Sunday, 24 December 2017

1969 Fender Deluxe Reverb Restoration

1969 Fender Deluxe Reverb Restoration -- a reprise from my old site [2008].


Above —  In Fall 2008, I had occasion to work on a friend's 1969 Fender Deluxe Reverb (DR) amplifier. Since I didn't own this amplifier, only necessary repairs and parts replacement were performed. This amp was a post - CBS Fender DR, but apart from a few different components such as the power transformer and rectifier tube, the circuitry and tone proved quite similar to the pre - CBS Deluxe Reverb amps I've worked on.


Above —   The 14 amp fuse found in the fuse socket. The fuse spring was missing and tin foil was used to make the contact to the fuse holder cap.  This scared me!

During physical examination and testing, I found the following problems:

  1. A 14 amp fuse in the fuse socket - plus the fuse spring was missing.
  2. A 14 foot (blue) AC power cord had been wired to the power transformer, plus, the grounding prong in the plug was missing.
  3. The power cord grounding wire was disconnected from the chassis inside the amp.
  4. A  number of bolts and potentiometer mounting nuts were loose or missing.
  5. I heard loud audio frequency hum.
  6. The pre-amp stage gain proved low; further,  many of the tubes appeared to be original issue. Some of the 12AX7s, including V1 sounded quite noisy.
  7. The reverb did not work.
  8. The Normal channel tone stack proved extremely noisy and unstable.
  9. Most of the pots were very scratchy/noisy when rotated.
  10. Burned out power on indicator lamp.


Above — This amp served as a favorite resting spot for our cat. It seemed obvious that this amp had been roughly handled over time. The first repair was to install a 1 amp slow-blow fuse plus a new spring-loaded fuse cap. Next, I pulled the reverb tank out of the cabinet and opened it up.



Above —  A photo of the reverb tank.  It was easy to see why the reverb did not work. The green plus black wires which connect the reverb tank input jack to the input transformer were not connected. It seemed obvious that a reverb stage repair had occurred in the past. Worse yet - the person used some bad solder such as acid-core and the transformer lugs were corroded plus badly damaged. I removed the bad solder with flux and cleaned up the mess. I then re-soldered the wires using rosin-core solder and it's never fun soldering patch wires to 30-32 gauge reverb transformer wires.



Above —  I pulled the chassis out of the wood. The "infamous" long blue AC power cord can easily be viewed at bottom right.  It had been grounded by placing the grounding wire under one of the power transformer bolts. Unfortunately this bolt had become loose. The 14 foot AC power cord was replaced with a 7 foot cord.  Further , I bolted a lug to the chassis and soldered the AC power cord ground wire to this lug.  After tightening all chassis bolts + nuts, I then installed a new "power on" light bulb.


Above — The stock Jensen 12 inch speaker appeared in good condition. The reverb tank patch wires with RCA connectors seen to the right of the speaker tested OK.


Above — The chassis laid out with the cover off of the main filter capacitor bank. The tubes (especially the power and rectifier tubes) were coated in a thick film. This DR really exhibited that "musty old amp" smell when I switched it on.
 

Above — Five 16 µF/450 VDC,  paper-covered Mallory electrolytic capacitors. I believe these were the original DC high-voltage filter caps and all tested leaky.  Other repairs were made — I found a cold solder joint on the Normal Channel tone stack along with evidence of a previous (sloppy looking) repair.
Additionally I measured high DC voltage on the treble pot that should have been blocked!  I corrected all this mess with new parts plus due care. The potentiometers were "exercised" by turning them back and forth repeatedly after a shot of CAIG DeoxIT.   I also soldered in a new 100 uF/100 VDC bias filter capacitor to stabilize the negative grid bias for the finals.


Above —  I replaced the tired, old Mallory filter capacitors with some F & T 22 µF/500 volt axial capacitors. This pretty much removed the hum from the audio chain. The old caps can be seen lying on the chassis for size comparison. 
Above —  I replaced all but 1 tube with mostly NOS tubes from my collection and with my oscilloscope and some test equipment, set the bias voltage on the new matched 6V6 pair. 

I found that by turning the cabinet on it side, I could connect up the reverb patch cords and speaker for ear audio testing with a guitar and not have to worry about electrocuting our cat. 

Above —  The repaired and tested chassis is laid on top the cabinet prior to reassembly.  Note the shiny new tubes. The rectifier is a Russian-made 5U4GB.

Above —  Another view of the nearly completed project. The DR was reassembled, final tested and returned to its happy owner. 


Above —  An original 6V6 tube from this amp. The original tubes left a grimy, stinky substance on my fingers.  Winner, winner -- cooked tube chicken dinner!

WARNING

Tube amplifiers operate at high DC voltages. Repairing, modifying or building tube amps can be dangerous, or in some cases, fatal.  Don't do it.

Saturday, 16 December 2017

Peerless Martin Taylor Maestro - a brief review




Peerless Martin Taylor Maestro

I got this from Lou at Guitars 'n Jazz in Summit, NJ, USA.

The guitar arrived on time from Fedex. After letting it acclimatize indoors for several hours, I opened the box. The string tension was lessened and paper plus packing lie between the strings and the fingerboard. Bits of packing and bubble wrap supported the guitar within its case. The case itself was sealed up and then wrapped in bubble wrap. Then, the cushioned guitar case was placed inside a stout cardboard box.  Got to give Lou and his crew 10/10 for packaging – I felt impressed by their packing job.

My first impression once holding this guitar was:  wow, is it ever small and light. At 15 inches wide and 2.75 inches deep, this guitar just cradles in your arms. It plays/feels very comfortably with a low fatigue factor. In fact, I can’t seem to put it down. No problem practicing >=3 hours per day on this axe.

The woodwork, binding and finish looks OK. This guitar plays like butter – unlike some of the vintage relic guitars I’ve tried over the years. It feels like playing a Les Paul with heavier gauge strings. It took me some time to mentally ingrain fret navigation as the fret markers are located on top and not in the fret space -- that coupled with the shorter than typical scale. The ebony fingerboard looks jet black. The frets seem well polished and I haven’t noticed any nut, fret or bridge buzz. The wide fret board feels very nice when going finger style.

With its solid top and small size, this guitar sounds bright acoustically. However, amplified, I’m able to get warm tones with no muddiness on the bass notes. The fundamental tones sound extremely clean and pure – pristine notes with a fast, woody attack – exactly why I wanted this guitar. 

Overall, I hear a brighter, resonant woody tone reminiscent of most solid top archies. I know some players prefer laminated top guitars for a subjectively more “wooden tone”. The solid versus plywood top debate proves endless. Get at least 1 of each might be the ultimate answer to that debate.

I played it with the stock round wound strings and then swapped in some new flat wounds strings since this is all I play on my arch tops. Fingerstyle provides a delicious tone with bass note clarity for days.  With a pick, this guitar also shines. I tried numerous picks and settled on the  D'Andrea Pro Plec 354 Shape (1.50mm). That pick with this guitar seem special. I played it through a 1963 black face Fender Deluxe reverb, my Polytone Megabrute and also a little Yamaha THH10 – it sounded good on all 3,

I saw and heard few negatives. 1 concern: I had to tighten the nut holding 4 of the Grover tuners as they were just barely hand tight. I noticed this during my first string change. I also wish the pick guard was a little lower, it's height gets constrained by the need to fir the volume control circuitry underneath it.

This guitar lacks a tone control circuit, but by lowering the volume pot, you roll off the highs enough that I don’t get by without a tone control. I also dislike a bridge pickup, switches, and 2 pairs of pots on my arch tops - so you now understand my bias.

The Eastern Asian Kent Armstrong neck mounted pick up features an Alnico 5  magnet and reasonably compliments the clear sonic tones emitted by the Maestro.  The ebony string trapeze contains  a wire to ground the strings. It's quiet plus free of hum and also surprisingly AF feedback resistant.

The Peerless Martin Taylor Maestro sounds lovely and plays beautifully --  if a 15 inch, shorter scale guitar is your cup of tea – it's worthy to consider.












— Update — October 2018


In October 2018, I modded my Peerless Martin Taylor Maestro. I'll show some photos and such.

I bought a new, floating pickup wound personally by Kent Armstrong in Vermont U.S.A..
Since I've not seen a lot of photos of this particular pickup on the Web, I took some macro shots of it at a few angles


Above — A nickel covered 12 adjustable pole humbucker neck mount.  Model KAHW-HJGN12-N


Above —Bottom of pickup showing Alnico 5 magnet. The adjustable pole pieces come in handy. I better balanced my amplified sound by lowering the B and E string poles since these strings were too loud compared to the other 4 strings. I also raised the G string poles slightly.




 Above — Measured inductance in Henrys.


Above — Measure DC resistance.

Above — Here's the schematic I gave to my luthier Gary.  I chose a vintage style tone network employing a 0.18 µF polyester tone capacitor. He used new 500KΩ CTS pots and I supplied the capacitor from my parts collection.  I prefer having regular size volume and tone pots as opposed to thumbwheel pots often seen on neck-mounted pickup guitars.


Above —The modified Peerless Martin Taylor Maestro: now with body mounted volume and tone controls. Since the pick guard no longer has to support a thumbwheel volume pot, he lowered it closer to the archtop and it seems more enjoyable now. Gary had to carve out the pickguard to accommodate the slightly larger hand wound pickup.



Above —  Gary also did 1 of his his amazing set ups on this guitar.  This included fret and bridge work.  I also asked him to implant small, mother of pearl fret markers into the fingerboard in the standard slots. This boosts fret board navigation and  is especially helpful when you change from a long scaled guitar to this short scaled jazz box.

 

Regards!

Saturday, 9 December 2017

Op-amps Make Life Better

Op-amps thrill me.  I mostly employ them as instrumentation amps, plus AF small signal boosters or filters.  With simple math (often embedded in software or spreadsheets) , we can calculate design parameters such as gain, frequency response or better yet, a stage's transfer function.  Once built, you can measure and analyze your circuit's outcomes in your lab.

I get many ideas and information from peer-reviewed journals. If your affiliated with a university, then your librarian may have access to many free journal articles.  Occasionally, you must purchase a journal article if you deem it essential to your progress. This supports the author(s),  publisher and in turn, spawns more research and journal articles. Circle of life stuff in academia.

Article abstracts provide a good way to learn too.  I think of them as free little packets of information.  At the very least, they may inspire you down a new, exciting path. I read a lot of abstacts on various subjects.

Further, I try to devote some study time to instrumentation circuitry because you get exposed to some brilliant engineering techniques, historical perspectives and often enough, cool new parts.  Apart from the usual RF measurement gear, I hold a special interest in chemical and atmospheric measurement circuits.

OK, back to op-amps:

A case in point follows. Op-amps prove essential for modern instruments -- without them, our digital circuits often wouldn't have any usable voltage to work with.  Analog isn't dead Malcolm!

This abstract sums it up perfectly.

Abstract

The Analog Revolution and Its On-Going Role in Modern Analytical Measurements.

The electronic revolution in analytical instrumentation began when we first exceeded the two-digit resolution of panel meters and chart recorders and then took the first steps into automated control.

It started with the first uses of operational amplifiers (op amps) in the analog domain 20 years before the digital computer entered the analytical lab. Their application greatly increased both accuracy and precision in chemical measurement and they provided an elegant means for the electronic control of experimental quantities.

Later, laboratory and personal computers provided an unlimited readout resolution and enabled programmable control of instrument parameters as well as storage and computation of acquired data. However, digital computers did not replace the op amp's critical role of converting the analog sensor's output to a robust and accurate voltage.

Rather it added a new role: converting that voltage into a number. These analog operations are generally the limiting portions of our computerized instrumentation systems. Operational amplifier performance in gain, input current and resistance, offset voltage, and rise time have improved by a remarkable 3-4 orders of magnitude since their first implementations.

Each 10-fold improvement has opened the doors for the development of new techniques in all areas of chemical analysis. Along with some interesting history, the multiple roles op amps play in modern instrumentation are described along with a number of examples of new areas of analysis that have been enabled by their improvements.

Reference

Enke, C. G. (2015). The Analog Revolution and Its On-Going Role in Modern Analytical Measurements. Analytical Chemistry, 87(24), 11935-11947.


With new appreciation for op-amps from reading this article, I plan to get on the bench and have some fun applying them.  Who knows, I might blog some of these circuits 1 day.

Also, please continue to cherish and support science.  Evidence -- not hype nor hope should guide our daily decisions.