Antique Sound Labs Tulip Stereo Power Amplifiers
I use a pair of tulip's in a vertical bi-amp configuration for my video system. I decided to purchase a good pair of amplifiers for my video system as I own a lot of music-video's and got tired of listening to them using my old AudioSource Power amplifier (the best value for money amplifier there is?). I bought them through audiogon and have not regretted my decision to buy them without first listening to them. I use a pair of Heybrook HB4 speakers, that at 90db efficiency and 6ohm impedence are not too difficult a load for these flea powered amps to drive. In fact, these amps drive them to sufficient sound levels in my small bedroom, where my video system is set up.
My primary purpose in buying these speakers were to experience first hand the sound of a 2A3 amplifier. They are certainly not as warm sounding as my Cary 805B monoblocks, but have a more dynamic and lively sound. Although my main speaker placement have a lot to do with their lack of bass, these amplifiers seem to produce deeper, tighter bass than the bigger 805's. I am also amazed at the effective power of these 3 Watt amps. I certainly did not expect them to drive my speakers with so much ease. Imaging and soundstaging are very good, although not in the same class as my 805's.
I have since promoted these to be my main amplifiers. This corresponds to my move to a pair of Zu Druid Mk.VI's as my main speakers. I run them bridged to mono, and have experienced no clipping driving the Druid's in my moderate sized room. I am also driving them with the cleaner sounding 45 tubes, rather than the stock 2A3. I play a wide variety of genres, that span the gamut from delicate small ensembles to large scale orchestral and film soundtracks. I upgraded from the Zu Soul to the Druid, and had some initial concerns about the speakers being too much for these amps, but after I got the Druid's all such concerns vanished.
Tube Rolling
These amps can be driven with 2A3’s, 300B’s with 2.5 volt filaments, and 45’s. Bias for 300B’s or 2A3 = 600mV. Bias for 45’s = 350mV.
I used the following strategy when switching from the standard 2A3 to the 45 tubes, which operate at much lower bias setting. I start with the 2A3 tubes, and adjust the bias all the way down to around 50mv. I then switch the amp off, and swap the 2A3's with the 45's. I switch the amp back on, and then gradually adjust the bias up to the 350mV level. Switching back is less of a concern, but I still follow the general policy of adjusting the bias down, swapping the tubes, and adjusting the bias back up to the desired level.