[morzh]

John

It's OK.

I like it.

[462ron]

Yes John I did. That Trol Master kicked around for decades, never knew what it was until the day the discussion of the ‘Gozinta’ or whatever it’s called, came up. Then the light went on and I finally knew what it was. I have a lot of tubes dad had but most were TV tubes. I have his signal generator and 2 tube testers and various hand tools that I still use. He also had a 5Mhz Oscope that I sold, and various TV alignment equipment and cap testers, mostly Heathkit stuff!

Ron

[morzh]

The guy who sold it to me on eBay said it was a bicycle pump.

[morzh]

https://www.ebay.com/itm/philco-radio-ph...%7Ciid%3A1


Someone is selling the proper phonograph for this radio. Not sure I want it for this much money - I paid as much for the whole radio. I could buy it for $20 total......just to play with it.

[morzh]

From what I understood the original phonograph had an electromagneic pickup, as the transformer is 0.2 Ohm to 5,500 Ohms.
The transformer was omitted, probably due to the V-M phonograph having the piezo pickup.

I re-did the wires with proper grounding, both the motor and the phonograph chassis (via the Phono cable). Also installed new RCA cables, both males with the F-F RCA slug in between them.


The grounding scheme is as follows:
The RCA pigtail from the radio has the shield as the GND and the centrai wire as the signal; the turntable has twin shielded wire; Both shield and one wire are connected at the shell; then the signal and the wire go to teh cartridge while the shield only connects to the turntable's chassis, therefor avoiding GND loop.

46-1213_Phono_Grounding.pdf Size: 16.83 KB  Downloads: 120

The phonograph plays fine, and this with  the old needle.

But. At a decent volume the hum is pronounced.
I did an experiment: disconnected the turntable with no reduction in hum, shorted the Radio's pigtale RCA, also with no reduction and then shorting the Phono input right at the tube socket - same result.

Significant reduction to very acceptable level occurs with me touching the chassis or simply connecting it to Earth GND.

I intend to use a 3-prong Earthed plug for this reason only.

[morzh]

IT IS GOOD TO BE PARANOID!

Today I got the small 3-prong cable (10A, AWG 18, so it fits through the existing bushing in the back).
I thought that since I have an extra Ground that was not used before plus an external load - the phonograph, plus it is not original - it would make sense to install a fuse.
And because this chassis is a super pain to take out - the fuse should not be an inline type, it should be accessible.
So I installed a 2" holder, put in 3.15A fuse, routed the wires, and - voila! - we have a nicely fused radio.
Then I connected the phonograph, the hum did diminish with the Ground though it did not go away completely, and the pickup could be heard when rubbed with a finger against the needle.
And then I turned the motor on, and the lights went out on the radio.
I immediately knew it was the fuse. Took it out, all black.
So I replaced it and repeated the whole process with an isolating transformer with the GND still connected. All worked fine.
But when plugged in the outlet directly - it blows up.

Upon examination I found out the wire connection of the phonograph is questionable, but obviously it worked since the Earth was absent. Not it does not.

Once I find out exactly what it is, I will describe it.

[morzh]

So.

What I had found is pretty hideous

Whoever connected the phonograph to the radio did a heck of a job in the literal sense of the word "heck".

The schematic has the 4-pin phono connector that provides 115V (Line and Neutral) to the motor and 6V for the lamp from the same winding that has the rest of the filaments of the tubes except the phono amp tube, one of the latter ones being also the Chassis GND.

The V-M phonograph has the ON-OFF-REJECT switch that has two wires connected to Line (Hot) at its output. The 1st goes obviously to the motor and the other probably went to some sort of light which had to be 115V light.

So.

The Nicola Tesla who did the connections :

1 . Connected the 115V L and N, L going through the switch.
2. The switch output 115V, the second wire he routed back to the Chassis GND.
3. The 6V lamp wire he routed via a capacitor as the GND for the motor.

DO I hear "Wow!".
But wait! It worked! Because....yes, because there was no GND or when it was it was floating due to the isolating transformer.
Once plugged into the outlet, it blew.

So. I left the motor wires, I connected the Chassis to the motor frame, and I fully disconnected 6V as it is not used and the second 115V wire after the switch as, again, it is not used either.

No blow-ups anymore, everything works.
It plays, and with the new needle will probably play that much better.

Now, the hum.
The GND did attenuate the hum, but at the maximum volume with the PHONO ON, it is still heard.
I changed the wire that comes from the volume pot for the shielded wire that I grounded to the chassis and that attenuated it some more, but not all the way.
I see the place it originates from (output of the phono amp) but it comes from some other place than the input as when I short the plug or even the tube's pin to the GND (which is 1/2 inch away) it still hums.

Will try some more things tomorrow, though it is acceptable. It would be more acceptable had it been the original player but the thing is, due to the impedance mismatch the volume is not very loud and it could benefit from the maximum loudness except that the hum could be heard when the player is not playing.

[morzh]

Today spent some time trying to chase that hum.

One of the suspects was the capacitor: the cap in he radio that filters the plate voltage on the 6AF7 (the phono amp) is 0.1uF but the parts list shows it as 1uF.
So I put 1uF in parallel, no effect at all.

As I said, shorting the input of this tube does not get rid of it but shorting the output (or extracting the tube) does.
Also the hum is only exists with phono, not with radio.
So, after replacing the tube with the old one (weaker but works fine) with no results, I decided to leave the radio the way it is.
The phonograph with the new needle plays OK. There is a lack of base. I suspect the correction filter is there for the transformer and not the piezo. The radio itself has excellent base.

If I ever get the original phonograph cheaply I might put it back as the transformer is good, I checked it. But then it will not play 33-1/3 rpm records. Or I might get a phono preamp that matches piezo with EM input.
Or I even might sell that radio as I already have an FM with a phonograph.

There is only so much could be done with this without modifying the sch which I am not eager to do, I try to keep things as original as possible.

Now to putting Humpty Dumpty back together again.

[NostalgiaRadioTime]

Not sure if this simple trick will help with the hum, Mike, but on my 47-1230 I got rid of the hum by grounding the phono table to the chassis. I just ran a wire from the frame of the phono compartment to the ground terminal on the chassis and it disappeared. And, of course, having not read every post in this thread maybe you already tried this!

[morzh]

Greg

The table is Grounded and the motor is grounded also separately.

But this is not the reason: the hum is there when the input of the phono is dead-shorted (it is 1/2" distance between the GND and the input of the tube so I short if with a screwdriver).

This is the tube and I am not sure what makes it hum. The power is super-clean.

[morzh]

Since the hum disappears in full when the 7AF7 tube is removed (it is the phono pre-amp) I knew the tube somehow makes the noise.
Eventually, after tracing the filament supply (it is routed away from the input and as a tight line, plus it is a separate winding from the transformer with a centertap) and not being able to do anything, I decide to try to shunt the Cathode with a cap to the GND.

On one hand, that should increase the gain in highs (and i already have little base, only when playing the records, likely due to the amp being made for EM cartridge with transformer vs the piezo, which is what I have now), and this is not my goal.
On the other hand I could deal with this later.

So, I unplugged the phonograph, put the volume to the max, heard the hum, touched a 20uF cap between the Cathode and the GND and....the hum disappeared. Varying the values, I found that the same effect is made when the cap is 1uF, but the hum persists if it is 0.047uF. So I soldered a small 4.7uF aluminum can, plus to the K and minus to the chassis, and the hum now is very low, I have to really put my ear against the speaker at max volume to hear something which is more like some white noise rather than hum.

Playing the record (I use Luis Armstrong) revealed practically the same playback quality with a bit more volume and just a bit more treble (not really much more). Still the lack of base.

Since the base is good when the radio is in receiving mode, I think it might be the input filter that is sized up for ElectroMagnetic pickup and the transformer rather than a piezo crystal. Now I need to research the input filter parameters and try to make it play a better base.

Then hopefully I will be done.

[NostalgiaRadioTime]

Good work, Mike. It's fun to experiment, especially if it leads to the desired results!

[morzh]

Greg,

If it were some high end radio with a phonograph and I were hellbent on making it work really quiet, I would probably put a rectifier bridge on that filament winding, then filtered it with a real good cap and got me a super quiet filament. Or maybe tried that potentiometer thing they often use, like in 37-690 when balancing the output direct heated triodes' filaments.

But this radio, as good as it is, is not really a high end, and as long as it sounds nice enough I am satisfied. I simply want to keep it close to original. I installed that 0.047uF yellow cap and left it yellow, so if I ever need to remove it, I know exactly what to remove; the rest of the chassis looks original as the resistors used were mostly carbon composite that looks like they should, and the caps were re-stuffed. So if I ever open it up, I know exactly where to look

[Ron Ramirez]

This is what Fisher did with preamplifier tubes; the filament strings were run with rectified and filtered DC to eliminate hum in those stages.

[morzh]

Ron


And that was a smart thing to do as the first stages have the highest gain and are therefore the most sensitive.

I also see that trick in many today's high end amps.
Not just that, they sometimes put the rectified and filtered voltages through a Linear regulator / LDO, which all but eliminates any ripple. That makes it super-quiet.