Me?
A troublemaker?
Hardly, child!

Child ? lol

i have 4 kids been married twice, i must be a very big child.

Allright, Mr. Repair Tech up in Philadelphia, PA, what is the problem with this set? You're the expert here.

Quit poking fun and playing games and instead provide some input into what might be going on with this set. I need your input.

I pulled the changer this afternoon, subbed a different stylus, and that made no difference. I did find a bit of corrosion on the headshell plug that plugs into the tonearm, so I polished that...again, no difference. There is no distortion being caused by the changer. I tried to hook up a big stereo speaker to it, but couldn't get it to work since RCA uses three wires to the speaker unit instead of the normal two wires to a speaker. That's another weird thing about this set.

So what's the third wire for?

-David

They run the tweeters/mid to one tap on the OPT, and the woofer to another.
It's an odd console with weird designs, that of course were retired for a more mainstream circuit.

Like.....
My......
RCA Victor Concertmaster Custom Deluxe!

Thanks, RT. That is strange -- have never seen it except for the German sets with electrostatic tweeters that they drive directly off the output tube plate, IIRC.

I wonder what the rationale was. Ol' General Sarnoff wouldn't spend for an extra wire and tap for no reason, even on a high-end set.

-David

The idea behind it was for impedance-matching I suppose.
Plus there were several multi-speaker choices depending on the model - so also for adaptability.

That is how canadian company electrohome did there speakers too.
one for the tweeter one for woofer and a common wire.

Last night I visited with my radio buddy, badrestorer on ARF, and the first question he asked me was had I cleaned the bandswitch? The answer was I had done a little cleaning on it, but not throughly. John indicated that a dirty bandswitch very well may be my problem in the Mark I. I checked the 3 section bandswitch and there is black oxidation and dirt on various places on the wheels that rotate under the little fingers. John said you can replace every capacitor and resistor in a radio, and it still may not sound good, or it might not even work at all, if you have a dirty bandswitch. So, I'm going to spend tomorrow cleaning the bandswitch. I am hopeful this will improve the performance of this set significantly. Here's a video John posted on You-Tube about cleaning the bandswitch.

http://www.youtube.com/watch?v=FgjGIa4CroQ

If additional troubleshooting is required, John is going to let me borrow his signal tracer to narrow down, and locate, the problem.

You know there is a problem with the bandswitch or the selector switch if, as you rotate it slightly about each position, the signal comes in and out, gets fuzzy, or produces a lot of static. You can temporarily improve the functioning of a dirty switch by exercising it back a forth a few times. That cleans it off.

-David

I sometimes dab the contacts with Tarn-X on a CueTip, let it sit, then flush the switch out with GC's Big Bath to remove the black tarnish from the silver contacts.

I cleaned all the rotating wheels with a pencil eraser. You can clean the larger areas by rotating the switch all the way from position 1 to position 4. Some of the smaller areas have to be cleaned between the fingers by gradually rotating the switch. I got the bandswitch totally clean today and also decided to replace all of the resistors from where the phono input connects to the bandwitch over to the 6C4 tube. The phono is sounding a lot better...no distortion, finally, but it isn't quite as sharp sounding as it should be. Going to replace some more resistors tomorrow. It seems that every part I replace makes an improvement in the sound. I couldn't tell that cleaning the bandswitch helped, but it will avoid problems in the future since it's clean.

I've never heard of resistors causing distortion if their values are correct. A bit of noise if in a preamp stage maybe, but not distortion. I think you are barking up the wrong tree. Distortion in an amplifier is usually caused by incorrect audio level overdriving a stage, or a stage with incorrect bias, which the DC measurements would pick up.

-David

David, the distortion in the phono is now gone, a direct result of changing out those resistors yesterday. One little tweak and it will be absolutely perfect. Just have to find that tweak.

MY MARK 1 IS FIXED!!! David, you were right... I was barking up the wrong tree...thinking the problem JUST HAD to be in the tuner circuitry. Today I decided to do resistrance ohm checks on every single pin of every single tube in the entire set. I started in the power amplifier. The 6V6s checked perfect, but I got up in the top 6AU6 (V11) driver tube, and pin one checked 56K ohms when it's supposed to be 260K ohms. Whoa... it has to be a bad part attached to that pin!!! There were two resistors and a capacitor coming off that pin. The cap is a .1 coupling cap going from pin 1 of that tube to pin 1 of the 12AU7 (V10) tube. I decided to replace that cap...installed a new one in it...rechecked the resistance at pin 1 of the 6AU6 and it was within tolerance.

This shorted cap was my entire distortion problem, and I could have saved myself days of tedious work had I just done those resistance readings first. Next time I'll know where to start.

So, the problems I've encountered here were all the result of shorted tubes. A 6AU6 in the radio circuitry in the tuner shorted, taking out three resistors around it. And, another faulty 6AU6 tube in the power amp took out a coupling capacitor. I'm glad I now have all new tubes in both the power amp and tuner... no need to trust tubes that are 56 years old, particularly in a set this powerful as the Mark I.

I'll say one thing... I learned a lot by working on these problems. It's been an education for sure!

I'm so happy to get this thing fixed. Think I'll have an adult beverage and celebrate!!!!

No, wrong.
The tube didn't "take out" a capacitor.
The cap was leaky from the start, and should have been replaced.

Matt, wrong. It was a new cap I installed in early February that the tube took out. I ALWAYS REPLACE ALL THE CAPS IN AN AMP AND TUNER, INCLUDING THE ELECTROLYTICS...I NEVER LEAVE ANY OLD WAX CAPS IN A SET. This particular original tube flashed the short light briefly when I tested it about a week ago. I suspected a problem with it, but I tested it again and the short light didn't come back on.

Who knows, it might have been a defective Chinese yellow cap from the beginning. I am beginning to doubt the durability of these yellow Chinese caps. I am becoming of the opinion that the white caps that Antique Electronics Supply sells are much better caps...more expensive, but certainly a lot better.

You're going to tell ME I'm wrong?
Doubt it.

For your information, those yellow axial lead .1 uf 630v caps have been known to be defective.
Perhaps you didn't know that a batch of defective ones are spread around.

Documentation and blogs address this issue.
That said, as I previously posted... the cap was leaky from the start.
Tubes don't take out *good* capacitors - it's electrically impossible

This is kinda like asking which came first, the chicken or the egg? Only the man upstairs knows for sure!!!