Judging by the activity on eBay and both my “snail” mail and e-mail requests for information during the last twenty-one years, the continuing popularity of the Knight Kit Ocean Hopper just never ceases to amaze me. It seems that a lot of us “cut our teeth” on this little regenerative receiver.
Front View of my Model 749 Knight Kit Ocean Hopper, circa ’61, that I rebuilt in Aug.’09. Shown with its 5 optional coils and high-sensitivity Baldwin Type “C” headphones, the front panel is original and the plastic 0-100 main tuning dial is in unusually good condition. This OH is the result of several years of work. In fact, it is a “composite unit”. The original Model 749 front panel, cabinet, bar knobs, 0-100 main tuning knob, the tubes, and even the coils, are from different OHs bought and sold over the years.
The “last generation” of the Knight Kit Ocean Hopper (OH), and the subject of this webpage, was released in late ’53 and appeared for the first time in the ’54 Allied Radio catalog. It was sold for 14 years, last appearing in the ’67 catalog, and was closeout priced at $18.88 in a May ’67 flyer which included the five optional coils and headset. The “last generation” OH featured a 12AT6 regenerative-detector, a 50C5 audio amplifier, and a 35W4 half-wave rectifier, all 7-pin miniature tubes. The frequency coverage was 155-470 KHz (’54 to ’59) or 165-540 KHz (’60 to ’67 – the long-wave coil’s frequency range was increased to 165-540 KHz to cover the 500 KHz International distress frequency for ships at sea) and 530 KHz to 35 MHz using a total of six 5-pin plug-in coils. The 530-1900 KHz Broadcast Band coil came with the kit, the other 5 were optional. An optional cabinet became available in ’57 and by the Winter of ’58 it was included with the kit. The OH is powered off of the 120 Vac line and the chassis is “hot” – one side of the line is connected to the chassis through a 0.05 uf/270K parallel RC network. The design is simple and straight-forward and after restoring/rebuilding several dozen of them during the last twenty-one plus years I have yet to find one that doesn’t work.
If you are fortunate enough to find an OH in original condition, the “Achilles heel” is the 3-section filter capacitor – it will be open. The original filter capacitor was 30/30 uf @ 150 Vdc and 20uf @ 25 Vdc and has the Allied Radio P/N 213301 printed on it. Fortunately, a satisfactory replacement is available from Antique Electronics Supply, their P/N C-ER33-47-22, a 33/47 uf @ 160 Vdc and 22 uf @ 25 Vdc. You can also use three individual capacitors and use the original mounting hole to install a terminal strip. Since these are “entry-level” kits and in many cases represent our first attempt at kit building, the quality of the wiring ranges from pristine to mediocre to horrible. Typically, there are three categories that I put OH’s into. The overall condition is:
such that it’s just not worthy of restoration. In this case, I “part it out”. This is especially true if the chassis has been modified with extra holes for tube sockets, etc. In addition, it’s not unusual to find front panels and cabinets with additional. Another major deficit is the absence of the original 0-100 plastic main tuning dial since replacements are basically “unobtainium”.
OK, but it needs to be rewired
OK and the wiring is acceptable
In all three categories, the condition of the steel chassis can also vary from pristine to completely rusted out - the plating used on the OH’s chassis does not appear to be very robust – and more times than not is responsible for the biggest single deficit in the cosmetic appearance of an OH next to the front panel. I have successfully used the following procedure in rebuilding a dozen or so OH’s in the third category (OK w/acceptable wiring). This procedure, like the OH, is relatively simple, straight-forward, inexpensive, and can breath new life into an OH.
Remove the three tubes and coil.
Remove the filter capacitor, filter choke (if there is one), and line cord.
Prepare the tube socket pins of the 35W4 for rewiring and new parts. Be very careful with the tube socket pins as they are easily broken off. I have had to replace several 35W4 tube sockets because of pins breaking off so I would suggest that you locate a spare before proceeding. A replacement 7-pin wafer socket will have 1-5/16” mtg. ctrs.
Disconnect the three wires to the main tuning capacitor and “ANTENNA TUNING” trimmer.
Remove the front panel and set it aside.
Remove all the 6-32 hardware from the chassis and the antenna fahnestock clip.
Carefully lift out the wired components from the chassis as one unit and lay it aside.
If there’s a label affixed to the rear of the chassis, remove it as carefully as possible.
If the chassis is just “dirty”, clean it in warm soapy water using a “Brillo Pad” or "S.O.S Pad". This shouldn’t be aggressive enough to remove the chassis’ protective plating. Typically, the underside of the chassis will be OK.
If there is a minimum of corrosion and rust, use wet/dry sandpaper or crocus cloth under running water. Do the entire top and rear of the chassis to create a uniform finish (remember, the front of the chassis will be covered by the front panel). After the chassis has dried, apply a coat of “Krylon Crystal Clear Acrylic” to protect the surface from rusting. Again, the underside of the chassis is typically OK.
If the chassis is severely rusted, use a wire brush in a ¼” drill or drill press. This creates a very coarse “line-grained” finish. Do the entire top and rear of the chassis to create a uniform finish. I have “saved” several chassis using this method. If the texture is too coarse for your taste, follow it up with an electric sander or wet/dry sandpaper and crocus cloth. I have taken a chassis following wire brushing and applied a coat of “Krylon Crystal Clear Acrylic” and the results have been acceptable. Or, the chassis can be painted with a primer coat. The advantage of the “Krylon Crystal Clear Acrylic” is that it’s cosmetically closest to the original. Or
In an extreme case, I have fabricated a new chassis from 0.062” aluminum, but unless you have access to a metal brake, I wouldn’t advise going that route and I certainly wouldn’t do it again – once was more than enough!! Having said that, if the chassis is junk, and the balance of the OH is near-pristine (as mine was), it might be a consideration.
Steel chassis from a Model 740 Ocean Hopper – notice the “extra” hole for the filter choke leads. There are still some spots of corrosion visible so it will need a second treatment. Changing to a coarser grade of wet/dry sandpaper might also be required if the corrosion is deep enough. In terms of overall cosmetic appearance, I think I would prefer using a finer-grade wet/dry sandpaper and more "elbow-grease" to minimize the visible line-graining. Also, keep in mind that even a "Brillo Pad" or "S.O.S. Pad" will result in very fine lines on the finished chassis.
Remove the “ANTENNA TUNING” trimmer from the front panel along with the two ceramic standoffs.
Clean the front panel in warm soapy water followed by several applications of “Meguiar’s Cleaner/Wax” or equivalent. Don't be afraid to use some "elbow grease" in rubbing out the panel.
Install the “ANTENNA TUNING” trimmer and standoffs on the front panel using new 6-32 binder head hardware. Do not over-torque the hardware or you will crack the ceramic standoffs. Use new terminal lugs if you have them (similar to Keystone #7332).
Clean the plastic main tuning dial and the two bar knobs with “Novus Plastic Polish” or equivalent.
Install new ¼” and 3/8” rubber grommets in the chassis for the filter choke leads (if there is one), the two leads to the main tuning cap, the antenna lead, and the line cord.
Now, pick up that wired assembly and install it back into the chassis using new 6-32 binder head hardware. I use the old 6-32 hex nuts unless they are rusted.
Install the fahnestock antenna clip. Don't forget to use the shoulder-washer and insulated washer. Use a new terminal lug if you have one (similar to Keystone #7332).
Install the main tuning cap and filter choke and audio output xfmr using new 6-32 binder head hardware.
Install the new 3-section filter capacitor (or individual filter capacitors). I use a 7/8” I.D. nylon cable clamp, Waldom P/N CCN-42 or equiv., to install the replacement 3-section filter capacitor from Antique Electronic Supply.
Install the front panel, bar knobs, and main tuning dial. Solder the antenna leads and both leads to the main tuning capacitor and install the wire from the main tuning capacitor to the left side of the antenna trimmer.
Discard the original unpolarized line cord and replace it with a 2-wire polarized line cord. I have used a black Radio Shack P/N 61-2852 6’ line cord, but any 2-wire polarized cordset can be used. The wider of the two pins is neutral and should be connected to the switch.
Install the tubes and coil.
At this point, the OH is finished and ready for testing. The above steps typically take me a total of 2-4 hours depending upon the condition of the chassis. If I coat it with “Krylon Crystal Clear Acrylic” I let it dry overnight before reassembling it or if it’s a warm sunny day, I’ll put it outside for several hours in the sun. All of the OH’s I have owned, restored, and rebuilt, have worked pretty much the same. That’s not to say that they haven’t had some individual “idiosyncrasies”. Like any regenerative-detector, selecting a 12AT6 for maximum gain and regenerative characteristics is time well spent. Improvements in the audio gain can also be achieved by selecting 50C5’s. Remember, using the original OH components, the gain from the antenna to the headphones is absolutely dictated by the tubes and there are considerable variations in gain from tube-to-tube, both as a detector and audio amplifier. Also, a tube checker will not be useful in determining detector gain and regen characteristics – it has to be done in the OH.
Depending on the original condition of the chassis, the results of your 2-4 hours of work in terms of before/after differences can be SPECTACULAR!!
WARNING and Comments on the Ocean Hopper’s “Hot” Chassis – Please Read
Over the years, I have received literally dozens of letters and emails regarding my decision to use the original primary wiring and a polarized cordset in the rebuilding the Allied Radio Knight Kit Ocean Hopper and Space Spanner. Words like "deathtrap" and phrases similar to "you're going to kill someone" were common. I have shared and discussed these letters and emails at length with Ray Osterwald, N0DMS, the owner/editor of Electric Radio Magazine, especially after my 1954 Ocean Hopper (ER#184, Sep.’04), Space Spanner (ER#193, Jun.’05), and 1946 Ocean Hopper (ER#200, Jan.’06) articles were published. Let's look at the issues with the 1954 Ocean Hopper:
First off, the chassis is "HOT" only in respect to the 0.05 uf/270K parallel RC-network connected between one side of the line and chassis ground. One side of the line is NEVER connected directly to the chassis. The original non-polarized 2-wire cord guarantees that the chassis will be "HOT" in terms of leakage current (approx 2.6 mA) 50% of the times it is plugged in and the power on.
Now, here is where the "devil is in the details". I chose to retain a 2-wire line cord, albeit 2-wire polarized. I also decided that the most risk to the operator was during the actual operation of the radio. As a result, I decided to minimize the ac leakage current between the chassis and earth ground while the power was on - during the operation of the receiver – by connecting the AC neutral to the power switch (reference the Model 749 Ocean Hopper wiring diagram below). So, this configuration is no worse than the "as- found" condition - the way it was originally wired if the original line cord is retained - which it is retained in a high percentage of the rebuilds.
I also wanted to keep the primary wiring as stock as possible. In keeping the primary wiring "stock", the chassis is now "HOT" during power off, the hi-side connected to the 0.05 uf/270K parallel RC-network to chassis ground through the relatively low-impedance filament string. So during power off, this leakage current is present "by definition" as long as it's plugged in. But it was also like that in the original design 50% of the time.
This is a view of the wiring of my recently rebuilt Model 749 Ocean Hopper circa '61. Note the position of the 0.05 ufd/270K parallel RC-network between the switched AC low and chassis ground.
The best way to address these concerns, especially using a 2-wire polarized line cord, is to completely change the primary wiring by putting the power switch in the hi-side of the line and revising the wiring of the grounds - fairly simple and straight-forward - but something I just chose not to do - I chose to stay with the original wiring configuration. And, I chose the original primary wiring configuration in my rebuild of the 1946 OH, 1954 OH, and Space Spanner.
Another way, and possibly the best alternative, to guarantee that the chassis is absolutely "COLD" is to use a 3-wire grounding line cord - something I have not routinely done in my rebuilds.
I have always stressed that using an isolation transformer was prudent using these radios. I have also checked the polarity of wiring in my home that uses polarized duplex-connectors, so I know what the leakage conditions are using a 2-wire polarized plug in my rebuilds...
Some additional comments might be useful in putting the above into some perspective:
The National Electrical Code (NEC) only defines wiring up to the receptacle – the "code authority" ends at the receptacle. The NEC doesn't cover equipment. In fact, there's no requirement that the equipment plugged into a receptacle is even UL Listed or carries any regulatory oversight. "Jungle Rules" are the order of the day – equipment Manufacturers can do anything they want with impunity with an unlisted product. The Ocean Hopper and other kits are NOT UL Listed so they cannot be intrinsically safe by any definition, and at a minimum, should always be approached with some caution (and especially since they ARE built from kits).
Millions of All American Five table radios used the same switching and grounding technique as the Ocean Hopper. As with the Ocean Hopper, the chassis of those radios were maintained at RF ground by a bypass capacitor (typically 0.05 ufd to 0.2 ufd) usually with a resistor connected across it (typically 220K to 470K). These radios were UL-Listed and their maximum leakage currents were limited by a UL Standard – probably UL 492, Sixth Edition (the Seventh Edition was published in 1950) or UL 813, First Edition (the Second Edition was published in 1954).
It's also useful to keep the Ocean Hopper's leakage current (referred to as "touch-current" in UL Standards) in perspective. Many current UL Standards allow a "touch-current" and that "touch-current" limit is Standard-specific. The Ocean Hopper's 2.6 mA "touch-current" is below at least two current UL Standards: UL 60065, Seventh Edition, Audio, Video, and Similar Electronic Apparatus – Safety Requirements, Section 18.104.22.168, 3.5 mA max, and UL 1950, Third Edition, Safety of Information Technology Equipment, Including Electrical Business Equipment, Section 5.2.2, Table 17, 3.5 mA max. It should be noted that although those 3.5 mA limits are for Class I equipment (The Ocean Hopper would be defined as Class II equipment under those Standards with a 0.5 mA and 0.25 mA max "touch-current" respectively), UL doesn't consider 3.5 mA to be a "shock hazard".
The leakage current requirements of UL 492 (5 mA maximum where voltage in excess of 42.4 V peak exists) were proposed to be reduced to 0.5 mA in May 1972. This was in direct response to the publication of the ANSI C101.1 Leakage Current Standard in November, 1970. UL's Research Department conducted some experiments involving humans (UL Melville Staff volunteers) that was used by the ANSI C101 committee to develop the 0.5 mA limit. An effective date of July 1, 1974 was established for this revision of UL 492 (12th Edition) with regard to leakage current limit.
For a historical review of the safety requirements for these types of radios, reference the IEEE Transactions on Consumer Electronics, Vol. CE-30, No.2, May 1984, "Safety Requirements for Radio and Television Receivers – 1928 to the Present", by S.W. Coen and S. David Hoffman, pgs. 38 - 45.
Finally, it might be useful to repeat the warning found in the Ocean Hopper's manual: CAUTION: NEVER TOUCH ANY PART OF THE WIRING WHILE THIS RECEIVER IS PLUGGED INTO A POWER OUTLET. NEVER USE OR TEST THE OCEAN HOPPER ON OR NEAR A GROUNDED METAL BENCH, RADIATOR, SINK OR OTHER GROUNDED METAL OBJECT. SERIOUS BODILY INJURY OR PROPERTY DAMAGE MAY RESULT IF THIS WARNING IS NOT HEEDED.
If you're going to use a 115 Vac to 115 Vac isolation transformer, I prefer the upright-mounting enclosed-type with an AC connector or AC power cord over the open-frame type with exposed/flying leads. Also, many of the upright-mounting enclosed-types also have exposed/flying leads and require an enclosure of some type. Some of the isolation transformers that I would recommend in the 100 to 150 VA class include:
Thordarson-Meissner 23V364 and 23V365
Comments on Completely Rebuilding Your Ocean Hopper:
If you decide to completely rebuild your Ocean Hopper, by far the most labor-intensive and tedious part of the rebuild is preparing the original components for the rebuild. I can't overstress the value of PATIENCE. Replacement 7-pin wafer tube sockets with 1-5/16" mtg. ctrs. are becoming "unobtanium", so every effort should be made not to damage them or break a pin, and I can’t caution you enough in handling them with “kid gloves”. Ditto the 5-pin wafer socket and the speaker and headphone connectors.
A small bench-vise is used as my third-hand and is indispensable as is the Weller Model No. WLC100 5-40W Soldering Station with ¼" "screwdriver tip" and Edsyn Model DS017 "SOLDAPULLT".
My goal in preparing the sockets and connectors for the rebuild is to use as little heat as necessary and as little mechanical force as necessary to clean the pins. In most cases, that means that I make no effort to save the discrete components connected to those pins, especially if saving them compromises my efforts to minimize damage to the pins.
The best way to remove the solder from the tube socket pins while doing the least amount of damage is to hold the socket in your hand, apply the soldering iron until the solder is molten, and then snapping your hand holding the socket against the bench top. Don't hit the socket against the bench top – just your hand – positioning the socket so that most of the solder will end up on the bench top. Using a sharp pair of diagonal cutters, trim all of the component leads as short as possible without cutting the socket pins. The soldering iron tip can now be used to remove the last remaining pieces of the component leads. After removing the solder, any component leads or wires, and flux from the pins, the pins are then retinned. An Xacto knife is handy in removing the old flux residue.
The same procedure can be used for the speaker and headphone connectors.
This is a sequence of completely rebuilding an OH 7-pin wafer socket with identical pins from a smaller 7-pin wafer socket. Typically, only one pin needs to be replaced. The thickness of the head of the 3-48 screw is 0.028” and mimics the thickness of the original rivet.
Some more random thoughts:
In many cases, the tubular capacitors were originally installed with relatively long leads. Remove them with as much of their leads intact without stressing the pins on the sockets or headphone connector. Verify that they are good before using them in the rebuild, especially their leakage-current. Having said that, don’t replace them if their only problem is being slightly outside their tolerance.
If the primary leads of the output transformer or filter choke leads are too short, splice them before the rebuild and insulate the splice with heat-shrink tubing. Remember that the filter choke leads will be going through a rubber grommet, so don't make those splices too close to the grommet.
Clean the output transformer's and choke's mtg bracket, the main tuning capacitor's frame, and the outside of the regen pot. Synthetic steel wool works very well for this. If they are really bad, they can be cleaned with a wire brush in the drill press, but be very careful. Those cleaned surfaces can be over-sprayed with “Krylon Crystal Clear Acrylic” to keep them from rusting again.
After the 10K regeneration control and switch are prepared, clean the control with DeoxIT D5 or equivalent.
Replace the hardware w/new nickel-plated 6-32 binder-head screws. The original small-geometry hex nuts can be used if they aren't rusted. Sometimes I have re-used the original 6-32 binder head screws by cleaning their tops with a bronze-bristled “tooth brush” (sometimes referred to as a gun-cleaning “tooth brush”).
Use the appropriate sized ¼” and 3/8” rubber grommets in the four (or five) holes (see the photos below).
Rear view of a rebuilt Model 749. Rebuilt in Apr.’92, this was the first OH I had owned since I built mine as a teenager in ’59. The chassis of this OH was very badly corroded and rusted so after cleaning it up with a wire brush and ¼" drill, the chassis had several coats of “Krylon Crystal Clear Acrylic” applied. If you look closely, the chassis is heavily "line-grained" because of using that wire brush, but at the time, I thought it was cosmetically acceptable. Your tastes may be different. In reviewing the photos, I think I could have used a slightly coarser grade of wet/dry sandpaper without getting so aggressive with the wire brush. The front panel and Knight-branded RCA tubes are original and this OH was completely rewired. Incidentally, I sold this OH almost ten years later, and the “Krylon Crystal Clear Acrylic” coating held up extremely well.
This is a rebuilt Model 740 Ocean Hopper that is a bit "unique" because it has been converted to octal tubes. The chassis of this OH was very badly corroded and rusted so after cleaning it up with a wire brush and ¼" drill, the chassis was painted with several coats of primer, top and bottom. The tube line-up left-to-right is 45Z5 rectifier, 35L6 audio amplifier, and 12SR7 regenerative detector. The performance of the octal version with the AM BCB coil is identical to that of the 7-pin miniature version. This unit was completely rebuilt in Dec.’92 and features a front panel made from 0.062" aluminum. The molded octal sockets had the same mtg ctrs as the 7-pin wafer sockets, so all I had to do is increase the holes to 1”. In spite of being a "forgery", this is my favorite Ocean Hopper.
Rear view of another Model 740, circa '58, with an original filter choke installed, that was rebuilt in Jan.’93. The tubes are the original Mullard. The chassis of this OH was very badly corroded and rusted so after cleaning it up with a wire brush and ¼" drill, the chassis was painted with several coats of primer, top and bottom. The tubes and front panel are original. The Allied Radio Winter '58 Supplement marked the transition from the Model "740" to Model "749".
Rear view of another Model 749, circa ’66, that was rebuilt in Feb.’03. The tubes are the original Knight-branded RCA. The lines are a bit more visible because a coarser grade of wet/dry sandpaper was used. Several coats of “Krylon Crystal Clear Acrylic” have been applied. The front panel is a reproduction and the wiring and tubes are original.
Rear view of another Model 740, circa '57, with an original filter choke installed, that was rebuilt in Aug.’03. The fine-lines from the wet/dry sanding process are just visible. Several coats of “Krylon Crystal Clear Acrylic” have been applied. The front panel is a reproduction and the unit was completely rewired by a previous owner.
Rear view of another Model 749 Ocean Hopper, circa ’59, that was rebuilt in Jun.’07. Allied Radio removed the filter choke from the Model 749 and replaced it with a 680 ohm 1W resistor, best guess, in ’63. The fine-lines from the wet/dry sanding process are just visible and I used a circular pattern in finishing the sanding. Several coats of “Krylon Crystal Clear Acrylic” have been applied. The front panel and tubes are original. The tube line-up viewed left-to-right is 35W4 rectifier, 50C5 audio amplifier, and 12AT6 regenerative detector. The coil is the standard 530-1900 KHz broadcast band P/N 111204.
Rear view of a Model 740, circa '57, with a Stancor P/N C-1707 filter choke installed, that was rebuilt in Jul.’08. The original chassis was pretty rusty so it was cleaned top and bottom with a wire brush in a drill press, followed with an electric sander, followed with several coats of “Krylon Crystal Clear Acrylic”. The frames of the tuning capacitor, filter choke, and audio output xfmr were also cleaned using the wire brush in the drill press. The front panel is a relatively rare 3rd-generation without the cabinet mtg. holes that was released in '57 just prior to Allied making the optional cabinet available and adding the two mtg. holes to the front panel. This unit was completely rebuilt and rewired, and the 12AT6 and 50C5 tubes selected for maximum performance.
This is a view of the wiring of a Model 749 Ocean Hopper, circa '59, that was rebuilt in Jun.’07. The filter capacitor is from Antique Electronics Supply, their P/N C-ER33-47-22 , held in place with a 7/8” I.D. nylon cable clamp Waldom P/N CCN-42 or equiv., and the line cord has been replaced with a polarized 2-wire Radio Shack P/N 61-2852 6' line cord. The wiring is 20 gauge solid wire using the colors specified in the assembly instructions. The tube sockets, speaker and headphone connectors, white tubular capacitors, output transformer, regeneration control, and bandspread capacitor are original. This is the most authentic rebuild of all the Ocean Hoppers I have rebuilt in 21+ years.
This is a view of the wiring of a Model 740 Ocean Hopper, circa '57, that was rebuilt in Jul.’08. The filter capacitor is from Antique Electronics Supply, their P/N C-ER33-47-22 , held in place with a 7/8” I.D. nylon cable clamp Waldom P/N CCN-42 or equiv., and the line cord has been replaced with a white polarized 2-wire cordset. The wiring is 20 gauge solid wire using the colors specified in the assembly instructions and I used right-angles where possible. Compare the "look" of this one to the one above. Which do you prefer??? The tube sockets, speaker and headphone connectors, output transformer, regeneration control, and bandspread capacitor are original. This particular Ocean Hopper had already been rebuilt when I received it, so the original capacitors were long gone. As a result, I decided to use the same series "modern" film capacitors throughout – 6 total (2 hidden in this view). This is the 3rd time this Ocean Hopper has been built!!!
This is a view of the wiring of my recently rebuilt Model 749 Ocean Hopper, circa '61, that I finished in Aug.’09. This is nearly identical to the one above. I added a 6-32 x 3/8” spacer to lift the filter capacitor so that I could use the short leads of the original 200 ohm 10W resistor
This is a view of the wiring of my recently rebuilt Model 749 Ocean Hopper, circa '63, that I finished in Jul.’13. This is virtually identical to the one above except that it was only wired with red 20 gauge solid wire. I also used carbon comp resistors from AES. I painted the filter choke and output xfmr’s mtg. frame gloss red to match the wire and the AES filter capacitor. As above, I added a 6-32 x 3/8” spacer to lift the filter capacitor so that I could use the short leads of the original 200 ohm 10W resistor. I used new binder-head 6-32 hdwr. and small pattern hex nuts
This is a view of the cabinet of my recently rebuilt Model 749 Ocean Hopper, circa '63, that I finished in Aug.’13. The vinyl covering was past saving, so I removed it. I removed the bottom feet and the coil door by drilling out the rivets and then using a center-punch to drive out the remaining portion of the rivet’s body. I sanded the case, stained it with a single coat of MINWAX Dark Walnut 2716, followed by three coats of Varathane Polyurethane Satin Interior with a light sanding between coats. It’s not a furniture-grade finish, but it’s quite acceptable. Send me an email and I will send you a detailed-procedure for staining the cabinet. I used the two holes from the discarded coil door to install a 3-1/2” replacement spkr. The spkr volume is “more than adequate” in a quiet room for all but the weakest stations. I also selected a 50C5 for maximum gain. I tried several 2”, 3”, and 3-1/2” spkrs before selecting the one with the loudest volume. Since the coil is not accessible unless you pull the Model 749 from its cabinet, this OH is a dedicated AM BCB radio.
Inside view of the installation of the 3-1/2” square replacement spkr. The spkr is an 8 ohm 0.5W from Workman Electronic Products, their P/N SA-350, with a frequency range of 250 Hz - 5 KHz. I used perforated aluminum painted gloss red as “grill cloth”. The spkr is mounted on a 4” x 4-3/8” x 1/8” board and the 3” hole for the spkr was cut with a circle cutter in a drill press. This spkr is a PERFECT match for the OH’s 3” x 3” cutout for coil access.
This is a view of the cabinet that I recently did for my octal-conversion Ocean Hopper (see above). I sanded the case, stained it with a single coat of MINWAX Red Oak 215, followed by three coats of Varathane Polyurethane Satin Interior with a light sanding between coats.
This is a Model 749 reduced to "kit form" in Jun.'07. All the original parts have been prepped for the rebuild. The front panel is original. The chassis of this OH was lightly cleaned with wet/dry sandpaper and several coats of “Krylon Crystal Clear Acrylic” applied. Start-to-finish, rebuilding an Ocean Hopper from "kit form", which includes the tear-down and prepping the chassis and parts for the rebuild, will take about 8 hours over several days. The rear view and wiring of this rebuilt OH are shown above.
A close-up of my rebuilt Model 749 Ocean Hopper with a relatively pristine original front panel. The plastic 0-100 main tuning dial is in unusually good condition – it's crystal clear - many of these plastic main tuning dials turn yellow as they age.
“Regeneration Fever”, David W. Ishmael, WA6VVL, Electric Radio, Oct.’92, issue #42, pgs. 20-25.
”Vintage Conversion”, David W. Ishmael, WA6VVL, Ocean Hopper Newsletter, K7JYE, Mar.’93, Issue #6.
“The Knight Kit Ocean Hopper”, David W. Ishmael, WA6VVL, Vintage Anthology, pgs.1-16.
”Ocean Hopper MKII – Vintage Conversion”, David W. Ishmael, WA6VVL, Vintage Anthology, pgs. 17-20.
”An Ocean Hopper Reunion”, Randy W. Barthel, KF8TV, QST, Jul.’93, pgs. 54-55.
“The Ocean Hopper Story”, World of Ideas Column (“Homebrew Classics From the Fifties – Part I”), Dave Ingram, K4TWJ, CQ Magazine, Feb.’94, pgs. 94-98.
"Ocean Hopping Dreams", Bart Lee, The Journal of the California Historical Society, Spring '94, Vol.18, No.1, pgs.9-14.
"Cleaning Up the Knight Kit Ocean Hopper", David W. Ishmael, WA6VVL, Electric Radio, Sep.'04, issue#184, pgs.24-27.