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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Sat 14, 2012 2:35 am 
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Location: 97381, USA
I managed to sneak the chassis into work today to cure some more ills 8) I've managed to quell a good amount of the hum and buzz by rerouting some leads and decided to start on the RF section.

Second IF 7H7 voltages: pin 3 is 280v, which is more than twice as high as it should be--correct? Pin 2 is at 263v which is a lot closer to where it should be. R11 and C15 have been replaced. This is the messed up loctal socket I plan on replacing. The tube tested fine but the filament doesn't light due to the faulty socket. Would that cause high voltage?
Ben

Edit:
I was reading the wrong voltage chart. On the 1226 pin 3 should be 105v so it way high
Also, pin 7 should be 1.5v and it's 6.8v


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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Sat 14, 2012 2:50 am 
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The First IF 7H7 voltages are also off.
pin 2 = 269
pin 3 = 184
pin 7 = 200mv
pin 8 = 1.6v
The caps connected to that one have been replaced but no resistors.
Ben


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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Sat 14, 2012 5:15 am 
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"Second IF 7H7 voltages: pin 3 is 280v, which is more than twice as high as it should be--correct? Pin 2 is at 263v which is a lot closer to where it should be. R11 and C15 have been replaced. This is the messed up loctal socket I plan on replacing. The tube tested fine but the filament doesn't light due to the faulty socket. Would that cause high voltage?
Ben

Edit:
I was reading the wrong voltage chart. On the 1226 pin 3 should be 105v so it way high
Also, pin 7 should be 1.5v and it's 6.8v

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The First IF 7H7 voltages are also off.
pin 2 = 269
pin 3 = 184
pin 7 = 200mv
pin 8 = 1.6v
The caps connected to that one have been replaced but no resistors. "

Ben, I think you are getting some erroneous readings probably due to bad tube socket connections as you have mentioned several times in this thread. You need to fix that before you can get any meaningful voltage readings.

You say you are getting 1.6 volts on pin 8 of the first IF. Should be 0 (zero). Pin 8 is a filamet connection that is grounded (or should be) and pin 1, the other heater connection should be 6.3 volts AC.

Are you using a Riders schematic? If so I can email you a PDF of the Sam's Photofact for that set. The scematic is much better to read. If you want it PM with your email address.


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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Sat 14, 2012 2:48 pm 
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Ben

Second IF pin #3, screen, voltage is supplied through a resistor, R11 - 33K. If this tube isn't lit no current is being drawn and voltage will be high.

Need to have filaments operating first, pin #1 and #8. Before voltage reading can have meaning need good socket contact. After that the radio may operate.

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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Sat 14, 2012 7:55 pm 
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I have a few new sockets coming in a few days, hopefully on my days off. That would be nice to get this running again. I'll post some pics of the restored cabinet and record player.


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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Sun 22, 2012 6:21 am 
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Back at it.
This is what I've discovered so far. IF2-7H7 socket was replaced and I carefully checked to make sure all was wired right. Still no filament lighting up. I swapped tubes between IF 1 and IF 2 and the 7H7 that didn't light in 2 lit in 1 so it's not the tube filament. Then I checked voltages and discovered something interesting.

Pin 1 and 8 were 6.7vac which is correct. Pins 1,4 and 5 are basically wired together so they also showed the 6.7vac. I accidentally touched the probe to pin 6 while I was in the AC mode and it too showed 6.7vac.

Pin 2 was 267vdc and pin three was high at 233vdc.

R10 has been replaced but the cathode resistor in 7H71 hasn't


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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Sun 22, 2012 1:51 pm 
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noisebox wrote:
Pin 1 and 8 were 6.7vac which is correct. Pins 1,4 and 5 are basically wired together so they also showed the 6.7vac. I accidentally touched the probe to pin 6 while I was in the AC mode and it too showed 6.7vac.
When you touched pin 6, if the other probe was on pin 8 that would be correct. The reason is that both pin 1 and pin 6 are at gound potential as far as the filament voltage is concerned (pin 1 is directly grounded, and pin 6 is grounded through the IF transformer).

Until that tube actually lights up nothing is going to work right and the plate and screen voltages will be way too high. If you have 6.3 VAC between 1 and 8 and still no filament light, there is a connection problem between the socket and the tube pins or an open filament. If you pull the tube and check the resistance between pins 1 and 8 it should read 20 to 30 ohms. You can't test this with the tube installed because all you will measure is the resistance of the filament winding of the transformer.

The cathode resistor isn't a concern until the filament works. Once the filament works then checking the plate, screen, and cathode voltage will be a good idea. It will also become a good idea to make sure the Phono switch part of the bandswitch is working correctly at that time.

Curtis Eickerman

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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Sun 22, 2012 3:28 pm 
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Curtis, I clip my DDM to ground on the chassis when I test voltages. That said, when I touched pin 6 I got the 6.7vac. Something's not right if I'm getting that voltage from the IF transformer 2 to ground.

I checked the pin 1 to 8 resistance on all my 7H7s and came up with 3.5 ohms with the tubes out of socket. I checked the sockets resistances on both 7H7s and there was zero resistance.

Now here's a funny thing. With each tube pulled one at at time I measured filament voltages in the sockets. 7H7 IF1 measured 6.7vac 7H7 IF2 measured around [b]20vac.[/b] I pulled a 6K6 just to see and it had 6.7vac.

I'm going to attempt to trace why this is happening and in the mean time go into the selector switch and do some inspection and cleaning.


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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Sun 22, 2012 4:58 pm 
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noisebox wrote:
Curtis, I clip my DDM to ground on the chassis when I test voltages. That said, when I touched pin 6 I got the 6.7vac. Something's not right if I'm getting that voltage from the IF transformer 2 to ground.
Yes, this would definitely not be right.
noisebox wrote:
I checked the pin 1 to 8 resistance on all my 7H7s and came up with 3.5 ohms with the tubes out of socket. I checked the sockets resistances on both 7H7s and there was zero resistance.
My apology, I slipped a decimal place. Yes, around 3 ohms would be right versus my incorrect 30 ohm statement.
noisebox wrote:
Now here's a funny thing. With each tube pulled one at at time I measured filament voltages in the sockets. 7H7 IF1 measured 6.7vac 7H7 IF2 measured around 20vac.I pulled a 6K6 just to see and it had 6.7vac.
Yet another indication that something about the wiring around that 7H7 is not right.
noisebox wrote:
I'm going to attempt to trace why this is happening and in the mean time go into the selector switch and do some inspection and cleaning.
This is definitely the right thing to do.

Curtis Eickerman

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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Tue 24, 2012 9:46 pm 
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Got the 7H7 to light :D
The problem was that the original socket had a ground to the mount/chassis. The ceramic replacement didn't. I ran a ground from pin 1 to chassis and it worked! This is one of my first aha moments for troubleshooting. I really appreciate all of the help from the pros.

As it stands now I haven't checked all voltages yet but I get a station, though weak. I still have a loctal socket issue with the 7F8 being intermittent. When I wiggle it the station cuts off. That's one I won't replace because it's right under the band switch.

I cleaned all of the contacts on the band switch. You don't realize how bad they are until you see the color that's revealed. Deoxit with a Q-tip works pretty good.

So, I'm going to go back, fix that socket and check voltages on everything to make sure all is well, then I'll try an alignment--which I think the reception issue might be.

Thanks again for walking me through these things. I learned that there can be compound problems and you have to work through these one stage at a time. I've also learned more of where to look.


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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Tue 24, 2012 9:53 pm 
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noisebox wrote:
Got the 7H7 to light :D ... As it stands now I haven't checked all voltages yet but I get a station, though weak. I still have a loctal socket issue with the 7F8 being intermittent. When I wiggle it the station cuts off. That's one I won't replace because it's right under the band switch.
Yeah! And at the same time too bad those sockets are such a pain. I certainly understand not wanting to dig under a bandswitch to replace one.

Good luck with the alignment.

Curtis Eickerman

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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Tue 24, 2012 9:56 pm 
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Thank you Curtis. One more thing--one of the 6K6s has a purple glow. I replaced it but the new one also has it. Is that a problem?


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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Tue 24, 2012 10:04 pm 
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noisebox wrote:
Thank you Curtis. One more thing--one of the 6K6s has a purple glow. I replaced it but the new one also has it. Is that a problem?
It may mean that the tube is a little gassy (minor loss of vacuum). It often is not a problem unless it leads to unacceptable distortion of the audio. It's not a major concern.

There are other reasons for this as well. Here is a pretty good write-up on the subject (lots of pictures of glowing blue tubes too). http://www.jacmusic.com/techcorner/ARTI ... ueglow.htm

Curtis Eickerman

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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Tue 24, 2012 10:54 pm 
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When doing the alignment, what is used for the output meter?


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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Tue 24, 2012 10:57 pm 
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noisebox wrote:
When doing the alignment, what is used for the output meter?
Typically you use a voltmeter set to AC and either connected across the output transformer primary (neither terminal of the meter is "grounded") or the speaker terminals (same as the output transformer secondary). The signal generator has to have AM modulation turned on (typically a tone).

Here is a pretty good video on how to do it.
http://www.youtube.com/watch?v=u7Humids ... AAAAHgAQAA
and
http://www.youtube.com/watch?v=TnlPvf46 ... ure=relmfu

Curtis Eickerman

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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Wed 25, 2012 1:09 am 
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Before I align I wanted to use my new Eico 324 sig generator. I replaced all of the paper caps but all I have on hand for the electrolytics are 33mf 160v. It calls for 20mf 150v. Will they work?

http://bama.edebris.com/manuals/eico/324/


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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Wed 25, 2012 3:20 am 
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Well, I have it roughed in using my older Eico Sig generator. I hate to say this but the 7FH socket has to go. It just won't get a positive connection no matter what I do. I'm also getting a loud humming thats different than the hum I get when I have the turntable working. The hum gets very loud when I tune through certain areas on the standard band.

I used my DDM as an output meter but I can see where a VTVM is essential for alignment.

I'm getting closer though. I was able to tune in to an oldies station I get good on my Mantola downstairs.

Any ideas on where to look to get rid of the loud hum?


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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Wed 25, 2012 3:42 am 
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noisebox wrote:
I used my DDM as an output meter but I can see where a VTVM is essential for alignment.
Analog meters are easier for performing alignments. It's tough judging the peak with digits flipping around.

noisebox wrote:
Any ideas on where to look to get rid of the loud hum?
Hum that varies across the band or comes up between stations is usually referred to as tunable hum. Tunable hum usually comes from something outside of the radio itself. Typical noise sources are florescent lights, motors, switching power supplies (laptop computer supplies), light dimmers and that sort of thing.

It could still be something in the radio, but I'd try turning any such things off first and see if it gets better.

This kind of tunable hum is often more of a 60 Hz buzzing too (kind of raspy). It can also get into your radio from the AC line cord. There is also the possibility of a heater-to-cathode short or leakage in a tube that can cause this. It is reasonably rare, but can happen.

Perhaps you can describe in a little more detail what this sounds like.

Curtis Eickerman

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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Wed 25, 2012 4:04 am 
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This is strange--when I touch the base of the 7H7 next to the 2nd IF --the one whos socket I replaced--about 90% of the buzz stops and reception gets a lot better. When I let go the buzz is kind of raspy and loud but the pitch remains the same.


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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Wed 25, 2012 4:07 am 
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I'm thinking I grounded it too far from the base of the tube. Someone else also did another ground like this from the 7C6 to the chassis a few inches away. That's where I grounded the 7H7 too. They used a pop rivet to stick the wire to the chassis--didn't look like the factory did that one.


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