Philco K1636X - Low Volume after warmed up

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Philco K1636X - Low Volume after warmed up

Post by ntp71 on Sat Mar 23, 2013 3:18 pm

Hello,

I am new to the forum and I will search for similar problems after I get done putting up drywall later today. However I thought I would ask the question anyway since I am pretty busy lately and am looking for a starting point.

I have a Philco K1636X, which is a tube console with phonograph. When the radio is turned on after a minute everything works fine. After about 10 minutes of run time, the volume could be at 10 and yet it is very low. I have part of the schematic and the other part was eaten by a shop vac. So I am looking for an idea of where to start looking for problem with this guy. I would also like to point out that if the phonograph is being used the volume is just as low.

Thanks for any help.

Neal

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Re: Philco K1636X - Low Volume after warmed up

Post by ntp71 on Sat Mar 23, 2013 3:38 pm


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Re: Philco K1636X - Low Volume after warmed up

Post by Bill Cahill on Sat Mar 23, 2013 3:54 pm

Have you replaced any of the paper capacitors yet? Or, the power supply electrolytics?
If this hasn't even been done yet, you are asking for trouble trying to use it.
How much electronics knowledge have you got? Please tell us about yourself. We need to know more so we can help you.
This scheamatic isn't readable. Sorry.
Take pictures of the radio. It would help.
Thanks.
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Re: Philco K1636X - Low Volume after warmed up

Post by ntp71 on Sat Mar 23, 2013 4:07 pm




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Re: Philco K1636X - Low Volume after warmed up

Post by ntp71 on Sat Mar 23, 2013 4:11 pm

Hello Bill and thanks for the reply.

This unit was being used by an old lady that I bought it from last year. I did not replace anything on it and it has worked well since I got it. However it is only usually used on the weekends for a few hours.

My experience is the following. I hold an Associates Degree in Electronics Engineering Technology, I held an Associate CET certification, I am a current/soon to drop out student at UNCC in the Bachelors program for Electrical Engineering Technology, and I am an Electronics Technician who works on the Electrical System of the TPQ/37 Radar System. I have take alot of theory classes concerning receivers, transmitters, and antennas, however I do not have alot of hands on experience with these types of radios.

That being said...I have ZERO experience working with tubes and tube radios.


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Re: Philco K1636X - Low Volume after warmed up

Post by Bill Cahill on Sat Mar 23, 2013 4:18 pm

Well, you need some basic test equipment, such as a tube tester, tolt-ohm meter, side nippers, screwdrivers, soldering itron, or, gun,
solder, desoldering tools, , etc.. I would reccommend on boning up on tube restorations. We have a good forum for tha here. Dr. Radio tells alot of good basics.
I suspect your radio is due for rebuilding.
Looks lie mid 60's to me.
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Re: Philco K1636X - Low Volume after warmed up

Post by ntp71 on Sat Mar 23, 2013 4:52 pm

I have most of that stuff except the tube tester..I will check out that forum later on. I don't want to get into a rebuild just yet..I have too many other projects going on at the moment.

Thanks

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Re: Philco K1636X - Low Volume after warmed up

Post by Bill Cahill on Sat Mar 23, 2013 9:17 pm

Well, you are most welcome here, believe me.
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Re: Philco K1636X - Low Volume after warmed up

Post by Wildcat445 on Sun Mar 24, 2013 12:04 pm

Bill's right. That schematic is pretty bad. However, I think I saw a 6CA4 rectifier and 6BQ5 output tubes. IT has a power transformer and 8 (?) tubes total. Might actually be a hybrid chassis. A rebuild is in order if you want to save the power transformer and that expensive rectifier. My first guess at the cause of the low volume problem would be coupling capacitors, probably in the output stage. Time to replace all the paper capacitors, electrolytic caps and go thru the turntable. Then you should be good until your grandkids are your age. I would strongly advise you to not operate your stereo until it is serviced and known to be in good condition.

Regards

WC

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Re: Philco K1636X - Low Volume after warmed up

Post by ntp71 on Sun Mar 24, 2013 12:22 pm

I may pull it out this week, set it on the table and do and E&I (Evaluation and Inventory) on it.

I'm trying to avoid staring a new project. I have to texture my daughters room, put 2 new windows in, build a greenhouse, and build a shed within the next month. However I could take it to work and do some work on it during my breaks.

I found a book at a yard sale last year called "How to Repair Old Time Radios". I got it for $0.75. I saw on amazon that it sells for $50+.

Thanks for your help. I will update as I go along.

Neal

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Re: Philco K1636X - Low Volume after warmed up

Post by Dr. Radio on Sun Mar 24, 2013 9:26 pm

Hi Neal,

Yes, please do not plug in/power up this unit anymore until at least the basics have been gone over.

That was a nice score on your book at the garage sale. Those usually bring a lot more $$$.

The "K" in the model number is apart of Philco's later alphabetical model year coding.

"C" = 1955
"D" = 1956
"E" = 1957
"F" = 1958
"G"= 1959
"H"= 1960
"I" = Intentionally skipped so it wouldn't be confused for a "1".
"J"= 1961
"K"= 1962
"L"= 1963
"M"= 1964
"N"= 1965


So your unit would have been new for the 1962 model year.
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Re: Philco K1636X - Low Volume after warmed up

Post by ntp71 on Fri Aug 30, 2013 8:58 pm

Hello Again.

I have been tinkering with the stereo lately it has made the project list and is getting almost one hour a day of attention, with possible more hours devoted on the weekend.

Here is a little overview of what I have found and know of:

I believe I have found the cause of my volume problem. I found a bad transformer on what I believe is the audio output section of the receiver. I was able to re-draw the part of the schematic where this section lies. From what I understand this transformer follows two 6BQ5 tubes in a push-pull configuration. I do not know what voltage values are supposed to appear at the transformer and it cannot be measured out of system. It seems the secondary section of the transformer has a short because I am getting no output (0v) on the secondary when tested on the bench at (10V) on the primary.

Red-Brwn 570 ohms +/-
Blu-Red 270 ohms
Red-Brwn 270 ohms

Blk-Green 0 ohms

I have the receiver pulled from the cabinet and am taking inventory of the mica caps and the transformers that I plan to replace. If anyone can tell me where I can get a suitable replacement for the burned out transformer (Philco Part# 32-8996-1), and the two smaller transformers that are used in this circuit (Philco Part# 32-8990-2) I would really appreciate it. Also if anyone knows a good place to buy capacitors from.


***I'm having a hard time uploading the pic of the schematic****

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Re: Philco K1636X - Low Volume after warmed up

Post by Bill Cahill on Fri Aug 30, 2013 11:00 pm

Sounds like the primary is shorted. Low, unmatched values. The resistance going to spkr would be extremely low.
You need to look up the impedence for push pull 6BQ5 audio out., and, how much voltage is applied. An ohm meter is not the same as impedence, and, not very accurate. But, it sounds like part of the primary winding is shorted. I assume you are checking accross the transformer only??
I think that set puts out 15 watts of audio power, so that must be figured in.
Shouldn't be too hard to find a new transformer for it.
Remember, the secondary would test 0. The impedence would actually be be 3 ohms. But, again, a meter cannot measure impedence.
I'd say you've found your problem.

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Re: Philco K1636X - Low Volume after warmed up

Post by jerryhawthorne on Fri Aug 30, 2013 11:50 pm

NTP, some clarification is needed on your measurements.
1:  you have two different red-brown measurements.  should the last one be blue-brown?  if so, the primary looks fine.
2:  when you indicated you put 10V on the primary, may I assume it was A/C?
As Bill indicated, the resistance as you measure it with a meter of the output of the transformer is low, especially if it is hooked to the speaker voice coil.
If you have the primary disconnected and the secondary hooked to a speaker, just touch a 9V battery to the primary (any two wires) and you should get a pop from the speaker.  Just a quick touch.
I believe your chasing a ghost here as I often do.  I really doubt the problem with your dropping off of volume has anything to do with your output transformer and more to due with a tube or more likely capacitor problem.  Replace those caps!  Also, if they are mica caps in the picofared range, don't bother with those.  They seldom fail.
Good luck,  Jerry

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Re: Philco K1636X - Low Volume after warmed up

Post by ntp71 on Sat Aug 31, 2013 8:23 am

jerryhawthorne wrote:NTP, some clarification is needed on your measurements.
1:  you have two different red-brown measurements.  should the last one be blue-brown?  if so, the primary looks fine. Jerry
sorry...you are right

Blu-Brwn 573
Blu-Red 270
Red-Brwn 270

jerryhawthorne wrote:
2:  when you indicated you put 10V on the primary, may I assume it was A/C?Jerry
sorry...I used DC...my mistake


I forgot to mention the pool of wax surrounding the transformer which lead me to believe the transformer was bad. Also, the caps I was planning on replacing were not Mica Caps..I mispoke...I meant Mylar (paper).


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Re: Philco K1636X - Low Volume after warmed up

Post by Bill Cahill on Sat Aug 31, 2013 10:51 am

If it has a pool of wax, it's definately shotred, but, it would have to be the primary. Not the secondary.
Remember, hose resistances aren't the actual impedence.
You don't need to put any voltage on them while checking resistances.

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Re: Philco K1636X - Low Volume after warmed up

Post by ntp71 on Sat Aug 31, 2013 11:03 am

Bill Cahill wrote:If it has a pool of wax, it's definately shotred, but, it would have to be the primary. Not the secondary.
Remember, hose resistances aren't the actual impedence.
You don't need to put any voltage on them while checking resistances.
Yes, definitely a pool of wax around transformer. I was only applying voltage to the transformer on the bench to determine if it was a step up type of transformer.

So having this bad transformer, I am guessing that that is why I had a steady low volume and was unable to adjust loudness. Thoughts?

Also, what type of transformer is it? I know its a center tapped transformer on the primary and how the positive wave flows on once side, and negative flows on the other and it is recombined on the output. So is this just a 1:1 coupling transformer?

Neal

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Re: Philco K1636X - Low Volume after warmed up

Post by Wildcat445 on Sat Aug 31, 2013 6:54 pm

My thoughts would be that I have not seen enough evidence that I would condemn the transformer at this point. This is a stereo unit, right? It should have two output transformers, one for each channel. Are both channels weak? If so, a single audio transformer will not cause that. A "pool" of wax around a transformer is not necessarily evidence of a bad transformer. Have you measured B+ at the rectifier cathode, and the positive end of the input filter cap? At the positive end of the output filter cap? On the plates of both output tubes? Low B+ can give you low volume. Have you changed all the paper coupling caps? An open or leaky coupling cap can cause low volume. Transformers cannot effect the function of a volume control. I feel that you have another problem. Without voltage measurements suggested and more, it will be difficult to come to a reasoned diagnosis. Good luck.

Regards

WC

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Re: Philco K1636X - Low Volume after warmed up

Post by ntp71 on Sat Aug 31, 2013 7:23 pm

Wildcat445 wrote:My thoughts would be that I have not seen enough evidence that I would condemn the transformer at this point.  This is a stereo unit, right?  It should have two output transformers, one for each channel.  Are both channels weak?  If so, a single audio transformer will not cause that.  A "pool" of wax around a transformer is not necessarily evidence of a bad transformer.  Have you measured B+ at the rectifier cathode, and the positive end of the input filter cap?  At the positive end of the output filter cap? On the plates of both output tubes?  Low B+ can give you low volume.  Have you changed all the paper coupling caps?  An open or leaky coupling cap can cause low volume.  Transformers cannot effect the function of a volume control.  I feel that you have another problem.  Without voltage measurements suggested and more, it will be difficult to come to a reasoned diagnosis.  Good luck.

Regards

WC
Hello WC, and thank you for joining in the discussion. The symptom was just a low volume in the speakers that could not be adjusted louder. It worked for awhile when it was turned on then the volume would fade out. Once that happened I shut the stereo down and have not run it since. My plan is examining the unit looking for any possible defects and replace the paper caps. Once I have done this I will reapply power to troubleshoot. As far as measuring the voltages I did not do that prior to removing the unit, because at the time I was not sure where to start so I took up some reading on the subject to become a little more acquainted with the unit prior to performing any work on it. So far I have removed the unit from the console, cleaned the dust from it, and started to take inventory of the paper caps. Upon doing so I found the supposed bad transformer. I have attached two schematics on the last page. One is the original, and the other is a sketch I made of where the bad transformer is.

Neal






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Re: Philco K1636X - Low Volume after warmed up

Post by Bill Cahill on Sat Aug 31, 2013 7:48 pm

Wait a minuite! I thought you said this was NOT a stereo! Is it, or, not??
What pins of the 6BQ5 do the primary wires connect to?? If they are the plate, it IS the audio output transformer.. That is not ca coupling trans. It would connect to the voice coil of one of the speakers.
How manny output tubes does it have? How manny transformers??

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Re: Philco K1636X - Low Volume after warmed up

Post by jerryhawthorne on Sat Aug 31, 2013 8:06 pm

I'm with Wildcat in that you should not condemn the transformer as it wouldn't provide the problem you describe and a pool of wax only indicates that the transformer has got hot. There are several things that could do that other than a "bad" transformer and indeed the transformer could still be just fine. Your measurements indicate a balanced primary.
Put the puppy back in and wire it up and compare the resistance readings to the other transformer on the other channel.
Do replace those caps, e-caps and wax caps, particularly those in the output section. Bad coupling caps in that area can cause your output tubes to draw way to much current and overload the output transformer.
Regards, Jerry

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Re: Philco K1636X - Low Volume after warmed up

Post by ntp71 on Sat Aug 31, 2013 8:41 pm

It's a Philco Stereophonic High Fedelity.

Please see the 2 schematics on the first page. If you click to make them larger and then right click the image and save it to your computer you can open it up in Microsoft Paint and enlarge it.

The drawing I made is of the section of the schematic that is torn based on tracing the wires.

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