Grebe Synchrophase MU-1 Restoration

A Very Brief History:

The Grebe Synchrophse MU-1 radio was produced from late 1924 through early 1927 resulting in a total production of about 150,000 units. It employs a unique chain drive mechanism from the center dial to adjust the two outer dials in unison and can receive radio wavelengths ranging from 150 to 550 meters.  This example uses five UX-201 4-pin tubes that are intended to be powered by a series of dry-cell batteries.  Since this example has chain-driven tuning and the binocular coils have small metal labels riveted to their tops, this is most likely a "middle" production unit.  The "early" variety lacked tuning chains and metal plates on the coils. My example also features a discrete six-position tone switch and a continuously variable volume control. The serial number "VZLR" is both hand written on the instruction card and stamped into the back of the front panel. The card tacked to the back of the radio indicates this radio was Patented March 10, 1925 and May 5, 1925.

Henry Rogers has a VERY comprehensive web page dedicated to this magnificent radio that is definitely worth a read.

Where It All Started:

As I was working on restoring my Philco and RCA radios, I spent a bit of time reading a number of web pages and learning about old radios.  Then, one day I stumbled across Mike Morando's webpage which featured an image of a 1925 Grebe Synchrophase radio with a Sonochorde Senior Reproducer speaker perched on top of it.  What a beautiful radio!  This is when I decided that I needed to have one of my own.  Thus began a search to find a reasonably priced example that wasn't too terribly beat up.  After months of searching, I found this one on ebay for a decent price, though the condition wasn't quite so nice.  Of course, the images of it that the seller posted managed to obscure most of the scratches and dings.  When it arrived, it actually looked like it had been laying around in a barn collecting pigeon and mouse droppings.  For an excellent description of this radio along with some history and trivia, I highly recommend Henry Rogers' write up on Radio Boulevard. Especially interesting is the discussion about Grebe's obscure serial numbering scheme and how it helped limit lawsuit liabilities...

Cabinet Assessment & Restoration:

A thorough cleaning with some Goop cleaned up the cabinet pretty well, revealing a host of dings and scratches in the surface. I was originally hoping to leave the cabinet alone, but each side was covered with a maze of scratches and dings. It was just too much to leave alone.

The lower set of images above are images made by the ebay seller for this radio and highlight it's generally poor condition.  The center image highlights the accumulated crud on the front panel as well as a closeup of the logo which explains why lots of people call this a "Crebe" radio instead of using the correct name of "Grebe."

I started the cleaning process by separating the radio from the cabinet and then removed the screws that held in lid in place so I could address the crack.  I used a small syringe to get some wood glue into the crack and clamped it closed for a little while.  You can also see in the image above that the trim on one side of the lid shifted a bit as the cabinet absorbed moisture over the years.  One nice little surprise was that the connection instructions for the antenna, speaker, and batteries are printed on a card that is tacked to the bottom of the radio. 

I selectively repaired the cabinet.  The lid was completely stripped and refinish, while other areas of the cabinet just received a quick spray of some toner lacquer to even up the color differences that resulted from corrosion over the years.  A neighbor of mine was kind enough to donate a strip of Mahogany wood to my cause and I used it make some color test strips with various colors of toner lacquer.  This allowed me to determine the right color choice (Mohawk Extra Dark Walnut) to match the original color of the Synchrophase cabinet before I started to refinish the lid.

At first, I attempted to reflow the existing finish without completely removing it.  I used some mineral spirits to soften the finish along with a fresh pad of 0000 steel wool.  This simply made a sticky and uneven mess of that was there, so now it definitely needed to be stripped.

Stripping the lid revealed the cabinet was not originally finished with toned lacquer.  More likely, the raw wood was stained and then some type of varnish was applied onto the colored wood.  With the original finish removed, the lid required a bit more work to even out the tones.  This was done with a gentle sanding with fine grit paper on the darker areas and then applying some grain filler to close up the wood pores before applying the new finish.

Similar stain patterns were evident once I removed the feet from the cabinet.  The below image shows one of the feet removed and turned upside down and placed next to where it came from. The original color was clearly the result of applying a stain.

So, after lots of time evening out the colors in the lid and applying layers of toner lacquer followed by several coats of clear lacquer, the lid cleaned up pretty nicely.  I also applied some toner lacquer to other areas of the cabinet to even up some of the discoloration that happened over the years.  Here are a few shots of the lid.  It was really difficult to capture the new finish.  The first image was made inside under incandescent lighting and  I failed to adjust the flash properly to compensate for this. The second image was made outside with natural light.  Either way, the lid looks way better after some work.

The Front Panel:

With the wooden chassis cleaned up, it was time to turn my efforts to the front panel.  This panel is bakelite with a beautiful Mahogany wood grain appearance to it.  It had also suffered from years of neglect and abuse and needed some effort to rejuvenate it.  Below is the front panel with all of the brass escutcheons removed.  There was a pretty clear layer of crust and debris present.

Even using some goop - that magical, non-water based cleaner that seems to get rid of all kinds of crud - couldn't get it as clean as I wanted it to be.  Reflecting the light above the table shows lots of embedded spotting that just wouldn't budge with a gentle cleaner.

So, it was time for something a little more drastic: I did some careful wet sanding with a 5000 grit sanding pad.  Going ever so gently so as not to sand through the Mahogany wood grain finish on the bakelite, I was able to remove all of the accumulated stains and gunk. The sanding pad dulled the surface shine a bit, so I used some car polish with a microfiber cloth to bring back the shine.

The last step for the front panel was to use some gold colored Rub'nBuff to fill in the logo that had long since faded.

Here are two useful thread about restoring the front bakelite panels on these radios:

https://www.antiqueradios.com/forums/viewtopic.php?f=7&t=208320&hilit=grebe+synchrophase

https://www.antiqueradios.com/forums/viewtopic.php?f=1&t=199880&hilit=grebe+synchrophase

The escutcheon pieces from the earlier Synchrophase radios were said to have been gold plated.  These appear to be brass with some sort of coloring agent applied and topped with a lacquer or shellac.  I cleaned these with the usual application of Goop and opted not to go any further.  I wanted them to be clean, but I didn't wish to strip them down to bare metal and start over again.  That wouldn't look right. The screws that hold the escutcheons in place, should you need a replacement or two, are coarse threaded brass machine screws with a slotted round head, size #2-56 that are 3/8" long available from Bolt Depot, item number 5664. Of course, brand new screws will be shiny and look out of place with 100 year old trim pieces, so be sure to pick up some Brass Ager (available at Amazon) darkening solution to tarnish them to match your existing pieces. 

So, putting the escutcheon pieces back on (or at least placed back where they came from) here is what a cleaned up front panel looks like.

Electrical Restoration:

With the chassis looking nice and refreshed, it was time to give the radio circuit itself some attention.  The Grebe radio has a couple of visually distinctive parts on the inside, too.  The first is three sets of vibrant green Binocular Coils and the second is the set of three variable tuning capacitors that are linked together with chains like the pull-chain on an old lamp socket that hangs from the ceiling.  This is where the name "Synchrophase" comes from, as the three tuning dials turn in unison due to the chains.  The image below is approx 20 megapixels, so you can download it and see greater detail.

The simplicity of the radio circuit is part of its elegance.  With the outside of the radio looking so nice and clean, I couldn't leave the inside looking that that.  It also had a terrible smell to it that was likely some sort of animal urine.  So, I carefully disassembled it piece by piece so everything could be cleaned.  The radio contained two UX-201-A and three CX-301-A tubes (in no apparent order), but one of them had a shorted plate, so I replaced it with one that I found on ebay.  As I continued to disassemble the radio, there were a few fun discoveries to appreciate about this circuit beyond the beauty of those green binocular coils.  The first is the grid leak resistor in parallel with the capacitor that it's mounted on top of.  At first, I didn't even realize there was a capacitor under the resistor... 

Do yourself a favor and get a box of small plastic snack bags (like you send the kids to school with) to sort and organize small screws and other tiny parts from each piece you remove.  Have some paper and a pen handy so you can write up a description of where the screws/parts came from.  Use your digital camera to make multiple images from multiple angles of each thing you disassemble and write the image numbers on your paper label as well.  This will GREATLY decrease your frustration level when it's time to put things back together again! 

I even disassembled and cleaned the capacitor, it was a stacked layer of mica insulated copper strips.  The simplicity here is just amazing. These little guys tend to measure in the pico- or nano-farad range and there is no way they can fail unless the mica stacks get cracked and fall apart, so I cleaned it up and carefully stacked it back together again, following the direction of the indents on each piece. Leigh Bassett wrote a great article about Grebe Mica Capacitors that was published in the Aug 2004 issue of Radio Age.  I've duplicated it below.

Then there were two of these black little metal boxes that turned out to be paper-wound capacitors.  Both are in the center of the radio, one in the back, one in the front under the variable capacitor.

Paper capacitors are typically not to be trusted with high voltages, they are very prone to failing as a short circuit, thus they need to be replaced.  This meant that I'd need to find a schematic so I would know what value of a modern capacitor to use to replace it.  After some digging around, I found a set of schematics for the MU-1.  As it turns out, there was an early, middle, and late version of the MU-1 before the MU-2 made is debut.  My example is from the middle production run made between mid 1925 and mid 1926. The schematics for each are below and can be opened full size in another window.  So, it looks like the capacitors in question are 1.0uF caps and need to be able to handle 90v DC (45v from each of two power supply batteries).  Both were replaced with metalized film caps (electrolytic caps have a service life of only 15-20 years) with the appropriate voltage rating.

Below is the disassembly and reassembly of the black box capacitor.  Unbending a few metal tabs allowed me to slide thing apart and replace the innards. I also repainted the black boxes so they would look nice and shiny clean. 

I removed all of the radio components from the base board, scrubbed the board and resprayed it with some toner lacquer, and cleaned each and every piece of the radio, including the solid-core wires.  All of this work had to be done very gently and carefully so the nearly 100 year old wires and solder connections wouldn't break.  Before final assembly, I connected the radio to my ARBE III Battery Eliminator to give it a listen.  Within a few minutes, I was able to tune in some local radio stations!  Way cool for such an old radio!

Now its Real Beauty Shines Through!

After some tedious and careful work, here it is all back together again and looking great!  The tuning dials also received a little bit of Rub'nBuff to bring out the numbers and division marks.  What a beauty! It's clear this radio is a design masterpiece and great care was taken to design one of the best functional radios, and in my opinion, one of the most beautiful radios of the time.

I was also able to find a few old radio magazine ads for this beautiful radio.  They are a bit small, but still fun to read - I've been particularly interested in the price point of these radios from nearly a century ago.  These prices are not trivial for the typical working person at the time. $155 during 1925 is the equivalent of about $2800 in 2024 after adjusting for a century's worth of inflation!  

The series of images below is from an excellent PDF article written by Dr. Hugo Holden in March of 2015.  It's an amazing collection of information!

The User's Manual:

And finally, the following is a verbatim copy of an article entitled "How to Get the Most Out Of Your Ready-Made Receiver, No. 7 - The Grebe Synchrophase" by S. Gordon Taylor from the August 1925 issue of Popular Radio Magazine. This is effectively an operator's manual for the radio.