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  #46  
Old 09-15-2018, 12:31 AM
mrjukebox160 mrjukebox160 is offline
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Just curious as o the reason to replace the 5U4.s
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  #47  
Old 09-15-2018, 01:31 AM
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Originally Posted by mrjukebox160 View Post
Just curious as o the reason to replace the 5U4.s
Perhaps the power trans runs hot or is a common failure point...That is the only reason I ever switch from tube to SS rectification (except for 6X5s which I have no faith in).
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  #48  
Old 09-15-2018, 02:50 AM
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Just curious as o the reason to replace the 5U4.s
I’m the owner of this set, but Mike who is far more experienced then myself is doing the chassis restoration.

Quoting Mike: “By doing these modifications it not only eliminates vacuum tube heat, it also eliminates a lot of unnecessary wiring that has the potential to cause arcing which of course is very undesirable.”

He said the wiring in the area is in poor shape.
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  #49  
Old 09-15-2018, 03:20 PM
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Originally Posted by etype2 View Post
I’m the owner of this set, but Mike who is far more experienced then myself is doing the chassis restoration.

Quoting Mike: “By doing these modifications it not only eliminates vacuum tube heat, it also eliminates a lot of unnecessary wiring that has the potential to cause arcing which of course is very undesirable.”

He said the wiring in the area is in poor shape.
It will also give you a stiffer(lower impedance) supply rail, which helps with voltage regulation when picture content changes. On the down side solid state devices are less resilient to voltage spikes. In heavy duty audio applications it's common to see 2 or 3 diodes placed in series to lessen the chance of a melt down if one shorts.
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  #50  
Old 09-16-2018, 03:47 PM
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We need two more.

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  #51  
Old 09-18-2018, 01:12 PM
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As long as the chassis is out, would you mind measuring the depth of the white screen mask, as in how deep it extends?

The one on my H840CK15 is missing, and I'm going to try to construct a duplicate.
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  #52  
Old 09-24-2018, 03:53 PM
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Originally Posted by Kamakiri View Post
As long as the chassis is out, would you mind measuring the depth of the white screen mask, as in how deep it extends?

The one on my H840CK15 is missing, and I'm going to try to construct a duplicate.
When I return to the shop, I’ll measure the depth.

UPDATE, SEPTEMBER 24, 2018, Day 55

Greetings Marshall. I have recapped the main power supply and verified the design voltages as they are at this time. They will likely be lower during later tests since I have the sweep circuits disabled for the preliminary testing. For the foreseeable future, and maybe permanently, I will be leaving the original design in place with the 5U4 tubes. We will see how that goes later. OK, now for the pictures.

Picture #1 shows a couple of caps replaced but except for that, the chassis is as I received it. Mostly "untouched" which is how I like to get them. These caps were actually broken off at the terminals so I went ahead and replaced them. They can be seen as orange and brown components at the lower left.
Picture #2 is the main power supply chassis before re-capping.
Picture #3 is the main power supply chassis after re-capping.
Picture #4 shows my oscilloscope screen showing the waveform of the grid drive to the Horizontal Output Tubes (6BG6's).

This tells me that the horizontal oscillator is running and the drive signal to those tubes is good even before recapping. This signal on the scope is about 200V P-P and the Photofact refers it to be 150 V P-P. Given the fact that most of the running voltages are a bit high right now because I have the main power to the sweep circuits disabled, it is expected that the signal would be a bit high. This is good at this point.

This step is important because it means now, that I can do some testing of the flyback transformer. It won't tell me everything about it, but I will tell me a lot.

Mike.

Link for full size images: https://visions4netjournal.com/westi...-carousel-6116

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Last edited by etype2; 09-24-2018 at 03:58 PM.
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  #53  
Old 09-24-2018, 05:44 PM
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The flybacks on the 15 inchers don't seem to be terribly failure prone. I would reinstall the jug at this point and try to get HV, horizontal deflection, vertical deflection, even in a brief test, and a quick check of the convergence circuitry and CRT itself before going any further. My 2 cents...

There's little sense in continued restoration efforts if critical parts are dead. I don't like the test results of the 15GP22 at all...
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  #54  
Old 09-24-2018, 05:47 PM
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The dynamic convergence transformer is T-701. It needs to be replaced with a Folsom reproduction ASAP, before you damage pots in the focus circuit.
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  #55  
Old 09-24-2018, 06:55 PM
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The dynamic convergence transformer is T-701. It needs to be replaced with a Folsom reproduction ASAP, before you damage pots in the focus circuit.
Thanks. Mike wanted to know if it was the T-701. I think I have John’s email.
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  #56  
Old 09-25-2018, 07:32 AM
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I'd be surprised if John has any left; I think my friend Ed got the last one about a year and a half ago as a precautionary measure.

My cabinet is home now and miniman82 is doing the complete restoration on my chassis. I don't have a good 15GP22, but at this point I'm thinking out a plan
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  #57  
Old 09-25-2018, 03:57 PM
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Good luck with it. Maybe we can compare notes. Nice Marantz. I have a Model 20.

The mask is so large, it could accommodate a larger CRT.
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  #58  
Old 09-25-2018, 10:18 PM
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I don't like the test results of the 15GP22 at all...
The 21AXP22 in our 21CT55 tested like this.



These figures are about the same as the test on 15GP22.

As we have posted on another thread, the 21AXP22 puts out a decent image despite the tired CRT. I wonder what criteria was used by the ETF. The CRT was described “good” and “excellent” prior to the auction. Fingers crossed.
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Last edited by etype2; 09-26-2018 at 12:01 AM.
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  #59  
Old 09-26-2018, 09:13 AM
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Originally Posted by etype2 View Post
The 21AXP22 in our 21CT55 tested like this.



These figures are about the same as the test on 15GP22.

As we have posted on another thread, the 21AXP22 puts out a decent image despite the tired CRT. I wonder what criteria was used by the ETF. The CRT was described “good” and “excellent” prior to the auction. Fingers crossed.
That 21AXP22 is definitely tired, and according to your own post, the green gun on the 15GP22 is even lower than the 0.8 reading you're getting on all the 21AXP22 guns.

Also keep in mind that for sufficient brightness, you'll have to draw more cathode current from the 15GP22 cathode as it runs a lower ultor voltage than the 21AXP22 does (or should) in the 21-CT-55. 19.5 kV for the CT-100 versus 25 kV for the 21-CT-55. The difference in apparent brightness with the two different ultor voltages will be not be negligible.

At the very least I would expect poor tracking, and quite possibly insufficient green. I suppose your saving grace here is that the weakest gun is the green gun. If it were red, you'd be in worse shape...

I too am curious as to what happened here as far as testing goes. Your results certainly don't look "excellent". I don't doubt Steve's integrity. Perhaps your tester needs looking at? Do you have an extremely strong like new tube to compare with?
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  #60  
Old 09-26-2018, 11:30 AM
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Originally Posted by benman94 View Post
I too am curious as to what happened here as far as testing goes. Your results certainly don't look "excellent". I don't doubt Steve's integrity. Perhaps your tester needs looking at? Do you have an extremely strong like new tube to compare with?
Personally, I have limited faith in the ETFs CRT tests. I've had "excellent" tubes test significantly lower than advertised at home, and 'bad' tubes that were good but lightly asleep and could have been confirmed good with a bit of patience...

I'm at the point where I rather test it myself before bidding my top dollar than trust the accuracy of the posted info.

My guess they either have an iffy tester, an iffy operator, are taking consigner's word for CRT health or some combination thereof.
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