[fwmartin2000]

I just got a Model 87 Hi Boy radio , I discovered that one of the three RF transformers has an open winding which feeds plate voltage to the second RF amp tubes.
I was hoping that someone on the forum might have one in their parts stash that would want to part with.
Thanks
             Fred Martin      fwmartin2000@gmail.com

[MrFixr55]

Hi Fred,

The issue is that these RF transformers are usually bad. The primaries open on most Philco RF or other transformers of this set, 0, 80, 89, 19 and others. The primary winding insulation and the actual wire was "eaten" by breakdown products of the celluloid insulation that was positioned between the primary and secondary.

Ron Ramirez and others are geniuses at rewinding these coils and can give you further info.

[Radioroslyn]

If you get tired of waiting it's not hard to rewind the primary. It's about 24 turns of #32 or #34 magnet wire. Wind it in the same direction as as the winding you removed and it probably would hurt to make a new insulator to go between the pri and sec. Primary turns count is not particularly critical as it's used to couple the rf signal. The secondary is as it's the tuned circuit that is resonant. Would not rewind it (2dary) unless I had to and had a precise way to measure the turns count/wire size involved.

Too many turns on the primary gives you poor selectivity. Not enough will lower the sensitivity.

Have worked on a few of the 87's and those bypass caps at the bottom of the primaries are usually leaky like shorted. So you you might want to take the 3 screws out and check the voltages w/those caps out of the circuit. 

https://philcoradio.com/library/images/schem/87.jpg

GL

[morzh]

As Terry has said already, it is not bad.

This is my 86 thread. Granted, it was the secondary...secondaries. But close enough.

https://philcoradio.com/phorum/showthrea...=philco+86

PS. Take a good look at them, they aare the one covered with celluloid and are oxydized ready to open. Maybe you might rewind both.

[radiorich]

Hello Fred Martin ,
Rewinding that transformer is fairly easy I am sure you won't have any issues .

Sincerely Richard

[fwmartin2000]

Thanks for the replys, I counted about 13 turns of wire which were very thin and brittle. I removed the old wire, wrapped a turn of masking tape and 14 turns of #41 magnet wire that I had on hand. Might be too thin, I could try #34 gauge wire. I did replace the
bypass caps and associated B+ resistors. I should take a closer look at the other 2 transformers even though I am passing B+ to the plates of their tubes. I'm not sure just what to expect out of this receiver as far as sensitivity. With the repair I just made, I can pull in
WLS in the Chicago area but that is all, not great volume.
Fred

[Radioroslyn]

After looking at Mike's coil I'd like to revise my turns count number down to 24 rather than 50. The 86 and 87 use the same coil all 3 of them. For what it's worth pn 3075A. 
Both sets a Neutrodyne. That means that it uses neutralize triodes as rf amplifier. The 87 is a Neutrodyne Plus [Image: https://philcoradio.com/phorum/images/sm...prised.gif]

It's not uncommon to find what is called green dot disease. The demise of the copper in the winding of the coil. Sometime it's a small dot you can see thru the wax. Other times the winding will show a high resistance.

[morzh]

Speaking of Neutrodyne and neutralizing, rather than use that socket with one pin missing in filament, I actually use a dud with open filament. Preferably of the same mfr/time. I think it will make for a better match, considering extra inductance and capacitance of an extra tube base.

[fwmartin2000]

Speaking of neutralizing, I have a bad 26 tube that I removed one filament pin and when I pull one of the RF tube and plug in the
dead dummy tube, my test signal drops to almost nothing so I'm not sure I'm doing it right. Also, WLS Chicago comes in pretty
good and loud but the volume control has no effect on the loudness. It seems odd to control the audio level at the front end of the
receiver by adjusting the antenna signal into the antenna transformer. unless,,the antenna transformer has an open winding, I'll have
to check that out.
Fred

[Chas]

The NULL is the correct response when neutralizing a common TRF. If the adjustment is not working something is wrong in the circuit(s). The correct tuner frequency to neutralize may not be the one specified. So if the set still oscillates at a certain receive frequency, neutralize at that frequency. All shields must be in place, if a bottom plate is used be sure it is on too. Do not work on a metal bench raise the radio a couple of inches if a metal bench is in use and there is no bottom plate required. it is best to keep the tubes in their respective positions once the set is neutralized.


Be sure the filament voltage is correct at all the 26 tubes, poor connections are a problem for those high filament amp tubes.

GL

Chas

[morzh]

Also:

A neutralizing tube is supposed to be a GOOD COLD TUBE. That is, if a bad tube is to be used for it, you have to be sure the reason it failed was the filament/lack of emisson and ONLY that. No other reason, like a short, crack or anything else.
It has to be otherwise perfectly fine tube without the heater.

[fwmartin2000]

I found that I also had an open primary winding on the antenna transformer. I rewound that coil with 24 turns of #31 wire and
also rewound the 2nd RF coil primary with 14 turns of the same gauge wire. Surprisingly, the receiver works really good.
I tried to do the neutralizing alignment using a dummy tube but the audio level of the 700 khz signal I generate with 400 hz modulation
drops so much that my AC Simpson AC volt meter across the voice coil doesn't read it, So I think I will not mess with it.
Fred

[Chas]

O.K!

Try the Simpson in AC mode across the primary of the output transformer, set for 100 volt scale more or less to start.

None the less, if your not getting any oscillation no matter where the dial is set, neutralization is good enough.

If either above below 1mhz is "less sensitive" when aligning the gang trimmers, move the calibration frequency up or down in the direction of the less sensitive area by about 30khz, more or less. That should balance out the sensitivity across the band. May have to neutralize a second time with that sort of compensation...

GL

Chas

Chas

[fwmartin2000]

Thanks Chas for the alignment tips I will try your ideas.
I don't think it will take much alignment. It seems to be receiving better than I thought it would. Now I need to figure out how to inject audio from my Alexa dot,as I do with all my radios. Putting the volume control at the front end of the receiver makes it difficult.
Fred