Mullard High Speed Valve Tester : help! - UK Vintage Radio Repair and Restoration Discussion Forum

zillerfish · 2nd Jul 2020, 5:09 pm

I inherited from a friend the above (later version with 'flat' cast handles)

I have recapped the tester and checked valves so far ...nothing else done.

When using the mains card there is no movement of the spot despite using the adjusting knob. The spot appears to be at the 'at rest' position.

I tried the other test cards but no movement in the spot occurs.

Seems nothing is giving any Y axis movement to the beam.

Can anyone suggest a process to investigate and determine where the fault may lie.

Cheers.

Electronpusher0 · 2nd Jul 2020, 6:13 pm

Do you have the circuit for the MHSVT? You really need one to make any progress in fault finding.
I was going to suggest buying Paul's valve CD rom which contains the service data for the Mullard but it seems to be temporarily unavailable.
I attach a section of the schematic for the type 4 which shows the relevent section. I hope thats OK with the Mods.
This shows the drive to the deflection plates.
You need to check the voltages around the EF91s. On mine both the EY51s had gone and had to be replaced.

Peter

frankmcvey · 2nd Jul 2020, 6:28 pm

You'll find the circuit for the E7600/4 (by far the easiest HSVT to work on!) in a link at the bottom of this page.

At the same place you'll also find a link to the manual for the military version, the CT80. This is a far better source of information and the component numbers etc for the CT80 are the same as those for the Mk4.

IIRC the input source to the indicator system for the mains voltage check card differs from the input source from the Reject card, which would seem to suggest that the fault lies in the indicator system itself, rather than the preceding circuitry. There is a separate section on the functioning of this circuit in the CT80 manual. Try checking voltages around the differential amplifier - careful, though, what DMM you use - there are voltages of up to 800V from the voltage doubler in this section.

Cheers,

Frank

PJL · 2nd Jul 2020, 8:03 pm

Do the presets D, E and F work correctly?
The indicator tube is driven by a differential amplifier whose inputs are switched to various test points by the selector switch.
If you have a decent spot then I believe the EY51's must be working OK.

zillerfish · 2nd Jul 2020, 8:59 pm

D,E,F controls working fine giving good spot.

I do have the original manual and circuit diagram

zillerfish · 2nd Jul 2020, 9:08 pm

Quote:

Originally Posted by frankmcvey

You'll find the circuit for the E7600/4 (by far the easiest HSVT to work on!) in a link at the bottom of this page.

At the same place you'll also find a link to the manual for the military version, the CT80. This is a far better source of information and the component numbers etc for the CT80 are the same as those for the Mk4.

IIRC the input source to the indicator system for the mains voltage check card differs from the input source from the Reject card, which would seem to suggest that the fault lies in the indicator system itself, rather than the preceding circuitry. There is a separate section on the functioning of this circuit in the CT80 manual. Try checking voltages around the differential amplifier - careful, though, what DMM you use - there are voltages of up to 800V from the voltage doubler in this section.

Cheers,

Frank

CT80 manual downloaded..useful info Thanks

PJL · 2nd Jul 2020, 9:22 pm

Set the mains selector to match your mains voltage to avoid doing any damage.
Using the REJECT card, do the presets B and C move the spot when following the instructions?
Have you checked the reference voltage on the 85A2 and the -200V rail created by the EZ90?
Because the tester leaves the heaters running when the lever is not activated, it is common for valves to have gone zero emission.

zillerfish · 3rd Jul 2020, 8:50 am

Im getting -85.5v and -189.9v at reference points

Quote:

Originally Posted by PJL

Set the mains selector to match your mains voltage to avoid doing any damage.
Using the REJECT card, do the presets B and C move the spot when following the instructions?
Have you checked the reference voltage on the 85A2 and the -200V rail created by the EZ90?
Because the tester leaves the heaters running when the lever is not activated, it is common for valves to have gone zero emission.

zillerfish · 3rd Jul 2020, 8:52 am

Reject card in ... no movement with spot on adjusting B or C

PJL · 3rd Jul 2020, 9:33 am

That suggests the fault lies in the differential amplifier as the amplifier is 'floating' and works independently from the rest of the tester.

Measure the +/- 450V on C3/C4 (4uF electrolytics) from the junction of C3/C4 (to avoid measuring near 1KV). The amplifier works off the +450V.

If they test OK then measure the voltage on the EF91 anodes and cathode from the junction of C3/C4.

Have you replaced C11 (0.25uF) as this can short the anodes together.

TAKE CARE!!!

zillerfish · 3rd Jul 2020, 9:37 am

Checking voltages at the anodes of v9 and v10 with mains card in and lever down

V10 -651v

V9 -105v

I see v9 also supplies v2 and v3 ....

zillerfish · 3rd Jul 2020, 9:38 am

Posted before I saw PJL post ... following those instructions now ... thanks !

zillerfish · 3rd Jul 2020, 9:51 am

Voltages Either side of C3 -84 and -99
And similarly for C4 -84 and -653

zillerfish · 3rd Jul 2020, 9:52 am

C11 has been replaced

PJL · 3rd Jul 2020, 10:05 am

When working on the differential amplifier you must measure from the junction of C3/C4 as the amplifier circuitry is not directly connected to the chassis.

It does look like the +450V rail is not right but we need the voltages measured correctly.

PJL · 3rd Jul 2020, 10:16 am

Assuming the +450V is low and you have already replaced C3 and C4 then you need to check R93 (18K) and R42 (4.7K). If these are OK you probably need a new EY51 (V9).

zillerfish · 3rd Jul 2020, 11:59 am

Resistor values 20.2 k and 5.1k so likely V9 then ... I’ve ordered one so will replace and pick up this thread when done so ... thanks for all help especially PJL ��

zillerfish · 3rd Jul 2020, 1:23 pm

Ok, so just found two EY51 in my collection of valves ( after having bought them online doh) they are soldered in but still not able to adjust the spot on mains.

Anode voltages vastly different on these valves using reference point junction of c3/c4 I get -590volts on v10 and effectively 0volts on v9

PJL · 3rd Jul 2020, 7:07 pm

Have you replaced C3 and C4? If you have then something is pulling down the +ve rail. It is not unknown for the mains transformer to go leaky - has it been kept in a damp environment?

zillerfish · 3rd Jul 2020, 7:42 pm

C3 and C4 have been replaced.

Unit was kept in an outside workshop for some years

Transformer !!!!! Ouch .....

2nd Jul 2020, 5:09 pm	#1
zillerfish Triode Join Date: Feb 2015 Location: Faversham, Kent, UK. Posts: 31	Mullard High Speed Valve Tester : help! I inherited from a friend the above (later version with 'flat' cast handles) I have recapped the tester and checked valves so far ...nothing else done. When using the mains card there is no movement of the spot despite using the adjusting knob. The spot appears to be at the 'at rest' position. I tried the other test cards but no movement in the spot occurs. Seems nothing is giving any Y axis movement to the beam. Can anyone suggest a process to investigate and determine where the fault may lie. Cheers.

2nd Jul 2020, 6:13 pm	#2
Electronpusher0 Nonode Join Date: Jun 2016 Location: Bognor Regis, West Sussex, UK. Posts: 2,296	Re: Mullard High Speed Valve Tester : help! Do you have the circuit for the MHSVT? You really need one to make any progress in fault finding. I was going to suggest buying Paul's valve CD rom which contains the service data for the Mullard but it seems to be temporarily unavailable. I attach a section of the schematic for the type 4 which shows the relevent section. I hope thats OK with the Mods. This shows the drive to the deflection plates. You need to check the voltages around the EF91s. On mine both the EY51s had gone and had to be replaced. Peter

2nd Jul 2020, 6:28 pm	#3
frankmcvey Rest in Peace Join Date: Jan 2015 Location: Cottesmore, East Midlands, UK. Posts: 858	Re: Mullard High Speed Valve Tester : help! You'll find the circuit for the E7600/4 (by far the easiest HSVT to work on!) in a link at the bottom of this page. At the same place you'll also find a link to the manual for the military version, the CT80. This is a far better source of information and the component numbers etc for the CT80 are the same as those for the Mk4. IIRC the input source to the indicator system for the mains voltage check card differs from the input source from the Reject card, which would seem to suggest that the fault lies in the indicator system itself, rather than the preceding circuitry. There is a separate section on the functioning of this circuit in the CT80 manual. Try checking voltages around the differential amplifier - careful, though, what DMM you use - there are voltages of up to 800V from the voltage doubler in this section. Cheers, Frank Last edited by frankmcvey; 2nd Jul 2020 at 6:41 pm.

2nd Jul 2020, 8:03 pm	#4
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: Mullard High Speed Valve Tester : help! Do the presets D, E and F work correctly? The indicator tube is driven by a differential amplifier whose inputs are switched to various test points by the selector switch. If you have a decent spot then I believe the EY51's must be working OK. Attached Thumbnails

2nd Jul 2020, 8:59 pm	#5
zillerfish Triode Join Date: Feb 2015 Location: Faversham, Kent, UK. Posts: 31	Re: Mullard High Speed Valve Tester : help! D,E,F controls working fine giving good spot. I do have the original manual and circuit diagram

2nd Jul 2020, 9:22 pm	#7
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: Mullard High Speed Valve Tester : help! Set the mains selector to match your mains voltage to avoid doing any damage. Using the REJECT card, do the presets B and C move the spot when following the instructions? Have you checked the reference voltage on the 85A2 and the -200V rail created by the EZ90? Because the tester leaves the heaters running when the lever is not activated, it is common for valves to have gone zero emission.

3rd Jul 2020, 8:52 am	#9
zillerfish Triode Join Date: Feb 2015 Location: Faversham, Kent, UK. Posts: 31	Re: Mullard High Speed Valve Tester : help! Reject card in ... no movement with spot on adjusting B or C

3rd Jul 2020, 9:33 am	#10
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: Mullard High Speed Valve Tester : help! That suggests the fault lies in the differential amplifier as the amplifier is 'floating' and works independently from the rest of the tester. Measure the +/- 450V on C3/C4 (4uF electrolytics) from the junction of C3/C4 (to avoid measuring near 1KV). The amplifier works off the +450V. If they test OK then measure the voltage on the EF91 anodes and cathode from the junction of C3/C4. Have you replaced C11 (0.25uF) as this can short the anodes together. TAKE CARE!!!

3rd Jul 2020, 9:37 am	#11
zillerfish Triode Join Date: Feb 2015 Location: Faversham, Kent, UK. Posts: 31	Re: Mullard High Speed Valve Tester : help! Checking voltages at the anodes of v9 and v10 with mains card in and lever down V10 -651v V9 -105v I see v9 also supplies v2 and v3 ....

3rd Jul 2020, 9:38 am	#12
zillerfish Triode Join Date: Feb 2015 Location: Faversham, Kent, UK. Posts: 31	Re: Mullard High Speed Valve Tester : help! Posted before I saw PJL post ... following those instructions now ... thanks !

3rd Jul 2020, 9:51 am	#13
zillerfish Triode Join Date: Feb 2015 Location: Faversham, Kent, UK. Posts: 31	Re: Mullard High Speed Valve Tester : help! Voltages Either side of C3 -84 and -99 And similarly for C4 -84 and -653

3rd Jul 2020, 9:52 am	#14
zillerfish Triode Join Date: Feb 2015 Location: Faversham, Kent, UK. Posts: 31	Re: Mullard High Speed Valve Tester : help! C11 has been replaced

3rd Jul 2020, 10:05 am	#15
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: Mullard High Speed Valve Tester : help! When working on the differential amplifier you must measure from the junction of C3/C4 as the amplifier circuitry is not directly connected to the chassis. It does look like the +450V rail is not right but we need the voltages measured correctly.

3rd Jul 2020, 10:16 am	#16
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: Mullard High Speed Valve Tester : help! Assuming the +450V is low and you have already replaced C3 and C4 then you need to check R93 (18K) and R42 (4.7K). If these are OK you probably need a new EY51 (V9).

3rd Jul 2020, 11:59 am	#17
zillerfish Triode Join Date: Feb 2015 Location: Faversham, Kent, UK. Posts: 31	Re: Mullard High Speed Valve Tester : help! Resistor values 20.2 k and 5.1k so likely V9 then ... I’ve ordered one so will replace and pick up this thread when done so ... thanks for all help especially PJL ��

3rd Jul 2020, 1:23 pm	#18
zillerfish Triode Join Date: Feb 2015 Location: Faversham, Kent, UK. Posts: 31	Re: Mullard High Speed Valve Tester : help! Ok, so just found two EY51 in my collection of valves ( after having bought them online doh) they are soldered in but still not able to adjust the spot on mains. Anode voltages vastly different on these valves using reference point junction of c3/c4 I get -590volts on v10 and effectively 0volts on v9

3rd Jul 2020, 7:07 pm	#19
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: Mullard High Speed Valve Tester : help! Have you replaced C3 and C4? If you have then something is pulling down the +ve rail. It is not unknown for the mains transformer to go leaky - has it been kept in a damp environment?

3rd Jul 2020, 7:42 pm	#20
zillerfish Triode Join Date: Feb 2015 Location: Faversham, Kent, UK. Posts: 31	Re: Mullard High Speed Valve Tester : help! C3 and C4 have been replaced. Unit was kept in an outside workshop for some years Transformer !!!!! Ouch .....