New to forum with Brunswick Panatrope 42DC

[startgroove]

Is your goal to remove the DC load on the primary of the coupling transformer? By doing so, you have also split the AC load. Ideally, the resistor should drop about ½ of the DC voltage when the tube is at rest, which it looks like it does. However, the AC is imposed on two (parallel) loads. One is the series circuit of the resistor and tube, the other is the series circuit of the resistor, capacitor and primary of the transformer. Is that series/parallel division what you want to do?

[rebrands]

Yeah, I see your point, the audio signal would be divided between the resistor leg and cap/primary leg. But wouldn't the 27K resistor be much higher impedance than the cap/primary? And too, the 27K resistor goes to B+, while the cap/primary goes to ground. The author was clear that the primary needs to go to ground, not back to B+.

Yes, the whole point is to remove the DC component from the primary of the transformer.

I pulled the idea from a Philco forum, here's the link to the whole article.
http://www.philcoradio.com/tech/audio.htm

[startgroove]

I looked at that link. I see that the circuit is intended to protect, or lengthen the life of, the primary windings of the coupling transformer. Yet it seems that it does not take into account the affects on equalization. There would be a frequency where the inductor (primary winding) and the capacitor would be equal in impedance, which could cause a significant change of the volume at and around that frequency. See, http://www.electronics-tutorials.ws/acc ... nance.html I have not calculated what that crossover point would be since the value of the inductor (primary winding) is not known. Just saying this is a possibility. I guess you would have to weigh the fear of losing another coupling transformer against the possible detrimental affect on equalization.

[rebrands]

Those are good points. I'll try to make some calculations and see what I come up with. Thanks.
reb

[Uncle Vanya]

The circuit to remove the direct current from a coupling transformer is usually used to prevent core saturation. This Stancor transformer has sufficient iron which is of sufficient quality so that saturation will not be a problem. You shouldn't need to worry about it.

[rebrands]

OK, good to know.

In other news, I have dismantled parts to gain access to two cap cans, one of about 2mf, and one with two 1mf caps. They have been heated with the heat gun to remove the guts, ready to stuff. Also, was happy that I was able to resurrect a bad power switch with WD40. It would have been next to impossible to remove/replace due to unusual design and the fact that the mounting nuts were soldered to the chassis to prevent them coming loose.

[rebrands]

It's been a while since I last posted, but I have made significant progress, still have a ways to go.

As a reminder, the Riders schematic for the Brunswick 42DC is completely different from this radio, even different tube lineup, the sockets are stamped with the tube numbers, so I'm sure they have not been changed out somewhere along the way. Hence, the necessity to making my own schematic.

Since I last posted I have dismantled down to bare chassis to enable me to lay eyes on parts that were obscured otherwise. I then have restuffed the two cap cans, installed the Stancor 4774 transformer, done a bunch of cleaning, replaced come wire, and re-assembled. I have also been busy tracing circuits and drawing a schematic, I've lost count of hours spent on the schematic.

So, I have a couple questions. In taking measurements and making the drawing I ran across an oddity. The input to grid 1 on V3 and V4 each have a resistance of 42K ohms, which seems odd. Also, the "resistor" appears to be a small sort of button arrangement on the side of the stator on C4C and C4D. (See photo in Word Doc) Is this in fact a resistor? I'm not a expert, so maybe this is just something that's normal that I haven't seen before. Maybe this question better posed to Antique Radio Forum?

Another question is the method of inserting the phono signal into the radio. The selector switch provides a ground for L10 in "radio" and a ground for R5 in "phono". What seems strange to me is the signal being inserted into the detector grid instead of the 1st AF grid. Is this right? Again, I'm not an expert.

Russie, your thoughts?

reb

[rebrands]

HI All,
Again, it's been a while since my last post. In the interim I have the radio working, although it needs some tweeking.
My challenge now is the turntable. I found that the motor would not turn on it's own, even at full voltage (110 DC), due to some sort of restriction. I have removed the motor and mount from the main platform. The motor now runs freely. But the issue I have discovered is with the motor mount. I know, you're going to guess that it is rotted due to being made of pot metal. Well, actually, it appears that happened long ago and was addressed by a previous restorer. The existing mount looks like it is of a similar heritage as the original, but I believe is different. Since I don't have an original one to compare it to, I can't be sure, but have a look. Of the four mounting screws, only three can be used, there are lots of washers used as shims, and more. It just doesn't look like it really belongs there.
I am guessing the restriction while mounted to the main platform was due to mis-alignment from the shims not being quite the correct, or equal, thickness. So my question to you all is: can this thing ever be made to run close to properly? The thing is that the shim thickness determines the height of the friction wheel that runs the changer mechanism. If it isn't pretty close to correct, it won't do it's job properly. Also, most of the wire has brittle insulation, so needs to be replaced. I'm close to throwing in the towel on the changer. Your thoughts?

[need4art]

Before throwing in the towel-head over to the Antique Radio Forum and see if anyone has some suggestions or better yet spare parts. You have gotten pretty far along and these are great looking units and there must be some way of making this work.

Post in the radio discussion area and in WTB-even if yoiu had to pick up a complete motor board and motor you wouid be ahead of having something frabricated.
Abe

[rebrands]

I've been on the AR site regarding the radio only, thought I'd hit TM first about the changer. It's a good idea though to run it by them too and see what pops up. I'm currently of the opinion that it is a case of mis-alignment from varying/improper shim thickness, or possibly from a slight shift in position due to some slop around the mounting screws, in other words, something that could be corrected. Yes, a new motor mount would be nice. From what I've read they are unobtainium, but it's worth a try.
Thanks,
reb