[murf]

Hi guy's,
Looking at my 300x and had a couple questions.
Noticed that as soon as I apply the power, I get all kinds of static and crackling noises. This is immediately upon turning it on, before the tubes warm up.
Anyone ever run into this before or have a suggestion as to what could cause this?
Then my second question is, why is there a plastic cover glued over the band selector windows that tell you what band your on.
The light comes on when your on any of the 3 bands, and goes out when switching to the pushbutton mode. Then another light on the bottom lights.
Did people complain about the lighted portholes for the different bands?
I kind of like having the band selector lights to be visible.
Also noticed that after let it run for about 10 minutes, the magnet on the speaker was pretty warm. Is this normal?
Have it plugged into a speaker out a 40-190. Same plug, but the 190 speaker says its an 1100 ohm. Don't see the ohm rating listed on the 300 speaker. WHen run to the 300 speaker, sounds the same.
No parts list for this one on Nostalgia.
Should probably get a parts list.

murf

[morzh]

Crackling nose right upon powerup is no good. Pull All tubes out, including the rectifier and see if it persists. Locate, fix.

Could be caps, could be..anything...transformer.

Field coil should get warm. Not unbearably hot. But quite warm, it dissipates rom a few to 10-plus Watts in various radios.

[murf]

Thanks for the info Morzh,
Did as you suggested and here is what I found.
Removed all tubes,no sound or static.
Installed the 80 rectifier, Had the crackling and static but at a lower volume.
Pulled the 80 and installed other tubes one at a time while powered up. No static or crackling.
Installed a different rectifier tube and now just have the normal amount of buzz, but without the crackling and static.
Maybe I will hook up the loop and see what happens.
Will let you know.
Thanks,
murf

[morzh]

I thought of the rectifier by name, but it is good to do a thorough check - you could have a breakdown in rectifier, gas maybe. Toss it.

[murf]

Tried it 3 times now with different 80 tubes, and now I get all the noise no matter which tube is installed.
Hooked up the loop and no change.
It does have new e caps in it.
Funny, because I get the static etc., but it is not affected by the volume switch.
I did test all the tubes before and there is one 37 tube that is weak.
I wish I had a few more tubes that are known good.
I hate to start replacing caps until I can get some reception out of it.
These Philco's always give me grief.
Thanks for the help and have a great evening.
murf

[morzh]

Murf

I don't quite get it.

What you refer to as "noise" - is it the same crackling noise?
So when you changed the rectifier the first time, the drackling stopped and then you changed the rectifier again and it is back? Even with the rectifier that seemed to stop it?
Does it stop when the rectifier is out?

If yes,

Get the crackling going.
Remove all tubes one by one, see if it stops at some point.
If not, see if you have a very dirty panel for rectifier or very loose contacts.
Poke around with an insulated wand, see if you can touch somewhere and make the noise.
Then if nothing helps, go to caps.


BTW - have you recapped it yet?

[murf]

Yes, the noise is the crackling and static noise I started with.
Goes away with rectifier out.
I tried installing tubes one at a time yesterday, and got no noise until I put the 80 back in.
For some reason, the first time I tried that, I had no noise with the tube installed(different tube).
The next time I tried with other 80 tubes, it went back to the original noise.
I will try as you suggest tonight and see if I can uncover anything.
Thanks,
murf

[morzh]

Basically the question is - is the crackling present when you have NO TUBES in OTHER THAN 80?

Install 80, remove the rest. Use a known good one.

See if the noise starts even before the 80 is able to warm up, that is the second you turn it on.

Also see if this by chance your power switch doing the popping? Or the transformer? The 80 presents the filament load; without it there is no load when other tubes are pulled out.

So you could also look at the 80's heater (5V) winding and all the connections.

Also look at the panel of 80.

Basically the big difference is, whether the noise starts immediately on turning the power knob when the 80 is in, or it waits a second or two before 80 starts warming up.

[murf]

I tried that yesterday and found that with all tubes pulled, the noise started as soon as the 80 was installed. Before it had a chance to warm up.
Pull the 80 and the noise is not present.
All tubes in but the 80, and no noise at all.(no audio at all).
I did try cleaning the switches to no avail.
murf

[morzh]

Murf

One more time:

Does the crackling start IMMEDIATELY upon insertion of the 80 (or if it is in cold, IMMEDIATELY upon turning power on) or a second or two later?

Meantime, start checking:

1. Output transformer - input winding to output winding (or to GND). Making sure there is no electrical breakdown.
2. Field coil to GND. Or to the metal part of the speaker if it is grounded.
3. Turn out the lights and in full darkness turn on the power. See if while hearing crackling you see arcing anywhere.

[murf]

Crackling noise starts Immediately like I said before.
I will take a closer look tonight.
I will do as you suggested before and pull tubes one at a time while powered up and see if there is any change.
Will then flip it over and check for loose connections etc. around the rectifier and go from there.
Thanks again for your help,
murf

[morzh]

If it starts immediately it is likely related to the section including the power transformer and the wiring towards the 80's filament. There is no other load there. And the current is fairly sizable so I would look at the 80's panel as well - arcing etc.
It is also possible the transformer is simply loose and what you are hearing is the metal plates vibrating and hitting each other in the power transformer's core when under load of 2A by 80's filament. Although then why other tubes do not do this? Their currents are smaller but together they amount to quite a bit, especially the two 42 tubes 0.7A each.

[murf]

Ok, this is frustrating for sure.
Powered it up and got crackling noise as stated before.
Started pulling tubes one at a time and found when I got to one of the 7b7 tubes it stopped after I pulled it. Rectifier is still in.
Pulled the last 3 with no change.
All I get is a very slight humm from the speaker.
Put the tubes back in, including the same 7b7 tube that was causing the problem, and now the noise is gone.
Replaced all the tubes and noise is gone.
Replaced the 7b7 tube in question with another, and still no noise.
Maybe dirty pins on the loctal tube?
I will let it cool down and try it again cold and see if the noise returns.
Maybe I should take the time to clean all the tube pins while I am at it.

[murf]

http://www.nostalgiaair.org/Resources/423/M0013423.htm

Crackling seems to be gone now, but I am getting no audio other than the very faint humm that you normally get.
Which tubes would control the audio end of it and which tubes control the reception?
murf

[morzh]

Murf

Can you post a link to the sch so we do not have to go to NA every time and look for it?

Your audio is the two 42 tubes.

I would clean and tightened all the panels' contacts.