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Old 12th Oct 2019, 4:33 pm   #21
Levente
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Default 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 !

Last edited by Levente; 12th Oct 2019 at 4:38 pm. Reason: missing
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Old 12th Oct 2019, 5:11 pm   #22
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Default Re: Vintage Radio and Phonograph cutter schematic

I got the dropbox link from here:

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

Lawrence.
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Old 12th Oct 2019, 5:24 pm   #23
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Default Re: Vintage Radio and Phonograph cutter schematic

thanks a lot! I did miss that thread.. ! have a great weekend Lawrence.
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Old 30th Oct 2019, 8:54 pm   #24
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Default 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...

PS: Slight correction, i did not change the power filter capacitor as read spot on 16+16 UF and very low Ohms.
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Old 30th Oct 2019, 9:09 pm   #25
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Default Re: Vintage Radio and Phonograph cutter schematic

Quote:
Originally Posted by Levente View Post
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....

Post the readings you took

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

I'm unsure as to what you mean by that
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Old 30th Oct 2019, 9:20 pm   #26
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Default 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...
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Old 30th Oct 2019, 9:36 pm   #27
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Default 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.
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Old 30th Oct 2019, 9:41 pm   #28
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Default 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...
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Old 31st Oct 2019, 12:44 pm   #29
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Default 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)

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Old 31st Oct 2019, 1:11 pm   #30
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Default 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?
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Old 31st Oct 2019, 3:14 pm   #31
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Default 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.

Last edited by ms660; 31st Oct 2019 at 3:20 pm.
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Old 31st Oct 2019, 4:10 pm   #32
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Default 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.
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Old 31st Oct 2019, 4:52 pm   #33
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Default 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.
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Old 31st Oct 2019, 7:10 pm   #34
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Default 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?

Last edited by Levente; 31st Oct 2019 at 7:37 pm.
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Old 1st Nov 2019, 11:31 am   #35
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Default 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...


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Old 1st Nov 2019, 2:20 pm   #36
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Default 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.
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Old 1st Nov 2019, 3:37 pm   #37
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Default 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?
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Old 1st Nov 2019, 3:44 pm   #38
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Default 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.
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Old 1st Nov 2019, 3:52 pm   #39
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Default 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...?
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Old 1st Nov 2019, 4:01 pm   #40
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Default 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.

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