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 !:wave:

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.

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.

Re: Vintage Radio and Phonograph cutter schematic
 

Thank you so much Lawrence ! I can not wait to start working on this :)

Thank you for the clarification. Will use a generic electrolytic caps then...

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

:wave:

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.

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 !

Re: Vintage Radio and Phonograph cutter schematic
 

The crystal needs to be voltage driven, hence the connection to the output valves anode where a large signal voltage is available.

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.

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... :-/

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...:idea:

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.

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

Re: Vintage Radio and Phonograph cutter schematic
 

I should have also said thank you to Levente.
Cheers
John

Re: Vintage Radio and Phonograph cutter schematic
 

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!

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. :)

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 !:wave:

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.

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!

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.

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?

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.

Re: Vintage Radio and Phonograph cutter schematic
 

Lawrence, a million thanks for this. Where did you get this manual? Looks like original one in pristine condition. This is fantastic and helping me heaps.

Really, thank you so much for sharing this.

With regards the cutter head, so the cutter head needs no DC that is why the 0.1uf is there and the AC comes from the 6v6GT plate / transformer primary.

Got it.

I am just playing with a thought in case the crystal head is gone which most likely will be a case, to rebuild tha cutter head with a piezo speaker element. But that I think from that output will not be possible but maybe a 4 ohm output from the secondary windings.. uuuh.. i am going to far here i guess..

Thanks

PS: sems that the cathode bypass capacitors are also higher...instead of 10uF they are 20uf here.....such a great service manual !

Re: Vintage Radio and Phonograph cutter schematic
 

I got the dropbox link from here:

https://audiokarma.org/forums/index.....536327/page-2

Lawrence.

Re: Vintage Radio and Phonograph cutter schematic
 

thanks a lot! I did miss that thread.. ! have a great weekend Lawrence.

Re: Vintage Radio and Phonograph cutter schematic
 

hey Lawrence and All,

I am getting some trouble with this old piece...off readings on some of the tubes compared to the chart Lawrence gave us in the previous post....

also, I am having 105 VAC in the chassis with some significant hum

All the drifted resistors are replaced and the cap's too one by one.

Where I am getting the off readings are the two 6SJ7's and the 6SF7 and the 6SA7. Before these tubes, the readings are spot on. So the rectifier, the 6v6 and the 6SC7 reads nearly spot on.

I have no histry of these tubes as it came with this old unit..... should I start swapping them out with other tubes and see the results?

I am not sure where the 105 VAC is coming into the chassis...:dunce:

PS: Slight correction, i did not change the power filter capacitor as read spot on 16+16 UF and very low Ohms.

Re: Vintage Radio and Phonograph cutter schematic
 

Lawrence.

Re: Vintage Radio and Phonograph cutter schematic
 

Thanks Lawrence, answering your questions backwards:

1. the 105VAC reads on my DMM between the chassy and the earth in the wall socket

2. the readings of 1st 6SJ7 ( after the 6SC7)

0 Pin1
0 Pin2
0.7 Pin3
-0.3 Pin 4
0.75 Pin5
20 Pin 6
6VAC Pin 7
25 Pin 8

2nd 6SJ7

0 Pin1
0 Pin2
0.7 Pin3
-0.45 Pin 4
0.75 Pin5
18 Pin 6
6VAC Pin 7
21 Pin 8

6SF7

0 Pin1
-1.3 Pin 2
0 Pin 3
73.5 Pin 4
-1.5 Pin 5
247 Pin 6
6 VAC Pin 7
0 Pin 8

6SA7

0 Pin1
0 Pin 2
246 Pin 3
74 Pin 4
-5.6 Pin 5
0 Pin 6
0 Pin 7
-.1.9 Pin 8


Some of them are really off...compared to that chart...

Re: Vintage Radio and Phonograph cutter schematic
 

Regarding the 105 volts AC between the chassis and your mains earth...try disconnecting the capacitor that's connected between the unswitched mains conductor and chassis, in the schematic in the dropbox link it's number 12.....C12 in the parts list, it's a 0.01uF capacitor, shown as .01 in the schematic and in the parts list.

I'll look at those voltage measurements tomorrow.

Lawrence.

Re: Vintage Radio and Phonograph cutter schematic
 

Thanks Lawrence... that cap is the one which I soldered in as the old one was in pieces... replaced with a Y cap.

Thanks again for your help...

Re: Vintage Radio and Phonograph cutter schematic
 

Shown as 6J7's on the schematics....is yours definitely fitted with 6SJ7's? (the 6J7 has a top cap connection the 6SJ7 doesn't)

Lawrence.

Re: Vintage Radio and Phonograph cutter schematic
 

hey

I am not with the machine right now but am 100% certain that there is no metal caps on those tubes. Will check again when I am home. I have not disconnected that Y2 cap yet. If I do so, will that be safe?

thanks

PS: it sis really confusing... the attachment is a different print, for the same model. Different reading chart and there are 6SJ7s.... but less AC and DC voltages I am getting for sure at the rectifier tube... seems like its a mix of the two schematics?

Re: Vintage Radio and Phonograph cutter schematic
 

The pin voltages look to be for 6SJ7's, more about that below.

First I would disconnect that Y Class capacitor and connect the chassis to mains earth, that will prevent the chassis from becoming live if there is any leakage, that AC voltage reading might be due to capacitance that exists between the primary and secondary windings of the mains transformer in conjunction with using a high impedance digital multimeter, if you do as above and the supply doesn't trip I would leave it like that for the moment (chassis earthed, Y Class capacitor disconnected)

For the valve voltages etc let's make it easy and number the valves V1, V2, V3, V4, V5, V6 and V7 from left to right (V1 to V6) then down for V7 (the rectifier)

Also note the voltages quoted by the manufacturer were measured using a 1,000 ohms per volt meter, this means that some of those measurements will be low or none existent compared to what you have measured using a DMM.

V1 (6SA7) You recorded no heater voltage for this valve but the -ve voltage on the oscillator grid (pin 5) suggests that the valve is working in that department, ie: the oscillator is working...This valve is used as the receivers mixer/oscillator (aka a Pentagrid Converter) The anode and g2g4 voltages (pins 3&4) seem reasonable and the other measurements seem ok except the heater...so can you check pin 2 and 7 again for 6 volts AC on one of them so as to clarify the situation?

V2 (6SF7) The voltages look reasonable to me....This valve is the receivers IF (Intermediate Frequency) amplifier and signal detector.

V3 and V4 (the two 6SJ7's) the voltages on the anodes (pins 8) and g2 (pins 6) look low if measured with a DMM, what's the voltage at the junction of C10 and R39 etc? (circuit refs are per the dropbox link schematic) So far as I can make out these two valves are voltage amplifiers for high or low level inputs from a microphone or high level inputs from an auxiliary source.

Lawrence.

Re: Vintage Radio and Phonograph cutter schematic
 

Thanks Lawrence,

Disconnected the Y2 capacitor and connected the chassis to the mains earth. No AC voltages can be measure in the chassy (does this mean that the brand new Y2 cap from Farnell was failing?)

Before i go further, I am feeding this turntable with 110VAC not 117VAC due to my step down converter, I assume some voltages will be a bit lower.

V1 has heater voltage of 6VAC.

Junction C10 and R19 is 172 V.

I found some discrepancies what I see in the unit and what I see on the schematic and what is in the component list...I hope I see this correctly...

the R39 on the schematic is 10kOhm but the R39 in the components list is 100Kohm

Also, the V3 and V4, the pin 3 i think it is the grid and the grid resistors both were 500kohm in the unit, but on the schematic V3 has 500kOhm and V4 has 100 Kohm. ....I did try to follow the schematic and when I did that the V4 anode pin 8 voltage went up to 137Volts. I put both resistors back how it was, both 500kOhms...

what would you advise Lawrence ? arent those anode and g2 voltages to high? nearly double compared to that chart...

with regards the mains cable, do i need to simply change the two prong to 3 prong? Many thanks for your help, as always.

Re: Vintage Radio and Phonograph cutter schematic
 

The problem is there's no consistency in the various schematics and voltage tables etc some were measured with a 1k ohm per volt meter, some with a 20k ohm per volt meter, the difference between the two would make for different readings when comparing what your readings are, all I can suggest is to ascertain the original nominal value of the anode and screen grid resistors which are fitted in your unit and check them for unusually high or low resistance and replace as required, as for capacitors, treat all with suspicion.

I would leave the Y Class disconnected and the chassis earthed for the moment for troubleshooting purposes.

Does the radio receiver work? V1 and V2 voltages seem reasonable, V3 and V4 aren't used when switched to radio so far as I can make out.

Lawrence.

Re: Vintage Radio and Phonograph cutter schematic
 

Thanks Lawrence. Yes, the radio works. I tuned in a station last night...the sound isn't clean as the antenna is just a wire and not connected to anything just hanging out... I did even tried for a very little time yesterday the phono playback, also works...( fitted a new playback head just to try, the rubber wheels needs attention, but that is later...)

there was some hum with it yesterday, maybe because of the ac was in the chassis, i have not tested it today for sound.

I will test it again tomorrow to find out if the hum is still there...

With regards the resistors, i went through all of them... some of them drifted significantly, i did replace those...

I also did replace all the caps but not the filter cap, that is still the original 16+16 uf from the 1940s. Checked with a cap tester, measuring spot on with
0.62 ohms ESR. Shall I still replace this?

The other caps did not replace are the two silver mica and there is something like a brown open tube covered with wax... not sure what is that I have not seen anything like that ....

shall I do another voltage testing tomorrow or this is OK as it is for now?

Re: Vintage Radio and Phonograph cutter schematic
 

Good Morning,

to follow up the yesterday's post, I did replaced the two 100k resistors R44 and R41 as they were drifted up to 130k

the volume pot's were crackling really loud while touching them and cleaned them nicely.

Turned on the unit, again a massive hum happening...50 cycle hum and the hum increasing and decreasing while the volume pot is operating... (bad pre-amp or output tube?) the pin 1s and 2s are grounded on both the 6SJ7.

All the caps and resistors now reads correctly.

Might replace the filter capacitor as it is old, no point now leaving that in as all the other components fresh and new i guess..

This Y cap is still bothering me a lot... not sure what to do with it...

:wave:

Re: Vintage Radio and Phonograph cutter schematic
 

The Y Class capacitor might or might not affect the hum level, you can determine that by experiment.

The maximum current that can flow via a 0.01uF capacitor that isn't faulty that's connected between 110 volts Live and Earth is approx. 350uA (350 microamps)….I = V/Xc…..Xc can be determined here:

https://www.electronics2000.co.uk/ca...calculator.php

Lawrence.

Re: Vintage Radio and Phonograph cutter schematic
 

Thanks Lawrence, understood.

I am measuring the cap to ground....it is 2.7A with 108 VAC ...which is much higher than the calculation is giving me 0.3 at 50Hz or 0.4 at 60 Hz approx.

I am trying to understand the reason for this..why is this reading?

Re: Vintage Radio and Phonograph cutter schematic
 

Check your readings and check your calculations, I've never had a new Y Class capacitor fail.

Your meter should be in series with the capacitor when measuring the current.

Lawrence.

Re: Vintage Radio and Phonograph cutter schematic
 

Bingo. Reversed the two prong plug...now I am getting 0.04 VAC and no hum at all...but my step down converter is also a two prong one...?

Re: Vintage Radio and Phonograph cutter schematic
 

I thought that might be the case, usually Y Class are only connected between Live and chassis if the chassis is earthed. Neutral and Earth will be connected together at some point in your electricity supply, hence the virtually no voltage reading you now have.

Lawrence.

Re: Vintage Radio and Phonograph cutter schematic
 

that means wherever I go with this or plug that in I do need to check the wall socket which is the Live and Neutral? I did mark now the sides with a red tape on the step down converter and also on the plug itslef...

there is only a slight hum, will solder back the Y cap and see what happens...

Thanks Lawrence for your help! :thumbsup:

Re: Vintage Radio and Phonograph cutter schematic
 

All wall sockets should be wired the same unless someone has wired them incorrectly, in the UK looking at the wall socket the Live is on the right and the Neutral is on the left if they have been wired correctly.

With the electricity supply I have here the Neutral is connected to an Earth mat buried in the ground back at the pole that the electricity distributors supply transformer is mounted on and at various points between there and the house, before the distributors Neutral connects to the electricity meter at the house it's connected to the main Earthing conductor that's connected to the consumer unit and from there via the various Earthing conductors to all the mains outlets.

Lawrence.

Re: Vintage Radio and Phonograph cutter schematic
 

Thanks... here the live is on the left side..i was not aware of that, just reading online articles...the question is which of the two prong should go to the left then... or just test it first..wonder if incorrectly plugged in which happened several times, did damage any other components connected to ground on the chassis...:'(

Re: Vintage Radio and Phonograph cutter schematic
 

Reversing the two prong mains plug shouldn't have caused any damage.

Lawrence.

Re: Vintage Radio and Phonograph cutter schematic
 

Thanks Lawrence for this. Have a great evening. :)

Re: Vintage Radio and Phonograph cutter schematic
 

Hey Lawrence, hope you a great Sunday there... just a quick question if I may.

Is it possible to disconnect that speaker field? and using one filter cap of 30uF instead? Just a thought as I would like to hook this up with a better external speaker...

Would this work? Or that speaker field needs to be there for the correct operation.

Thank you.

Levente

Re: Vintage Radio and Phonograph cutter schematic
 

No, don't bypass the field coil of the internal loudspeaker, that winding is essential for the proper operation of the unit.

An external loudspeaker can be used plugged into the jack socket provided.

That will disconnect the internal loudspeakers voice coil, the external loudspeaker can be either of the permanent magnet type or the electrodynamic type, if an electrodynamic type is used it will have to have its own field coil supply.

Lawrence.

Re: Vintage Radio and Phonograph cutter schematic
 

Thank you so much ! :thumbsup: Understood.

Levente

Re: Vintage Radio and Phonograph cutter schematic
 

Hey Lawrence, another quick question and thank you for your advise in advance as always...

I thinking to change the value for the second filter capacitor. Would a 100uF ,275 WKG 350 Surge be an acceptable choice? I know the voltage calls for a 450V rated cap but there I will not get more than 250V and these can capacitors I have are really a god quality.

I kept the first filter connected to the 5Y3 the same 16uF/450V

Would this reduce the hum?

Many thanks!

Re: Vintage Radio and Phonograph cutter schematic
 

It should be rated the same as the reservoir capacitor which is 450 volts, here's why...

1) The rectifier is a directly heated rectifier, the rest of the valves aren't, that means that the voltage on the rectifiers cathode and the rest of the HT line can be much higher than it otherwise would be after the other valves have warmed up and drawing their full current.

2) A fault condition could exist such as the heater supply for all the valves other than the rectifier goes missing for whatever reason, ie: poor connection, open circuit heater winding on the transformer etc, if that were to happen the HT voltage would rise to the peak value of the AC voltage that's presented to the rectifiers anode(s) The manual gives a figure of 320 volts AC at the anode(s) that is the RMS value, however, as said, the reservoir capacitor would charge up to the peak voltage of the AC therefore putting the HT line at a DC voltage that's equal to the peak of the AC voltage, the peak value of a sinusoidal AC voltage is its RMS value multiplied by 1.414, ie: 320*1.414 which equals approx. 450 volts....

Would increasing that capacitors value reduce the hum to a noticeable extent....It depends where the hum is coming from, soon find out if a suitable one is fitted.

Lawrence.