[radionut1929]

Well, I looked at the schematic of the Kolster K-27. At first, it appears that the Kolster transformer would substitute for the Philco 511 transformer.

But it won't. Why?

Notice the Kolster transformer's high voltage winding is 600 VCT (300-0-300).

After some searching, I finally found the Philco's ratings. Its high voltage winding is only 375 VCT (187.5-0-187.5).

To use the Kolster transformer would make the B+ run too high throughout the Philco, and would likely cause the B+ on the 71A plate to exceed its design ratings (180 volts max.


You can do what you wish, but I personally would not do it.

Here are rough specifications for the Philco transformer. I can't guarantee the current specification of the high voltage secondary is correct, but 60 mA is greater than the total plate current draw of the entire set which according to Bulletin 5 adds up to just over 34 mA. Bulletin 5 specifies "30 mA per plate" on the plates of the 80 rectifier. Therefore, 60 mA was selected as a nice round figure. Anyone is, of course, welcome to add their two cents' worth to this. The filament currents were obtained from a tube manual - the 1.5V filament current is equal to the total filament current draw of four 26 tubes.

Primary - 125 volts AC, tapped at roughly 110
Secondary #1: 375 VCT (187.5-0-187.5), looks like 60 mA
Secondary #2 (26 tubes): 1.5V, 4.2A
Secondary #3 (27): 2.5V, 1.75A
Secondary #4 (71A): 5VCT, 0.75 to 1A? (0.5A for 71A tube plus additional current of pilot lamp)
Secondary #5 (80): 5V, 2A

Hi Ron,

Ok, I will take your advice and not use the Kolster transformer.
I will just wait until I have enough money to get the transformer rewound.
By the way, do you know where I can get a Philco model 86 junker set?
Please let me know what you can do to put the word out and I will be
thanking you for what help you can offer.

Sincerely,
Radionut

[Radioroslyn]

For what it's worth I would say if the Kolster set uses the same tube lineup you should be in good shape to use it for the replacement in the Philco. For a year or so that lineup was a popular one but once the New Screen Grid tube(24A) became available 26's disapeered. You not have to neutralize them and have more gain. And you don't need that 1.5v filament winding. It's the only tube that has a 1.5v @ 1.5a. Anyway I'd give it a try but I'm CHEAP.
The important thing is that it has all the filament windings and center taps that the original had. If the HV winding is a little high that can be dealt with by using the right caps or changing it to a choke input.
My two cents
Terry

[Ron Ramirez]

And you don't need that 1.5v filament winding.

How else is he going to power the filaments of the 26 tubes?

The high voltage winding of the Kolster transformer is too high for the Philco. Of course the resulting B+ could be dropped with a resistor, but I don't particularly like "kludges."

[Radioroslyn]

To be clear I was speaking of the 24A tubes. They require a 2.5v heater supply. Sets that use the 26 tube do require the 1.5v winding for the filament.
Sorry if I wasn't clear. I try really I do.
Terry

[Ron Ramirez]

It's all good...but the 511 does not use 24/24A tubes. In fact the first Philco to use the 24 tube was Model 65 in June 1929.

[Eliot Ness]

..........I will just wait until I have enough money to get the transformer rewound.
By the way, do you know where I can get a Philco model 86 junker set?..........

I don't recall if you mentioned trying Gary at Play Things Of Past yet like gvel (Greg) suggested? If he doesn't have one I'd be tempted to move the set aside for a while until a junker chassis came along with a good transformer.

It all depends on how fast you want the set finished and how much you're willing to pay for a transformer from Heyboer. I'd at least run an ad in the Wanted Ads forum here and see if anyone responds.

[radionut1929]

And you don't need that 1.5v filament winding.

How else is he going to power the filaments of the 26 tubes?

The high voltage winding of the Kolster transformer is too high for the Philco. Of course the resulting B+ could be dropped with a resistor, but I don't particularly like "kludges."

Hi Ron,

Listen I know you would like to see keep the set original condition and I agree with you all the way.
However, since I am dealing with 84 year old equipment I have to make some hard choices. All I want to do is to make this radio play once more.
Now you mentioned a resistor I can install in the set. What kind of resistor should I use?

Sincerely,
Radionut

[Ron Ramirez]

Use Ohm's law to determine the amount of resistance needed to drop the resultant B+ from the Kolster transformer to a level acceptable for use in the 511. To do this, you'll have to hook up the Kolster transformer, turn the 511 on just long enough to measure the B+ on the plate of the 71A and then immediately turn the set off.

Philco Service Bulletin #5 calls for a 71A plate voltage of 148 volts @ 115 volts AC line. Taking into consideration today's higher line voltage and more accurate multimeters, what measured 148 volts in 1928 will measure around 160 or so today. Take the difference between actual measured voltage and 160, then use the following formula:

R = E / I

where R = the resistance in ohms you need, E = the difference in volts you wish to drop (actual B+ - 160), I = current in amps. Use 0.0345 (34.5 mA) for I.

Now, once you have the resistance, you will need to know the wattage.

P = I 2 R

where P = power in watts; I = current in amps; R = resistance in ohms.

I can't do a superscript 2 here, so know that I 2 is "I squared." Again, use 0.0345 (34.5 mA) for I.

[radionut1929]

Use Ohm's law to determine the amount of resistance needed to drop the resultant B+ from the Kolster transformer to a level acceptable for use in the 511. To do this, you'll have to hook up the Kolster transformer, turn the 511 on just long enough to measure the B+ on the plate of the 71A and then immediately turn the set off.

Philco Service Bulletin #5 calls for a 71A plate voltage of 148 volts @ 115 volts AC line. Taking into consideration today's higher line voltage and more accurate multimeters, what measured 148 volts in 1928 will measure around 160 or so today. Take the difference between actual measured voltage and 160, then use the following formula:

R = E / I

where R = the resistance in ohms you need, E = the difference in volts you wish to drop (actual B+ - 160), I = current in amps. Use 0.0345 (34.5 mA) for I.

Now, once you have the resistance, you will need to know the wattage.

P = I 2 R

where P = power in watts; I = current in amps; R = resistance in ohms.

I can't do a superscript 2 here, so know that I 2 is "I squared." Again, use 0.0345 (34.5 mA) for I.

Dear Ron,

After some dilligent searching I have found a model 86 transformer.
Now the question is, what is the color scheme are the wires and where do they go?
Do I look for them on the Nostalgia Air website or can you provide me with the color scheme? If you can that would be helpful.

Sincerely,
Radionut

[Arran]

Before spending a pile of money or going on a massive parts search I would make absolutely sure that the transformer is broiled, disconnect everything from the secondary side and hook up a light bulb in series with the primary. If the transfomer is find the lamp will light up briefly when you apply power then drop down to a dim level, if one of the secondary windings is shorted internally the lamp will not dim much if at all. I would also make a few ohm meter checks, the high voltage winding should read near equal DC resistance on both sides of the center tap, one side should be within 20-25 ohms of the other, if one side is substantially lower then the winding is shorted. I would also check the wiring in the rest of the set between B+ and B- which the ohm meter in case there is an external short.
I hate dealing with bad transformers, fortunately most of the bad ones I have found are in sets from the 1940s when things were standardized a little more, ones with 300-0-300, 5 volt, and 6.3 volt windings where they are easier to find.
Regards
Arran

[Ron Ramirez]

An original 86 power transformer would have a set of terminals at the bottom, not a bunch of loose wires. You can figure out which wires do what with an ohmmeter, but it will take some time.

[radionut1929]

Dear Ron,

I have installed the transformer and now I am getteing too much B+ and I think I know why. The model 86 set has to drive a electrodymanic speaker that is acting as some kind of choke but the model 511 set does not. If you look at the diagrams I posted you will see what I am talking about. What can I do to correct this problem? I have a Utah electrodymanic with a dry disc rectifier and power transfomer all in one unit.
Do you think that the speaker would work or should I try something else?
I thank you for your time.

Sincerely,
Robert

[Ron Ramirez]

Ah HA! I wish I had found this before I recommended an 86 power transformer to you...

I owe you an apology, Robert. At the time I recommended the 86 transformer, my mind was on wrapping up college instead of being fully focused on your transformer problem.

I thought I had a Model 86 & 82 service manual, but if I do, I can't find it right now. So until this morning, I was unable to find the specifications for the 86 power transformer. I have it now...thanks to an ancient Philco parts catalog from 1933 or so.

Specifications:

Model 511 (Part No. 3073)

High voltage: 375 VCT (187.5-0-187.5), 37 mA; 1.5 V @ 4.3 A (26 tubes); 2.47 V @ 1.87 A (27); 4.85 VCT @ 0.35 A (71A); 4.8 V @ 2 A (80).

Model 86 (Part No. 3271)

High voltage: 575 VCT (287.5-0-287.5), 80 mA; 1.5 V @ 4.3 A (26 tubes); 2.47 V @ 1.87 A (27); 5 VCT @ 0.6 A (71A); 4.8 V @ 2 A (80).

So you need to drop 100 volts in your B+ line.

The easy fix would be to add a resistor in line with the B+ source to drop the voltage to a level acceptable to the 511. It's still a lot cheaper than having Heyboer custom wind a 511 transformer. Yeah, I know I called it a "kludge" but sometimes you gotta do what ya gotta do...

The Utah will work with the 511 if it has an audio output transformer to match the 511 high impedance output to the Utah's voice coil. I used to have one of those units, finally gave it away at an IHRS swap last Fall. But as far as dropping the B+, the Utah won't really help you, since its electrodynamic speaker has a built-in power supply.

Just add a resistor to the B+ source of the 511. We know the current draw of the B+ in the 511 - 37 mA. We know we need to drop 100 volts. So, applying Ohm's law - R=E/I - we get R = 100 divided by 0.037 which equals 2702.7 ohms. Let's use 2700 as a nice round figure. Now, we need to determine the dissipation in watts. For this, P=I squared R, so P = 0.037 x 0.037 x 2700 = 3.7 watts. Let's double that for safety, which comes out to a little over 7 watts. Therefore, you need a 2700 ohm resistor rated at 10 watts to safely drop the B+ to a level usable by the 511.

You will need to break the connection between terminal 2 of the filter capacitor bank and terminal 2 of the large power resistor, and insert the new 2700 ohm resistor in this line, as shown here:

[Image: http://i326.photobucket.com/albums/k420/...mod_sm.jpg]

Click the image, or click here for a larger version of this partial schematic.

Again, I apologize for the mixup.

[TA Forbes]

Ron, after reading your last post I went outside and looked at the sky, and the moon was BLUE.

Is this a coincidence????

[radionut1929]

Ah HA! I wish I had found this before I recommended an 86 power transformer to you...

I owe you an apology, Robert. At the time I recommended the 86 transformer, my mind was on wrapping up college instead of being fully focused on your transformer problem.

I thought I had a Model 86 & 82 service manual, but if I do, I can't find it right now. So until this morning, I was unable to find the specifications for the 86 power transformer. I have it now...thanks to an ancient Philco parts catalog from 1933 or so.

Specifications:

Model 511 (Part No. 3073)

High voltage: 375 VCT (187.5-0-187.5), 37 mA; 1.5 V @ 4.3 A (26 tubes); 2.47 V @ 1.87 A (27); 4.85 VCT @ 0.35 A (71A); 4.8 V @ 2 A (80).

Model 86 (Part No. 3271)

High voltage: 575 VCT (287.5-0-287.5), 80 mA; 1.5 V @ 4.3 A (26 tubes); 2.47 V @ 1.87 A (27); 5 VCT @ 0.6 A (71A); 4.8 V @ 2 A (80).

So you need to drop 100 volts in your B+ line.

The easy fix would be to add a resistor in line with the B+ source to drop the voltage to a level acceptable to the 511. It's still a lot cheaper than having Heyboer custom wind a 511 transformer. Yeah, I know I called it a "kludge" but sometimes you gotta do what ya gotta do...

The Utah will work with the 511 if it has an audio output transformer to match the 511 high impedance output to the Utah's voice coil. I used to have one of those units, finally gave it away at an IHRS swap last Fall. But as far as dropping the B+, the Utah won't really help you, since its electrodynamic speaker has a built-in power supply.

Just add a resistor to the B+ source of the 511. We know the current draw of the B+ in the 511 - 37 mA. We know we need to drop 100 volts. So, applying Ohm's law - R=E/I - we get R = 100 divided by 0.037 which equals 2702.7 ohms. Let's use 2700 as a nice round figure. Now, we need to determine the dissipation in watts. For this, P=I squared R, so P = 0.037 x 0.037 x 2700 = 3.7 watts. Let's double that for safety, which comes out to a little over 7 watts. Therefore, you need a 2700 ohm resistor rated at 10 watts to safely drop the B+ to a level usable by the 511.

You will need to break the connection between terminal 2 of the filter capacitor bank and terminal 2 of the large power resistor, and insert the new 2700 ohm resistor in this line, as shown here:

[Image: http://i326.photobucket.com/albums/k420/...mod_sm.jpg]

Click the image, or click here for a larger version of this partial schematic.

Again, I apologize for the mixup.

Dear Ron,

Could you somehow put the modification in a more pictorial diagram?
Sometimes I have a hard time reading the wireing diagrams unless they are more pictorial
in nature. I hope that I am not putting you through too much trouble in asking for this little favor but my autism sometimes gets in the way. If you could do this for me that would help me a lot.

Sincerely,
Robert