Magnavox 175-67 questions

[guitargrump]

The capacitor I have circled is C19B...

The diagram shows C19A connects to ground...

C19A was removed from my 175-67 module... Why?

Is C19A the infamous death capacitor?

Shouldn't C19B be a safety Capacitor?

 

[Pondoro]

I think C19A is a death capacitor. I’ve only heard guitar guys talk about them. They are connected to the amp and kiss microphones, stereo listeners just touch the plastic knobs. Still looks like a danger, if it shorts.

 

[guitargrump]

I think C19A is a death capacitor. I’ve only heard guitar guys talk about them. They are connected to the amp and kiss microphones, stereo listeners just touch the plastic knobs. Still looks like a danger, if it shorts.

Yes That's why I asked I believe that is why it's voltage rating is so high...

Safety cap assortment is added to list of maybe needs...

It's a two leg capacitor....

I made/had alot of progress last night...

I removed a bunch of stuff from the pre-amp connection.

"hot, neutral, main power coil wire black, and the two heater coil wires Brown" Are what was removed.

I put a drop of liquid tape on All the loose wire Connections and shrink wrapped up the heater coil wires...

That was all for the console connector until I get to the feedback loop...

This is prep for the power switch and fuse....

I also removed the speaker connector and it's wires and attached longer speaker wires for the bench test work on the output turret...

Whew

Long night it's almost noon nap time... I need a Big printout this Sam's pdf is awesome but paper doesn't go to sleep lol...

 

[Pondoro]

It is “shocking” how much crazy info is out there on the internet (I just searched “death capacitors.”) People claiming that power supply capacitors have “thousands of volts” and maintain lethal charges “for years.” No guys, death caps are tiny caps that can short and energize the chassis.

 

[guitargrump]

It is “shocking” how much crazy info is out there on the internet (I just searched “death capacitors.”) People claiming that power supply capacitors have “thousands of volts” and maintain lethal charges “for years.” No guys, death caps are tiny caps that can short and energize the chassis.

That's exactly what it looks like in the screenshot of the diagram above look at C19A see how it connects to the main incoming power line and chassis...

Lol I never thought I'd ever see that kind of connection...

I've looked for that connection for over 30 years every time I looked at a diagram this is the first time I've ever owned something that had had one that's probably why it was removed...

I had always thought Death Capacitor was just a Urban Legend even though I have always looked for that kind of a connection...

We used to toss charged 20uf 200volt caps as a prank to each other in training "Think Fast"

You learned to not grab one pretty fast...

In retrospect it was pretty dumb but us recruit's we were a pretty wild and rough group of youngster's...

I always discharge caps with a light bulb pigtail because it will light up a little if there was a significant charge... Be safe

 

[markmcmuz]

They are there to filter out RF noise. I usually replace them with new X1Y2 ( I think that is the correct version) caps.

 

[guitargrump]

I hadn't planned on doing anything to the ceramic capacitors but testing their ESR and replacing any out of spec ones... Their supposed to be pretty reliable.

They are there to filter out RF noise. I usually replace them with new X1Y2 ( I think that is the correct version) caps.

Thank You for the replacement part # I was debating replacing that one filter cap with a safety Capacitor but I'm still just reading the circuit and doing the basic must have modification's like power switch, fuse speaker binding posts I'm still waiting for the supplies to arrive...

 

[guitargrump]

You can eliminate 99% of any potential shock hazzard from that cap by changing the line cord to a polarized one and running the neutral side of the line to the cap. Then it will only be the line ground to chassis if the cap fails by a short. But it would be better to have it go from the hot side to the neutral to detour the line noise and power spikes from lightning, etc..

Hmm both Excellent Points... I believe that I will leave the line power filter cap on... and replace it with a new safety cap...

I think the dangerous cap is the C19A not C19B... C19A was already removed... if C19B shorts it will just kill the power...

Thank you for your input

 

[guitargrump]

Made some minor progress today I drilled the switch and fuse holder holes...

I also have them soldered in...

I can't wait for the parts to start arriving...

 

[guitargrump]

Okay I have another question....

I have this huge box of old tubes some NOS and mostly working pulls...

When I sorted through it I was just looking for 6v6gt and 12ax7 tubes... But it's a very old box of tubes...

Ecc83 / 12ax7 / 7025 are a few of the tube's in the box...

What are the other 12ax7 equivalent tubes Old RCA numbers and US EU Russian designations??? Is there a tube equivalency chart?

 

[egellings]

Music and a doob were meant for each other. I recall once when I had this little 6 transistor pocket radio; I was carrying it playing a song I liked into the house, having just returned from a doob session. So here I am in the living room, buzzing away at 0dBm, boogying to a pocket radio while a nice stereo setup sat silent in front of me. It be that way sometime.

 

[markmcmuz]

ecc83's are = to 12ax7's. I think a 7025 is 1/2 of a 12ax7.

 

[guitargrump]

ecc83's are = to 12ax7's. I think a 7025 is 1/2 of a 12ax7.

No the 7025 is a early low noise version of the 12ax7

RCA and later GE made the 7025... 12ax7 is a later standardized naming

It's the other 12ax7 equivalent tubes numbers I'm trying to find like for 12au7 ect... the pre standardized numbers that RCA and GE used ...

boogying to a pocket radio while a nice stereo setup sat silent in front of me. It be that way sometime.

Lol I hear you there I hope to have many more of those times myself...

Tube equivalent charts ??? Anyone???

 

[Dswankey]

It's the other 12ax7 equivalent tubes numbers I'm trying to find like for 12au7 ect...

Do you mean like this?

https://www.radiomuseum.org/tubes/tube_12ax7.html

http://www.audiotubes.com/12ax7.htm

 

[guitargrump]

Do you mean like this?

https://www.radiomuseum.org/tubes/tube_12ax7.html

http://www.audiotubes.com/12ax7.htm

Yes I was just wanting a direct replacement equivalents tube chart because I have all these tubes and most of them are the non standardized manufacturers numbers...

So far the ones that I can I'D all have been good...

Some are pretty rare...

I found a great database of tube info
http://www.nj7p.org/Tubes/SQL/Tube.php

 

[guitargrump]

I made a few more changes to the amp today...

I removed the rest of the unneeded wire's from the molex connector...

I also bucked the incoming power supply with the unused heater winding from the pre-amp to counteract some of the higher incoming line voltage of today's power... Per DG's revised design...

I also tucked the extra black and brown wire away and zip tied them out of the way...

I'm Still waiting on supplies...

 

[guitargrump]

The supplies finally started arriving...

I've been busy...

Lots of stuff is done...
Three prong chord
Indicator Light
Speaker binding posts

Most of the Capacitor and resistors are new now... Old one's saved for a different project...

So far so good... My soldering station died spectacularly... So I am waiting on it's replacement to arrive... I also have a few parts still on the way... Postal Shipping is so slow right now...

 

[guitargrump]

I finished the last of the Capacitor replacement's tonight...

I had to cut the soldered twist tabs off my soldering iron wouldn't get hot enough...

I removed a dent in the transformers cover and repainted it...

 

[guitargrump]

Okay I have a question about the incoming power section...

I was checking the input voltage "red wires" of the 5u4 rectifier and it's reading 320 and 319vac...

the schematic shows 290vac at the red transformer wires... Isn't 320vac still a bit too high???

I bucked the transformer already...

My wall line voltage is 124vac...

The yellow heater wires show 6.1vac with the 5u4 tube unplugged... that seems okay...

My voltage readings after that get worse the output voltage of the 5u4 is 455vdc the schematic shows 355vdc

Any ideas???

Edit: I had the brown buck coil wires reversed...

The 5u4 red wire input voltage is now 284-285vac... Better...

The 5u4 output voltage is still a little higher 402vdc than the schematics 355vdc though... Way better than before... Still high..

 

[cademan]

The voltages should go down to mostly normal levels when all the tubes are in. Without the tubes, voltages will naturally be higher.

You will notice that the original can capacitor says 450 volts so you are fine and still under voltage percentage wise.