My experience building a DRD d3A/300B amp

[2wo]

Hi all ,

I have built the DRD style amps, currently as 45s.

You can find bits of it over at "Audio round table, group build"

I used Lundel and James outputs, Jacks DRD chokes and the Lady Day style power transformer from DIY HI FI. If I am not mistaken , Thorsten had a big hand in it’s design.

This is a very flexible transformer. Between it’s multiple HV taps, buck boost taps, full or half wave and cap or choke input filters. There is a very wide range of voltages to play with.
Not to mention the clever filament secondary arrangement. Worth a look.

I first breadboarded these as a 45 amp with plans to run 2a3 and 300b as a series of post to ART.

I first set one up with a 6an4 driver , parts bin "fast rectifiers" and some honking big adjustable cathode resistors that could accommodate all 3 tubes. Dialed up the various voltages and had a listen . good. Build another .

Now one of the stated objectives of this project was to try some alternatives to AC heating But with this lash up. There is almost no hum. With my 96db/w speakers, I think what I hear is the diode switching noise. It has to be a very quiet night in N-town before this level of noise is heard.

I have been very busy at work and have not had a lot of time to play. I did toss a pair of 300’s in as a quick and dirty experiment but my heart was not in it. I did not have the time to do it properly and the 45’s were working well for me. I will get back to it as time permits.

In the mean time this is a very worthily configuration to consider…John