DETECTION AND REMOVAL OF HOT SPOTS ON VACUUM TUBES

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP82-00046R000300060012-9
• Release Decision: RIPPUB
• Original Classification: S
• Document Page Count: 3
• Document Creation Date: December 22, 2016
• Document Release Date: June 17, 2009
• Sequence Number: 12
• Publication Date: November 27, 1953
• Content Type: REPORT

Approved For Release 2009/06/17: CIA-RDP82-00046R000300060012-9
SECRET
,,..:r ~. , a r. r
REPORT
25X1
COUNTRY Czechoslovakia
DATE DISTR. 2' by, 1963
SUBJECT Detection and Removal 'of Hot Spots on NO. OF PAGES 3
Vacuum Tubes
PLACE
ACQUIRED
ACQUIRED I
DATE OF INP
NO. OF ENCLS,,
(LISTED BELOW)
SUPPLEMENT TO
REPORT NO.
THIS IS UNEVALUATED INFORMATION 25X1
1. Insignificant and invisible particles of metal which settled on the
inside of glass envelopes formed "hot sppots"..
This would occur during
evacuation of the glass envelope. She shaded area.(a) of the attached
sketch indicates where "hot spots" would occur most frequentiy..7 When
vacuum tubes which had "hot spots were put into operation the-high-
frequency field would heat the area in which the metal particles had
been deposited, and being an area of conduction, would become hot.
This area would, become so hot that the glass envelope would soften and
implode. Vacuum tubes with "hot spots" were very common in Czechoslo-
vakia, because of the fact that the materials used were not of good
quality, and because the manufacturing methods did not conform to good..
practice.
'2. Until 1949 there were no methods'in the Tesla industry to determine
heth
"
"
w
er
hot spot
existed until actually placed in operation at which
time the defective tubes failed. Starting in 1949 the Tesla-Vrsovice
plant used a very thin white tissue paper to ascertain if "hot spots"
.existed. This paper was placed. around the glass envelope and the tube
was placed in operation, and where "hot spots" occurred, the paper
.turned brown showing the location,.the size, and the intensity of the
hot spot. The vacuum tubes.showing "hot spots" were not used for
oscillation (power amplifier) purposes.
The method used to remove hotspots.was developed in the Tesla-Vrsovice
plant in 1951. When the process of evacuating the glass envelope was
half accomplished, air was admitted in the tube again and then
exhausted to a pressure of the order of 1.0 to i0-1. rim. of mercury.
Approved For Release 2009/06/17: CIA-RDP82-00046R000300060012-9
 Approved For Release 2009/06/17: CIA-RDP82-00046R000300060012-9
-2-
The vacuum y he T4 rmed in, an dleatri" urnaee to a tempera-
ture just bovethe transformation temperature (where the internal
tension of the glass dissolves) below the melting point. The vacuum
tube stayed at such a temperature for 15 to 30 minutes. After this
heating had been completed, the glass envelope was then evacuated
completely. This treatment was applied preventively In Tesla-Vrsovice
on all types of medium-powered vacuum tubes, which experience had
shown were likely to have "hot spots". This treatment was applied
retroactively on the remaining medium-powered tubes and on all high
powered tubes which showed "hot spots" when tested. This technique
was not applied to small vacuum tubes where the processing was too
expensive. - the method used to ascertain the presence 25X1
of hot spots ana to. remove them was known only in Czechoslovakia.
MARES, chief vacuum technician with the Tesla-Vrsovice plant visited
Marcbni's Wireless Telephone Company, Ltd., in London two or three
times before 1949 and did not learn any method to alleviate "hot
spots" on vacuum tubes,
Approved For Release 2009/06/17: CIA-RDP82-00046R000300060012-9
 Approved For Release 2009/06/17: CIA-RDP82-00046R000300060012-9
LEGEND
F. Filament
G. Grid
A. Anode
a. Part of the envelope where the "hot spots" occurred most fre-
quently.
Approved For Release 2009/06/17: CIA-RDP82-00046R000300060012-9