Decca DR101 dual standard TV - Page 3 - UK Vintage Radio Repair and Restoration Discussion Forum

TonyDuell · 2nd Jul 2018, 2:37 pm

As for the older one, it looks like both chokes are normally in-circuit (as smoothing components) and their magnetic effect on the system switch armature/linkage cancels out so that stays in whatever position it is in.

When the setting of the switch on the tuner and that of the system switch (SW3 and SW6 on your circuit) disagree then one of the chokes is shorted out, causing the other one to move the system switch linkage. The tuner and system switch then agree so both chokes end up in-circuit for smoothing.

ms660 · 2nd Jul 2018, 3:03 pm

The first schematic looks ok, the second schematic doesn't, it looks to me as though SW3 and SW6 are in the 625 position while SW13 is in the 405 position, set SW13 to the 625 position and all looks normal to me.... Schematic error?

Lawrence.

FERNSEH · 2nd Jul 2018, 3:10 pm

In the rough hand drawn circuit diagram one of the two smoothing chokes is shorted out depending on which line standard is selected. This is the circuit arrangement in my set and differs from circuit in the Trader service sheet.

The other circuit is the one in the DR31. No short circuits across the chokes. Instead, that 0.25microfarad capacitor is connected across CH2 on 405 and on 625 across CH1.
So how does that work? Is it some kind of resonant circuit introducing a high energy pulse across the appropriate choke when the user changes line standards. Enough energy induced into a choke in order to move the switch lever.

DFWB.

TonyDuell · 2nd Jul 2018, 3:22 pm

No, I think that 0.25uF capacitor is just a spark supression component.

Consider the circuit with the switches as drawn. Both chokes are in series and in-circuit. The tuner switch (SW13) is shown in a 405 line position, I assume SW3 and SW6 are in the state shown when the system switch is set for 405 lines.

Now consider changing SW13 to the 625 line contact. CH2 is shorted out via SW6 and SW13 (on that contact). CH1 remains in-circuit to move the system switch. That changes SW3 and SW6 over, so after the system switch is re-set for 625 lines CH2 is no longer shorted out (as SW6 is open). So at the end of the system change, both chokes are in series and in circuit.

In that state, if you go back to a 405 line contact on SW13 then CH1 is shorted out via SW3 (remember now closed) and SW13. The system switch moves back, SW3 and SW6 go back to the state shown on the circuit, again both chokes end up in series and in circuit.

ms660 · 2nd Jul 2018, 3:45 pm

TD's got it.

Lawrence.

FERNSEH · 2nd Jul 2018, 4:21 pm

But why is the capacitor flipped around when the other line standard is selected?

DFWB.

FERNSEH · 2nd Jul 2018, 5:36 pm

The switches could be make before break so that as suggested a choke is momentarily short circuited before the switch breaks contact.
There might be a Trader sheet for the DR31.
I reckon Decca had problems with this circuit.

DFWB.

TonyDuell · 2nd Jul 2018, 5:40 pm

I think the choke is supposed to be short-circuited. It is the fact that one choke is still in-circuit (and thus producing a magnetic field) while the other is shorted that provides the force to move the system switch.

ms660 · 2nd Jul 2018, 7:03 pm

Here's one for the Professors concerning the DR31 circuit that's under discussion, the choke/solenoid would have a certain pulling force without a capacitor connected across it, with a capacitor connected across would the same solenoid have the same pulling force, less pulling force or a greater pulling force?

Lawrence.

Jac · 2nd Jul 2018, 7:35 pm

Quote:

Originally Posted by FERNSEH

There might be a Trader sheet for the DR31.
DFWB.

And I might have that.
I'll check this and scan it.

Jac

Jac · 2nd Jul 2018, 7:53 pm

David,

DR31 Trader Sheet sent by email.
I hope it is of use to you.

Best regards,
Jac

Pieter H · 2nd Jul 2018, 8:02 pm

I tend to an alternative to the explanation given by Tony in post #44.
To me it is not logical that in the quiescent state current flows through both coils CH1 and CH2. Like in the DR101 schematic by Dave it is much more likely that either one is drawing current, the other being short-circuited.
It all depends on what the status is of the DR35 schematic as drawn.
My interpretation:
V3 and v6 are in the UHF position as shown.
CH1 is active for UHF
CH2 for VHF
Under that assumption, if V12 on the tuner is put into channel13 UHF mode CH2 will be short-circuited, CH1 is active and V3 and V6 as shown.

If the tuner is now put on a VHF channel the capacitor C65 will be switched in parallel to Ch2, with current temporarily flowing through both coils in series. My guess is that the coli with parallel capacitor give a short duration resonance that helps CH2 to attain a (temporarily) higher voltage to trigger the system switch activation and avoid sticking.

Assuming the system switch is activated V3 flips and CH1 is nor short-circuited, CH2 keeping the system switch in VHF mode.

Assuming this is true, it is interesting to note that the system will ALWAYS be in UHF mode at switch-on. This is also what Dave reported. Switching it with the VHF tuner to channel 13 (UHF) and then back to a VHF channel should make the system switch.

My theory. Cheers, Pieter

FERNSEH · 2nd Jul 2018, 8:13 pm

Quote:

Originally Posted by Jac

David,

DR31 Trader Sheet sent by email.
I hope it is of use to you.

Best regards,
Jac

Good evening Jac,
I've sent you an Email.

Regards,

David.

FERNSEH · 2nd Jul 2018, 9:25 pm

Thanks to Jac and G8KBG Tony I have all the information we need to discover how the system switch circuit works.
Tony Duell had offered up the correct explanation.

From the Trader service sheet, a description on how the solenoids operate the switch lever:

"S3 and S6 form part of the changeover assembly, and accordingly they are b and a to indicate that they close on 625 and 405 respectively as are all the other system switches. It follows therefore that with the selector at a VHF channel, as shown in the diagram, S6a will be closed and S3b open.
The system switch assembly is operated by solenoids, forming a magnetic relay, which pulls the armature in opposing directions and the solenoid coils GH1 and CH2 are used as smoothing chokes on both systems, but one of them is bypassed during the actual changeover operation.
If the selector is turned from the VHF channels to the UHF stud, with S6a still closed, CH2 will be short-circuited, HT current will by-pass it, and it will cease to be energised. The "pull" on CH1 will the cause an armature linked to the system switch assembly to move over to the UHF position, closing all the "b" switches. It can be seen correspondingly that if the selector subsequently turned to any VHF channel S3b closed at the time, CH1 will be shot-circuited. It's "pull" will cease to hold the armature and as CH1 is now energised it will pull the armature in the opposite way and move the system switch to 405
The control switch unit is connected in series with S6a on the other. But when it is set to UHF S6a automatically opens and when it is set to a VHF channel S3b automatically opens.
As a result, although one choke is short-circuited during the changeover, both are energised as soon as changeover is effected and assist in smoothing the HT current. The armature remains passive while both chokes are energised; it only moves when the magnetic of one choke collapses."

No mention of the function of the capacitor C65.

DFWB.

ms660 · 3rd Jul 2018, 10:25 am

Quote:

Originally Posted by FERNSEH

Thanks to Jac and G8KBG Tony I have all the information we need to discover how the system switch circuit works.
Tony Duell had offered up the correct explanation.

From the Trader service sheet, a description on how the solenoids operate the switch lever:

"S3 and S6 form part of the changeover assembly, and accordingly they are b and a to indicate that they close on 625 and 405 respectively as are all the other system switches. It follows therefore that with the selector at a VHF channel, as shown in the diagram, S6a will be closed and S3b open.
The system switch assembly is operated by solenoids, forming a magnetic relay, which pulls the armature in opposing directions and the solenoid coils GH1 and CH2 are used as smoothing chokes on both systems, but one of them is bypassed during the actual changeover operation.
If the selector is turned from the VHF channels to the UHF stud, with S6a still closed, CH2 will be short-circuited, HT current will by-pass it, and it will cease to be energised. The "pull" on CH1 will the cause an armature linked to the system switch assembly to move over to the UHF position, closing all the "b" switches. It can be seen correspondingly that if the selector subsequently turned to any VHF channel S3b closed at the time, CH1 will be shot-circuited. It's "pull" will cease to hold the armature and as CH1 is now energised it will pull the armature in the opposite way and move the system switch to 405
The control switch unit is connected in series with S6a on the other. But when it is set to UHF S6a automatically opens and when it is set to a VHF channel S3b automatically opens.
As a result, although one choke is short-circuited during the changeover, both are energised as soon as changeover is effected and assist in smoothing the HT current. The armature remains passive while both chokes are energised; it only moves when the magnetic of one choke collapses."

No mention of the function of the capacitor C65.

DFWB.

I don't follow that description, to me it seems in error....Switch shorts out CH2,CH1 pulls......Switch shorts out CH1, CH1 pulls.

?

Lawrence.

FERNSEH · 3rd Jul 2018, 12:46 pm

The description how the system switch operates was copied from the Trader sheet. Was the text copied from the original Decca manual or was it the Trader's interpretation how the system switch works?
Decca Radio and Television Ltd never made a 625 convertible TV receiver, however, they did market a Decca badged convertible set manufactured by Thorn, the model DR41.

The DR31 was released in September 1962, the DR101 the following year.

More from the Trader service sheet: "In this receiver the system changeover switch is operated upon turning the conventional VHF selector from thev13-channel sector to "UHF" or vice-versa. Ganged with the sector spindle is a 14 position wafer switch unit shown in the circuit diagram as the 405/625 control switch unit, and the position of the wiper determines whether the system switch is set to 405 or 625."

The DR31 is said to have a fourteen position tuner, most likely not be of Philips manufacture although like the AT7639/22 unit in the DR101 the UHF position permits the IF output from the UHF tuner to pass through for further amplification, one of the reasons why these sets performed well on UHF. We know that the Philips valve tuner was one the best of it's type.

DFWB.

FERNSEH · 3rd Jul 2018, 1:45 pm

The Philips AT7639/22 tuner as fitted in the 1965/66 Decca DR123.

DFWB.

Pieter H · 3rd Jul 2018, 8:59 pm

I'm also still struggling with this Decca switch system, in the sense that when you have a switching mechanism with two activation coils, one for one switch position each, it is totally strange to have the "stable" situation with current flowing through both coils. But according the description this is what they did. Then, in order to switch, one coil was temporarily shorted. The funny thing is that, according the description, both coils were kept energized to act as smoothing coils for the HT, but in this arrangement every time a switch is made between VHF and UHF the HT will feature major ripples due to the temporary shorting of one of the coils.

In that sense the arrangement in Dave's DR101, where the system really switches between one of the two coils, is better, although also here the HT will see switching ripple in case of switch-over.

Overall it seems a bit of strange cost saving (essentially one smoothing coil in the HT line) resulting in a complex and unreliable system switch.

As to the tuner, it is interesting to see that the system switch disk on the tuner as used in the DR101 (and probably also DR31) apparently was not part of the tuner (see the picture in Dave's last post) but added by Decca itself. Which makes sense, because I haven't seen this construction in any Philips set.

Cheers, Pieter

Brigham · 4th Jul 2018, 12:43 pm

From my experience of dual-standard sets, one would think that "...a complex and unreliable system switch..." was a design criterion. It would be very unusual for an early-sixties set to have 625 as the default setting. The general rule was 'avoid switching to 625 unless you actually WANT BBC2'.
Smoothing coils have a long history of 'being something else as well', going back at least as far as energised loudspeakers.

FERNSEH · 4th Jul 2018, 12:54 pm

Like Pieter I'm having second thoughts about the theory of operation of the DR31 system switch.
Consider rotary switch SW13: When the VHF channel selector is turned the connection between the junction of the chokes and the sliders of SW3 and SW6 is well and truly broken. This would leave the capacitor C65 isolated until contact with either choke is established again when a channel is selected.
So it follows is the 0.25microfarad capacitor C65 an active component in the operation of the system switch?

Perhaps what we read in the Trader service sheet is the author's interpretation on how the circuit works.

C65 is now shown as 0.25uF and not 0.25mF. Can you imagine a 0.25milli-Farad capacitor in a TV set of 1963? Huge!

DFWB.

2nd Jul 2018, 2:37 pm	#41
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Re: Decca DR101 dual standard TV As for the older one, it looks like both chokes are normally in-circuit (as smoothing components) and their magnetic effect on the system switch armature/linkage cancels out so that stays in whatever position it is in. When the setting of the switch on the tuner and that of the system switch (SW3 and SW6 on your circuit) disagree then one of the chokes is shorted out, causing the other one to move the system switch linkage. The tuner and system switch then agree so both chokes end up in-circuit for smoothing.

2nd Jul 2018, 3:03 pm	#42
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Decca DR101 dual standard TV The first schematic looks ok, the second schematic doesn't, it looks to me as though SW3 and SW6 are in the 625 position while SW13 is in the 405 position, set SW13 to the 625 position and all looks normal to me.... Schematic error? Lawrence.

2nd Jul 2018, 3:10 pm	#43
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Decca DR101 dual standard TV In the rough hand drawn circuit diagram one of the two smoothing chokes is shorted out depending on which line standard is selected. This is the circuit arrangement in my set and differs from circuit in the Trader service sheet. The other circuit is the one in the DR31. No short circuits across the chokes. Instead, that 0.25microfarad capacitor is connected across CH2 on 405 and on 625 across CH1. So how does that work? Is it some kind of resonant circuit introducing a high energy pulse across the appropriate choke when the user changes line standards. Enough energy induced into a choke in order to move the switch lever. DFWB.

2nd Jul 2018, 3:45 pm	#45
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Decca DR101 dual standard TV TD's got it. Lawrence.

2nd Jul 2018, 4:21 pm	#46
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Decca DR101 dual standard TV But why is the capacitor flipped around when the other line standard is selected? DFWB.

2nd Jul 2018, 3:22 pm	#44
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Re: Decca DR101 dual standard TV No, I think that 0.25uF capacitor is just a spark supression component. Consider the circuit with the switches as drawn. Both chokes are in series and in-circuit. The tuner switch (SW13) is shown in a 405 line position, I assume SW3 and SW6 are in the state shown when the system switch is set for 405 lines. Now consider changing SW13 to the 625 line contact. CH2 is shorted out via SW6 and SW13 (on that contact). CH1 remains in-circuit to move the system switch. That changes SW3 and SW6 over, so after the system switch is re-set for 625 lines CH2 is no longer shorted out (as SW6 is open). So at the end of the system change, both chokes are in series and in circuit. In that state, if you go back to a 405 line contact on SW13 then CH1 is shorted out via SW3 (remember now closed) and SW13. The system switch moves back, SW3 and SW6 go back to the state shown on the circuit, again both chokes end up in series and in circuit.

2nd Jul 2018, 5:36 pm	#47
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Decca DR101 dual standard TV The switches could be make before break so that as suggested a choke is momentarily short circuited before the switch breaks contact. There might be a Trader sheet for the DR31. I reckon Decca had problems with this circuit. DFWB.

2nd Jul 2018, 5:40 pm	#48
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Re: Decca DR101 dual standard TV I think the choke is supposed to be short-circuited. It is the fact that one choke is still in-circuit (and thus producing a magnetic field) while the other is shorted that provides the force to move the system switch.

2nd Jul 2018, 7:03 pm	#49
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Decca DR101 dual standard TV Here's one for the Professors concerning the DR31 circuit that's under discussion, the choke/solenoid would have a certain pulling force without a capacitor connected across it, with a capacitor connected across would the same solenoid have the same pulling force, less pulling force or a greater pulling force? Lawrence.

2nd Jul 2018, 7:53 pm	#51
Jac Heptode Join Date: Jun 2006 Location: Eindhoven, Netherlands. Posts: 642	Re: Decca DR101 dual standard TV David, DR31 Trader Sheet sent by email. I hope it is of use to you. Best regards, Jac

2nd Jul 2018, 8:02 pm	#52
Pieter H Tetrode Join Date: Sep 2017 Location: Waalre, Netherlands Posts: 67	Re: Decca DR101 dual standard TV I tend to an alternative to the explanation given by Tony in post #44. To me it is not logical that in the quiescent state current flows through both coils CH1 and CH2. Like in the DR101 schematic by Dave it is much more likely that either one is drawing current, the other being short-circuited. It all depends on what the status is of the DR35 schematic as drawn. My interpretation: V3 and v6 are in the UHF position as shown. CH1 is active for UHF CH2 for VHF Under that assumption, if V12 on the tuner is put into channel13 UHF mode CH2 will be short-circuited, CH1 is active and V3 and V6 as shown. If the tuner is now put on a VHF channel the capacitor C65 will be switched in parallel to Ch2, with current temporarily flowing through both coils in series. My guess is that the coli with parallel capacitor give a short duration resonance that helps CH2 to attain a (temporarily) higher voltage to trigger the system switch activation and avoid sticking. Assuming the system switch is activated V3 flips and CH1 is nor short-circuited, CH2 keeping the system switch in VHF mode. Assuming this is true, it is interesting to note that the system will ALWAYS be in UHF mode at switch-on. This is also what Dave reported. Switching it with the VHF tuner to channel 13 (UHF) and then back to a VHF channel should make the system switch. My theory. Cheers, Pieter

2nd Jul 2018, 9:25 pm	#54
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Decca DR101 dual standard TV Thanks to Jac and G8KBG Tony I have all the information we need to discover how the system switch circuit works. Tony Duell had offered up the correct explanation. From the Trader service sheet, a description on how the solenoids operate the switch lever: "S3 and S6 form part of the changeover assembly, and accordingly they are b and a to indicate that they close on 625 and 405 respectively as are all the other system switches. It follows therefore that with the selector at a VHF channel, as shown in the diagram, S6a will be closed and S3b open. The system switch assembly is operated by solenoids, forming a magnetic relay, which pulls the armature in opposing directions and the solenoid coils GH1 and CH2 are used as smoothing chokes on both systems, but one of them is bypassed during the actual changeover operation. If the selector is turned from the VHF channels to the UHF stud, with S6a still closed, CH2 will be short-circuited, HT current will by-pass it, and it will cease to be energised. The "pull" on CH1 will the cause an armature linked to the system switch assembly to move over to the UHF position, closing all the "b" switches. It can be seen correspondingly that if the selector subsequently turned to any VHF channel S3b closed at the time, CH1 will be shot-circuited. It's "pull" will cease to hold the armature and as CH1 is now energised it will pull the armature in the opposite way and move the system switch to 405 The control switch unit is connected in series with S6a on the other. But when it is set to UHF S6a automatically opens and when it is set to a VHF channel S3b automatically opens. As a result, although one choke is short-circuited during the changeover, both are energised as soon as changeover is effected and assist in smoothing the HT current. The armature remains passive while both chokes are energised; it only moves when the magnetic of one choke collapses." No mention of the function of the capacitor C65. DFWB.

3rd Jul 2018, 12:46 pm	#56
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Decca DR101 dual standard TV The description how the system switch operates was copied from the Trader sheet. Was the text copied from the original Decca manual or was it the Trader's interpretation how the system switch works? Decca Radio and Television Ltd never made a 625 convertible TV receiver, however, they did market a Decca badged convertible set manufactured by Thorn, the model DR41. The DR31 was released in September 1962, the DR101 the following year. More from the Trader service sheet: "In this receiver the system changeover switch is operated upon turning the conventional VHF selector from thev13-channel sector to "UHF" or vice-versa. Ganged with the sector spindle is a 14 position wafer switch unit shown in the circuit diagram as the 405/625 control switch unit, and the position of the wiper determines whether the system switch is set to 405 or 625." The DR31 is said to have a fourteen position tuner, most likely not be of Philips manufacture although like the AT7639/22 unit in the DR101 the UHF position permits the IF output from the UHF tuner to pass through for further amplification, one of the reasons why these sets performed well on UHF. We know that the Philips valve tuner was one the best of it's type. DFWB.

3rd Jul 2018, 1:45 pm	#57
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Decca DR101 dual standard TV The Philips AT7639/22 tuner as fitted in the 1965/66 Decca DR123. DFWB. Attached Thumbnails

3rd Jul 2018, 8:59 pm	#58
Pieter H Tetrode Join Date: Sep 2017 Location: Waalre, Netherlands Posts: 67	Re: Decca DR101 dual standard TV I'm also still struggling with this Decca switch system, in the sense that when you have a switching mechanism with two activation coils, one for one switch position each, it is totally strange to have the "stable" situation with current flowing through both coils. But according the description this is what they did. Then, in order to switch, one coil was temporarily shorted. The funny thing is that, according the description, both coils were kept energized to act as smoothing coils for the HT, but in this arrangement every time a switch is made between VHF and UHF the HT will feature major ripples due to the temporary shorting of one of the coils. In that sense the arrangement in Dave's DR101, where the system really switches between one of the two coils, is better, although also here the HT will see switching ripple in case of switch-over. Overall it seems a bit of strange cost saving (essentially one smoothing coil in the HT line) resulting in a complex and unreliable system switch. As to the tuner, it is interesting to see that the system switch disk on the tuner as used in the DR101 (and probably also DR31) apparently was not part of the tuner (see the picture in Dave's last post) but added by Decca itself. Which makes sense, because I haven't seen this construction in any Philips set. Cheers, Pieter

4th Jul 2018, 12:43 pm	#59
Brigham Octode Join Date: Mar 2006 Location: Co. Durham, UK. Posts: 1,117	Re: Decca DR101 dual standard TV From my experience of dual-standard sets, one would think that "...a complex and unreliable system switch..." was a design criterion. It would be very unusual for an early-sixties set to have 625 as the default setting. The general rule was 'avoid switching to 625 unless you actually WANT BBC2'. Smoothing coils have a long history of 'being something else as well', going back at least as far as energised loudspeakers.

4th Jul 2018, 12:54 pm	#60
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Decca DR101 dual standard TV Like Pieter I'm having second thoughts about the theory of operation of the DR31 system switch. Consider rotary switch SW13: When the VHF channel selector is turned the connection between the junction of the chokes and the sliders of SW3 and SW6 is well and truly broken. This would leave the capacitor C65 isolated until contact with either choke is established again when a channel is selected. So it follows is the 0.25microfarad capacitor C65 an active component in the operation of the system switch? Perhaps what we read in the Trader service sheet is the author's interpretation on how the circuit works. C65 is now shown as 0.25uF and not 0.25mF. Can you imagine a 0.25milli-Farad capacitor in a TV set of 1963? Huge! DFWB. Attached Thumbnails Last edited by FERNSEH; 4th Jul 2018 at 1:01 pm.