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Hello/Tek 547 issues.

 

Hello, my names Andy AKA Diabolical Artificer. I build valve amps & interested in vintage tech as well as using a 545B daily as my main scope. I also have a 585A & currently trying to get a 547 working. I'm on a few forums as well as having a small Youtube channel where I post my doings.
I've been working on a 547 ser # 100091 for the last few weeks. after testing/re-forming all the big PSU caps I powered it up. After sorting some silly mistakes I'd made I checked all the PSU rails - all were in spec. However after the scope had been powered up for a few hours the EHT tfmr was found to suffer from the usual insulation breakdown. I replaced the EHT tfmr & replaced the valve diodes for silicon diodes.
I have a trace but it's not the full width of the CRT, it's "stuck" on the LHS. Suspected hor amp. I've done a lot of checking on the horizontal amp. I took DC voltage readings - noted a V reading on the OP of V584B cathode - +3.95v (should be 325v ish) I checked all the transistors (I'll call em Q's for short) in the scope as well as the diodes. I also checked the valves - all ok. Found some dead Q's - Q543 & Q554, replaced with 2N1893 & 2N4890. also found some dead diodes - D561 & a diode in TB B multi vibrator circuit. I used what I had, not the right Tek parts.
So, TB B is working, TB A not, I have limited X trace length also limited Y adjustment & no intensity adj. At the moment I'm concentrating on the X & Y OP circuitry then I'll move onto getting the TB's sorted. Any ideas where to look re X limited trace length?
Regards, Andy.
 

One thing to check is whether one of the horizontal plate connections isn't, well, connected. They're easily pulled off, so take a look around the crt connections (not at the base, but where the plate terminals emerge from the side of the jug).

Hope you get lucky!

-- Cheers
Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
420 Via Palou Mall
Stanford University
Stanford, CA 94305-4070

On 3/14/2025 12:09 AM, Diabolical Artificer via groups.io wrote:
Hello, my names Andy AKA Diabolical Artificer. I build valve amps & interested in vintage tech as well as using a 545B daily as my main scope. I also have a 585A & currently trying to get a 547 working. I'm on a few forums as well as having a small Youtube channel where I post my doings.
I've been working on a 547 ser # 100091 for the last few weeks. after testing/re-forming all the big PSU caps I powered it up. After sorting some silly mistakes I'd made I checked all the PSU rails - all were in spec. However after the scope had been powered up for a few hours the EHT tfmr was found to suffer from the usual insulation breakdown. I replaced the EHT tfmr & replaced the valve diodes for silicon diodes.
I have a trace but it's not the full width of the CRT, it's "stuck" on the LHS. Suspected hor amp. I've done a lot of checking on the horizontal amp. I took DC voltage readings - noted a V reading on the OP of V584B cathode - +3.95v (should be 325v ish) I checked all the transistors (I'll call em Q's for short) in the scope as well as the diodes. I also checked the valves - all ok. Found some dead Q's - Q543 & Q554, replaced with 2N1893 & 2N4890. also found some dead diodes - D561 & a diode in TB B multi vibrator circuit. I used what I had, not the right Tek parts.
So, TB B is working, TB A not, I have limited X trace length also limited Y adjustment & no intensity adj. At the moment I'm concentrating on the X & Y OP circuitry then I'll move onto getting the TB's sorted. Any ideas where to look re X limited trace length?
Regards, Andy.
 

Thanks Tom, I looked having got caught by that one in the past, the connections look good. To be certain of a good connection I pulled the lugs off then popped them back on.

Andy.
 

I think you should probably review what was done with the EHT transformer replacement. My guess is its running unregulated and the output is way too high. That would cause reduced horizontal and vertical deflection and probably the lack of intensity control.
 

Thanks, I'll look at that. Andy.
 

"That would cause reduced horizontal and vertical deflection and probably the lack of intensity control." Could you explain why please Tom?

I've tested the regulator circuit which is working ok. However I have too high a voltage at the cathode IE -2200v instead of -1850v but too low a voltage on the intensity part of the circuit IE -1606v instead of -1950v which doesn't make sense as both have the same diode replacements - two R5000F's.

Will do some digging, Andy.
 

I guess a simple explanation would be that the higher the accelerating voltage is, the faster the electrons go from the gun to the screen, and spend less time passing the deflection plates, therefore the deflection plates have less influence in changing the direction of the electrons. So the higher the EHT voltage, the lesser the deflection is
 

To second that I can add the fact that any crt TV will behave like this: EHT too low will produce "picture too big" whereas EHT loo high will show a reduced picture size. Was very common to deal with through the early 1970s when Philips ctv with PD500 and PD510 EHT regulation triode valves were popular in Europe. Still have some
Joe
 

I changed R803 the 56k anode resistor for V814 to 68k to reduce V800's screen grid voltage, & adjusted the EHT to minimum. The CRT display is a lot less bright but I still have no intensity adj and the display is still half width of the CRT. The OP of V800 is way lower than spec. I can only suppose the forward bias V of the silicon diodes is less than a 5642 valve diode: the datasheet gives no voltage spec.

Next I'll check all the resistors in the potential dividers that feed the focus & intensity pots and power supplies again. BTW I have limited focus adj.

Andy.
 

Andy,

In the hv section, see if the .01mfd condensers are ceramic or tubular. If the latter, replace with film or ceramic types. You can increase the capacitance if you want to say .015mfd. The 56,000 ohm resistor to the screen and plate should be 5W. The decoupling condenser and the .001mfd across the primary could be bad. See if the valves are good. The resistors in the high voltage are likely out of tolerance. That will cause the voltages to be off. In these sections of these types, I used 1% 2W types. I also replaced carbons in mine with 1% types with a few of 5% in areas where I had them and the tolerance is fine. There are a number of resistors in these series that are too small in wattage and will show overheating. Check the pots in the horiz. sections. The pots could be bad/dirty. The .01mfd condensers in the power supply are known to become leaky. Orange Drops are a good type to use as replacements. Clean the high voltage section. The black dirt that gets there is a leakage path. This includes the crt. I have seen the crt black on the funnel. This was slick. Cleaning helped.

Mark
 

"In the hv section, see if the .01mfd condensers are ceramic or tubular" Are the ones you refer to high voltage types IE 1KV +?

Yesterday I pulled the CRT in order to clean the X & Y plates connecting pins. I cleaned the CRT, it wasn't too mucky. I checked the connections at the start but always a bit wary of them due to corrosion etc elsewhere in the scope. I tried to removed the oxidation of the pins with 800 grit wet & dry as well as twisting by hand a small drill bit inserted into the spade type crimped connections.

I noticed the trace had moved to the right a bit after this & whilst trying to take V measuements on the X/Y CRT pins my meter probe slipped, big sparks & a small bang, switched off. I'd vaporized a wire lead to V574B and a 47r grid stopper. Interestingly the trace is now the opposite of what it was stuck on the RHS.

This leads to once again suspect the horizontal amplifier but I'll still check the EHT supplies etc & make sure all connected components are in spec or caps not leaky. I can test up components up to 10KV using a vintage equivalent of a Megger. Here's a link to the videos so far - not the best filmed & produced films but should show whats what.

Thanks again for all your help & support, Andy.
 

Andy,

By your video, the high voltage condensers are ceramic. It is possible/likely one or more of the 5W blue resistors will be open. I have seen these open in 500 series before due to being run close to or over the rated wattage.

Mark

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