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16B chassis — questions - Printable Version

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RE: 16B chassis — questions - Radioroslyn - 12-27-2018

I put a bunch of work into mine and used to watch it pretty regularly in the early 2000's but back in '13 we did a big renovation on the house. The set ended up in the shed. If it's any help somewhere I have the Admiral service manual, probably buried in the shed. Sam's can be found here:  http://www.earlytelevision.org/pdf/admiral_20a1_sams_77.pdf

RE: 16B chassis — questions - mwoodruff - 12-28-2018

Thanks. I have found copies of the Admiral manual and the Sams. The Admiral manual is nice in that it also walks you through the each stage of the set with an top-level explanation of what it does (Colpittts osc., etc.).

Do you know if there is something similar for Philcos? Or will a basic radio text do? (I need some refreshing ...)

Incidentally, I live in fear of the day when my wife will “renovate” all my toys to the shed. Cheers.

RE: 16B chassis — questions - Radioroslyn - 12-28-2018

<Do you know if there is something similar for Philcos?

The post war Philco service info does have a service friendly overview w/ block diagrams, test points, and simplified diagrams. For instance  http://www.nostalgiaair.org/pagesbymodel/625/M0013625.pdf  Personally I don't like this style as the schematic is broken up and a bit of an overkill. Rather have it all together.

> Or will a basic radio text do?

That might be a better bet. Let's face it pretty much all of these AM superhet sets are the same, some have more tubes and maybe more features but the basics functions is the same. A good start is to understand what these functions are and how they work. Once that is understand these principles you can work on just about any of them.
The grandson of your 16B is the 37-116 this set makes your 16B look like a crystal set. It's got a lot going on. So how do you eat an elephant? One bite at a time.

As a practical matter on the 16B would break the schematic down into sections starting w/the power supply then work up to the audio, detector, if amps, mixer, and avc. The important issues in the p/s check the transformer for heating, polarity of the filter caps, and check for open inductors (choke and field coil).

OBTW do you have any pics of the cabinet?

RE: 16B chassis — questions - mwoodruff - 12-31-2018

Here's a pic of the cabinet:

   

and here's a little label that a found under the tuning condenser:

   

I think that this is an early run, since the dial starts at 5.8 on the SW broadcast band and there is a can cap for #75 that is mounted on the chassis.

Haven't found a serial number or a date stamp yet.

Will be posting some pics and Q's about caps #86-88 in a bit ...

Thanks as always.

Matthew W. Woodruff

RE: 16B chassis — questions - mwoodruff - 12-31-2018

The 16b chassis that I pulled from the attic is missing the two electrolytic cap cans at the rear (#87 & #88) and there are a few (3?) stray wires as well.  

The attached pic shows the current situation.

   

Green arrow points to the lead from the center tap of the power transformer.  This is 400 volts, correct?  

My understanding is that this goes to the two cans at the rear and then to #75 (10 uF, 50v).

1.  Does this lead go to the center terminal of the cans or to the outside?  For all three cans?  Or is the wiring reversed for #75 (pos. chassis ground)?  Are there jumpers to make the connection (in an original set)?

White arrow points to two leads running from two side tabs on bakelite cap. #86.  One has a terminal (not shown); the other appears to have been cut.

2.  Same question as above:  In an original set do these go to the center terminal of the cans or to the case?  What is the polarity? (Positive? Because the center tap on the xfrm is negative?)

3.  Since the cans are supposed to be insulated from the chassis, I assume that this is the reason that the neg. chassis ground on #87 & #88 does not short with the positive chassis ground on #75 -- or am I all wet?

Red arrow points to a cap (value unknown) that appears to have been retrofitted at some point in the past.  This appears to be wrong for  a number of reasons:  (a) it does not conform to any part of the schematic for #87 or #88, which are connected to the center tap of the transformer and not to the resistor #81; (b) if it is a replacement for cap #75, it should be positive-grounded to the chassis.

I am assuming that the bottom-most tap on the voltage divider resistor #81 is not grounded (because is is offset by a fiber/felt washer). 

4. Is the string of resisitors (#81-84 and #91) what creates the voltage drop from 400 v at the transformer to 50 v at cap #75?

Finally, bakelite cap #86 (nominally 0.3 uF per the schematic) appears to be made in internally of two 0.15 caps that are wired in parallel by a jumper between the end terminal and the middle terminal, correct?

5.  If I want to use two caps instead of a single 0.3 uF as a replacement (i.e., keeping the jumper and the outward appearance), which terminal has the common end of the two caps?  It seems that it should be terminal nearest the mounting lug (i.e., the one without the jumper from the end terminal), but can anyone confirm this?

I want to retain the original appearance as much as possible but will probably use a terminal strip for #87 and #88 until I can find replacement cans to restful and mount (is that what Kutztown is for?).  Happy to post pics/notes when this phase is done.  

This site is a fabulous resource!!!

Cheers and Happy New Year,

Matthew W. Woodruff

RE: 16B chassis — questions - Radioroslyn - 12-31-2018

Hi Matthew,
>Green arrow points to the lead from the center tap of the power transformer.  This is 400 volts, correct? 
Not so much when it's all wire back up correctly it's abt -17vdc

1 The lug that the green arrow is pointing to is the negative terminal from one of the filter caps (86 or 87), I'm thinking that was two of them originally one for each cap.
Yes 75 has the + side connected to the chassis and it is lower voltage that the others. It's there to filter and decouple the -bias for the 42 tubes

>I am assuming that the bottom-most tap on the voltage divider resistor #81 is not grounded (because is is offset by a fiber/felt washer).
The end isn't grounded cause if it was it wounld ground the ct of the transformer and kill on any bias voltage.

>  If I want to use two caps instead of a single 0.3 uF as a replacement (i.e., keeping the jumper and the outward appearance), which terminal has the common end of the two caps?  It seems that it should be terminal nearest the mounting lug (i.e., the one without the jumper from the end terminal), but can anyone confirm this?
My best recollection is that the two .15 cap are connected together inside the bakelite block and doesn't have a jumper. Just connected to the block terminals.

Here's the cliff notes for the cap connections

RE: 16B chassis — questions - mwoodruff - 01-07-2019

How are the pins numbered (lettered) on the big square filter condensor / capacitor bank?

Mine may have been molested, uh, modified, and I am having trouble matching the existing wiring to the schematic (#62a-e).

Thanks.

RE: 16B chassis — questions - EdHolland - 01-07-2019

The diagram in this link has the lettering schematic for the square filter block/can:

http://www.flickriver.com/photos/pvkantiqueradios/3256997590/

Watch out, as the letter ordering is not particularly systematic with the pin positions. This caused me quite a bit of confusion Icon_smile

RE: 16B chassis — questions - mwoodruff - 01-08-2019

Thanks!

Of course, once you think about it, isn’t it obvious that the tabs should be lettered a-b-E-c-d counterclockwise starting in the upper RH corner (when viewed from below)?

RE: 16B chassis — questions - mwoodruff - 01-08-2019

I am going to start recapping  my 16b this weekend, but first some (more) questions:

My 16b has the four position tone control (#79) with the external Bakelite cap (#78).

From the first schematic below, it looks like the original tone control (i.e., the 3-way switch without the external Bakelite cap) is connected to the plate of the 1st AF stage.

   

From the second schematic, it looks like the 4-way version of the switch (with the external Bakelite cap) has been moved between the resistor and the cap in the circuit leading from the volume control. 

   

The cap that is grounded in the original volume-control circuit is now replaced by a cap (0.09 uF grounded) in the new, two-cap Bakelite block with the second cap (0.006 uF ungrounded) being connected on one side to the plate of the 1st AF stage and on the other side to the fourth position of the tone control. That cap is grounded only when the switch is in the 4th position.

I know that Electrical Engineers are fiendishly clever, but this does make some sense to an old English major.

The attached pic shows my actual situation. The black wire with broken insulation (green oval) leads to the plate of the 1st AF stage, but instead of going directly to the Bakelite block (red oval), it first goes to the tone control (as in the original version) and only then (via the red wire) to the end tab of Bakelite block. The white wire with black tracer leads back from the block to the fourth position of the tone control and then (through the switch) to ground.

   

This means that the plate of the 1st AF stage is always in the circuit instead of being switched-in only when the tone control is in the fourth position. That’s wrong, right?

And could that be the reason the insulation has deteriorated so much? (What gauge wire should I use? Don’t want any fires.)

I don’t know what the internal circuitry of the Bakelite block is, but it seems the the two caps have to be independent electrically (i.e., no common ground, since the 0.006 uF is grounded only when the switch is in the 4th position).

Sorry for being so long-winded, but can anyone provide one or more clues?

RE: 16B chassis — questions - Radioroslyn - 01-08-2019

>My 16b has the four position tone control (#79) with the external Bakelite cap (#78).

Good that's the better of the two designs.

>This means that the plate of the 1st AF stage is always in the circuit

Yes it has to be or the audio signal would end there.

> instead of being switched-in only when the tone control is in the fourth position.

The last position grounds the .006 cap thus cutting off some of the high frequency response.

>And could that be the reason the insulation has deteriorated so much?

No looks like old age/rubber coated wire.

>What gauge wire should I use?

Not particularly critical not much current flow. 22 or 24Ga is fine (pretty standard size for hookup wire).

Sorry for the large text laptop has gone nutz and didn't want to retype.

RE: 16B chassis — questions - mwoodruff - 01-25-2019

I am going to try restuffing the electrolytic caps on the power supply this weekend and wondered if the following is a bad  idea: 

   

I plan to use to use two 16 uF in series to yield 8 uF; and 1 meg resistors for the voltage divider.

This is for caps #87 and #88 on the schematic.  In this case, the positive end connects  to the filter choke and the negative end to the center tap of the power transformer, yes?

Cap #75, on the other hand, will be a single 10 uF with the POSITIVE end to ground, right?

Thanks for any help--on my actual chassis this entire part of the circuit has been hacked out so I am trying to reconstruct it.

RE: 16B chassis — questions - Radioroslyn - 01-25-2019

See post #36.
You can put two ecaps in series and use equalizing resistors to balance the voltage across them. But why? Modern 450v caps should have enough peak rating the handle the hv produced by the power supply.

RE: 16B chassis — questions - mwoodruff - 02-22-2019

This is a question about our values:

My model 16b, code 121, appears to be somewhere between runs 5 and 14 (based on the tone control) and corresponds to the schematic that is in Service Bulletin 165-B

Attached is a pic of the schematic that shows how the double cap #52 (7296-G) has been divided into two parts.  

   

On my set, the 0.5 uF cap (#52) is a paper tubular; the 0.002 cap (#52a) is bakelite cap with part no. 3903-AH stamped on the side.  

I understand that this corresponds to a 3903-OSG, which has a value of 0.01 uF.

So, which is correct?  0.002 uF per the schematic or 0.01 uF per what was actually in the chassis (and looks original)?

To my (uneducated) eye this appears to be some kind of frequency filter tied to the AVC circuit that gets activated when the switch to the right is open (when closed, everything gets shorted to ground).  True? In that case, is the value of cap critical or not?

Always grateful for the kind and informed responses to these newbie Q's!

Matthew W. Woodruff

RE: 16B chassis — questions - mwoodruff - 02-22-2019

And another question:

Where can I find those little caps that go on the top of the Type 77 and Type 78 tubes?

I am missing a couple of these (man, is this set beat up ...).