A family friend is moving out of state and he wanted me to look at his radio that belonged to his mom before he left. Unfortunately the mice pretty much destroyed everything. I don’t care about the switches, tubes, and passives being junk, but most of the OSC, IF, and ANT transformers were eaten by the mice; making new coils is beyond me. He mentioned that if the dial light worked, that would be good enough. If it were mine and all it did was light up then it would never be used, so I decided to try and put in a solid state amp and at least make it somewhat functional.
Full Picture Album Link: Full_Picture_Album
Chassis:
-Finish: Removing the chassis revealed a nice mouse nest. All of the components were pretty much toast so the chassis was stripped and sandblasted.
I started with the tuning assembly, lightly sandblasting the worst parts and then ran it through an ultra sonic cleaner with a mixture
of water and vinegar. I didn’t want to tape the whole thing off to paint so it was left raw and sealed with clear electrical varnish. The varnish
has a slight amber hue which kind of added to the patina. The chassis was going to be painted but it wouldn’t match the tuner so it got the same
vinegar bath and then varnished; Sprayway EL600 Clear.
-Sub Panels: In order to fit the new components, three sub panels were made. The sub panels were mounted on standoffs using the existing tube
socket mounting screws; only one extra hole in the chassis was added. Three sub panels were required due to the height of the new components
and clearance with the OEM sockets/caps. Everything fit except the the transformer for the 5v power supply. In order to make room, half the windings
of the original transformer were cutoff; transformer was shorted so I didn’t feel too bad about wrecking it. All analog circuitry was placed on it’s own
panel isolated from the chassis using plastic M3 bushings ( Digikey # AE10910-ND ) used for TO-220 parts and the like. Since I didn’t know what grounding scheme would work, I figured it would best to start with no ground.
–Sub Panel 1: AMP
The first sub panel has a 100 watt mono amp (ICEpower 100AS1) and switched 120v power distribution. The amp has Nippon-Chemicon caps and an
actual manual so it looked like the most reliable solution.
–Sub Panel 2: 5v Power Supply
There is a 8.5vac transformer (Hammond 166L8) and linear regulator set to 5vdc (CZH-Labs blank regulator board for LM317/78xx, PCB-A230-1) for lights and other controls.
–Sub Panel 3: Analog/Lights
—-Lights:
The radio has 4 controls apart from the the tuner knob. The new control scheme had the top left knob assigned as the Bluetooth/line select, the bottom left became power, center was the tuning dial, and the bottom right would be volume. This left the top right knob with no function, so I decided to make it a dial lamp brightness control.
-Originally I thought of using a 555 timer to vary the duty cycle but that looked cumbersome, so I did some digging on Digikey and came across
a voltage controlled pulse width modulator chip made by Analog Devices. There are two variants, 0-100% or 5-95% duty cycle, set with a simple
0-1v(0.1 – 0.9v) signal. Only 3 resistors are required to set the OSC frequency. 2 resistors are for DIV code, which when set, don’t change. The third resistor sets the OSC frequency; basically change the frequency with one resistor instead of an RC network. They also provide a handy calculator that specifies the required resistors for a given frequency. It’s not cheap though at $6.41 single piece price, but for a one off and simplicity of implementation it fit the bill. I used the 0-100% duty cycle variant ( LTC6992HS6-1#WTRMPBF ). For the 1v control signal a 1.024 V REF ( MCP1501T-10E/CHY ) was used to supply the POT. The OSC output can sink/source 20ma so a logic level 3A 60v Mosfet ( NTF3055L108T1G ) was used to control the LEDs.
-Since all the parts were surface mount, it forced me to pick a CAD program and figure out how to make my own board. I choose DipTrace because
it looked like the most intuitive and if I need to actually buy it for more complex boards, then you can actually buy it and not be tied to a stupid
subscription service or have online only limitations which seems to be ever increasingly the norm. I found it very easy to use, granted I don’t know
any design rules or best general practices, but I had a board designed after 3-4 hours messing with the software and no tutorials. I glanced at Mr. Carlson’s boards and the Digikey PCB ruler for general guidance. The traces were made just about as big as the pads for better reliability during the toner transfer and grounds were kept as short as possible; also got away with only one jumper link. The board had to be replaceable as well, since I won’t be able to service it directly, so plugs were added. 3mm Pitch Micro MATE-N-LOK connectors were used. (2 POS Header Part Number Reference, 2-1445053-2)
-There were two versions of the board, with the second adding optional gate and drain smoothing cap pads if required; all parts 1206.
The only required component between the OSC output and Mosfet gate is either a current limiting resistor or jumper. Right hand pad is for an optional
Zener diode, left hand pads for optional caps/res. Gate drain resistor not required since output is push/pull. One pad was added to the Mosfet drain for
a smoothing cap. I added this to compensate for the long flying leads used on breadboard, which solved itself with final installation.
The final install has much shorter leads and lower capacitance, but the cap (4700pF) was left on the board. This can be seen with the ramp when the Mosfet is turned off. The optimal LED switching frequency seems to be up for debate so I went with 25kHz to start. With the board mounted next to the audio transformer, I wasn’t sure if there would be any noise pick up, so the frequency was set above that of the speaker. I didn’t notice any issues, but if that frequency didn’t work, 1 resistor swap and it can be something else. A 5K POT was used with the 1.024VRef. The VREF output is current limited with a 470 ohm resistor that drops the POT supply voltage to 0.938v; there is a little dead span at the top and bottom range of the POT. The board voltages are stable and it works as intended, although I’m sure there could be many improvements by someone who actually knows what they’re doing.
-I had a bunch of empty BA9 sockets left over from the ultra probe build and figured mounting four 5mm LEDs behind the dial would work. A pinball place
had long mounting tab sockets that could be attached to the tuning cap; Pinball Life # 24-8793. The sockets have 3 terminals. The center terminal is isolated, which gave me the perfect spot to put the current limiting resistor. Putting the resistor on the socket allows the dimmer board to be completely removed and plugged directly into 5v with a Y cable if need be. Warm white LEDs were used since they’re a little closer to incandescent bulb temperature and not as sterile as 5000K-6000K bright white LEDs. The longer mounting tab helped spread the light more evenly, but there were still bright spots. Sanding the bulb heads with 600 grit sand paper really helped diffuse the light and soften the bright spot, but it didn’t completely eliminate it. With the bulbs being replaceable,
different colors can be swapped in. Green washes out the dial colors, but look like a giant magic eye which may be neat for Christmas.
—-Bluetooth/Relay MUX:
The original plan was to have the audio selectable between Bluetooth and external DAC. I didn’t have time to research active MUX solutions,
so a dual DPDT relay board was installed to switch between EXT Line and INT Bluetooth.
-Bluetooth:
-I ended up trying 3 different BT modules. The first was the DROK board which is everywhere on Amazon. While it connected right away and
didn’t have any clicking issues it sounded like a tin can and no amount of EQ could fix it. The second option was the Arylic Up2Stream Mini WIFI/BT board
paired with an external DAC board which sounded great except for the sometimes intermittent, sometimes constant popping issues. It would play fine for
a couple minutes and then the output would crackle. Stopping playback and immediately restarting playback the crackle would go away for a couple minutes and come back. It almost seems as if it’s a buffer problem or something similar. It’s worse when sending over a constant tone, but stopping and starting
as fast as you can, the problem goes away for a minute or so. I’m not the only person to have this problem. Either way, it’s a poor design or
is too sensitive to externals factors so it was pulled.
Arylic Up2Stream Solutions Tried
-2 different modules
-Wrapped board in Kapton then completely with copper tape, floating/grounded.
-On-Board DAC and External DAC.
-Short custom I2S Cable, no shield, braided shield, grounded braided shield.
-Isolated board, 0v ground reference, actual ground reference.
-Different antennas and shorter coax.
-Mounted in the box or on the bench.
-House wifi off.
-Cell Phone off.
-Used multiple BT sources
-Looked at the I2S Bus, MCLCK is pretty stable but the other lines are kind of erratic or have a lot of jitter.
-I couldn’t find any board level solutions so an external module was installed. The external module is the BluDento B1. It sounds good and
doesn’t crackle during playback. I sent it a 1kHz tone and the output looks clean. My only gripe is I can hear digital Bluetooth noise if the volume POT
is at 25-50% with no audio playing; nothing noticeable during playback. Maybe a higher end model would have a quieter noise floor or be better designed to
eliminate the computer noise. After buying 4 modules I’m out, if he wants something better then it’s easy to swap out.
-Since I had to use the external line input jacks, the relay MUX was no longer needed. A terminal block for the switched 5v power and external
accessory barrel jack were installed. It took a long time to terminate all the cables, so they were left in place and a tag board was made to
splice the line input and volume POT cables. As a side note, Mogami cables were used for the analog signal routing. I was struggling to strip the
wires without taking any copper strands. The wire insulation is really bonded to the wire. The best method is to place a cut around the wire with
a wire stripper as if you’re going to strip it. Then, with a pencil hot air station, heat the wire insulation down to the cut for 5-10 seconds.
Place the wire stripper back on the cut part of the insulation and it just slides right off without damaging the copper strands.
—-Volume/Audio Transformer:
-Audio Path:
-A passive volume control scheme was used since I didn’t have time to research active solutions. I wasn’t quite sure on what the optimal impedance
matching would be but here is what the audio path ended up being with readily available parts. It sounds good and the POT tracking between
left and right is around 10mv or less. Is this a reasonable setup?
-Line input to dual gang 5k Potentiometer.
-5k Potentiometer to Edcor stereo to mono transformer ( WSM6400 ) Input Impedance 10k
-Edcor transformer, balanced 600ohm output to AMP.
-AMP Input Semi-balanced, Non-Inverting Input Impedance 2.8k, Inverting Input Impedance 1.8k
-Noise:
-In order to reduce speaker hum, the first step was to ground the analog sub panel to 0v on the 5v supply. This got rid of some noise from the BT module
when it was mounted inside the box. A ground strap was then connected from 0V to chassis ground at the 5v distribution terminal block which
brought the hum even lower. Connecting an external line feed from a DAC (DAC optical input, isolated linear power supply), with both L/R and grounds
completely isolated from the chassis had hum. Grounding the line grounds at the transformer input got rid of external line source hum. The transformer output line had noise and amplitude problems. A two wire shielded cable was used to feed to the AMP input. The shield of the cable was tied to the AMP’s analog ground. This caused problems. Disconnecting the shield made a big difference. My best guess is that the AMP’s analog ground has a 22ohm series resistor, so it’s not actually ground. A new cable was made with the shield terminated to the analog sub panel at the base of the audio transformer.
-Testing:
-I don’t have an audio generator, so the PC program Soundcard Oscilloscope was used to generate a tone to check signal integrity. Don’t play audio
tones found on youtube. While messing around I tried playing a 400hz tone track and was left wondering why the amplitude wasn’t consistent. It was coming
from the DAC. Using the Soundcard Oscilloscope signal generator, problem went away; bad upload or youtube’s variable bit rate?
Chassis Misc:
-Dial Assembly:
-The dial had some warping, but otherwise it was in good shape considering the state of the rest of the radio. Dial was cleaned with water and
re-installed. Since I had a roll of 1/8″ cork/rubber, that was used to replace the original cork gasket. A 3/16″ strip was cut and applied to the face.
The mixture of cork and rubber also worked great as camouflage for the splice; splice is at the 5 hash mark on the outer ring. The dial glass was then installed
and tabs bent over, giving only slight pressure against the glass.
-I’m a fan of Grayhill’s series 19 rotary switches, but they are expensive. A 4 position switch was used for radio power because I found a NOS
one on Ebay cheap.
-The rear LED use to be the Bluetooth connection status indicator, but is now the AUX 5v enabled indicator for external BT power. The pushbutton
was connected to the old BT module but is no longer used and was left in place.
-The mounting feet threaded holes were completely rusted, so they were drilled out, and PEM inserts were installed. The zinc plating was removed
from the insert and then tack welded onto the foot.
-Switch shaft extensions were required for power and volume. Radwell ( RAD-POT-SHAFT-EXT-.25IN ) had some brass extensions that were longer then what I needed, but were easily cut to fit. Flats were also added to prevent knob slipping issues.
-Resin reproduction knobs were readily available from Renovated Radios. The radio originally had 5 of the smaller diameter knobs (1″ Dia), but I wanted
the power and volume to be bigger (1 1/8″). They were molded two different tones which kind of matched the two tone cabinet so they worked out. The
larger knobs have a 3/8″ hole instead of the standard 1/4″ so brass knob bushings were installed; they happen to be roughly 25/64″ OD so the knob was drilled out to 25/64″. A ring of super glue was used to help hold in place.
Speaker Assembly:
-The original speaker was a little smaller than a standard 8″ speaker. So a jig was made to serve as a saw guide to increase the hole size as well as
alignment for mounting screws. After staining and sealing the wood, the speaker cloth was installed. A green and gold cloth which matched the dial was
applied to the wood with Simply Speakers Glue; essentially rubber cement. It’s sticky enough to allow the cloth to be repeatedly stretched and it holds where you left it. The cloth was from the usual antique radio supply guys, and while I think it looks nice, it’s a little too thick for a modern 8″ speaker. The cloth was
stretched very tight, but any moderate bass would puff out the cloth. In order to give the speaker some breathing room, the cork/rubber gasket was given a
3/4″ notch in between the mounting screws. The cloth wasn’t going to be replaced, so the air was given some place to go. This solved high bass rattle.
-Speaker Part #:
–Speaker #: Dayton PS220-8, 8″ Point Source Full Range, 40watt/8ohm/96.5dB
–Cork/Rubber 1/8″, 1/2″ x 50′ #:94545K53, McMaster Carr
–Cork/Rubber 1/16″, 1/2″ x 100′ #:94545K33, McMaster Carr
Cabinet Restoration:
-Cabinet Prep:
-The cabinet was thoroughly soaked with mice urine. I tried cleaning it with bleach then enzymatic pet cleaner with only minor improvement.
It would ultimately just have to be stained and sealed over. After sealing the cabinet and chassis platform it no longer smells.
-Staining:
-After hand sanding the entire cabinet and cleaning out the pores in the wood, it was ready for stain. It seems a lot of radio guys use Mohawk
products so that’s what was used to stain and seal the cabinet. The two colors chosen were Medium Dark Walnut and Extra Dark Walnut. After staining
the cabinet, there was a little more contrast between the colors then I wanted; either the lighter parts should be darker or the darker parts lighter.
It’s hard to gauge what a color might end up looking like on the finished product versus the color on the monitor. You’d go broke buying every tone
to find exactly what you want, so lesson learned for the next one. Paper was cut to minimize tape contact area. A lot of forums recommend Frog tape’s green and yellow tape. The yellow tape for delicate surfaces actually felt stickier than the green, so green was used. I only had a weekend to finish the cabinet so here’s what I did. Also, I know nothing about wood finishing and trying to glean info from various forums only proved everybody does it different. But, I did find out why sanding sealer and wood grain filler exist.
—-First Color Application:
-Stained wood with microfiber sponge.
-Wait one hour to dry.
-One coat of lacquer applied to seal stain. Sealed 1st color so taping off the next color would not remove stain upon tape removal. This worked
well as any second color stain the seeped past the tape was easily wiped off.
-Tape removed
-Wait 1 hour before taping off next color.
—-Second Color Application:
-Tape off previous color
-Stain 2nd color
-Immediately removed tape
-Clean any stain bleed or tape residue.
-Let dry for an hour
-Added 2 coats of lacquer and left to dry for 3 days
—-Lacquer Application:
-Cabinet lightly sanded to remove any rough spots
-3 to 4 coats were applied with 1 hour dry time between coats
After 6-7 total coats, the wood grain still wasn’t completely filled. I wanted a glass finish and while that was achieved on the lower porous wood used
for the base and trim, the walnut just wouldn’t take. The next radio I’ll have to try sanding sealer before applying the lacquer and see if that helps.
Either way, it is what it is, not the best but not awful either.
Chassis Install:
-3 holes were added to the chassis platform in between the AMP and 5v sub panels to help with convection cooling. Drilling the holes in the wood
released a lot more mouse smell so it was stained then coated heavy with wood hardener; this sealed away the smell. For safety considerations, a
mica/silicone sheet ( McMaster Carr # 85955K112 ) was glued down to the wood to help prevent any fire in case of massive failure. It’s not as good as a
steel base but is rated for 1832 deg F. Rubber strips were also applied for vibration dampening and to help with dial glass final alignment with the bezel.
A bracket was made to hold the Bluetooth module. 1 foot cables were used to connect the Bluetooth module to the AMP. 90 degree adapters were tried
in order to keep the cable profile tight, but the cables hit the platform and I didn’t want to tear it all apart again and notch it out. Other than installing a power cord strain relief clamp the radio is complete. It sounds good and works pretty well for what it is. It could be better, but I learned a few new things as
well as learned how much I don’t know.
Final Testing:
-The radio was left to run for few hours. The rectifier tube was removed so the AMP’s base plate’s temperature could be measured. It holds stable at about 115 deg F with an ambient of 70F.
–Remaining Minor Issues:
-Bluetooth digital noise noticed if volume is turned up with no playback.
-If source volume is set to max and radio’s volume knob is set to min, some audio can still be heard if you press your ear up to the speaker.
My guess is the signal is bleeding through the POT. It’s not the end of the world since the volume is probably going to be left at 50% or so and adjusted
on the source end (phone/computer).
You’ve done a beautiful job on that. I’m not sure I would have had the patients.
Woodb180
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