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38-116 needs Dr. Philco.Resolved. - Printable Version

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38-116 needs Dr. Philco.Resolved. - murf - 01-17-2016

I pulled the chassis on the 38-116 again hoping I can find something.
Has crappy sound quality with lower than expected volume.
Literally has no bass response. Sound like a cheap table radio.
I re-capped it 3 years ago and replaced a handful of resistors.
Did not work when I brought it home.
Checked all tubes a replaced a few.
Checked voltages on the 6l6 tubes today and found the following.
Pin 2 checks 5.9v ac. should be 6.3.
Pin 3 checks 256v cold and 245v after warmup.Should be 290v.
Pin 4 checks 260v cold and 243v after warmup. Should be 300v.
Pin 7 checks 0v and should be 6.3v.

These readings apply to both 6l6 tubes.
What would cause it to lose the 6.3v on pin 7?
Any idea's?
Please put it in laymans terms so I can understand what you are talking about.
Some people get way to technical in their responses which don't help much if it flies right over my head.
Thanks in advance for any help.
Almost forgot, this is a code 121 chassis.
murf

RE: 38-116 needs Dr. Philco - morzh - 01-17-2016

Murf,


>What would cause it to lose the 6.3v on pin 7?


Maybe....cause it is grounded? As per the schematic?

RE: 38-116 needs Dr. Philco - murf - 01-17-2016

Ok, makes sense I guess, if that is what it is supposed to read.
Just going by the values given on the schematics.
Noticed one of the 6L6 tubes had a weird vertical glow going on, where as the other did not.
Tested it in my hikock tester and it showed shorts on about 3 settings.

murf

RE: 38-116 needs Dr. Philco - morzh - 01-17-2016

Murf

I am not sure what you mean by schematics don't apply, but if your tester (provided you trust it, and do so for a reason) shows shorts, well, you need to see what would happen if you tried known good tubes. BTW shorts might lower some voltage readings....sometimes all the way to zero.

RE: 38-116 needs Dr. Philco - murf - 01-17-2016

Thanks for the response Mike,
I am still struggling with schematics.
Brenda said that the voltage readings would read low if checking from chassis ground on this set.
I see what you mean by pin 7 being grounded. Thanks.
Will see if I can round up another tube.
I appreciate the help from you guys on the forum.
Will let you know if the tube helps.
murf

RE: 38-116 needs Dr. Philco - morzh - 01-17-2016

Maybe that tube is the whole reason for all your ills.....

RE: 38-116 needs Dr. Philco - murf - 01-19-2016

New tube helped a lot.
Also , seems there was a resistor out of place and I found a .1 cap installed where there was supposed to be a .01.
Volume is much better now.
Just need to get the bass response working better and I will call it good.
Checked tube bias tonite and looks great on both 6l6 tubes.
Will continue to poke around.
murf

RE: 38-116 needs Dr. Philco - morzh - 01-19-2016

See? You don't need no stinkin' expert, you can do it all by yourself.

RE: 38-116 needs Dr. Philco - murf - 01-20-2016

Takin baby steps on this one.
Thanks,
murf

RE: 38-116 needs Dr. Philco - AI2V - 01-21-2016

The first voltage I would have measured is pin 5 of the 6L6; that's typically around -15 volts.  

I would suspect that you have a problem in the resistor network that's connected to the B+ center tap winding.  If the pin 5 voltage is wacky, go to those resistors; one of them has gone way high in value.

RE: 38-116 needs Dr. Philco - murf - 01-23-2016

(01-21-2016, 02:18 PM)AI2V Wrote:  The first voltage I would have measured is pin 5 of the 6L6; that's typically around -15 volts.  

I would suspect that you have a problem in the resistor network that's connected to the B+ center tap winding.  If the pin 5 voltage is wacky, go to those resistors; one of them has gone way high in value.
Did that and they check -20v on both tubes.
I am satisfied now that it has about as good a sound as it gets.
Plenty of volume as well.
Back in the cabinet now and on to the next one.
Thanks for all the help everyone.
murf

[Image: http://i1161.photobucket.com/albums/q509/murphy51051/th_38-116.jpg]

RE: 38-116 needs Dr. Philco - murf - 01-31-2016

Finished the radio up, and what do you suppose I did yesterday?
Guy called me up and offered me a real nice 37-116 for a good price.
Just happened to have a 38 and a 37 stashed in his basement.
Brought home the 37-116 as I already have  a 38.
I am sure I will have some questions once I tear into this new one.
murf

RE: 38-116 needs Dr. Philco - morzh - 01-31-2016

Good for ya! You can make a surround sound system out of those.