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UNCLASSIFIED 
AD NUMBER 



AD095319 


CLASSIFICATION CHANGES 

TO: 

unclassified 

FROM: 

confidential 


LIMITATION CHANGES 


TO: 

Approved for public release, distribution 
unlimited 


FROM: 

Distribution authorized to DoD only; 
Foreign Government Information; 19 JUN 
1944. Other requests shall be referred to 
The British Embassy, 3100 Massachusetts 
Avenue, NW, Washington, DC 20008. 


_ AUTHORITY _ 

DSTL, AVIA 26/694, 4 Nov 2009; DSTL, AVIA 
26/694, 4 Nov 2009 


THIS PAGE IS UNCLASSIFIED 
















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No. T 1692 



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(1908) Wt. 58994—4723 15M 3/44 G&St, Gp. 690 

JUN 13 1956 

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U.S. CONFIDENTIAL 


T.R.E. REFOR3 
jI/R22/SCC/GW 


Summary 


MODIFIED HANDUNG 


SC.iELIFIED ; JODULATOR FOR COMPONENT TESTING 


It is frequently necessary to oonstruot a modulator for the purpose 
of life-testing or factory-testing major items suoh as valves'and networks. A 
straightforward system for use in these oases was dovisod. It oontains no 
valves other than H.T. roctifiors and a Trigatron or open gap. The small 
number of components involved renders the unit readily serviceable, reliable and 
troublo-froo. 

Gonoral Principles 

The basio circuit is shown in Drawing No. ATR.70/775 Figure 1. A 
high voltage transformer is grounded at ono end and the other end is attaohod 
to the network via a rectifier, arranged to charge the oapacity negatively. 

The same transformer winding is likewise connected to a second rectifier in 
opposition with the first. This rectifier charges a small condenser C 
(100 to 500 uuF) connected bet to on the trigger eleotrode of a spark gap S 
and earth. '' 

The spark gap S, which may be CV85, CV125 or CV100 according to voltage 
requirements, is used to discharge the network N into the load R. The sequence 
of operation is as follows. N is charged nogotivoly during one half of the 
supply cycle and tho negative charge is maintained. On the positive half-cyole 
of the supply the condenser C charges positively through a resistance R1 (about 
1 m-ohm in value) to a value sufficient to break down tho trigger-anode gap. 

Tho main charge in N thereafter discharges into the load R. The limiting 
resistance R1 is used to reduce the current through the trigger-anodo-ground 
circuit to a reasonably low value. At the same time R1 is such that tho time- 
constant CR1 does not prevent the rise of voltage of C from being nearly equal 
to that of the supply waveform. The resistance R2 across C is generally 
10/20 times R1 in value and the time-constant CR2 is roughly equal to a quarter 
of the time of one cycle of the supply frequency. None of the values is 
critical, however, and a fairly extensive range of frequency can be tolerated 
on a given system arrangod with the above principles in viow. 

The network N is charged to nearly the peak nogative value of the 
secondary waveform. Likewise the condenser C may be charged to approximately 
the peak positive value (provided CR1 and R2 are properly chosen). It may be 
found desirable to have this positive value higher than is obtained from a 
singlo cannon winding though this depends on the characteristics of tho gap. 

In such cases it is not difficult to extend the winding to give the extra 
voltage at a low current rating for triggering purposes. 

Operation as a Full-Wave Circuit 


The mode of operation on full-wave output can be deduoed from Figure 1 
and Figure 2 of Drawing GTR70/81A, The output pulso is always nogative in 
this arrangement. The circuit constants were chosen for a supply of 50 c/a 
frequency (output repetition rate 100 pps). The positively charged network 
requires inversion of tho gap V6 and the anode and trigger are oonnocted by 
20 M-ohms, Tho positive charging of tho triggering condenser is offectod 
through the blocking condenser of capacity ,002/uF. Thus 0.8 of tho peak 
voltage E is available for breakdown of the trigger electrode. This fraction 
could bo increased if dosirod by, roduoing the trigger capacity to less 
than 500yyuF. 


This is only offooted by altering tho supply frequency. However 
it is usually desirable to maintain constant repetition rate and this is 

/automatically 



- 2 


automatically ensured. A 50 c/s source con be used at 50 or 100 pps. 
Generators of 400 and 500 c/s are available and aircraft generators may be 
usod to cover ranges from 800 c/s to 2500 c/ 3 . by changing gear-ratios. 

Thus frequencies separated by discrete stops may be made available and 
ropotition rates from 50 to 5000 pps realised. 

Typical Waveforms 

The waveforms observed at various parts of the circuit are shown 
in Drawing ATR70/775, Fig.l, and Drg. GTR70/814, Fig.2, for half-wave and ■ 
full-wavo operation respectively. The last refers to operation at 100 pps. 
with a oircuit operating on a 50 c/s input supply frequency. It will 
bo noticed that there arc slight differences observed in the pulse shapes 
obtained on the altemato cyolcs. It seems that those differences aro due 
to the effects of stray capacities and inductances which aro not exactly 
alike duo to the asymmetry of components. 

It should bo notod that the circuit is of the hold-off typo and 
deionisation difficulties arc less marked. Higher repetition ratos may 
bo cmployod than with the constant current charging systems. 


Authors; S.C. Curran 
G.T. Hawkins. 


Approved for Circulation: A. Ward. 


19th June, 1944 
scc/mb. 


Numbered Pages: 2. 

Drawings: ATR70/775 
GTR70/814. 


S,No,9087. 



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Defense Technical Information Center (DTIC) 
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AD#: AD0095319 

Date of Search: 4 November 2009 

Record Summary: AVIA 26/694 

Title: Simplified Modulator for Component Testing 

Availability Open Document, Open Description, Normal Closure before FOI Act: 30 years 
Former reference (Department): T-1692 
Held by: The National Archives, Kew 


This document is now available at the National Archives, Kew, Surrey, United 
Kingdom. 

DTIC has checked the National Archives Catalogue website 
(http://www.nationalarchives.gov.uk) and found the document is available and 
releasable to the public. 

Access to UK public records is governed by statute, namely the Public 
Records Act, 1958, and the Public Records Act, 1967. 

The document has been released under the 30 year rule. 

(The vast majority of records selected for permanent preservation are made 
available to the public when they are 30 years old. This is commonly referred 
to as the 30 year rule and was established by the Public Records Act of 
1967). 


This document may be treated as UNLIMITED .