• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Audio Preamplifier with PCC88

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#5
New tube/valve preamplifier-shematic

Hi all!
I came across this pattern for a tube/valve preamplifier and therefore is asking for comments. Is good for making tube preamplifier percent for this schematic for the power supply is quite low Ucc = + /-40V.
What changes should I do on the instead of the tube 6922 schematic to put PCC88.
thank you
 

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#8
I use PCC88's in SRPP configuration (1.5k cathode resistors, no bypass capacitor at the lower cathode). The gain is 16x (24dB), excelent linearity and sound. I have heard that the ECC88 is produced from a batch of "raw" PCC88's by degenerating one side by forced heating until the transconductance of both halves becomes the same. The heater is identical.
 
#9
oshifis said:
I use PCC88's in SRPP configuration (1.5k cathode resistors, no bypass capacitor at the lower cathode). The gain is 16x (24dB), excelent linearity and sound. I have heard that the ECC88 is produced from a batch of "raw" PCC88's by degenerating one side by forced heating until the transconductance of both halves becomes the same. The heater is identical.
Click to expand...

Is be the schematic ?😕
thank you
 
#10
I am sorry, but I have not drawn a full schematic. The circuit diagram I can explain in one or two sentences, but what is not reproducible is the mechanical construction. The SRPP is very sensitive to good power supply, and I consider it part of the mechanical construction. So let me try to describe it.
My construction is dual mono in a single box. The mains transformer has 220V secondaries, separate for both channels. An C-R-C-R-C-R-C filter follows, where R is 4.7k and C is 1000uF/450V photo flash capacitors. I use 100k bleeding resistors parallel to each C.
The raw heating voltage is 12V AC, stabilized with LM317T for each tube separately. Heating is always on, the B+ is switched at the transformer secondaries, before the rectifiers.
The gain stages themselves are identical: the well-known SRPP stage, with 1.5k in each cathode, and 100R directly connected to the grids for preventing HF oscillation. The grid leak resistors are 100k, the coupling capacitors are Russian PIO K72-U9 1uF/250V. There are some 0.22uF/400V PIO bypass capacitors at each tube B+. I don't use any bypass capacitor parallel to the cathode resistor of the lower triode.
One stage is the line preamplifier, and another three stages are for RIAA phono. The equalization circuit is split between the stages. The rest is input selector (relays), volume control, and other mechanical stuff. Star grounding is essential.
I hope you can draw your own circuit diagram based on this information.
 
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