Completed Project How to modify an EICO 950B to convert the 1629 eye tube to run on 6E5S tube?And change the 6x5 tube?

Thread Starter

Rahulk70

Joined Dec 16, 2016
536
Hi folks,

I've an EICO 950B capacitance tester with me. It has an aging 1629 magic eye tube. I have a bunch of 6E5S tube with me. Can you guys guide me with the modification?

I know the first step to this is to reduce the filament voltage to 6.3V for the 6E5S. But something that bugs me is, can a simple resistor voltage drop get it done? I'm worried that this path might have issue which might kill the tubes very fast. Hoping to get some expert opinions here.

Also I've heard the 6X5 tube have the habit of killing the transformer as they die? I'm thinking of changing it to something like a selenium or silicon rectifier?

Thanks.
 

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AlbertHall

Joined Jun 4, 2014
12,345
Hi folks,

I've an EICO 950B capacitance tester with me. It has an aging 1629 magic eye tube. I have a bunch of 6E5S tube with me. Can you guys guide me with the modification?

I know the first step to this is to reduce the filament voltage to 6.3V for the 6E5S. But something that bugs me is, can a simple resistor voltage drop get it done? I'm worried that this path might have issue which might kill the tubes very fast. Hoping to get some expert opinions here.

Also I've heard the 6X5 tube have the habit of killing the transformer as they die? I'm thinking of changing it to something like a selenium or silicon rectifier?

Thanks.
For the magic eye, this should help:https://threeneurons.wordpress.com/magic-eye-stuff/

I do not recommend using a semiconductor rectifier. Remember the original problem with the +200V/-500V rails. They are balanced by the currents being drawn from them. With a valve rectifier the HT voltage will rise slowly as the magic eye begins to conduct so the voltages should stay roughly balanced. With a semiconductor rectifier the HT will rise instantly to its full voltage but the magic eye will be drawing no current so the 200V will rise very high and you have seen the effect of that already.
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
536
The transformer secondary has 6.3v and 12.6v outputs.

What else do you want to modify?
Hi,

So, I can just use the 6.3V directly and there wouldn't be any issues, right?
Also, are the other connections for the 6E5S tube are going to be the same as in the 1629 tube?

Just want to get everything right before I go ahead with the mod.
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
536
For the magic eye, this should help:https://threeneurons.wordpress.com/magic-eye-stuff/

I do not recommend using a semiconductor rectifier. Remember the original problem with the +200V/-500V rails. They are balanced by the currents being drawn from them. With a valve rectifier the HT voltage will rise slowly as the magic eye begins to conduct so the voltages should stay roughly balanced. With a semiconductor rectifier the HT will rise instantly to its full voltage but the magic eye will be drawing no current so the 200V will rise very high and you have seen the effect of that already.
Hi,

Thanks for the info. The sudden rise in voltage didn't cross my mind. I guess I'll stick with the 6X5 then. I got four 6X5's for $4 on eBay.
Also is there any good substitute for the 6X5 that doesn't kill the transformer as it goes out?
 

crutschow

Joined Mar 14, 2008
34,285
Also is there any good substitute for the 6X5 that doesn't kill the transformer as it goes out?
Wally to Dilbert: :cool:
You might possibly be able to use a solid-state rectifier as a replacement if you add a relay delay (or possibly a triac delay) circuit in series with the transformer AC output so the voltage doesn't come up until the magic eye filament has warmed up and it can conduct DC.
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
536
Wally to Dilbert: :cool:
You might possibly be able to use a solid-state rectifier as a replacement if you add a relay delay (or possibly a triac delay) circuit in series with the transformer AC output so the voltage doesn't come up until the magic eye filament has warmed up and it can conduct DC.
I'll definitely give it a thought and try to make a circuit. Hope this experiment won't take my transformer with it though:rolleyes:
 

dl324

Joined Mar 30, 2015
16,846
I've an EICO 950B capacitance tester with me. It has an aging 1629 magic eye tube. I have a bunch of 6E5S tube with me. Can you guys guide me with the modification?
Wouldn't doing that cripple the instrument?
EDIT: Didn't realize the 6E5S was similar except for heater ratings and pinout... Thanks for the info @Reloadron
upload_2018-10-14_18-57-27.png

I forgot that I had one of these.
 
Last edited:

AlbertHall

Joined Jun 4, 2014
12,345
Wally to Dilbert: :cool:
You might possibly be able to use a solid-state rectifier as a replacement if you add a relay delay (or possibly a triac delay) circuit in series with the transformer AC output so the voltage doesn't come up until the magic eye filament has warmed up and it can conduct DC.
Another idea worth considering is to put a 200V+ zener across the 200V supply. This would soak up any surplus current and keep the voltages sane. I think the maximum current would be 5mA so a 2W zener would be appropriate.
 

Reloadron

Joined Jan 15, 2015
7,501
I've an EICO 950B capacitance tester with me. It has an aging 1629 magic eye tube. I have a bunch of 6E5S tube with me. Can you guys guide me with the modification?
While the two tubes share identical characteristics the pin out is not the same and they use different filament voltages. This old comparison is worth a look. I see the swap as more trouble than it is worth.

Thanks for reminding me I have an old (maybe circa early 60s) Eico 920 B laying in the basement. :)

Ron
 
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