[marty]

Hi All;
To try out the two transformers that I have for now, untill I get another number 19 Tube..
Can I on a Breadboard hook up Via 4 wires clipped to the bottom of the Socket of the Tube 19, a 12AU7 with a seperate Filament on the 12AU7 just for testing to see If both of my Transformers are working ?? This would be very tempory and until I can order another 19 Tube..
THANK YOU Marty

[codefox1]

No, this will not work. You can test continuity of transformers with an ohmmeter.(with power disconnected of course.)

[marty]

Hi All;
Thank You Codefox for your reply.. I am just wondering, (Since you didn't give any reasons) Why you have said no ?? Since they are both Twin Triodes.. I have already done the continuity test..
THANK YOU Marty

[codefox1]

Filament is different, type 19 is power triode, 12AX7 is for small signals. Only thing they have in common is being dual triodes. No way would I try this on one of my sets, but go ahead if you wish.

[morzh]

Marty

Why going for all this rigmarole and not simply plug the XFMR into a Variac and then simply measuring the voltage? Aside from the voltage being a tad higher without a load you will still be able to make sure the thing works.

[marty]

Hi All;
Thank You both for your answers.. Codefox, As I stated above I knew that the filaments were different that was why I said I would use a different filament transformers for the 12AU7 and why I said I would use only four wires, two for the plates and two for the grids.. It is not permentant just to pass a 400 hertz signal to a 4" speaker..
Morzh, I like that suggestion, I would have been afraid of damaging something.. But, I'll try it.. When I was testing some of my Power transformers to find the correct primary, at first on one of them it tripped the "reset fuse" button.. So I have been a little leary since then about using my variac..
And I don't want to wait the week out and not doing anything while I wait for the new tube to arrive.. So, I can start checking some of the different stages out.. Thank You both for some great suggestions..
THANK YOU Marty

[morzh]

Marty

If you take an unloaded transformer and you DO know where your primary is (finding it by experimentation is not a good idea by any extent of imagination) you simply connect it to variac and bring it up with your voltmeter on at the output winding.

But even if you do NOT know where your primary is it is still OK to try it with the Variac, and here's how: you connect your assumed primary to the Variac output, and have your voltmeter at the assumed secondary; you should know the expected output. Calculate the ratio of the Prim to Sec, then set your variac to say 10V. See if the secondary conforms to the expected ratio or it does not. For instance say your secondary is 6.3V. Set your assumed Primary to 11V by Variac and see 0.6V output. If it is not 0.6V and quite otherwise, say over a 100V - your suspected primary is not really a primary.

[marty]

Hi All;
Thank You Morzh, I had measure the different windings, and I Had picked the wrong one, it was a 5.0 (I think) Secondary, and it measured about or close to what I had expected to be the ohmage for the Primary.. Once, I had the correct primary, I could measure the output voltages.. But, I like Your suggestion of trying it at a lower initial voltage.. Thank You for Your Insight and Suggestiions..
What voltage would you suggest I try on the transformers, I plan on testing both the input transformer as well as the output transformer.. (seperately)..
THANK YOU Marty

[morzh]

Logically thinking you want your test voltage upon plug-in to be on the order of what you expect from the lowest of the voltages you have from your secondaries.

For example if you have your 110V/6.3V+12V+2V transformer you want to start from about 2V to 5V and then look at the rest. Be careful though - your 110V will produce 260V if you put 5V to 2V winding and touch the 110V with both hands you will be unpleasantly surprised. Just hook up the meter and keep measuring. Once you see that the outputs do not produce much voltage it is likely you found your correct primary (as 5V divided by about 20 will be in 200mV range) and you can start gradually bringing your voltage up until it is 110V and you see the respective outputs. They will be somewhat higher but plausible. Maybe 7V instead of 6.3.

[marty]

Hi All;
Morzh, Thank you for the more detailed explanation..
What about the two Audio transformers, the input transformer is fed by a number 30 tube fed by a 135 volt B+.. (I think I just answered my own question) then it goes to the number 19 tube.. the Output of the 19 tube goes to the Output transformer, which is also powered by B+ of 135 volts, thru the center tap.. So, just to verify, I could use it at 135 volts or maybe go about one half to one third of that figure to test each transformer ?? The transformer that is center tapped I would use half of what I would use on the other transformer, correct (Assumming I would be applying voltage to one side of the tap) ?? Once I (hopefully) found each transformer to be good I could put 135 volts to the one side and then find out the correct voltage for the other side of the transformer ??
THANK YOU Marty

[morzh]

OK, just to make sure you understand - transformer does not care about the DC voltage. It cares about AC voltage. The AC voltage is the current the tube puts through it times the load (the speaker's voice coil impedance) reflected to the primary (that is squared turn ratio times that voice coil impedance).

We can assume that the voltage across the primary is in tens to a hundred plus of volts. The output voltage is in units of volts. Say if your voice coil impedance is 1 Ohm it will take 1V to produce 1W of the power. For 8 Ohm it will take about 3V to do the same.

General rule is: the primary in the tube amps has a high AC across it and the secondary usually low.

So, take 20-30V AC from your variac and apply it across the primary. Watch the secondary give you some meaningfull voltage of probably a hundred to 3 hundred millivolt.

MAKE SURE you know whichh the primarfy is. If you switch them and apply 30V to the secondary, the primary may give you too much voltage and if you touch it.....notwithstanding it can damage your meter.

[Mondial]

A 135V DC supply voltage does not necessarily mean there is a 135 AC signal on the transformer primary. In fact the maximum AC signal is dependent on the volume setting and most likely would much less. You could test the transformer with a much lower voltage, like 10 VAC.

The turns ratio of the primary to secondary will determine the output voltage and it will always be proportional to the input. For example with a 3 to 1 stepdown ratio which might be typical of a Class B driver transformer for a type 19, with 10VAC in you might have 3.3VAC out.

You could easily test the audio output transformer by momentarily touching a 9V battery to the primary (19 tube plate) terminals and listening for a click in the speaker.

[marty]

Hi All;
Thank You all for makeing things clearer for me.. I knew that the 135 volt DC was not AC, but with the modulation, I thought that it was a kind of AC, or modulated AC riding on a DC carrier..
The 9 Volt battery is more to my liking than any so far..
I would like to find some way, to have a speaker hooked up like my 4" speaker, and work my way back stage by stage, using my speaker as a guide as to whether anything is happening..
Only putting in the next in line tube only after I have checked out that stage going from the back to the front of the schematic.. The back being the speaker and the front being the Antenna..
My four inch speaker has its own output transformer but it does not seem to be balanced, so I will not use that transformer..
The speaker that came with this set is badly torn the voice coil is fine in it, but until I can make the cone more stable or solid, I don't want to use it..
But, not having a good 19 tube, and not wanting to wait the week, I am looking for another answer, such as my origional question.. So, given my limited tube supply, I could use a 6SN7, or a 6V6, I don't know if I have a pair of 6V6's to use as a push pull, but I wanted to keep it simple, using a twin triode, since that is what is in the Radio.. And easy to wire up.. Could the 6V6 be used like the Triodes ??
THANK YOU Marty

[Mondial]

No none of those tubes are compatible. The type 19 is a Class B output tube which operates with zero grid bias. All the other tubes you mentioned need a negative grid bias to prevent the tube from drawing excessive plate current.

My advice would be to wait for the proper type 19 tube to arrive, as it is not easily substituted. In the meantime you might start checking some other components with an ohmmeter for problems like off tolerance resistors and open antenna or RF coils

[marty]

Hi All;
Mondial, Thank You for letting me know that I need to wait for the tube to come in..
Yes, I have checked all of the resistors, and have the replacements and I have two coils to go.. The others are fine.. At first look, none of the coils have that wire rott, that seems so prevelent in other sets..
I don't have a reliable cap checker, my friend has one, but may be awhile before I can have Him bring it over.. I do have the Replacement caps, except for two of them, but I can make them up with two or three other caps for now..
I do need to make my Power Supply (Battery Eliminator) for it, so that is on top of the list..
So, that alot has already been done, untill I can get the proper tube.. And then power it up for the first time, since I have had it..
THANK YOU Marty