My Dad's Vintage Hi-Fi Fisher Amplifier KX-100 / KX60 Tuner

[joeqsmith]

On the audio channel I linked, some of these guys will polish the entire chassis, tube shields, knobs....   My dad's will continue to just look like a nice old amp.

[joeqsmith]

Buffed out the case and inserted the grill.  Using natural resources, even though it's just particle board and plywood, it's a pain to work with.  Wood doesn't take same the stain throughout the surface.  You can use some treatments but blah.  Then grain structure reflects light differently.   In this case, 90% of the stain on top is original.  Blending stains is somewhat like trying to match paints.  I am not very good at it.   

The strings that hold the box lid up are also 60+ years old.

I've been listening to the amplifier for a few days now.   It's getting a good workout and not showing any new problems yet. 

[joeqsmith]

The amplifier still has not been buttoned up.   When running it for several hours, I noticed that the power transformer gets fairly warm to the touch.  I have nothing to gauge it on.   Our AC mains is running 122-123V.  Seems when I was growing up with my analog meter, the mains was around 110.  How accurate that old meter was, or my memory, hard to say.   They spec'ed the amplifier to run from 120-105, or 112.5 +/-7%ish.  Seems tight.  They claim 160W draw, guessing full volume.  They fuse it at 3.2A, slo-blo.  Still has the original fuse.

Looking at the input/output with a scope, it doesn't appear the transformer is starting to saturate with the higher voltage.  Tried to run the AC at two voltages to see if it had any effect on the temperature.  I am measuring at the top of the transformer where there is a small grove cut into the laminates.  Pretty much center.  I have no idea what the winding to laminates theta is.   In both tests, the amplifier was allowed to run for 3 hours.  Same load, volume....   Data was taken using a Kill-o-watt meter.   

At 106.3V, power factor was 0.84, 132 VA, 112W, 1.24A, reached 51.3 deg C or a 29.5 rise.   
At 122.7V, current draw was 1.46A and it reached 53.7 or 31.9 deg rise. 

Guessing that it's normal for it to run this hot. 

Over the last week, guessing I have about 25 hours of runtime on it now listening to music and outside of the transformer temps, I'm not seeing or hearing any problems.   Started looking at headphones.  A friend has one of these amplifiers:

https://www.schiit.com/products/asgard   

Friend suggests reading the FAQ.  You have the artsy-fartsy, touchy-feely people asking questions to the engineering group.  It's pretty funny.     I like that 0.002% THD vs my dads amp at 0.5%.  Dad's old amplifier has a headphone output which is basically tied to the 4ohm output through a 330 ohm resistor to limit the power (11.6^2/330+8 or 398mW).  My modern 70's/80's headphones, you have to crank up the volume to hear them and then you are getting into where the amplifier starts to clip.  I used to have a set of KOSS HV/1LC which were much higher impedance.    I had tacked on a couple of resistors in parallel with the 330s to get me a bit over a Watt when driving the old time 8ohm headphones.   

Wow, used asking price for the Koss, I think is more than I paid for them new.   
https://www.ebay.com/itm/185916149315

Plan to borrow a few different sets from friends to see if they sound any better than my vintage tech.  While searching for headphones, came across this site which uses a more analytical approach to doing reviews.   I bet they get some flack from audio fanboys...      

https://www.soundguys.com/how-we-test/

 

[IanB]

Headphones are interesting. They seem to fall into two camps: monitoring, or listening.

Headphones designed for sound engineers can be extremely accurate and flat in their response, so you hear exactly what is there. Sound engineers need this, but the result can be clinical and perhaps lacking when listening for pleasure.

Headphones designed for listening may have deliberate sound shaping, designed to produce a better listening experience at the cost of technical accuracy.

Each has a place, but it is good to know what your requirements are before buying.

[joeqsmith]

My wife has never heard the amplifier and has never used anything besides ear buds for a headset.  I had her try out out the amplifier with a new set up Skull ear buds.  I then had her try my 70s headphones.   Got an interesting look on her face as she was hearing details in the music that she wasn't used to.  We will see what she thinks about the ones I borrow.

I was thinking to buy a set from Audio Technica.  I like the M70x, not for the 40kHz range, which I can't come close to hearing anymore, but the pads look comfortable.   Then a friend showed me their Beyerdynamic.  Guessing it is like having soft kitty fur surrounding your ears.   

https://www.audio-technica.com/en-us/headphones/best-for/studio
https://www.sweetwater.com/store/detail/DT700ProX--beyerdynamic-dt-700-pro-by-closed-back-studio-mixing-headphones

[joeqsmith]

When I was a kid, I had for some reason scribble the tube socket on the inside of the lower case cover.  Rather than cleaning it off, I left it.  Started out with 5 coats of poly on the case but by the time I buffed it out, I am sure I lost a layer.

Also shown is my buck transformer I used to test the low line. 

[joeqsmith]

Almost made it two weeks of moderate use but then it started to make an odd noise that almost sounded like audio from the local station for maybe a quarter second, then it was gone.   I kept it running and this pulsed audio would come and go at random.   This eventually turned into a 60Hz hum, which of course would also go away.   This went on for a few hours and eventually it didn't recover.  Nothing odd with the voltage levels,  plate wasn't glowing and the filaments appeared normal.   Let if cool, pulled it back apart to have a look and it was back to working fine.     Problem was only on one channel so I swapped the two tube sets and let it run.  Sure enough the problem eventually returned but on the other channel.   Eventually tracked to the output stage.   Two of the output tubes were still originals to the amplifier and sure enough, another is starting to go.   They do not appear to be gassy but noticed a small flake inside one of the tubes.  Attempting to hunt down a few more NOS parts. 

Shown with one of my vintage Pioneer headphones.   To me, these sound very good but we will see what the wife has to say when I do my headphone shootout for non audio buffs....

[joeqsmith]

With the amplifier sorted out,  started work on the FM receiver.   Actually, I've been listening to the amplifier while I work.   The string style tuner was locked up.  Took most of it apart and cleaned/lubricated all the moving parts.  Then some minor cleaning of the remainder of the chassis.  The glass face was really a mess after 60+ years, had a layer of crud on the backside and plenty finger crud on the front.   Note the old selenium bridge rectifier. 

First problem I noticed was one of the lamps has failed.  These have a custom house number 150082-7.  Looking at them under a microscope, there is some marking but I can't make it out.  The filament is crush inside some bent over copper rather than welded like a modern bulb.   Note how they have painted all the lamps with white paint on the backside block the light.  The paint is flaking off.   

All in all, it looks in decent shape.  Not finding much wrong with it. 

[TimFox]

In tube units of that vintage, the plastic-coated paper capacitors (many visible in the underchassis view) are suspect.
Especially, screen by-pass capacitors may have absorbed moisture, and thereby reduce the screen voltage.
They can be replaced with modern polypropylene axial- or radial-lead units, whatever fits better.

[joeqsmith]

Like the amplifier, I have no plans to do a cross the board part replacement.  Just replacing the parts that are bad and will keep everything as original as possible.  Lots of old carbon resistors in the tuner.  Everything looks good and so I powered it up.  Was curious if the beam tube would still work.    It's been running about an hour connected to the amp. 

[TimFox]

As a conservative approach, you can verify the DC voltages at points bypassed by paper capacitors to see which need replacing.

[joeqsmith]

I've been pulling one lead and running them up to about 10% higher than their rated voltage and checking for leakage.  Plus measuring their capacitance and ESR.   Same technique I did with the amp.  In some cases I could test them in-circuit.

Thinking about the worse thing I own for dead caps, my first DSO.  I would guess I have replaced 10 or so Tants since I bought it.  I bought a bag of 20 or so to have on-hand.  I hate to think what it would require for me to change them all.   This tuner and amplifier have another 20 years on that scope. 

Looking at the case, the wood is in decent shape.  A few minor scratches.  I sanded them out and will stain it tomorrow.   

It's been running since I powered it up.   Put the face plate on finger tight until I sort out the bulbs to show what it looks like.  None of that AM rubbish. 

***
Vintage I-POD being used for the local radio station, commercial free.   

[joeqsmith]

The cabinet has a good sized chip missing on the outside edge.   A bit more difficult to match, so cut out a sliver from the inside top to use for raw materials to repair it.

[joeqsmith]

With the glue for the grafted slivers now set, time for some sanding.

[joeqsmith]

Was able to sand most of the scratches out.  There are some deep battle scars that I left behind.   

[rsjsouza]

Caracter...

[joeqsmith]

Indeed.   

No luck finding replacement bulbs.  My motorcycle trailer uses something similar.   They are a bit shorter and fatter but will fit.  These are made for 12V and running them a bit lower voltage, you get about the same intensity.   With them having such a short filament, the coupling to the glass creates a hot spot.  They also draw about double the current even at these lower voltages.    It looks like a few places are offering LED replacements.    Based on their dimensions, looks like they will fit.  May try a few and see how they look.   

Electronics is simple.  Finding lightbulbs and fixing damaged wood, that's where the time goes.   

[richnormand]

In a similar vintage receiver I made a simple diode/resistor/led replacement.
Used two warm white LED in a frosted 3D printed translucent "bulb" tube to diffuse the light.
Replaced all the set so the are the same colour.
Works wonderfully at much less current draw that the originals.

In reading the whole thread I would like to mention that it is worthwhile to check grid voltages to make sure a leaky coupling cap does not shorten the tube life.
Fast and easy to do if you have a schematics with the proper voltage on it.

These will go forever with the proper TLC....

[joeqsmith]

In a similar vintage receiver I made a simple diode/resistor/led replacement.
Used two warm white LED in a frosted 3D printed translucent "bulb" tube to diffuse the light.
...
In reading the whole thread I would like to mention that it is worthwhile to check grid voltages to make sure a leaky coupling cap does not shorten the tube life.
Fast and easy to do if you have a schematics with the proper voltage on it.
...

I'll let you know how the aftermarket LED replacements work out.  Would much rather use the OEM lamps but have had no luck finding one.   

As I posted early on, I checked the caps for leakage with a HV supply running them above their rated voltage.  I also checked their capacitance and ESR.  This was done before power was ever applied.   When it was ready to be powered, I checked all the voltage levels.  The schematic provides pretty much all the grid, plate and supply rails.  After, I started checking the AC performance.   Then slowly splitting each identified problem in half till I found the root cause. 
Once everything has been repaired, I do a long test to see if things are going to be stable.  Pretty much the same technique I would use to bring up any old equipment of this era.   

I did think about making a test jig to sweep the power output tubes after the one started to go intermittent. 

[richnormand]

Perfect.
Sorry to have missed that these were the coupling caps in your previous post.

Should last another lifetime now.
Still have an old Heathkit receiver from my dad in use everyday in my shop!

[tautech]

I'll let you know how the aftermarket LED replacements work out.  Would much rather use the OEM lamps but have had no luck finding one.   

That style lamp is known as Festoon lamps/bulbs and were also used in automotive where if they were placed horizontal road vibrations made for a short life.
The best style of filament carrier wire were gold flashed where they were folded/crushed onto the filament.

Available in different lengths and voltage/wattage configurations.

[joeqsmith]

I wasn't able to find anything close.  The ones for the trailer have a much shorter filament and draw about 600mA @ 6.8V.   The glass diameter is a bit thick and there is a clearance issue with a mounting screw.  End caps are also a larger diameter. 

See attached for data on the stock bulb sizes.

[Roehrenonkel]

Hi Joe,
 
you are looking for 6V-bulbs, right? Will 3W do?
https://www.elting.de/Soffitte-6x36-mm-3W

Best regards

[themadhippy]

another source for those lamps is old illuminated door bell switches ,a nighttime wander around your neighbourhood may turn up a replacement

[joeqsmith]

Hi Joe,
 
you are looking for 6V-bulbs, right? Will 3W do?
https://www.elting.de/Soffitte-6x36-mm-3W

Best regards

Notice how short the filament is.  I suspect they used such a long filament in the original lamp to avoid making a hot spot where it couples to the glass. 

This is one problem I see with the trailer lamps I have.    I could add a diffuser to try and get it to give a more uniform coupling.