schematic and it was redrawn by Sean Weatherford of Bean Amplifiers, so that was probably the last one the seller got five bucks for.

It is now the world's property, and it would make a great home brew project. Why make yet another tweed Deluxe? This'll get you there in style, plus vibrato to boot.

I've got an 84-23 which is the same amp with an extra 8 inch PM speaker, and it's undergoing a refit as we speak.

How's it sound? Sharp, edgy, and full of fight. It's not smooth at all like a Deluxe but edgy and in your face like you'd expect a guy from Jersey to be.

Monday, January 2, 2012

Vox AC30CC2 Normal Channel Shutdown Hissy Fit



I've got a Vox AC30CC2 named Sophia Loren that is presently up for sale. This may be a cautionary tale about Resistentialism-which is the philosophical notion that things are out to get us. It also supports the notion that things have feelings and ways of punishing us.

I mean, you have to know that this amp has never been abused or scorned-it has never left my non smoking house either. It has, in a word, been spoiled rotten.

So a guy came to look at the amp and the normal channel quit working right in the middle of my sales pitch. Of course he more or less figured out at that point he was a Fender guy at heart, and so am I, which is why Sophia Loren was up for sale anyway. She was acting more like Roseann Barr at that point.

I got a little time today to dig into things and schlepped the chassis out and down to the laboratory. I started checking voltages and the preamp voltages seemed OK. Then a little grid disturbance testing led me to the first preamp tube's normal channel grid which produced no noise. Then, as if by magic the normal channel sprung to life. So, I tightened up the tube socket pins and retested and things were still on again, off again.

Looking through the holes in the vertical preamp chassis I could see that not only was pin seven-the one at issue-on the first preamp tube a lousy solder job, but pin seven on the second preamp tube was equally dodgy. I was able to reach through the holes and resolder the connections, and things are back to normal.

I know now that it's not right to threaten eviction when a needy and dependent lover is on the receiving end.