[winkydink]

I have 4 different 42-PT95's which I am giving away as Christmas Gifts. I have made repairs on some, and others I have had others do recapping etc on them. Let us call them Radios A, B, C & D

Radio A is working fine

Radio B needs a new power on/off switch - On order

Radio C works find but low volume is too loud - new switch on order

Radio D is what my question is about.

Radio D plays well, good reception, crisp sound, able to tune stations in clear. After about 15 minutes (I set a stop watch), the tuning deteriorates, and I can no longer get crisp sound, the sound is slightly garbled.

I did what my current knowledge level allows me (I am a newbie, I can replace a capacitor or resistor, but struggle mightly at diagnosing almost any problem). I checked all the tubes. As it turned out the 7C6 tube was marginal (with readings of 50%, 62%, 65% for the 3 stages). I took another tube out of a different radio (a 7C6) and tested to see if it was better. I am going to test this at Lunch to see if this made a difference.

Here is my questions

(1) could a marginal/defective 7C6 tube cause this problem (especially when it did not occur till after 15 minutes

(2) What else might this be ? A defective resistor that is starting to fail when it gets warm ????

My quandry is that unless it is the tube, I don't have the time or expertise (right now) to solve the problem. I need to make a decision today to ship it our for repair so I may have some hope to get it back before Christmas. At another time of the year, I would just wait, but.... oh well.

In any case, if Phorum members could chime in as to what the possible causes of this might be, this will help me in my decision to ship it out or not.

Thanks

[morzh]

marginal tube may still work fine, but: tubes with gas do actually develop problems as they heat up, so: have you checked this tube of yours for gas?

[Ron Ramirez]

Have all of the paper and electrolytic capacitors been replaced?

If not...replace them and then get back to us.

Sounds to me like a classic symptom of a paper cap that has gone bad; the trouble manifests itself after the radio plays a while. Sometimes it may come on and play with distortion right away, too.

This is why all of these must be replaced if you intend to use the radio.

[winkydink]

Ron,

All the paper capacitors have been replaced. Same with the electrolytics. I will double check the photos that I have.

Mortz - How would I check a tube for gas ?

I came up with a compromise. I have a working Philco 42-PT94 which I use every day at work to listen to the radio. I decided to swap chassis of the pt94 with the pt95 and use that as the "gift" radio.

The PT94 case with the PT95 chassis, I have sent for repairs. It may or may not get back before Christmas, but doesn't really matter, because this will become my personal radio.

I think ? With crossed fingers, that except for intalling new on/off/volume controls, I am finished with these radios and they will be ready for Christmas.

Thanks again for all your help.

Once Christmas ends, no more sending radios out for servicing, I have a project radio or two for the winter, that I am going to work through myself and attempt to apply some of the learning (through the school of hard knocks) that I have gained the past few months.

[chris25260880]

You sure give great Christmas gifts, How do I get on your list?

[morzh]

Winkydink:

1. Follow Ron's advice and replace the caps first. It is simple, especially if you do not restuff the old ones and simply replace them (although with Philcos I'd restuff them to keep the appearance: it is also fairly simple with those black backelites).
2. To test a tube for gas you need a tester that tests for gas; I take it not every tube tester does it, but most Hickoks do. If you have a tester, see if it tests for gas; usually the word "gas" appears on the front panel over some buttons and in the manual.

What gas does is cause unplanned ionization (there should be no ions in a tube) radically changing tube's VA characteristics. Getter is pllaced inside tubes to bind residual gasses after evacuation, by either chemical recombination or by adsorption, but sometimes gas is released back, or exuded by the materials from which the tube is made.
Gas is tested as the last test, when the tube has warmed up sufficiently.

[winkydink]

Hi morzh,

My tube tested is a rather basic one, a Heathkit TC-2. It does not have a Gas Checker, although I can test for shorts.

Ron and your advice regarding the capacitors was very close with regard to what actually was the case.

I farmed out the repair to Jeff of Radiotiques, who identified the problem and fixed it quickly. This was his assessment.

" Finished the repairs this morning. I found a coupling capacitor that was leaky, replaced it, and the radio works fine. I also replaced 3 other paper caps, tightened the dial cord, and realigned the receiver. The company that you used to repair the radio replaced some of the old paper caps using NOS (new old stock) capacitors. The danger is that the NOS molded caps are actually paper caps inside and can go bad. That was the problem with the cap they installed from the output of the 7C6 (audio driver) to the 50L6 (audio output). Its not that they did bad work, simply that they assumed the NOS capacitors would work fine. "

Two points.

(1) I would highly recommend Radiotiques. Jeff has done quality work for me, has fast turn around time and has excellent pricing [though this is not an advertisement]

(2) I WOULD NOT recommend a certain repair shop in Pittsburgh. I had a total of 6 radios repaired by them and 4 of the 6 have had problems. I have learned a great deal since then, and in hind sight, would not use them given a second chance.

I am going to look over another radio that I had repaired by the Pittsburgh company. That radio had a bad audio switch (not their fault), but does not play well after the swich has been replaced. I am going to very carefully check for lose wire and see if any other paper capacitors have not been replaced (I was told that they were, but I have since found out this wasn't exactly the case). I will start there and see where it leads.

Thanks again Ron, Morzh and all the other members of the Phorum who have helped along the way !

[winkydink]

Oh and chris25260880, they will only be great gifts if the radios actually work ... :-D

Perhaps you will make the list next year .... if you are good ....

[Ron Ramirez]

I have never met Jeff but have corresponded with him in the past. Jeff is a good guy, one of the better guys in this hobby. He has lots of radios, radio chassis, etc. for sale, and his prices range from reasonable to dirt cheap.

Check out his site:

http://www.radiotiques.com/

[morzh]

...and the lesson we learn is that no matter how many of good guys there are around, if all caps are replaced there may be no immediate need to bother them (and to pay for that).

I say, let's resort to good guys' help when it is really warranted, but changing all caps is a very basic thing to do and this saves you time and money.

[Ron Ramirez]

Good point.

[Paul Philco322]

I recently picked up a Philco from Jeff, Radiotiques is OK. Jeff is a good egg. Do I sound old just saying that? Good luck Winky. Experience is a great teacher. Learn from your errors and the gang at the Phorum.

Paul

[winkydink]

I just got the radio back from Jeff [Radiotiques] yesterday. I had the opportunity to play it for about 45 minutes consecutively. It works great. I am a very happy camper!

I haven't had a chance to look at my other malfunctioning radio yet for ommited paper caps, but if I were a betting man, I would take the bet that there are still some in there.