• 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.

45 Vs. VT-52: How Do They Sound??

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I am currently using a 45 tube (ST style) to drive my SE 300B output stage.

The amplifier topology is 2-stage: an input transformer provides around 24 dB of voltage gain, and drives the grid of the 45. The 45 is transformer coupled to the grid of the 300B. The input to my amplifiers are driven by a transformer volume control (TVC). Both the 45 and 300B are DC heated with constant current regulators. Loudspeakers are the Altec A-5, with the Hiraga crossover and the 1505 multicellular horns.

This system sounds wonderful (to me at least), but I am always looking for possible improvement in the sonics. I do have a number of WE and National Union VT-52s here, and I am wondering how they compare sonically with the 45.

The VT-52 is essentially a drop-in replacement for the 45, except for the filament voltage, which from what I understand is around 6.3 V. It is not easy for me to provide the 6.3 volts required to heat this tube from my existing amplifier circuitry; hence my question to the group as to how the VT-52 compares sonically to the 45, before I begin any modifications to my equipment to find out myself.

Thanks for any input!
Bruce
 
Last edited:
Hello Bruce,

I can't say anything about the relative sound of the two DHTs, but maybe I can help with the voltage arrangements...

The dc voltages required for 45 (2.5V) and VT-52 (6.3 or 7.0V dc ?) can be generated (including the overhead for Coleman filament regulators) with a 6.3V rms trafo, so long as it can deliver 4A rms - so ideally, rated for 6-8A rms.

For the 45, use a normal bridge-rectified dc, as shown in the manual.
For VT-52, change the rectifier arrangement to a voltage doubler.

The doubler parts are (per channel):

trafo: 6.3V 6A rms
rectifier: 2x MBR1045
capacitors: 22000µF 16V snap-in type, Panasonic, Nichicon, EPCOS (reliable makers, IOW)

PSUD2 file attached. Change filename to .PSU, from .txt,
search Duncan PSUD2 if you don't have the application.
 

Attachments

  • DOUBLER-6V3-6A-12V5dc.txt
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Status
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