Back to home page
Back to audio electronics page
Back to the VT52 page

VT 52 Single-Ended SRPP


This amp uses a SRPP as input stage and a VT52 heater voltage of 5V (Hytron are normally 6.3V and Western Electric 7V). It is advised to adapt the heater voltage to the tubes used.
I converted this amp to a low power 300B amp and will rebuild it as a treble amp avoiding completely electrolytic caps in the supply.

Back to Top

Power Supply

Back to Top

ECC81 Version

You can replace the ECC83 by an ECC81, the gain and output impedance of the SRPP stage is lower.

Back to Top

Printed Circuit & components Insertion

This printed circuit groups the supply for the driver heaters and discharging circuit.

vt52_ci.gif (16634 octets)

Back to Top

Construction & Tests

The amp during the tests:

From left to right: the generator, oscilloscope, calculator, multimeter, amp with, in the back, the 8.2Ohms/50W resistors mounted on large radiators, some ECC83 tubes, a 2KV probe and a pair of probe clips.

The base is a multiply board which has been treated with a lead foil and a layer of asphalt to reduce the board resonances. The lead foil is grounded to serve also as an electromagnetic screen.
To reduce microphony, the tubes sockets are mounted on silicone joints. These are molded using carton tubes from ... Tampax tampons, then cutted in slices and drilled.
I've used Hytron VT52 tubes (US Army production dated september and november 1943 !) and Sovtek 12AX7WXT+ for the prototype and keep a pair of Western Electric as spares.

Full-power square waves, measured at the output with a 8.2 Ohms resistor as load:




10KHz, the small ringing is due to the Tango U808 100KHz resonance


40KHz, the square wave is progressively rounded to a sine wave.
Roll-off starts around 45KHz.

And some square waves at the SRPP output and VT52 plate:

100Hz, SRPP output

100Hz, VT52 plate

20KHz, SRPP output

20KHz, VT52 plate. Ringing due to the OPT at 100KHz
Back to Top