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Old 23rd Sep 2019, 2:46 pm   #1
Levente
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Default Vintage Radio and Phonograph cutter schematic

hello wonderful people!

I have a very old schematic...attached.

I made some circles on the picture, assuming that the audio path is going through these capacitors, but please correct me if I am wrong on that...

According the user manual the coupling caps are papers, the eceltrolytics a self explanatory but there one LINE CAPACITOR of 8mfd... i have never heard of LINE capacitors...what types are they?

and the candohm resistor are they some special types of two in one resistors or variable's?

Please direct me on this... this machine is from 1947.

Thank you !
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Old 23rd Sep 2019, 3:38 pm   #2
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Default Re: Vintage Radio and Phonograph cutter schematic

The only line capacitor I can see is the 0.01uF that's connected from the mains AC line to ground/chassis, if you replace that one you should replace it with a Y Class type.

The Candohm resistor is 4.5 ohms wire wound, so far as I can make out it's a dummy load for the output stage when the loudspeaker is disconnected, probably mounted on the chassis, you can replace it with a similar value wire wound resistor rated at 10 watts.

Lawrence.

Last edited by ms660; 23rd Sep 2019 at 4:05 pm.
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Old 23rd Sep 2019, 3:56 pm   #3
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Default Re: Vintage Radio and Phonograph cutter schematic

The only capacitors in any signal path are marked up as RF or AF in the pic attached.


The 8uF 450V is simply an HT decoupling electrolytic type. All of the other ringed capacitors look to be decouplers of one sort or another.
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Old 23rd Sep 2019, 4:47 pm   #4
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Default Re: Vintage Radio and Phonograph cutter schematic

Quote:
Originally Posted by ms660 View Post
The only line capacitor I can see is the 0.01uF that's connected from the mains AC line to ground/chassis, if you replace that one you should replace it with a Y Class type.

The Candohm resistor is 4.5 ohms wire wound, so far as I can make out it's a dummy load for the output stage when the loudspeaker is disconnected, probably mounted on the chassis, you can replace it with a similar value wire wound resistor rated at 10 watts.
Thank you so much Lawrence ! I can not wait to start working on this

Quote:
Originally Posted by Herald1360 View Post
The only capacitors in any signal path are marked up as RF or AF in the pic attached.

The 8uF 450V is simply an HT decoupling electrolytic type. All of the other ringed capacitors look to be decouplers of one sort or another.
Thank you for the clarification. Will use a generic electrolytic caps then...

Many many thanks for marking the signal caps out, really appreciate it.

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Old 23rd Sep 2019, 6:59 pm   #5
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Default Re: Vintage Radio and Phonograph cutter schematic

In the schematic the function switch is shown in the Radio position and the switch wipers shown on the switch wafers rotate anti-clockwise to select the other functions, so from Radio function going anti-clockwise it's Phono...Record Mike...Record Radio...Public Address.

The Gain switch is shown in the Normal position, the Gain switch wipers rotate clockwise for the High position.

In the schematic you posted, the resistor shown without a value that's in the cutters feed circuit is the 27k 1watt listed in the parts list.

If that helps.

Lawrence.
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Old 24th Sep 2019, 9:53 am   #6
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Default Re: Vintage Radio and Phonograph cutter schematic

Definitely helping and thank you for that, and if I may throw in a few other questions:

It looks like the output transformer primary is also connected to the cutter head. Is this because of the crystal cutting head needs more power than a magnetic head?

And the cathode bypass capacitor.. can that capacitor be a non polarized electrolytics? I see that on this schematic is a polarized one but when I check a Fender Champ schema, looks like the bypass cap is a non polarized 25mfd eletrolytic capacitor.?

Thanks !
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Old 24th Sep 2019, 11:13 am   #7
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Default Re: Vintage Radio and Phonograph cutter schematic

Quote:
Originally Posted by Levente View Post
It looks like the output transformer primary is also connected to the cutter head. Is this because of the crystal cutting head needs more power than a magnetic head?
The crystal needs to be voltage driven, hence the connection to the output valves anode where a large signal voltage is available.

Quote:
And the cathode bypass capacitor.. can that capacitor be a non polarized electrolytics? I see that on this schematic is a polarized one but when I check a Fender Champ schema, looks like the bypass cap is a non polarized 25mfd eletrolytic capacitor.?
In the Meissner schematic you posted the polarization symbol (+) for the output valves cathode bypass capacitor has been omitted for some reason, however, being an electrolytic type it is polarized, +ve to cathode.

Rough rule of thumb, capacitors above 1uF are normally electrolytic types.

Non polarized electrolytics were mainly used in loudspeaker crossover networks.

Also found this on web about the early era recording systems etc, it might be of interest:

https://americanradiohistory.com/Arc...I/CREI-309.pdf

Lawrence.
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Old 24th Sep 2019, 11:26 am   #8
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Default Re: Vintage Radio and Phonograph cutter schematic

Understand. Thank you so much. And that read is awesome... i am at this one at the moment

https://www.bbceng.info/additions/20...g%20Manual.pdf

..also good read how the BBC done it back in the days... I think I was born in the wrong era...
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Old 24th Sep 2019, 5:30 pm   #9
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Default Re: Vintage Radio and Phonograph cutter schematic

Okay... I am reading do much about this and really into it... just a thought on frequency responses vs cutter head.. would it be possible to increase the frequency response of the given crystal cutter if:

1. the cutter is wired for modified constant velocity ( i think, looking at the schematic, it is)

2. Knowing the capacitance of the cutter head and calculating the impedance at 100 cycles and the highest desired cycles

and the this (copied) :

If, when using the crystal cutter, the impedance of the driving
source is made equal to the impedance of the cutter at any frequency,
the cutter response drops at the rate of 6 db per octave above that frequency. The impedance of the .007 pi capacitance of the RC -20 cutter
for instance, is approximately 44,000 ohms at 500 cycles. If it is fed
by a 44,000 -ohm source, response (stylus movement) will be constant
for all frequencies below the 500 -cycle point of equal impedances ; but,
as the frequency rises, it will be reduced at the rate of 6 db per octave.
Under these conditions, the response is exactly the same as a magnetic
cutter cutting modified constant velocity ! Merely by adjusting the
source impedance we can adjust the characteristic for any desired turnover frequency or we can cut constant amplitude, which is merely a
characteristic in which the turnover frequency is above the usable frequency range, and so, practically speaking, does not exist.

4. raising the cutter head voltages 75 RMS is the working voltage, but capable of 280 according the data sheet...

5. (copied) When modified -constant -velocity response is cut with a crystal
cutter, driving voltage may be increased. With the RC -20, a turnover
of 500 cycles will permit driving voltage of 150. Voltage overloads must
be carefully avoided, or the crystal may be cracked.

considering the above, a cutter head of 7500 cps would be capable to produce higher frequencies? or am I getting confused on this...
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Old 24th Sep 2019, 6:12 pm   #10
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Default Re: Vintage Radio and Phonograph cutter schematic

I wouldn't bother trying to get a better frequency response etc out of it, it is what it is and that's assuming the crystal is ok which it might not be, both in the cutter and the pickup.

Radiomuseum has some info to download on the X-26 crystal cutter:

https://www.radiomuseum.org/r/astati..._x_26_x26.html

Lawrence.
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Old 24th Sep 2019, 6:54 pm   #11
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Default Re: Vintage Radio and Phonograph cutter schematic

I would like to thank you Lawrence for the link to the history of recording, excellent reading.
Cheers
John
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Old 24th Sep 2019, 6:56 pm   #12
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Default Re: Vintage Radio and Phonograph cutter schematic

I should have also said thank you to Levente.
Cheers
John
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Old 24th Sep 2019, 10:33 pm   #13
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Default Re: Vintage Radio and Phonograph cutter schematic

Quote:
Originally Posted by ms660 View Post
I wouldn't bother trying to get a better frequency response etc out of it, it is what it is and that's assuming the crystal is ok which it might not be, both in the cutter and the pickup.

Radiomuseum has some info to download on the X-26 crystal cutter:

https://www.radiomuseum.org/r/astati..._x_26_x26.html

Lawrence.
Sure. Was just playing with a thought... downloaded the astatic head pdf. On the Meissner, the resistor and the capacitor goint to the cutter head, i think it is a 27kOhm and .1uf in series....the Astatic manual is referring to a 50kOhm coupled/ paralell with the .01 uf cap.. that is interesting...

will deal with the cutting head at very last...

Thanks Lawrence!
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Old 10th Oct 2019, 6:08 pm   #14
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Default Re: Vintage Radio and Phonograph cutter schematic

Hey Guys,

Starting this project and thought will post a few pic of this unit. I have received a few weeks back. Maybe some of you out there also refurbished or in a process to refurbish such gear...great fun!

Opened up and it the look of it is really pretty and it is in a very good shape considering the age.

Checked visually what is going on inside and took my DMM to measure first the capacitors.

I see plenty of bee wax one Zenith written on...Surprisingly these caps are spot on on my DMM. I know, I should replace them with new film caps, just mentioned that as all the other film caps in the unit are out of spec's. The Zenith's are within spec's and it seems that these are kind of a tone capacitors?

I found the 0.01 cap to chassis is in pieces ! So that will be the Y2 one and there is another one a 0.05 to ground at the motor switch.

The power capacitors are 16+16 uf and measures 1 Ohm's on the ESR meter.

The two 25 uf bypass caps are over 40 Ohms on the ESR meters.

Switches seems smooth. power cord is two prong, will keep this as it is, I have no issues with it.

The motor switch was broken, replacing with a Push button ones.

Posted few pic's and will be doing so if some of you is interested in this thread, it is a lovely challenge. (tubes are looking really good in shape too).

One thing I can not put into place is at the tube 6v6GT

At Pin3 Plate there is a wire hanging and not going anywhere an should - according to the schematic- should not go anywhere else besides the .01uf / 1000V and the 0.04uf at the switch. Maybe someone soldered that in his way and forgot to clip that off....who knows...

Have a great evening and if any of you interested, please follow this thread.
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Old 12th Oct 2019, 3:03 pm   #15
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Default Re: Vintage Radio and Phonograph cutter schematic

hey Guys...if any of you still around this thread, could you please help me finding out what voltages I should expect at the output transformer primary going to the .1uF and 25k resistor showing on the schematic?

I do not have any information on the output transformer..nothing is written on it please if you could help me out on this would appreciate it.

Is this the plate voltage? I see a 0.01uF at the 6v6GT plate rated 1000V means the plate should be there around 400-450? but Is that also on the transformer primary winding directly connected to the 25k resistor .1 400V rated capacitor to the switch and the cutter head?

or this should be much lower as that cap is rated only 400v?


thank you so much !
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Old 12th Oct 2019, 3:45 pm   #16
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Default Re: Vintage Radio and Phonograph cutter schematic

The plate voltage given for the 6V6 in the Riders service info is given as 230 volts DC, the DC voltage on the transformers primary feed to the cutter should be the same as the 6V6's plate voltage.

Lawrence.

Last edited by ms660; 12th Oct 2019 at 3:53 pm. Reason: ammended
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Old 12th Oct 2019, 3:48 pm   #17
Levente
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Default Re: Vintage Radio and Phonograph cutter schematic

Thanks Lawrence... jeez that is a lot of DC in the cutter head? or that 25k resistor will reduce this to the operating voltage if the crystal cutter...?

The crystal cutter head operating voltages is 75V according to the Astatic X-26 manual

Thanks again..

Missing question: could you please let me know which manual you referring to? I have few pages of this unit and on that the 6v6GT plate is 240V ? many many thanks!

Last edited by Levente; 12th Oct 2019 at 3:57 pm. Reason: missing question
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Old 12th Oct 2019, 4:06 pm   #18
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Default Re: Vintage Radio and Phonograph cutter schematic

The cutter head is isolated from the DC on the plate by the 0.1uF capacitor.

Info from Riders can be seen in here (scroll down to Meissner pages 16-1 to 16-9):

https://www.americanradiohistory.com...r-1946-MNO.pdf

Lawrence.
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Old 12th Oct 2019, 4:17 pm   #19
Levente
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Default Re: Vintage Radio and Phonograph cutter schematic

Thank you

This is weird..i have a different manual for the same unit with slightly different values... but where did you see the 222V just out of curiosity? i can not find that ...its probably me being silly again

and does that mean that the cutter head not getting any voltages at all?
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Old 12th Oct 2019, 4:25 pm   #20
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Default Re: Vintage Radio and Phonograph cutter schematic

There's another one here (220VDC on the plate):

https://www.dropbox.com/sh/0yfx95n1i...616_073254.jpg

The cutter needs an AC signal not a DC voltage, the amplifier valves amplify the AC signal but they need DC on their plates/screens in order to do so.

Lawrence.
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