Marantz Model 19 Scope

Does anyone know anything about these ? I know the basics but there are det ails missing from the print, LIKE THE PINOUT of the CRT !

I can see though (thank you Drs Budrous and Stewart) so I can see the thick er wires, those are pretty much at cathode potential, -500 volts. I can als o find the deflection plates and with the centering make the DC voltages eq ual, still no display.

Unless there's something I missed I need to get into the grid and focus vol tages and if those are all there, the CRT is bad ?

From what I hear you would need a SWAT team and a bunch of automatic weapon s to get a replacement CRT. Even people with experience on these things, ho w many receivers had built in scopes ? I saw one in another brand once but can't remember what it was, maybe a Kenwood ? Other than that only Marantz and then even very few models.

I got the other problems fixed, it had a fault on the one power amp board a nd a bad transistor on the tone amp board which is by the way stuck to the chassis with double sided foam tape ! For what they charged fro these thing s, foam tape ? And you should see the PITA it is to remove, I was thinking "This board it gonna break", but it didn't.

What you really need is a Fein cutter with an L shaped blade. (they are nor mally used to cut windshields out of cars)

Anyway, thanks in advance for anything useful on this matter. It makes a bi g difference in the value of the unit.

Reply to
jurb6006
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Pinouts here :

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replacement here (bit spendy) :

Ebay item no 254200412600

Reply to
JC

The service manual is available at HiFiEngine.com (free registration required to download). The scope-module schematic is on page 62 of the original and the tube ponout is given.

The scope V901 is "CRT with 13-pin Nixie base", Marantz part number

337-1000. According to one article I read elsewhere, it's originally a Siemens D3-II GJ.

After all of these years, I wouldn't be surprised if the cathode were worn out (low emission) or the CRT has become gassy.

From what I read, it's well beyond that now... you'd need the services of at least four demigods, and several falling asteroids to blast one loose. They're probably mostly in the hands of owners of Marantz receivers in that series, being preserved against a Time Of Need.

Some Macintosh tuners had scopes. Mac seems to have used a more common/popular tube variety (a 3RP series), for which there are still some used-but-good tubes available and even a few Chinese-build clones.

One guy who wrote, said that he'd sold a Model 19, and had also sold a new-old-stock replacement CRT he had for it. He got more for the CRT than for the receiver.

I've been dealing with a slightly similar problem myself... I bought a CTS service monitor whose scope is working-but-dim. Fortunately it has a 3RP CRT (like the Cushman and Macintosh systems do) and I have a local source for a used tube (and there are online sources as well).

I was thinking of trying to cons up a solid-state replacement. I think one could probably be made by using a Raspberry Pi or similar processor as a core, hooked to a reasonably fast (audio-speed) two-channel SPI-based ADC which would sample the horizontal and vertical deflection voltages (suitably attenuated and centered of course). The Pi would capture the data, and then draw it to a 2" color LCD.

Reply to
Dave Platt

shango66 on youtube does some good explanations re CRT emission problem fixing. Though I don't remember him discussing EHT boosting.

NT

Reply to
tabbypurr

Aren't you going to run the risk of X-Ray production if the EHT is increased beyond a reasonable point? The link below says 5KV and up can produce X-Rays:

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We have a problem in my industry with 13" colour tubes being over driven by ignorant people using the wrong HV transformer (from 19" monitors) and getting the tube into the soft X-ray range...

John :-#(#

Reply to
John Robertson

I guess it's largely been answered :) Depends what voltage you're running at, how much boost & how much leeway you have with xray production. I would not consider EHT boosting until other options were exhausted. A 500v tube is not an issue though.

Medical x-rays use much higher voltages so the rays are harder, ie penetrate more.

NT

Reply to
tabbypurr

Thanks, it might help. However the tube socket is wired to a set of wires t hat do down to a socket on the board. There is no way to tell for sure the connections aren't changed from what you would get straight at the base of the tube. I haven't found a decent page on the CRT in the manual, in fact i t says something like "provisional" as if they weren't quite sure whose tub es they going to use.

Having the pinout, even in low resolution is better than nothing.

Reply to
jurb6006

S service monitor whose scope is working-but-dim. Fortunately it has a 3RP CRT (like the Cushman and Macintosh systems do) and I have a local source for a used tube (and there are online sources as well). "

Have you tried boosting the filament voltage ? For one it is the best way t o extend the life of a CRT, rather than rejuvinating. I wouldn't recommend that for a CRT unless it was in a TV, the color CRTs pull quite a bit of cu rrent and guess where it all comes from - the cathodes.

But scope cathodes don't get loaded heavily. they can be just as bright as a tube pulling 20 times more current easily because they are not generating a raster.

If it turns out to be weak emission in this tube I am not exactly sure how to boost the filament voltage. It seems to run off a resistive divider, but for a small tube which is a RAY type tube not a raster type it is sufficie nt. But then doing anything in that circuit might do something to the G1 bi as or whatever.

Thing is also figuring out how to actually test the thing if/when all the o ther possibilities are eliminated...

Reply to
jurb6006

I'll have to look into that. Nobody in their right mind would try to save an old CRT by boosting the main accelerating voltage.

First I will try the grid bias, if that does it fine, that is IF that is the problem and it isn't some other fault.

Thing is I just heard from the customer that he scope used to work, he actually found the burning -500 rectifier. There are no shorts currently, the new rectifier is doing fine in there.

But no trace.

Reply to
jurb6006

On Sunday, 28 April 2019 20:16:35 UTC+1, snipped-for-privacy@gmail.com wrote: NT:

Well I've done it when all else failed, and it would not result in excessive x-ray emission. I kept one such set for 10 years or so, it kept going just fine. Why do you dislike it?

NT

Reply to
tabbypurr

Well you got lucky. High voltage components are particularly prone to failure even at their rated voltage and you may not have had problems, but I bet out of 10 times at least 7 would be a problem.

Another thing is what did you do about deflection sensitivity ?

How do you know it did not result in excessive Xray emission ? Piece of plywood and some photographic film in a dark room ?

Reply to
jurb6006

On Monday, 29 April 2019 04:03:25 UTC+1, snipped-for-privacy@gmail.com wrote: NT:

ssive x-ray emission. I kept one such set for 10 years or so, it kept going just fine. Why do you dislike it? "

lure even at their rated voltage and you may not have had problems, but I b et out of 10 times at least 7 would be a problem.

There is a small failure rate at the original voltage. TV parts are general ly run well below parts mfrs' rated voltage to improve reliability, eg 25kV on a 40kV part, 15kV on a 25kV part. Failure rate climbs as you apply more , but it only takes a small boost, 5-10%, and the increase in failures is n ot great for that much. But yes it's there. However the key phrase is when all else fails. 90% beats 0% by a long way.

Cleaning the EHT stuff always helps, dirt degrades insulation capability..

Raise B+ the same amount. In TVs the easiest way is just to raise B+ across the board.

lywood and some photographic film in a dark room ?

The OP has a 500v tube. Otherwise look up the datasheet for the CRT, they'r e often run below rated v.

You can also use a counter. It can't measure all the tube's output, but it can measure background, and relative original & boosted outputs. Then you k now what %age the increase is and can see if that's within requirements.

NT

Reply to
tabbypurr

etails missing from the print, LIKE THE PINOUT of the CRT !

cker wires, those are pretty much at cathode potential, -500 volts. I can a lso find the deflection plates and with the centering make the DC voltages equal, still no display.

oltages and if those are all there, the CRT is bad ?

ons to get a replacement CRT. Even people with experience on these things, how many receivers had built in scopes ? I saw one in another brand once bu t can't remember what it was, maybe a Kenwood ? Other than that only Marant z and then even very few models.

and a bad transistor on the tone amp board which is by the way stuck to th e chassis with double sided foam tape ! For what they charged fro these thi ngs, foam tape ? And you should see the PITA it is to remove, I was thinkin g "This board it gonna break", but it didn't.

ormally used to cut windshields out of cars)

big difference in the value of the unit.

to extend the life of a CRT, rather than rejuvinating. I wouldn't recommend that for a CRT unless it was in a TV, the color CRTs pull quite a bit of c urrent and guess where it all comes from - the cathodes.

A common trick to boost filament voltage as well as grid voltage was throug h the use of aftermarket transformer 'CRT boosters'...Basically a dongel th at was inserted between the crt socket and the crt pins. Been so long, I f orget how they were sized, and am sure you would be hard pressed to find on e nowadays...

Reply to
three_jeeps

These were a simple step-up auto-transformer designed for 50/60Hz. I have one or two lying around my shop and any old radio/TV museum would have a pile of them I'm sure.

John :-#)#

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Reply to
John Robertson

That's all well and good, but those had one of 4-5 common TV picture tube plug/socket pairs. I seriously doubt you could find one with the matching connectors for a bastard CRT.

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Jeff-1.0 
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Reply to
Fox's Mercantile

tube plug/socket pairs. I seriously doubt you could find one with the matching connectors for a bastard CRT.

I just looked on E-bay - a number of crt boosters are available. One would have to compare pinouts/sockets (for location & form factor) to see if the y match. In the event they didn't match, one could break apart the sockets to expose the crimped wires and then individually mate them to the pins on the crt (and the original socket as well). It would save a little time as compared to rolling your own.

Reply to
three_jeeps

ld have to compare pinouts/sockets (for location & form factor) to see if t hey match. In the event they didn't match, one could break apart the socke ts to expose the crimped wires and then individually mate them to the pins on the crt (and the original socket as well).

With most TVs it's easier to put an extra turn on the LOPTF

NT

Reply to
tabbypurr

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