UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Test Gear and Workshop Equipment

Notices

Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders.

Closed Thread
 
Thread Tools
Old 13th May 2018, 6:50 am   #1
Diabolical Artificer
Dekatron
 
Diabolical Artificer's Avatar
 
Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 7,636
Default LOW EHT Tele D43 scope.

I have a D43 on the bench and the eht is intermitant/low. I'm reading about 800v but have had it working with a trace at 2kv, then the trace dims and the eht drops.

All other HV rails are ok. I've replaced the two K8 50's with three 1.2kv rated diodes in series and tried several of my eht caps, some are the wrong value, but I know are not leaky. Also tried disconnecting the CRT neck connection (final anode?) Have also replaced all diodes in the PSU apart from one zener - MR301. Can't think what is pulling it down or why the doubler isn't working; did wonder if the paxolin or whatever eht board is conductive.

I did find N310 the neon in the X sens circuit was dead. I replaced it with a neon I had, but I think it has a different striking voltage, I'm reading 80v instead of the 60v ont schematic, but would have thought it will still work.

Apart from that I have a non working timebase which I'm in the process of checking R's and changing the germanium diodes as recommended in the various threads on the D43 and Les's handy R replacement list.

I tried swapping the TS41 timebase for a TD42 Ed kindly sent me, however I'm not sure what V9 should be. V9 sits on a daughter board behind the TB SW, for now I tried an ECC88. Anyone got a schematic for the TD42 TB BTW?

Andy.
Attached Thumbnails
Click image for larger version

Name:	Screenshot from 2018-05-13 06-46-03.jpg
Views:	127
Size:	82.1 KB
ID:	162719   Click image for larger version

Name:	Screenshot from 2018-05-13 06-46-30.jpg
Views:	125
Size:	63.9 KB
ID:	162720  
__________________
Curiosity hasn't killed this cat...so far.
Diabolical Artificer is online now  
Old 13th May 2018, 9:38 am   #2
Diabolical Artificer
Dekatron
 
Diabolical Artificer's Avatar
 
Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 7,636
Default Re: LOW EHT Tele D43 scope.

Ok, getting somewhere... checked the diodes in the doubler, three were leaky ( ebay fakes??) , luckily I'd bought some 2kv PIV jobbies from Farnell to make an order up to £20, installed two in series now have 2kv ish ( still on iso tfmr and variac) and two dots.

It looks like there is another iteration of the PSU apart from the S43 that is. Mine has N401-3 missing and an 11v zener in place of, which doesn't make sense. What are they doing? Are they regulation? What is the 1v PP? Can't see a TP on the board so presume I ave to check for a 1v P-P sine between ground and the top of R409/ junction R406. Could this be the probe test OP? Just thinking out loud.

Next try and sort the TB. Also have no up/down control on the vertical, so I have my work cut out for me. I think I'm going to have to go through the TB and the plugin's and check more or less every component.

Fun, fun, fun... Andy.
__________________
Curiosity hasn't killed this cat...so far.
Diabolical Artificer is online now  
Old 13th May 2018, 10:09 am   #3
ronbryan
Octode
 
Join Date: Jan 2003
Location: Guildford, Surrey, UK.
Posts: 1,958
Default Re: LOW EHT Tele D43 scope.

The 1V p-p is the calibration square-wave output, for setting up probes and gain checking. It is brought out on to the front panel of the Y amp plug-ins. The resistors, neons and/or zener are to clip the sine-wave to form a square-wave.

V109 on the TD42 timebase is an ECF80 according to the manual.

Ron

Last edited by ronbryan; 13th May 2018 at 10:16 am.
ronbryan is offline  
Old 13th May 2018, 7:23 pm   #4
WME_bill
Octode
 
Join Date: Oct 2007
Location: Exeter, Devon, UK.
Posts: 1,553
Default Re: LOW EHT Tele D43 scope.

D43. Glad to see you are making progress.
I just wonder if you have the manual for your version. There seem to have been several versions concurrently.
The manual for the S43 single beam version is not very helpful for the main frame power supplies.
The D43 came out in 1963. The TB module used ECF80 and one ECF804. The valves stuck out the back, and it was all hard wired. Described in October 1965 manual.
The 1969 manual shows the timebase module on a Printed Circuit Board, using all ECF80.
Yet I have a 1964 D43 with TD41 with the PCB assembly, and it has the improved X amplifier centering as used in the 1969 TD42.
The TD42 had extended TB ranges (to 0.5us), a Single Shot system using 2 transistors (SPS2506 = 2N3904), and the improved X Amplifier centering around RV195 and V109.

The ECF804 was a short lived frame grid version of the ECF80 introduced by Brimar for wide band amplifier use. Only made by Brimar, and rapidly discontinued. Was in effect replaced by EF184 and ECC88 combination by other scope manufacturers.

I agree with Ron Bryan about the three missing neons N401 to 3. Looks like you have a very early model diagram. Replaced by a 11V zener MR407to chop and limit from the 150v rail to give a very reasonable square wave, positive from ground, which will appear at the junction of R406 and R404. What is your R409- not in any of my manuals. The multiple neons would have given a constant sine wave only.

I assume you are not also looking at the 11V zener MR406 which is used to give a +/- voltage around the +250v rail for the X Alignment setting on the CRT, RV313.

V109 is a ECF80. See circuit for the TD42. The triode section acts as the X Amplifier input stage. The pentode section stabilises the grid voltage of the X Amplifer pair stage, to centre the X shift control range. RV109. From the circuit I have seen, plugging in an ECC88 should give very interesting results.

Neon N301 in the tube circuit stabilises the voltage across the brightness controls, at the top of the EHT resistor chain, so that changing the brightness of one trace does not affect the other. Also as part of this, the 27v zener MR301 keeps a constant voltage across the balance control for the X plates.
Part of the complexity of extra set-up devices needed for a two gun tube like the 1074H used in this scope.
It is Hivac XC12 (CV6004) a high stability 60v, 0.6 ma. A 80v replacement will do , though the range of the brightness controls will be wider.
A little indicator neon is an alternative without the series resistor. They are generally 55V to 60V.

No shift on the vertical suggests trouble in the Y amps. If on both traces, then it must be power supply, though each Y Amplifier plug-in has a separate feed from the +380v rail, via that whopping great 40watt multiple resistor R412 to R415. What if you take out one or both the Y Amplifier Plug-in units.

As part of your fault finding, have you actually measured the voltages around all the valves in the TB module and power supply.
Now you have sorted out the failed EHT rectifiers and smoothing capacitors, I suggest that changing lots of other components can sometimes create more problems than it solves. These valve circuits can keep working even with components vastly off specification.
wme_bill. m0wpn
WME_bill is offline  
Old 14th May 2018, 6:47 am   #5
Diabolical Artificer
Dekatron
 
Diabolical Artificer's Avatar
 
Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 7,636
Default Re: LOW EHT Tele D43 scope.

Thanks Ron.

I have a hard copy manual for the scope Bill, but there are some disparity's though nothing too far off. The TS41 TB uses mostly ECF80's but also one ECC88 and an EB91, havn't seen a ECF804. Yesterday I started going through the TS41 TB, checking R's and replaced the germanium diodes with 1N4148's. Some of the germanium's were leaky. I only replaced R's that were way off, like one that was 80k high as I'm aware valve circuits are tolerant of off spec value's.

"I assume you are not also looking at the 11V zener MR406" I found this zener dead, so replaced it with the nearest I had a 10v one.

I'll find a better replacement for the neon in place of N301, just wanted to get a trace.

I started measuring voltages on the TB, some were way off, but most within about +/- 5v

Thanks for the circuit description's and suggestion's Bill, I'm slowly getting things square.

Andy.
__________________
Curiosity hasn't killed this cat...so far.
Diabolical Artificer is online now  
Old 14th May 2018, 12:12 pm   #6
karesz*
Heptode
 
Join Date: Jun 2010
Location: Zurich, Switzerland
Posts: 538
Default Re: LOW EHT Tele D43 scope.

Well, its depending of pert of circuit, but I think, it`s not 100% solution to exchange Ge-diodes generous with Si-s; I would do it rather with Schottkys...
rgds, Karl
karesz* is offline  
Old 15th May 2018, 6:20 am   #7
Diabolical Artificer
Dekatron
 
Diabolical Artificer's Avatar
 
Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 7,636
Default Re: LOW EHT Tele D43 scope.

Good point Karl, but I havn't any Schottky's. If I get this scope running and it's a good un, I'll go round and spend some money and treat it to few new parts. As it is, it's sulking so doesn't get any sweetys : )

Some progress... after checking the HT again and reading - 90v instead of 250v I found some numpty had replaced MR401/402 the wrong way round. HT now back.

I now have the TB running - ish. SW TB on, dots move to right, then vanish. Also have an issue with the X amp I think as the dots drift and I have to keep adjusting X shift.

Checked TB voltages, all ok but low, by about 10v, still on variac though.

Will check Y amps today as one dot appear's then zooms off.

Andy
__________________
Curiosity hasn't killed this cat...so far.
Diabolical Artificer is online now  
Old 15th May 2018, 11:06 am   #8
Diabolical Artificer
Dekatron
 
Diabolical Artificer's Avatar
 
Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 7,636
Default Re: LOW EHT Tele D43 scope.

TB started working on it's own.

Checked voltages on one plugin, can't find anything off, but still no up/down, will have a look at the pots.

Also have a line where it should be a dot, maybe the neon I put in is the cause?

More later, A.
__________________
Curiosity hasn't killed this cat...so far.
Diabolical Artificer is online now  
Old 15th May 2018, 11:25 am   #9
WME_bill
Octode
 
Join Date: Oct 2007
Location: Exeter, Devon, UK.
Posts: 1,553
Default Re: LOW EHT Tele D43 scope.

D43. Glad that a voltage check has shown up the major fault - inverted rectifier diodes. I won't ask if you know who did it!

The missing 3 neons for the calibrator. I have found the circuit, used also in the D31, produced before the D43. They of course produce a square wave for the calibration, not a sine wave as I said. My mistake.

I suspect you are using manual posted by Jon's invaluable Valve Page, which includes both the 1965 and 1969 trigger circuits, but all the rest appears to be as the 1969 manual.

The1965 circuits use the ECF804, in the TB and in the Y Amplifers (as well as ECF80 and ECC88 etc). You don't say what valves your Y Amps have.
So if it will help, I attach the 1965 and 1969 versions of the circuits for the Main Frame and Y Amp.

I agree with karesz about caution over the use of silicon diodes to replace germanium. If you want some germanium ones, I have lots, used and similar to OA91. If you want half a dozen, I'll check them and post to you.
wme_bill m0wpn
Attached Files
File Type: pdf TelequipD43_1965 & 1969_circuits-wm.pdf (853.5 KB, 93 views)
WME_bill is offline  
Old 15th May 2018, 3:43 pm   #10
Diabolical Artificer
Dekatron
 
Diabolical Artificer's Avatar
 
Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 7,636
Default Re: LOW EHT Tele D43 scope.

The sq wave calibrator works, though it's not a great sq wave.

The manual I have is a hard copy, published the same year I was born, 1965. I also have various circuits offline, essentially the same.

I have two TB's, a TS41 and TD42. As far as I can tell, they are essentially the same, both use mainly ECF80's, a EB91 and ECC88's - no ECF804's.

The Y amp's are type C and use an ECC82 as the preamp, followed by two ECF184's, those being followed by ECC88's.

The main problem's I have are 1) HT's voltages on the low side, I'm going to go through the PSU again, but doubt there's anything I can do there. All caps are original and check out with a quick ESR check, but I would think a recap would improve things a bit, but would cost too much for too little gain.

2) Xgain/shift control's iffy ( X drift), till the scopes been on a while, then settle, but I have a line instead of a dot. Replaced N301, with a 60v type,no change.

3) Focus/Brightness/ Astig controls a bit cr*p. Have replaced R's/caps and cleaned pots, will have to put up with them.

4) A sinewave makes it to the display on one Y plugin, but is very attenuated and looks more like a square wave that's been through a tone control, IE slanted tops/bottoms. Have re-read manual a few times, but apart from the various inductor's maybe needing a look at, can't think of the cause. will follow a signal through to trace the fault. Also when on AC x1, signal is attenuated more than it should be.

Plugin two has 200v ish on one Y out, 100v on the other, hence trace vanishes. I think both plugin's need a good clean and a look at the switches, they're very mucky with some resistor leads tarnished badly.

Apart from that it's fine : ) Slowly getting there. thanks for the files Bill, much appreciated.

Andy.
__________________
Curiosity hasn't killed this cat...so far.
Diabolical Artificer is online now  
Old 16th May 2018, 7:33 pm   #11
MotorBikeLes
Nonode
 
Join Date: Dec 2012
Location: Kirk Michael, Isle of Man
Posts: 2,346
Default Re: LOW EHT Tele D43 scope.

There is another, earlier D43, but if you have TS/D41/2 you have later version.
Power supply low, look at the two voltage doubling capacitors. (C404/5). I seem to recall replacing one about 30+ years ago. Yours will be 30 years older and drier.
I probably have a good used correct neon somewhere if you dicide you need one.
The calibrate square wave, if DC coupled, may not be perfect, but if you take the central flattish part, top and bottom, it will be a good reference. Of course you need to calibrate the scope first, then make a once only adjustment to the cal if required.
Remember with both X and Y amps, if you scope the feeds to the plates, you should be able to watch one go up as the other comes down, and when they read the same (approx half the rail voltage), your spot/line should be central.
If you don't have a working scope, use a very slow sweep speed and an AVO on DC volts (X-amp), and if you make a simple variable DC source (1.5v battery into a 1K pot), the wiper output can be varied slowly as you watch Y output voltage vary on your AVO.
Les.
MotorBikeLes is offline  
Old 18th May 2018, 6:55 am   #12
Diabolical Artificer
Dekatron
 
Diabolical Artificer's Avatar
 
Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 7,636
Default Re: LOW EHT Tele D43 scope.

Thanks Les. I'm going backwards with this scope, I was all set to have a good look at the Y amp's tother day, turned scope on, no trace. Am pretty sure it's the X gain/shift as you can see a trace very briefly at SW on. I measured the x plates and got 100 and 245v ish, so it's sitting at one end, hiding round the corner sort of thing.
Having to keep re-reading the manual as it's been a long time since i worked on scopes and have forgotten what I did know.

Andy.
__________________
Curiosity hasn't killed this cat...so far.
Diabolical Artificer is online now  
Old 18th May 2018, 8:28 am   #13
ronbryan
Octode
 
Join Date: Jan 2003
Location: Guildford, Surrey, UK.
Posts: 1,958
Default Re: LOW EHT Tele D43 scope.

Flyback blanking is applied by a pulse on the 'mod plate' electrode of the tube. It shifts the X deflection off screen for the duration of flyback. I had a broken track on the 10k 2 Watt resistor R183 which caused the X deflection to be permanently off screen. R183 is a large carbon resistor mounted vertically, so the track underneath can be broken by handlng.

It is worth checking that this is not the cause of your problem.

Ron
Attached Thumbnails
Click image for larger version

Name:	mod-plate-and-sweep-out_web.jpg
Views:	66
Size:	42.2 KB
ID:	163098  
ronbryan is offline  
Old 19th May 2018, 6:22 am   #14
Diabolical Artificer
Dekatron
 
Diabolical Artificer's Avatar
 
Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 7,636
Default Re: LOW EHT Tele D43 scope.

Thanks Ron, traces look ok, but I'll check.

Essentially the TB is working, but it's intermittant and very sensitive. One problem that needs sorting is the X shift/Xgain. I can't get a dot, only a short line. So I measured the voltage on the X plates. One is 100v, one is slightly lower at about 80-90v.

I noticed the bigger the disparity, the shorter the trace. So I checked the circuit around V107B and V10A, ie the two cathode R's (10k) they're withing spec. I checked RV171, and noticed it isn't wired as per the schematic. The wiper isn't tied to point 30, but goes instead to point 16 on the X shift part of circuit. I have noticed another disparity in the Y amp, more of that later.

The X shift is intermitant too, sometimes I can adjust the trace to cover the whole screen, others not. So how does the X gain/shift work? Also what does the X sens (sensitivity) circuit do, and could it be part of the problem here?

I'm slowly working through the Y amp also but the integraty of the signal is dire after it comes out of the first EF184 after the preamp stage. I'll post a schematic and oscillogram later.

Today I'm going to try and be a bit more focused and systematic, I've been trying to fix all the faults at once, so I'll try and get the display and X circuit sorted first.

Andy.
__________________
Curiosity hasn't killed this cat...so far.
Diabolical Artificer is online now  
Old 19th May 2018, 9:10 am   #15
ronbryan
Octode
 
Join Date: Jan 2003
Location: Guildford, Surrey, UK.
Posts: 1,958
Default Re: LOW EHT Tele D43 scope.

You will only get a 'dot' from the X deflection if the timebase is switched off (variable time/cm fully anti-clockwise) or if the 'Stability' control is adjusted so that the timebase is not triggered. Consequently, if you get a 'line' from the X deflection, the timebase is free-running or is being triggered. If you have a working Y amp, it is useful to have an input from the 'Cal' signal fed into the Y amp input, as you can then see a bit more of what is going on.

There is a procedure in the manual for setting up the Trigger circuit and the 'X sens' preset is part of that adjustment procedure.

The voltage on the X deflection plates should vary in a 'see-saw fashion' as the X shift control is adjusted. With the X shift in the middle of its travel, and X gain fully anti-clockwise, the voltages on the X plates should ideally be the same.

The 'X shift' control adjusts the balance of the currents in the long-tailed pair X deflection amplifier V107B, V109B and so sets the voltage on the X plates.

I can't think of any reason why the wiper of the X gain pot should go to point 16 on the X shift circuit.

Ron

Last edited by ronbryan; 19th May 2018 at 9:26 am.
ronbryan is offline  
Old 19th May 2018, 11:42 am   #16
WME_bill
Octode
 
Join Date: Oct 2007
Location: Exeter, Devon, UK.
Posts: 1,553
Default Re: LOW EHT Tele D43 scope.

D43.
I agree with ronbryan. The slider of the X shift pot should go to the resistorR165 and then to the grid circuit of V107B of the X amplifier.
With the X shift central, the voltages at the anodes of the X Amplifer paraphrase pair V107B ,V10B (or the X plates) should be equal for central spot. With the TB turned off of course, with Stability fully counter clockwise.

Your short X line suggests trouble in the X Amplifier. It is always easier to stop the TB when working on the X Amplifier. When that is working, then look at the TB and Trigger.

Moving the X gain control should barely alter the spot position. If it does, then that suggests that the voltages on the grids of the two parts of the X Amplifier are different.
I think you will need to look at the circuit around the extra valve V109B, added in the later TD41timebase module similar to the TD42. That extra valve adjusts the standing voltage at the grid1 of the right hand XAmp, V10B.
Tweak R195 to change the voltage on the grid, so that it is comparable to that on the other grid V107B with the shift control central.
Wme Bill.
WME_bill is offline  
Old 26th May 2018, 6:10 pm   #17
Diabolical Artificer
Dekatron
 
Diabolical Artificer's Avatar
 
Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 7,636
Default Re: LOW EHT Tele D43 scope.

After a break from the D43 to get some other jobs done, I resumed work on it today. I've been reading an old ETI that had a "How to fix scopes" article in. In it and on another thread scope related thread, it mentioned checking for ripple on the PSU rails, as a possible cause of low HT.

I checked all the rails again, and found the 380v rail at the top of R411 measured 252v DC, 21v AC
I replaced 404/405 and now have 392v. This is a bit high probably because there is only one plugin fitted.

Next I tried to suss out the X shift fault. After measuring voltages around V107/108, it showed a high anode reading for V107B. I checked the control grids, V107's grid V was changed by twiggling the X shift control, but not V108's. So as suggested by Bill above, a check of V109 showed low voltage on V109B's grid.

This is adjusted by RV159, which I'd had a look at previously for a loose wiper, but found it ok. I had around 100v at one end of RV159, 85v on the wiper, but no 85v at pin 2 of V109B. Checked R194, ok there, but there's a little trace that jumps over the standoff; it looks fine even under a magnifying glass. Anyhoo, took R194 out, and tacked a 100r R in. Ouila! R159 now adjusts/ balances g1 on V107B and V108A.

This centre's the dot in the screen and the dot is now a dot, and not a dash.After some adjustment of RV148 and a couple of tweeks here and there, the X part of the circuit seems to be working ok.

This has boosted the old morale, I was getting a bit fedup with getting nowhere...On to the next fault, which is a dim trace. With a plugin on the top slot, the trace is very dim and hard to see, dropped the plugin to the bottom slot, good trace.

I checked the brightness/focus controls, took V readings. RHS brightness, from bottom to top;-
-1018v, wiper -900v, top lug -899v. LHS -1012v, -833v, -833v, bit low but nothing drastic. Next focus
RHS, bottom to top, -660v, -375v, -362v LHS -645v, -475v, -374v . This with all controls fully CW. Can't see anything amiss there apart from LHS wiper higher voltage. I'll check the CRT side connections. Like a lot of Telequipment scopes, they use those daft blue "plugs" which arn't a great, tight fit, and are liable to drop off if you move wires about.

Now I have the TB working and the trace stable, I'll tackle the C type plugin. I've got a load of new 100u 350v caps to replace those red plastic cased TCC Elkomold's, a few of which I've found leaky. I've traced a signal through the preamp valve, into and out of the EF184's, but am getting an odd signal at the next valve inline, an ECC88, this without a signal IP. I'll post a pic soon.

Thanks for all your help, much appreciated, Andy.
Attached Thumbnails
Click image for larger version

Name:	DSC00698.jpg
Views:	93
Size:	66.2 KB
ID:	163559  
__________________
Curiosity hasn't killed this cat...so far.
Diabolical Artificer is online now  
Old 1st Jun 2018, 5:58 am   #18
Diabolical Artificer
Dekatron
 
Diabolical Artificer's Avatar
 
Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 7,636
Default Re: LOW EHT Tele D43 scope.

Getting there... I now have one good trace with a signal displayed, and everything seems to work. I've still got to go through and calibrate/jiggle various pots.

I have two plugin's working, a Type C and a type G which I re capped, replaced a few R's and swopped valves.

However one trace you can hardly see. This is odd as as the voltages are the same as the other "channel". With 0v between cathode and grid, it's still not bright like the other. So I checked connections on the back of the CRT, and cleaned the pins/socket, no improvement. I checked continuity from the the brightness/focus pots to said sockets, looks ok. Puzzled. I notice that on the schematic and circuit, there is a 10k R on one grid (LHS pic 2 post 1), so tried a 10k on the dodgy channel, just for kicks, nada.

Does this mean one "channel" of the CRT is kaput? Can't think what else it cound be.

Andy.
__________________
Curiosity hasn't killed this cat...so far.
Diabolical Artificer is online now  
Old 1st Jun 2018, 3:38 pm   #19
WME_bill
Octode
 
Join Date: Oct 2007
Location: Exeter, Devon, UK.
Posts: 1,553
Default Re: LOW EHT Tele D43 scope.

D43. It is a true dual beam cathode ray tube with two separate tube assemblies, apart from common X deflection plates. Common feed to the accelerator anodes a1,but separate feeds to the focus anodes a2 and the final accelerator a3.
Your symptoms suggest that one gun is failing.
Have you checked the voltages on the two a3 pins. I assume you have tried swopping over the two Y Amplifier plug ins. Or experimented with swopping over the pairs of wires to the Y plates and to a3.
With no Y deflection, I assume the second X trace /line is much more dim. Does it vary much with the brilliance controls.
You comment of results with zero volts for each gun between grid1 and cathode sounds very drastic. It should give a violently bright trace, or even damage the tube.
Have you measured the actual voltages on each control grid and each cathode. These are both a full EHT (1kv). Use a high impedance probe or a digital meter, as any current load onto grid1 from an Avo could burn the tube out by swinging the grid violently positive of cathode.

Details of the tube (1000H as 1074H) and connections I posted onto Frank Philipse's Tube Data page.
wme_bill
WME_bill is offline  
Old 2nd Jun 2018, 8:17 am   #20
Diabolical Artificer
Dekatron
 
Diabolical Artificer's Avatar
 
Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 7,636
Default Re: LOW EHT Tele D43 scope.

Thanks Bill, I was going to look at the anodes as you suggest, can't think what else it could be. Could a damaged CRT be the cause? I'm not really familiar with CRT failure modes.

Have swopped the two vert plugin's, it's not them. I'll try swopping the wires as you suggest.

I now have Y deflection, I had two bad ECC88's, changed them and they came good.

Thanks for the heads up on the CRT connection's, I looked online but could find nothing.

One other thing, I found the 25r pot that controls scale illumination OC. Luckily I found a used pot in my stash that had the same pot as part of it and managed to fettle a replacement. One of those times where saving old pots off old scopes pays off. To my question - I'd taken the wires off a year or so ago
and didn't take a pic or make a note of the connections. In the manual it say the pot is wired so it forms a constant load to the htr winding, so I presume it's wired - 6.3v AC from tfmr - RHS tab, bulbs - wiper, LHS - ground, this looking at the pot from the back, tabs upwards facing.

Andy.
__________________
Curiosity hasn't killed this cat...so far.
Diabolical Artificer is online now  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 4:00 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.