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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders. |
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2nd Jul 2020, 5:09 pm | #1 |
Triode
Join Date: Feb 2015
Location: Faversham, Kent, UK.
Posts: 31
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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 |
Nonode
Join Date: Jun 2016
Location: Bognor Regis, West Sussex, UK.
Posts: 2,300
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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 |
Rest in Peace
Join Date: Jan 2015
Location: Cottesmore, East Midlands, UK.
Posts: 858
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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 |
Dekatron
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
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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. |
2nd Jul 2020, 8:59 pm | #5 |
Triode
Join Date: Feb 2015
Location: Faversham, Kent, UK.
Posts: 31
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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, 9:08 pm | #6 | |
Triode
Join Date: Feb 2015
Location: Faversham, Kent, UK.
Posts: 31
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Re: Mullard High Speed Valve Tester : help!
Quote:
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2nd Jul 2020, 9:22 pm | #7 |
Dekatron
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
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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, 8:50 am | #8 | |
Triode
Join Date: Feb 2015
Location: Faversham, Kent, UK.
Posts: 31
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Re: Mullard High Speed Valve Tester : help!
Im getting -85.5v and -189.9v at reference points
Quote:
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3rd Jul 2020, 8:52 am | #9 |
Triode
Join Date: Feb 2015
Location: Faversham, Kent, UK.
Posts: 31
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Re: Mullard High Speed Valve Tester : help!
Reject card in ... no movement with spot on adjusting B or C
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3rd Jul 2020, 9:33 am | #10 |
Dekatron
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
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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 |
Triode
Join Date: Feb 2015
Location: Faversham, Kent, UK.
Posts: 31
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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 |
Triode
Join Date: Feb 2015
Location: Faversham, Kent, UK.
Posts: 31
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Re: Mullard High Speed Valve Tester : help!
Posted before I saw PJL post ... following those instructions now ... thanks !
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3rd Jul 2020, 9:51 am | #13 |
Triode
Join Date: Feb 2015
Location: Faversham, Kent, UK.
Posts: 31
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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 |
Triode
Join Date: Feb 2015
Location: Faversham, Kent, UK.
Posts: 31
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Re: Mullard High Speed Valve Tester : help!
C11 has been replaced
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3rd Jul 2020, 10:05 am | #15 |
Dekatron
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
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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 |
Dekatron
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
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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).
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3rd Jul 2020, 11:59 am | #17 |
Triode
Join Date: Feb 2015
Location: Faversham, Kent, UK.
Posts: 31
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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
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3rd Jul 2020, 1:23 pm | #18 |
Triode
Join Date: Feb 2015
Location: Faversham, Kent, UK.
Posts: 31
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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 |
Dekatron
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
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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?
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3rd Jul 2020, 7:42 pm | #20 |
Triode
Join Date: Feb 2015
Location: Faversham, Kent, UK.
Posts: 31
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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 ..... |