[bambuter]

Hi,

I an restoring a model 91 chassis #126 (purchased in 1975)  and have run into a few problems.  I replaced the capacitors and out of range resistors and am using a variac to limit the voltage to around 100V. 

It powers up and the audio stages are fine.  No stations are received. 

Here are the problems so far.
1)  The schematic shows the shadow box has a 1K (R14)  resistor attached at one end to the shadow box and the other end to the screen grids of the 42 output tubes.  I cannot not find any trace of R14.
2)  The schematic also show C27 connected to one end R14 and then to ground.  There is no trace of this capacitor.  I have two model 91 schematics that show theses parts, so I am looking for a confirmation on this.
3)  I am missing the front metal piece of the shadow box  Anyone know where I can get one.

I have a feeling someone attempted repair and removed some components. 

I would appreciate any information or advice.

Thank you

Bruce Ambuter   KB1ORG

[Radioroslyn]

Hi Bruce and welcome,

1)  The schematic shows the shadow box has a 1K (R14)  resistor attached at one end to the shadow box and the other end to the screen grids of the 42 output tubes.  I cannot not find any trace of R14.

I would check to see if there is hv @ the plate of the rf amp. It's not uncommon the coil in the shadowmeter to go open. Some later sets there  was a resistor in parallel w/the coil so if the coil was bad the set would sill play. I see that R-14 is in series. You could check the total resistance from the sg of the 42 over to the plate of the 44 rf amp. The coil is going to be abt 1K (have seem them from 1.2K down to 800 ohms depending what version it is)

2)  The schematic also show C27 connected to one end R14 and then to ground.  There is no trace of this capacitor.  I have two model 91 schematics that show theses parts, so I am looking for a confirmation on this.

I looked at the Rider's it has the under chassis view. It show C-27 is a bakelite block next to the 39/44 tube socket. Look closely at the small screw size holes where it would have been mounted to see if there are any threads cut into the metal.

3)  I am missing the front metal piece of the shadow box  Anyone know where I can get one.

If it's the part I'm thinking of it's a small piece of celluloid. For testing purposes tape a piece of paper w/clear tape. This will give you the proper reflection of the vane inside the meter. If you have an old broken dial you can fashion a piece of it to replace the missing front cover.

Here just some general notes. On the meter it's important that the set is working well and is properly aligned for the meter to work well. Lamp alignment is important to get a good image on the window in the front. Some of the meters have an adjustment screw on the back. It sets the tension on the vane, too loose vane swings a lot too tight narrow shadow and not much movement.
Not too uncommon for the osc coil to have an open feedback winding and or the ant coil to have an open primary. Both pretty simple to rewind.

Happy troubleshooting!
de N3GTE

[klondike98]

Welcome to the Phorum!

[bambuter]

Hi Terry,

Thanks for responding to my post.  Based on your information, I have made some progress, just no entirely the kind I want.

1)  I still have not found R14 on the schematic, although as stated it is shown on the schematics I found. 
2)  It turns out that the  shadow box coil is open, I put a 1K resistor across the two shadow box leads.  This allowed the plate voltage to go to 353 volts.
3)  The power switch coupled with the band control is not working properly.  I bypassed the power switch, but I am not sure if the band switch is working.  There is no information that I can find about this switch other than the part number.

The radio started to motorboat, which led me quickly finding a missing tube  #44 shield on.  I have the shield but no mounting socket.  One of the socket rivets was pulled through.  So I need a rube shield base and then have drill out both the 44 tube socket and the associated corner bracket in order gain access so that I can reinstall both the tube socket and shield base.  Not what I wished for.  With the tube shield held manually down, motor boating stopped but cannot receive any stations. 

I need the following components and would appreciate suggestions as to where to get them.

a)  Shadow box for the Philco 91 receiver
b)  Shield base and associated shield for #44 tube
c)  Grill cloth for the model 91 version 126 radio.

Thanks

Bruce
I hate to give up on this set as the cabinet is good and I had refinished it several years ago.  I have a model 90, which is next on my list of projects.

[Radioroslyn]

Hey Bruce
>This allowed the plate voltage to go to 353 volts.

Seems a bit high you want to check it by measuring it as per the service literature. There it has you measure from plate to cathode and should see abt 200vdc. Tiz a 44 not a 4-400.

> motor boating stopped but cannot receive any stations.

Might want to try a listen for the LO. It's going to be 260kc above the incoming signal. Could be the osc isn't running.
You can connect a generator to the grid cap of the mixer and use a 260kc signal W/400cy modulation to check the IF strip and you can give a tuneup too.

> Shadow box for the Philco 91 receiver

If you have nothing but time on your hands checkout post #49 or so.  http://philcoradio.com/phorum/showthread...829&page=4

> Grill cloth for the model 91 version 126 radio.

A few years back there where a number of sources to obtain grill cloth but most have folded. Now there's two or three so may be difficult to find an original style of cloth for your particular set. Ron could tell you better than I what would be a suitable replacement.

> I have a model 90, which is next on my list of projects. 

The model 90 is a little tricky as there are three different versions an early, mid, and late. Easiest way to tell is the output tube/tubes.

Terry N3GTE

[bambuter]

Hi Terry,

I went through all the coils on the Model 91 and found two open primaries in addition to the other problems.  I kind of think this radio got too many problems for right now and have put aside.

With respect to the Model 90 which has one 47 output tube; a check of the coils revealed an open primary on the first detector xfmr  Part number 03015.  Any idea where I can get one?  There is no point going further without, although I had previously recapped the capacitors and replaced out of range R's/    The lesson I learned from this is to check all coils prior to component replacement or swapping. 

I would rather find another 03015 First detector transformer than rewind it, I am now on the lookout for one. 

Thanks

Bruce

[morzh]

Bruce

The radio will work without shadowgraph with a resistor in place.
Also those early radios had easy-to-rewind coils, so I would not put it aside just for that.
It is fixable now, and later you could put finishing touches on it.

[Radioroslyn]

+ Mike
>I went through all the coils on the Model 91 and found two open primaries in addition to the other problems.

The ant and rf coils are simple to prepare. Peel off old (small winding on the outside) winding, remove celluloid strip, replace w/mylar strip, wind abt 20t of small magnet wire (like 32-38g), replace it back into the set. THe primary is not part of the tuned circuit (that's the large winding) so it's very forgiving. THe feedback winding on the osc coil is a little trickier as it must but phased (wound) is the same direction as the other winding. It's not uncommon to find green dots on the old windings this is where the copper wire has rotted and has created a open circuit.

> I kind of think this radio got too many problems for right now and have put aside.

You know if you keep that up you'll end up like me w/ 50 chassis all a part and remembering what goes to what!

>With respect to the Model 90 which has one 47

That would mid alliteration of the model 90.

<a check of the coils revealed an open primary on the first detector xfmr

I would have a close look at the open coil to see if the wire is broken at the terminal. May just need a little solder.

[Ron Ramirez]

>With respect to the Model 90 which has one 47

That would last alliteration of the model 90.

...ummm...the 90 with a single 47 is the second or "middle" version. The third or "late" version has two 47 output tubes.

[bambuter]

Hi Terry,

I removed the 1st detector Philco ( part number 03015)   coil from the model 90 .   This allowed me to validate that the primary winding was not just broken at the solder end.  Unfortunately, I still get an open winding.  You mentioned about 20 -30 turns, but I can see there are a lot more than that. 

Do you have any idea where I can get a coil.  Hopefully, would like to find some one who sells new old stock.  As the  wire gage, resistance of the coil, and the inductance are not stated, I really don't feel comfortable rewinding the coil.
I am also missing the larger shield mounting bracket which at some point in time must have broken off.  If I leave the shield off, I am concerned I might well end up with motor boating. 

Thanks for your help.

Bruce  KB1ORG

[Radioroslyn]

< You mentioned about 20 -30 turns, but I can see there are a lot more than that.

Yes this is true but the coil you are speaking of is the 1st IF transformer. The above is true for the rf and osc coils as they are used for coupling not resonant part of the circuit.

The IF transformer consisted of two tuned circuits which are resonant @ 175kc, which would take a lot of turns. Back in the day replacement parts providers sold complete IF transformers and you could buy separate coils too to be fitted to the original core if so desired. Your fortunate  that it's a common frequency. Depending on the construction a lot of time the coil is held in place by wax so a heat gun can loosen it up and fit the replacement. 

<Do you have any idea where I can get a coil.

No.

<Hopefully, would like to find some one who sells new old stock.

GLOM

<As the  wire gauge, resistance of the coil, and the inductance are not stated

Gauge and resistance aren't particularly critical, gauge determines the physical size and current capabilities. Number of turns and inductance can be calculated.

< If I leave the shield off, I am concerned I might well end up with motor boating.

I  would concur best guess is that's why it has one.

[Ron Ramirez]

The IF transformer consisted of two tuned circuits which are resonant @ 175kc

260 kc in model 91.

<Hopefully, would like to find some one who sells new old stock.

GLOM

I'll ditto that. Good luck finding a NOS coil, which may have the same issues due to the nitrocellulose insulator used between windings, which breaks down and causes the windings to corrode. You're better off rewinding the coil yourself, or finding someone to rewind for you.

< If I leave the shield off, I am concerned I might well end up with motor boating.

Yes, it will squeal and/or motorboat without the shield.

[Radioroslyn]

>I removed the 1st detector Philco ( part number 03015)   coil from the model 90 .
<260 kc in model 91.


> may have the same issues due to the nitrocellulose insulator used between windings

Have not had an IF transformer apart from a 90 but typically the coils in an IF transformer are not wound one over the other but are two separate winding that are spaced apart from each other. Wouldn't need an insulator between the plate and grid coils. If you wind one over top of the other there is too much coupling between them. This causes poor selectivity. The further apart they are the sharper the selectivity but the less gain.


Bruce,
Come to think of it I have a spare National RAS (brother of the HRO) it has a 175kc IF. The chassis is beat I'll see I can find a good transformer
for you to tinker with. Are you good in qrz? I'll send it out when you get the 91 working [Image: http://philcoradio.com/phorum/images/smi...wisted.gif][Image: http://philcoradio.com/phorum/images/smi...on_lol.gif]
Don't know if you are active but you'd like to get together on 40mtrs sometime shoot me a pm.

GL

[Ron Ramirez]

Is this thread about a model 91 or a model 90???

[bambuter]

Hi Ron,

The thread I posted was initially about the model 91.  After finding all the problems pertaining to the model 91, I thought it perhaps better to attempt to get the model 90 I have working.  So I guess this means I have two threads open albeit with much the same problems but obviously different part numbers.

Sorry for the confusion.

Bruce