Interstage Transformer

LL1635 is an interstage transformer for tube (valve) amplifiers available in Push-pull or Single-end versions.

The transformer is highly sectioned, and wound with a special low capacitance winding technique which results in very good frequency response. The transformer has a special high flux, low distortion audio C-core of our own production.

Weight Turns ratio Static resistance, each primary Static resistance, each secondary
0.5 Kg 1+1 : 1+1 500 Ω 500 Ω


Type LL1635/PP LL1635/5mA LL1635/20mA
Primary DC current, primaries in  series ( for B0 = 0.9T)   5 mA 20 mA
Maximum DC current before saturation, primaries in  series   9 mA 35 mA
Primary inductance (primaries in series) > 300H 130H 30H
Frequency response, primaries in series
(Source 4 kΩ  for PP and 5mA, 2 kΩ for 20 mA.  Load 68 pF)
5 Hz - 60 kHz
+/- 1 dB
10 Hz - 60 kHz
+/- 1 dB
20 Hz - 75 kHz
+/- 1 dB
Group delay @ 20 kHz (Source and load as above) 0.5µs 0.5µs 0.5µs
Max. output voltage @ 30 Hz 2x220 V peak
(tot. 310Vrms)
2x90 V peak
(tot. 125Vrms)
2x90 V peak
(tot. 125Vrms)
Recommended max DC current through any primary section 40mA 40mA 40mA
Isolation between primary and secondary windings /
between windings and core
4 kV / 2 kV 4 kV / 2 kV 4 kV / 2 kV


Associated downloads

LL1635 Leaflet