My new project

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Re: My new project

Post by 75X11 on Mon Oct 27, 2014 5:45 pm

In that circuit's setup, yes. they would all lose filament. If you don't have a tube tester you could isolate a bad filament by a continuity test across the tubes' filaments out of the circuit.
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Re: My new project

Post by frank1956 on Mon Oct 27, 2014 8:22 pm

Found the culprit the 35W4, swapped it out for another one and everything came back on line. Have sound in speaker, but just like a steady hummm sound, no static, stations etc. Volume control does not control the sound steady all the way across. Took some more voltage reading both AC & DC.

(1) 12BE6 pin's  1 -4.5, 3 23, 4 8.8 5 97 and 6 96
(2) 12BA6 pin's 3 35, 4 22, 5 20 and 6 97
(3) 50B5 pin's 2 5.34, 3 35, 4 86, 5 126 and 6 95
(4) 35W4 pin's 3 86, 4 124 and 7 134
(12AT6 pin's 3 12.6 and 7 54.7

Frank
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Re: My new project

Post by 75X11 on Mon Oct 27, 2014 8:39 pm

I would let the Dr. or WC chime in before running it too much.
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Re: My new project

Post by frank1956 on Wed Oct 29, 2014 12:26 am

75, You are right, not going to mess with it anymore until I know for sure or at less have a better understanding of what is going on with it.

Frank
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Re: My new project

Post by 75X11 on Wed Oct 29, 2014 12:32 am

You appear to be getting close. I just didn't want to see you have any finish line calamities. Very Happy
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Re: My new project

Post by frank1956 on Wed Oct 29, 2014 9:09 pm

Yea but not sure how close. Did find out the 505B tube had a leakage so have a NOS on the way. I know that was some of the problem, not sure why I have slightly higher voltage on some tubes, some are close to be within tolerance, but yet not there. I have a standby speaker to replace the old one if that might be apart of the problem. I will wait to the 50B5 tube arrives and proceed from there.

Frank
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Re: My new project

Post by frank1956 on Fri Oct 31, 2014 10:35 pm

Received a NOS 5OB5 tube today, put it in a still have slight hum on radio, volume control does not control volume steady all the way across. Need some help on this one!!! Could speaker be bad, did the hot solder to volume control terminal and got a sound. Took voltage reading which are posted on the second part of this thread.

Frank
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Re: My new project

Post by 75X11 on Fri Oct 31, 2014 10:41 pm

Does the level jump as you move the volume control? If so you may have a dirty or bad volume pot. Sometimes they will jump where the "wiper" has sat for long periods of time.
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Re: My new project

Post by Wildcat445 on Fri Oct 31, 2014 11:38 pm

Did you re-check your wiring, particularly around the volume control? I can't read the schematic symbols, so what is the voltage on the screen of the 50B5?

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Re: My new project

Post by frank1956 on Fri Oct 31, 2014 11:40 pm

75, No up down or in between. One low steady hum. Don't even get any static?? Just replaced speaker still the same. All the other tube test good.

Frank
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Re: My new project

Post by frank1956 on Fri Oct 31, 2014 11:49 pm

Wildcat445 wrote:Did you re-check your wiring, particularly around the volume control?  I can't read the schematic symbols, so what is the voltage on the screen of the 50B5?

WC

WC, I am not sure which one is the screen, but here is the voltage I have taken within the last 48 hours.

Tube 5OB5 Pin 2 (K) 5.3 Volts, pin 3 (H) 35 volts, pin 4 (H) 86 volts, pin 5 (P) 126 volts and pin 6 (G) 95 volts. The letter are what is on the schematic socket voltage chart.

I will re-check the wiring around the control.

Frank
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Re: My new project

Post by 75X11 on Sat Nov 01, 2014 12:34 am

If you get no audio response when touching the center lug (wiper) of the volume pot, it should be after that if it is a audio signal loss. Usually a 60 hz hum is when there is no signal applied to an amplifier stage and that amp is only amplifying residual noise from your power being applied as opposed to the signal that it should be getting.
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Re: My new project

Post by frank1956 on Sat Nov 01, 2014 4:50 pm

75, I do get an audio response when I touch the center lug of the volume pot. I was re-checking my wiring and notice on the 12AT6 tube pin # 5 there is a tail where something was removed, not sure what that might have been. Checked all my cap' and resistor they seem to be all there. Per the schematic it look's like it is a common wiring, but to where I am not sure. I have attached a picture.

Frank

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Re: My new project

Post by 75X11 on Sat Nov 01, 2014 5:45 pm

From the schematic, it appears that pin 5 is an additional signal connection that has been grounded to render it inert. Make sure it is connected pin 5 to ground and nothing else. When you say the caps and resistors are all there, I assume you mean they are all present and wired correctly. I am wondering if you may have a problem with one of your capacitors that carries the signal between the stages. such as the one connected inline to pin 6 of your 12AT6 tube. They can fail, I have had it happen and it blocks the signal. The tube still has most of it's operating voltages but it has nothing to amplify nor mix nor detect. If you have a capacitor tester you can check them, or you could get a substitution box to try a known good one in that circuit, or have a few mica spares of likely values. Also make sure your resistors are close to their posted values.
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Re: My new project

Post by frank1956 on Sat Nov 01, 2014 10:16 pm

75,
Yea that is what I meant all the cap's and resistor are present and wired correctly. It look to me like that pin # 5 12AT6 need to tie into the 470 K resistor, just going by what I see on the schematic and how I traced it out. If that is the case my pin # 5 is not tie into nothing.


Frank

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Re: My new project

Post by Dr. Radio on Sat Nov 01, 2014 10:50 pm

Hey Frank, sorry for the delay. Been a crazy week.

Your pin 5 and pin 2 from the 12AT6 definitely need to tie to the common B-.

Here's what I have suggested to others in the past to quickly determine if your audio circuits work.

Grab a battery powered portable radio, walkman, cd player, mp3 player whatever, as long as it has a earphone jack. "Sacrifice" an old set of earphones/headphones by leaving the little plug alone, but cut off the part that went on your ear(s).  If it is a stereo set-up, leave one channel (left or right) just left un-connected, but leave the wires apart so they don't short together. You just need one set of "output" wires. When you strip the cable you'll have a shield (raw wire) and a colored insulated wire. This is....drum roll...you're new audio injector!

Take the audio "ground" or shield/raw wire and connect to B- of your radio.  Take the signal wire (insulated wire) and install a .1 uF @ 600 volt capacitor in series with it (this protects your portable from stray voltage). The other end of the cap is now your probe. (If this is just a mono earphone, there are no shield/center conductors, just separate the wires and connect either one as described.) Connect this probe point (the other end of the cap)to the input side of your radio's audio circuitry. In your case, you'd connect it to where the 47k resistor, the .00025 cap and the 3.3M resistor all tie together. Does the radio play your own music wonderfully?  IF it does, the AF (audio frequency) circuitry is fine. If no, you've got some tracing and checking to do.


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Re: My new project

Post by frank1956 on Sat Nov 01, 2014 11:07 pm

Dr. Radio,
So if I understand correctly I need to tie pin # 2 & pin # 5 12AT6 together i.e. with a bare wire? Thanks for the advice, but I have none of though devices, will a signal generator do the same thing?? Vice playing your favorite song.

Frank
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Re: My new project

Post by Dr. Radio on Sat Nov 01, 2014 11:18 pm

Frank,

Yes 2 and 5 will tie together, but remember, in addition, the junction you make also has to tie to B-.

So in other words, if Pin #2 is already connected to B- in the radio, all you have to do is connect a piece of wire from #2 to #5.

You need something that puts out AF (audio frequency) alone. You don't want it modulated. If your RF generator has a jack set-up that just puts out the audio tone, that will work. You don't want to use the regular output you use to align radios.

I suggest trolling around the Goodwills, Salvation Army's etc. It's easy to find some old hand held am/Fm radio or something for a few bucks that will make your life simpler when it comes to injecting audio signals. I like to use something to "real" audio rather then just a tone to hear how things are coming through (distortion, etc). Just my 2 cents.
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Re: My new project

Post by frank1956 on Sun Nov 02, 2014 12:12 am

Dr. Radio,

Pin # 5 connected to B-. I just do not remember anything connected to pin # 2, all my work on 12AT6 was on pin's 6 & 7. I don't think I connect a capacitor in a wrong spot? Pin 5 definitely has a tail were I or someone removed something.



Frank
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Re: My new project

Post by 75X11 on Sun Nov 02, 2014 12:18 am

It shouldn't have anything else connected to it according to the schematic, just B-.
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Re: My new project

Post by Dr. Radio on Sun Nov 02, 2014 12:49 am

Ok, Frank Smile

It's late, I'm tired and on a tiny touch screen so maybe my eyes are playing tricks on me.....

But the between the schematic and the picture you took, to me, I see some incorrect connections on that 12AT6 socket.

I'll have to get to real 'puter again, but if you're still up, carefully check your pin-outs on the 12AT6 and how those connect to the volume control.
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Re: My new project

Post by frank1956 on Sun Nov 02, 2014 10:23 am

Dr. Radio,
The connections on 12AT6 seem to be correct, but again I am still learning this and do appreciate all the help I am getting.

Curiosity question if the volume control was bad, there would be no sound of any kind produced out of the speaker correct??

Frank
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Re: My new project

Post by Dr. Radio on Sun Nov 02, 2014 9:21 pm

Hey Frank,

It's hard to tell where all the wires go, but the more I look at it, it does appear that you have it wired correct. The schematic doesn't agree--that's the issue, but that's not your fault. Looks like a mess-up or a later production change.

The every radio schematic I've seen has a coupling capacitor between the center pin (the wiper) of the volume control and the detector tube. The schematic shows a direct connection. You have clearly wired a capacitor in there (seems fine to me, especially if that is how you found it). That's one of the things throwing me off.

Pin 2 and Pin 5 on the 12AT6 both need to "see" B- or "common", not chassis ground.

From what I can tell?  They are good? Not sure from the angle.



"A" is connected to Pin #2. Does this indeed connect to B- ?

"A2" is connected to Pin #5. Does this indeed connect to B- ?



As far as your question, it depends on the failure mode of the volume control. If the volume control looses it's B- connection on the internal resistance track, no volume control, radio will play loud. Break in the wiper connection, no audio output, but you may get hum from induced noise in the circuitry. Break in the "hot" side of the volume pot resistance track, again, no output.

I'm assuming (I hope you are using an isolation transformer for safety). ......

If you are, you can take a paper clip and unfold it touch pin #1 of the 12At6 tube. Keep your other hand off of the chassis completely. You should hear a loud HUMMMMMMMMM out of the speaker with the volume turned up.
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Re: My new project

Post by frank1956 on Sun Nov 02, 2014 9:48 pm

Dr. Radio,
A is connected to Pin # 2, But from what I see does not connect directly to B-. A2 is connected to Pin #5 and does connected directly to B-. I have attached a pic for clarification. I have tried the hot solder to the middle lug on the volume control and got a hum out of the speaker, is that the same as touching Pin # 1 12AT6?



Frank
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Re: My new project

Post by Dr. Radio on Sun Nov 02, 2014 10:39 pm

Frank,

Pin #2 is the cathode of the 12AT6 tube. It MUST absolutely connect directly to B- or the tube will not work properly. You need to correct the mis-wire, not just jumper the circuit as is to a B- connection or that will cause more grief.

Yes, touching pin 1 induces noise, your body acts like a big antenna for noise so there is plenty of "hum" test signal, more so then with the iron, but either will work.

You must get the stages wired correctly first or you still can't proceed.
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