Telefunken tubes from the classic Berlin and Ulm era carry a production date — you just have to know how to read it. Two different systems were used: a two-letter code on tubes made from 1930 through 1968, and a seven-character numeric code that replaced it at the end of the 1960s. This page explains both, lets you decode a tube in seconds, and includes a cleaned-up, cross-checked version of the full two-letter chart.
Which code does my tube have?
- A code starting with B or U followed by digits (for example
U9208811) → late-1960s or later production. B = Berlin, U = Ulm. Use the numeric decoder. - A pair of lowercase letters, usually with a letter in front and a number after (for example
B qe 25orbkq03) → production between 1930 and 1968. Use the two-letter lookup.
Reading a full two-letter marking. The date code rarely appears on its own. It is normally printed between other factory markings, with or without spaces:
B qe 25 → February 1965 bkq03 → June 1957
The first letter appears to identify the factory (B for Berlin, matching the later numeric code), the two letters after it are the date, and the trailing number is a further production code that is not part of the date. You can type the whole marking into the lookup below and it will pick out the date letters for you.
Two-letter code lookup
Insert:
Numeric code decoder (B/U + digits)
Reading the later numeric code (late 1960s onward)
The code begins with the factory letter and is followed by digits, sometimes with a trailing letter. Only the factory letter and the first five digits carry the date. The digits are scrambled in a fixed way:
- Day — digits 1 and 2, read in reverse order
- Month — digits 3 and 5 together
- Year — digit 4, the last digit of the year
Example 1: U 9 2 0 8 8 11
Factory U = Ulm. Day: 9 2 reversed = 29. Month: digit 3 (0) + digit 5 (8) = 08, August. Year: digit 4 = 8 → 1968. Made in Ulm on 29 August 1968.
Example 2: B 2 0 0 9 3 00
Factory B = Berlin. Day: 2 0 reversed = 02. Month: 0 + 3 = 03, March. Year: 9 → 1969. Made in Berlin on 2 March 1969.
Watch the decade. The year is a single digit, so it repeats every ten years — a “2” could be 1972 or a later decade. Use the tube’s construction, printing style and box to confirm the decade.
How the two-letter code works (1930–1968)
Each month of production was given its own pair of lowercase letters. The alphabet used skips j, and occasionally includes ä, ö and ü. Early postwar tubes from Berlin use a capital A or B (aA = January 1946, aB = February 1946). The code marks the month of manufacture.
Before 1955 the assignments look essentially random, so the chart is the only way to decode them. From 1955 onward the system becomes regular: all three months of a quarter share the same first letter, and that first letter moves one step through the alphabet every quarter. The second letter normally rises through the quarter — 1955, for example, runs aq as at · ba bc bf · ca cc cd · db dc dh.
That gives you a shortcut. For a tube you know is from the mid-50s or later, the first letter alone pins down the quarter:
| Year | Jan–Mar | Apr–Jun | Jul–Sep | Oct–Dec |
|---|---|---|---|---|
| 1955 | a | b | c | d |
| 1956 | e | f | g | h |
| 1957 | i | k | l | m |
| 1958 | n | o | p | q |
| 1959 | r | s | t | u |
| 1960 | v | w | x | y |
| 1961 | z | a | b | c |
| 1962 | d | e | f | g |
| 1963 | h | i | k | l |
| 1964 | m | n | o | p |
| 1965 | q | r | s | t |
| 1966 | u | v | w | x |
| 1967 | y | z | a | b |
| 1968 | c | d | e | f |
The cycle wraps around after z, so the same first letter returns roughly every six years (for example, e = early 1956, spring 1962 or summer 1968). If two dates are possible, the tube’s construction usually settles it. This cycle also exposes errors in the original chart — see the data notes below.
Year-by-month chart
Read across a year to see every code used that year. Useful for checking a matched pair, or for confirming that a seller’s claimed date actually matches the code.
ab* corrected placement (see notes) ab? uncertain in the source — no code known
| Year | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1930 | cf | cp | cw | ou | oa | du? on? | de? | — | dg | er | ek | es |
| 1931 | dm | da | dn | ab | ai? | au? | te | tc | tn | uz | uh | — |
| 1932 | mi | mn | me | ae | ag | ak | rr | rs | re | ku | ko | kl? ug? |
| 1933 | lt | le | ln | ib | in | id | co | cs | ce | hd | he | hr |
| 1934 | en | ei | eö | xe | xa | xh | pn | — | pr | ot | or | oe |
| 1935 | ys | ye | yn | an? | al | aa? tl? | tr | ta | — | sp | se | sk |
| 1936 | cg | df | nd | am | ic | vh | dt? xb? | po? | rf | el | vz | — |
| 1937 | — | ke | ss | ik | sf | wi | ia | ri | wa | — | kg | wo |
| 1938 | gu | ok | su | dk | wb | mw | vs? | wf | ul? | hg | ru | st |
| 1939 | ar | fo | — | ip | kv | hi | nn | ob | dr | pa | lx | we |
| 1940 | si | iu | fh? vd? | mk | ii | pt | xr | tb | kf | cy | kz | yq |
| 1941 | oi | ct | om | cz | br | tq | uy | rk | fz | kk | mb | oo |
| 1942 | rz | fy | um | kr | yi | mz | fu | mf | xy | km | iz | zz |
| 1943 | iy | — | ük | äk | öz | äz | ui | uk | — | zu | ää | üü |
| 1944 | ka | na | la | fk | bk | ck | ad | gd | rd | fv | mv | uv |
| 1945 | ap | ep | rp | gt | — | — | — | — | — | — | — | — |
| 1946 | aA | aB | — | nr | cr | lr | hf | ff | xf? | bd | — | kd |
| 1947 | qz | qr | ql | mg | pg | tg | ah | dw | et | go | it | of |
| 1948 | ra | rw | rx | wk | wp | wt | so | sm | sl | un | ua | uo |
| 1949 | ac | af | ao | va | vr | vk | yt | ym | yd | cb | cl | ch |
| 1950 | kb | kh | ky | ga | gm | gr | hc | hk | hu | rg | rh | rn |
| 1951 | mc | mm | my | — | zw | sy | wh | wg | wm | gb | gz | gy |
| 1952 | vb | vm | vt | sa | sg | — | uf | ur | uw | be | bt | by |
| 1953 | fa | fm | fx | if | im | iv | td | tm | tw | eb | em | ez |
| 1954 | fc | fp | fw | kc | kp | kw | vc | vp | vw | xc | xp | xw |
| 1955 | aq | as | at | ba | bc | bf | ca | cc | cd | db | dc | dh |
| 1956 | ea | ec | ed | fb | fd | fe | gc | ge | gf | ha | hb | hh |
| 1957 | ie | ig | ih | ki | kn | kq | lb | lc | ld | ma | md | mh |
| 1958 | nb | nc | ne* | oc | dp? od | og | pb | pc | pd* | qa | qb | qc |
| 1959 | rb | rc | rl | sb | sc | sd | tf | th | ti | ub | uc | ud |
| 1960 | ve | vf | vg | wc | wd | wl | xd | xg? | xi | ya | yb | yc |
| 1961 | zb | zc | ze | av | aw | ax | bg | bh | bi | ci | cm | cn |
| 1962 | dd | di | dl | ee* | ef | eg | fg | fi | fl | gg | gh? | gi |
| 1963 | hl* | hm | hn? | il | io* | iq | ks | kt | — | lf | lg | lh |
| 1964 | ml | mo | mp | nf | ng? | nh* | oh | ol | op | pe | pf | ph |
| 1965 | qd | qe | qf | rm | ro | rq | sh | sn | — | tk | to | tp |
| 1966 | ue | up | uq | vi | vl | vn | wn | wq | wr | xk | xl | xm |
| 1967 | yf | yg | yh | zf | zm | zn | ay | az | äa | bb | bl | bm |
| 1968 | cq | cu | cv | do | dq | — | — | eo? | eq* | fn | fq | fr |
No codes are recorded for May to December 1945, the months right after the end of the war in Europe.
Complete code list, A–Z
All 452 entries from the original chart in alphabetical order. Umlaut codes are filed under their base letter. Struck-through dates are readings the letter cycle shows to be wrong; the corrected date follows the arrow.
A
aaJun 1935?aAJan 1946abApr 1931aBFeb 1946acJan 1949adJul 1944aeApr 1932afFeb 1949agMay 1932ahJul 1947aiMay 1931?akJun 1932alMay 1935amApr 1936anApr 1935?aoMar 1949apJan 1945aqJan 1955arJan 1939asFeb 1955atMar 1955auJun 1931?avApr 1961awMay 1961axJun 1961ayJul 1967azAug 1967äaSep 1967ääNov 1943äkApr 1943äzJun 1943
B
baApr 1955bbOct 1967bcMay 1955bdOct 1946beOct 1952bfJun 1955bgJul 1961bhAug 1961biSep 1961bkMay 1944blNov 1967bmDec 1967brMay 1941btNov 1952byDec 1952
C
caJul 1955cbOct 1949ccAug 1955cdSep 1955ceSep 1933cfJan 1930cgJan 1936chDec 1949ciOct 1961ckJun 1944clNov 1949cmNov 1961cnDec 1961coJul 1933cpFeb 1930cqJan 1968crMay 1946csAug 1933ctFeb 1941cuFeb 1968cvMar 1968cwMar 1930cyOct 1940czApr 1941
D
daFeb 1931dbOct 1955dcNov 1955ddJan 1962deJul 1930?dfFeb 1936dgSep 1930dhDec 1955diFeb 1962dkApr 1938dlMar 1962dmJan 1931dnMar 1931doApr 1968dpMay 1958?dqMay 1968drSep 1939dtJul 1936?duJun 1930?dwAug 1947
E
eaJan 1956ebOct 1953ecFeb 1956edMar 1956eeApr 1961eeApr 1962efMay 1962egJun 1962ehAug 1958eiFeb 1934ekNov 1930elOct 1936emNov 1953enJan 1934eoAug 1968?eöMar 1934epFeb 1945eqSep 1958→ Sep 1968*erOct 1930esDec 1930etSep 1947ezDec 1953
F
faJan 1953fbApr 1956fcJan 1954fdMay 1956feJun 1956ffAug 1946fgJul 1962fhMar 1940?fiAug 1962fkApr 1944flSep 1962fmFeb 1953fnOct 1968foFeb 1939fpFeb 1954fqNov 1968frDec 1968fuJul 1942fvOct 1944fwMar 1954fxMar 1953fyFeb 1942fzSep 1941
G
gaApr 1950gbOct 1951gcJul 1956gdAug 1944geAug 1956gfSep 1956ggOct 1962ghNov 1962?giDec 1962gmMay 1950goOct 1947grJun 1950gtApr 1945guJan 1938gyDec 1951gzNov 1951
H
haOct 1956hbNov 1956hcJul 1950hdOct 1933heNov 1933hfJul 1946hgOct 1938hhDec 1956hiJun 1939hkAug 1950hlMar 1963→ Jan 1963*hmFeb 1963hnMar 1963?hrDec 1933huSep 1950
I
iaJul 1937ibApr 1933icMay 1936idJun 1933ieJan 1957ifApr 1953igFeb 1957ihMar 1957iiMay 1940ikApr 1937ilApr 1963imMay 1953inMay 1933ioMay 1961ioMay 1963ipApr 1939iqJun 1963itNov 1947iuFeb 1940ivJun 1953iyJan 1943izNov 1942
K
kaJan 1944kbJan 1950kcApr 1954kdDec 1946keFeb 1937kfSep 1940kgNov 1937khFeb 1950kiApr 1957kkOct 1941klDec 1932?kmOct 1942knMay 1957koNov 1932kpMay 1954kqJun 1957krApr 1942ksJul 1963ktAug 1963kuOct 1932kvMay 1939kwJun 1954kxSep 1968kyMar 1950kzNov 1940
L
laMar 1944lbJul 1957lcAug 1957ldSep 1957leFeb 1933lfOct 1963lgNov 1963lhDec 1963lnMar 1933lrJun 1946ltJan 1933lxNov 1939
M
maOct 1957mbNov 1941mcJan 1951mdNov 1957meMar 1932mfAug 1942mgApr 1947mhDec 1957miJan 1932mkApr 1940mlJan 1964mmFeb 1951mnFeb 1932moFeb 1964mpMar 1964mvNov 1944mwJun 1938myMar 1951mzJun 1942
N
naFeb 1944nbJan 1958ncFeb 1958ndMar 1936neMar 1956→ Mar 1958*nfApr 1964ngMay 1964?nhMay 1964→ Jun 1964*nnJul 1939nrApr 1946
O
oaMay 1930obAug 1939ocApr 1958odMay 1958oeDec 1934ofDec 1947ogJun 1958ohJul 1964oiJan 1941okFeb 1938olAug 1964omMar 1941onJun 1930?ooDec 1941opSep 1964orNov 1934otOct 1934ouApr 1930özMay 1943
P
paOct 1939pbJul 1958pcAug 1958pdSep 1953→ Sep 1958*peOct 1964pfNov 1964pgMay 1947phDec 1964pnJul 1934poAug 1936?prSep 1934ptJun 1940
Q
qaOct 1958qbNov 1958qcDec 1958qdJan 1965qeFeb 1965qfMar 1965qlMar 1947qrFeb 1947qzJan 1947
R
raJan 1948rbJan 1959rcFeb 1959rdSep 1944reSep 1932rfSep 1936rgOct 1950rhNov 1950riAug 1937rkAug 1941rlMar 1959rmApr 1965rnDec 1950roMay 1965rpMar 1945rqJun 1965rrJul 1932rsAug 1932ruNov 1938rwFeb 1948rxMar 1948rzJan 1942
S
saApr 1952sbApr 1959scMay 1959sdJun 1959seNov 1935sfMay 1937sgMay 1952shJul 1965siJan 1940skDec 1935slSep 1948smAug 1948snAug 1965soJul 1948spOct 1935ssMar 1937stDec 1938suMar 1938syJun 1951
T
taAug 1935tbAug 1940tcAug 1931tdJul 1953teJul 1931tfJul 1959tgJun 1947thAug 1959tiSep 1959tkOct 1965tlJun 1935?tmAug 1953tnSep 1931toNov 1965tpDec 1965tqJun 1941trJul 1935twSep 1953
U
uaNov 1948ubOct 1959ucNov 1959udDec 1959ueJan 1966ufJul 1952ugDec 1932?uhNov 1931uiJul 1943ukAug 1943ulSep 1938?umMar 1942unOct 1948uoDec 1948upFeb 1966uqMar 1966urAug 1952uvDec 1944uwSep 1952uyJul 1941uzOct 1931ükMar 1943üüDec 1943
V
vaApr 1949vbJan 1952vcJul 1954vdMar 1940?veJan 1960vfFeb 1960vgMar 1960vhJun 1936viApr 1966vkJun 1949vlMay 1966vmFeb 1952vnJun 1966vpAug 1954vrMay 1949vsJul 1938?vtMar 1952vwSep 1954vzNov 1936
W
waSep 1937wbMay 1938wcApr 1960wdMay 1960weDec 1939wfAug 1938wgAug 1951whJul 1951wiJun 1937wkApr 1948wlJun 1960wmSep 1951wnJul 1966woDec 1937wpMay 1948wqAug 1966wrSep 1966wtJun 1948
X
xaMay 1934xbJul 1936?xcOct 1954xdJul 1960xeApr 1934xfSep 1946?xgAug 1960?xhJun 1934xiSep 1960xkOct 1966xlNov 1966xmDec 1966xpNov 1954xrJul 1940xwDec 1954xySep 1942
Y
yaOct 1960ybNov 1960ycDec 1960ydSep 1949yeFeb 1935yfJan 1967ygFeb 1967yhMar 1967yiMay 1942ymAug 1949ynMar 1935yqDec 1940ysJan 1935ytJul 1949
Z
zbJan 1961zcFeb 1961zeMar 1961zfApr 1967zmMay 1967znJun 1967zuOct 1943zwMay 1951zzDec 1942
Data notes and corrections
The source chart was transcribed from a smudged German original, and a few entries were unreadable or misread. Checking the post-1955 codes against the quarterly letter cycle resolves most of them — every code from 1955–1968 fits the cycle except the ones listed here, and in most cases the correct date also fills a month that was otherwise blank.
pd(listed Sep 1953?): Clashes with tw (Sept 1953). Fits September 1958 exactly (pb, pc, pd); the 3 and 8 were likely confused on the smudged original.ne(listed Mar 1956): Clashes with ed (March 1956), and “n” codes of this era belong to 1958 or 1964. Almost certainly March 1958 (nb, nc, ne), a month otherwise missing.dp(listed May 1958?): Clashes with od (May 1958). Possibly May 1968 instead (do, dp, dq run in order) — but the chart also gives dq as May 1968, so treat both with caution.eh(listed Aug 1958?): Clashes with pc (Aug 1958) and does not fit the letter cycle for 1958. Unresolved.eq(listed Sep 1958): Does not fit the 1958 “p” quarter. Most likely September 1968 (eo, eq), with the decade digit misread.ee(listed Apr 1961): Listed twice. April 1961 is already av, and the 1955–68 letter cycle puts every “e” code of that era in 1956, 1962 or 1968. Use April 1962.io(listed May 1961?): Listed twice. May 1961 is already aw. May 1963 (il, io, iq) is the reading that fits.hl(listed Mar 1963): Clashes with hn. The run hl, hm, hn reads naturally as Jan, Feb, Mar 1963, and January 1963 is otherwise missing.nh(listed May 1964): Shares May 1964 with ng. The run nf, ng, nh points to June 1964, a month otherwise missing.eo(listed Aug 1968?): Marked uncertain in the chart, but it fits the letter cycle for 1968.kx(listed Sep 1968?): Does not fit the 1968 “e” quarter (eo, eq). Unresolved.
Unresolved pre-1955 clashes. These months have two codes listed and, since the early codes follow no pattern, there is no way to tell which is right: Jun 1930 (du / on), Dec 1932 (kl / ug), Jun 1935 (aa / tl), Jul 1936 (dt / xb), Mar 1940 (fh / vd).
Months with no known code: Aug 1930, Dec 1931, Aug 1934, Sep 1935, Dec 1936, Jan 1937, Oct 1937, Mar 1939, Feb 1943, Sep 1943, Mar 1946, Nov 1946, Apr 1951, Jun 1952, Sep 1963, Sep 1965, Jun 1968, Jul 1968, plus May–December 1945.
Sources
The two-letter chart comes from a German factory listing obtained by a European collector, published by Eric Barbour in The Tube Collector (Vol. 2, No. 4) and later posted online by Brent Jessee Recording & Supply (audiotubes.com), who also documented the numeric code. Reorganization, the 1955–1968 letter-cycle analysis and the corrections above are by Tube Maze. Treat any single date as a strong guide rather than an absolute guarantee.