[Central-Electronics] CE-100V Scope

Mon Sep 9 00:10:57 EDT 2013

Well, if we think about it a little, there are really only a few likely 
problem sources here.  Either the CRT beam centering voltages are not 
correct (unlikely), the circuit that produces the signals for the CRT to 
display is not providing the necessary or correct signals (possible), or 
said signals are not making it to the correct places within the tube (more 
likely).

Some more observations would be helpful before further conjecture is in 
order:

1. Per my previous post, what happens to the trace as you reduce the power 
level?

2.  As explained previously, the trapezoid pattern will not appear until 
modulation is applied.  Can you observe a trapezoid anywhere on the tube 
face when power is reduced and modulation is applied (in any modulated mode, 
not just AM)?

3. Can you investigate and verify the integrity of the connections to the 
CRT at the socket?

73 de Stu, W7FE
Henderson, NV

----- Original Message ----- 
From: "Gordon" <gordon at n6wk.com>
To: <central-electronics at mailman.qth.net>
Sent: Sunday, September 08, 2013 5:16 PM
Subject: Re: [Central-Electronics] CE-100V Scope

> Hi Stu,
>  I replaced all the 2.2 meg, the 470k and the 100k Resistors and the .01 
> caps that are on the tube socket bracket.
> Everything there is new. I verified the 500K and the 100K pots are good 
> for the Focus and the intensity.
> I have tried another 6U8, but no change.
> I get a vertical line , completely top to bottom when I push the PTT in 
> *any* mode with or without a Mic connected.
> In AM, I think there might be a Trapezoid pattern, but if so,it is off the 
> top of the screen, so I can not really tell.
> I replaced the 50PF Cap that is under the finals, but no change.
> I am enjoying restoring this 100V, but it sure has become a lot of 
> Work!..LOL
>
> 73,
> Gordon
> N6WK
>
>
> On 9/7/2013 11:31 PM, w7fe wrote:
>> Hi Gordon,
>>
>> Normal operation of the CE 100-V's front panel oscilloscope display is as 
>> follows:
>>
>> The 'scope is inoperative until the transmitter is enabled to produce an 
>> RF output signal.  Upon generation of a  continuous CW signal a vertical 
>> trace appears, filling about 3/4 of the 'scope area and roughly on the 
>> tube's vertical centerline.  When RF modulation (of any type) is 
>> generated, a trapezoid (or triangle) -shaped pattern appears, roughly 
>> centered in the 'scope display area, and expanding and contracting in 
>> size concurrent with the modulation.
>>
>> It would appear that the scaling resistors for the 'scope circuit in your 
>> 100V are out of tolerance such that the pattern is filling too much of 
>> the 'scope display area. The "garble" you see may well be the trace which 
>> appears inside the trapezoid pattern.  You may verify this hypothesis by 
>> reducing the 100V's power output control until the trapezoid pattern 
>> appears.  It may not be in the center, but at least some recognizable 
>> portion of a trapezoid/triangle pattern should become visible.
>>
>> Most likely the necessary repair will be to check and replace any 
>> out-of-tolerance resistors in the 'scope circuit to get a properly scaled 
>> and centered  pattern to appear.  I believe that some of these will be 
>> the 2.2 Meg resistors that I found necessary to replace in my 100V a few 
>> years ago in order to center up the displayed trapezoid/triangle pattern 
>> on the 'scope.
>>
>> If you're interested, the way this works is that an RF signal sample from 
>> the PA is applied to the 'scope tube's vertical plates when transmitting. 
>> Simultaneously, an RF sample from the driver stage is demodulated (thus 
>> becoming an AF signal when in the audio modulated modes) and applied to 
>> the horizontal plates (there is no time-based "sweep" circuit as found in 
>> a bench 'scope).  In the carrier-suppressed modes, the pattern produced 
>> will be a very nearly perfect equilateral triangle.  If carrier is added, 
>> the short end of the pattern will be truncated (thus producing a 
>> trapezoid) until 100% modulation is achieved whereupon a triangle is then 
>> displayed. Overmodulation will add a 'tail' to the left point of the 
>> triangle. Issues such as under-loading, under/over-biasing, splatter, 
>> spurs, and others may be observed using this display scheme but are 
>> unlikely to appear on the 100-V (there are no front panel 'adjustments' 
>> available.to correct them anyway).  Images of  the patterns produced by 
>> these anomalies can be found in any monitor scope manual (such as the CE 
>> MM-2, Heath HO-10, etc.), available via a quick Google search.
>>
>> I hope that the preceding notes will help you identify and correct your 
>> 100-V's front panel oscilloscope display problem.
>>
>> 73 de Stu, W7FE
>> Henderson, NV
>> 100V S/N  E73
>>
>>
>>
>> ----- Original Message ----- From: "Gordon" <gordon at n6wk.com>
>> To: <central-electronics at mailman.qth.net>
>> Sent: Saturday, September 07, 2013 3:21 PM
>> Subject: [Central-Electronics] CE-100V Scope
>>
>>
>>> Trying to get my scope working correctly.
>>>     When I start off in Standby, I show nothing on the scope, which 
>>> appears the way it should be.
>>> When I switch to operate, I get a *vertical* line, the completely across 
>>> the scope, from top to bottom.
>>> When I talk into the Mic and transmit, there is all Garble that appears 
>>> to the left of the line.
>>> It does not appear to be any sort of pattern.
>>> Is the line supposed to start off as vertical, or do I have my CRT 
>>> clocked wrong?
>>> Any ideas why the pattern is NOT a pattern? I have changed V21 with a 
>>> new 6U8, but no help.
>>>
>>> Thanks,
>>> Gordon
>>> N6WK
>>>
>>>
>>>
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>>
>
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