[jcassity]

resto in work and so today for a little bit i swapped out one capacitor at at time.,, then verifying the unit still works and moving on.

towards the end of the cap replacement i took a phone call while the radio was playing.
suddenly the speaker noise went quite so... i raced over to the work bench and turned it off and unplugged the radio.

the last two caps i was dealing with were tied to the antenna terminals both "ANT" and "GND".

the "ANT" terminal had what appears originally as a .1MFD cap.  the diagram showed a .01 MFD.,, which leads to the designated "T1".
I decided to install a .01MFD cap for the ANT ckt to match the diagram.

the antenna "GND" had an original .01MFD cap in i replace it with the same value.

when my Minerva unit speaker when quiet, i powered down but soon powered back up to see if i could finish off any resistor that was letting out the magic smoke... in other words see if the radio could show me where it is broke.  Nothing,, all is well ,, just no sound.

at this point i all i can tell is that both my 6SK7's are barely getting above room temp but they are not lighting up nor getting anywhere hot,, they do seem to get a tiny bit "warm".  I traded thier spots to see if it was just one bad tube but still no luck.

the nostalgia air diagram includes two prints,, my model is the top print "model w117 early" from what i can gather now that i have compared all the caps and a few resistors.

i have no 6sk7's avail,,, i have 6sc7's though but i dont think they will work.

attached is the schematic i am using.

does anyone think my antenna capacitor is wrong?  and could it be causing this?  i highly doubt it myself but just asking.

this is one of those typical  "it was just working" situations,, im sure we all have been here before.

[jcassity]

    here is the bottom of the set.

from my research the bare metal bar is what i "think" supposed to be the DC Buss.
right now i have no voltage on this bar.

i have also read that in nearly all cases the 50L6 tubes are wired in parallel,, so when there is a problem with one ,, all current passes through the other one and killing it by default.   This is only what i recall from early this morning reading up.  
there is a mod to rewire the 50L6's in series so that when one goes,, the other simply does not operate but it does not get killed.

i am trying to apply all the things ive learned here and from terry,, so tell me if i am tracking this correctly.

[35Z5]

here is the bottom of the set.

from my research the bare metal bar is what i "think" supposed to be the DC Buss.
right now i have no voltage on this bar.

i have also read that in nearly all cases the 50L6 tubes are wired in parallel,, so when there is a problem with one ,, all current passes through the other one and killing it by default.   This is only what i recall from early this morning reading up.  
there is a mod to rewire the 50L6's in series so that when one goes,, the other simply does not operate but it does not get killed.

You could rewire the parallel 50L6 to use 25L6 in series, all the tubes would then be 300ma. That's what every set I can remember used. Musta got a helluva deal on 50L6.

A 6SK7 doesn't draw enough current to get more than barely warm.

I suspect the buss is floating ground, B+ usually requires enough resistors to drop for various points that it's just a few wires. You need to check plate & screen voltage on each of the tubes., BUT start by verifying cathode voltage on 25Z6. Ground will begin at negative side of filter caps...

[jcassity]

I ran out of yellow looking caps and the orange / brown drops to replace caps but i had a bunch of proper .01 in those disc types... are those ok to use,,, i know caps have their own characteristics but is it ok for this application?

will start on what you said,, thanks!

trying to figure out what happened, cause the 50L6's light up,, nothing is blow that i can see yet,, but no buss voltage would be made by the 25z6,, so i will start there.

[Arran]

I personally would not use the disc caps in a 1940s vintage radio, even if I was not planning on restuffing the original caps I prefer using the yellow axial lead ones, or orange and brown drops with radial leads (which are also film caps), discs just don't look right. Electrically I don't know if there is a difference in most cases, but disc caps drift in value with heat, and they do not like high frequency pulses such as the vertical circuits in a TV, and some claim that they don't sound as good in audio circuits but I've never been able to confirm that. Since the Tropic Master probably needs new resistors I would get some new film capacitors with them. One more thing, please don't pig tail new components onto old leads, it's just not a good practice, with that you are relying on 70+ year old solder joints at either end, and a new joint on well oxidized old wires, this is how freshly "recapped" sets suddenly quit playing or end up with weird faults.
Regards
Arran

[jcassity]

fault still same- no audio out,, set was working then suddenly went silent... no smoke or nothing either.

I am posting up a diagram of this "early" Minerva tropic master for our records if thats ok.
I looked at my rectifier tube 25z6 and noticed something. earlier i was saying this was a 25L6,, so i will correct now.
when you look into the glass all the wire leads mesh into a stright line all encased in the glass.
there is are two leads that have a tab but no tiny wire is touching them like on the other leads.
this is true for two leads i see.  this may be why the set is not working,, because the tube is bad.
the 25z6 tube lights up but i dont have any reasonable higher dc power on this tube coming out on any of the pins.
I guess just because it lights up does not mean its good or working ,,, correct?

does anyone know if there is a standard for how to "count" the leads inside the tube,, as in which one is pin 1, 2 and 3 and so on?
I ordered a few tubes for this and some caps today.
also..
on the diagram below,, the tube line downstream of the power plug show the grid power if i am correct.
what pin numbers can i "assume"  are shown. 
the print assumes the user is qualified and trained so leaving off the pin numbers  ,,, i dont mind but i want to document them on the print by hand myself.
I am still looking for a very clear version of the diagram but this one will have to work for me.

if i find the set works with a new rect tube,, i need to see if there was a reason as to why it blew.  It may have something to do with the cap that was ready to blow up but i powered down in time... dono..........

placed an order with Gary at PTOTP,, hope he fills it soon.

[Radioroslyn]

Hi Scott,
>I guess just because it lights up does not mean its good or working ,,, correct?
It means that the heater (the part that lights up) is good but you may have it in the wrong socket. A lot of octal tubes share the same heater pins (#2 and7).
As drawn your schematic is wrong. It will only work if it has 25L6's in it NOT 50L6's Or as Tom sez parallel the two 50L6 heaters like this:

[Arran]

I think it's clockwise from the key, bottom side, counter clockwise from top side, on octal and loctal tubes you start from the key counting clockwise.
Regards
Arran

[jcassity]

aaran,,,

looking in the glass itself ,, what is the pin count and which side to i start on?

from previous post.. i see two tabs without wires tied to them

[35Z5]

As Terry stated schematic is wrong, radio must be correct or the 150ma 50L6(s) would have excessive heater voltage and other tubes with 300ma heaters just barely lighting. The late version shows 50A5 wired correctly.

Tube pin count is always clockwise from locater key(or space for miniature tubes). 

There are two unused pins on 25Z6
25Z6 [Image: http://www.nj7p.org/Tubes/SQL/Bases/7Q.png]

[Radioroslyn]

Just to clear something.
What Scott is asking is which wires coming off of each electrode go to which pin at the base of the tube. He sees two metal tabs near the evacuation point in the glass that he thinks should have some sort of connection.
I told him that the tube has 5 elements and 6 wires leaving two of the pins blank.

We talked on the phone and some previous repair a 400mfd cap was installed as the input cap in the power supply. We checked out the ac side thing and it's good but on the dc side no dc cathode volt at the rectifier. Methinks the 400mfd cap took out the 25Z6. He has one on order and some caps. The heater string is ok so far.

[jcassity]

redoing but shortening up my pupose of post.

radio was free
owner said its been working for years
owner says radio recently started making a poping noise,, so he had not turned it on since last fall.

I take it home and power up.
it does pop some , thinking its a silver mica issue i turn it off after hearing a very agressive sounding "POP".
flip over the set and find a cap that is litterally on the edge of blowing,, the foil is showing.

i proceed to inventory caps and one at a time replace all paper caps.
I also use disc type caps at a temporary till my new order arrives of caps & tubes and spares for this set.
I power up after each cap is installed and all works fine.
i do not have a .25uf cap so that one remains until my order arrives.
I conclude cap replacement and take a phone call with the radio playing.

while on the phone call the radio goes silent yet all the tubes remain lighted except for the 6sk7's which i cant see light nor feel much warmth.

I have no dc output on the 25z6,, i have 120vac output where the dc is supposed to be.
~~ this rectifier tube must be shorted internally.

****my question was when you look into the glass of a tube you can see all the socket pin transitions to the internals of the tube, further these transitions are in a straight line.
is there a way to count the straight lineup inside the glass so you can identify pin 1 ect.? perhaps it is never the same because the tube type dictates how the pins *in the glass* are arranged.

I expect to simply drop in a new 25z6 and the set work,,

In my picture there is a bare tinned copper bar running across the bottom of the chassis.
from what i have read and what i can tell, this bar is supposed to have my DC power, seems kinda hazardous to me but oh well.

[Radioroslyn]

So on your to do list:

Find the 25 ohm resistor that connects to the cold side on the off/on switch. The side far of that resistor is going to be where the - side of the 1st filter cap connects not to B- or the chassis. The + side connects to pin 8 or 4 of the 25Z6.

Remove and chuck that 400mfd cap, it's a trouble maker and it WILL take out your new 25Z6 if it isn't out of there. It's - connection is where you what to connect the 2nd filter cap. + side goes over to pin 4 of one of the 50L6's.

Replace that .25 mfd cap. It's tied across the hi volt dc and if it's leaky it can pull down the hv and in an extreme case it could take out the 25Z6.

Take 600 aspirins and call me in a year.  [Image: http://philcoradio.com/phorum/images/smi...on_lol.gif]

[David]

If the 25Z6 shorted and the output is 120 AC your 2 40uf Ecaps are fried. I would replace them before turning the set on. David

[Radioroslyn]

He just has 1 400mfd cap in the power supply. The 2nd cap is awal.