“Shiny Eyes” SE 45

This is a gem and I could confidently say: a reference amplifier. I’ve built it to compare with my PSE 4P1L and the results are amazing. If one has the appropriate speakers for SE tube amps and low power ( the 1st watt is all that matters), than this amp is a must to experience. I’ve spent many hours to experiment with different driver tubes. My goal was to make a 2 stage amplifier where the driver has minimum distortions with a dominant 2nd harmonic. This way the amplifier as a whole will get a predominant 2nd harmonic and will reveal the gorgeous sound of the 45. I also desired to make it less complex in comparison with my PSE 4P1L.

main-side-front

The result of this brainstorming was an amp with lower input sensitivity. I used type 76 triode to drive the 45. The 45 has a Miller capacitance of about 40 pF ( including some stray) and it is easy to drive in class A by using a low  current driver such as the 76 at 5 mA, without introducing slewing distortions.

The power supply was built in a separate enclosure for a hum free DHT amp. It uses all Hammond transformers and chokes. Hammond 272Hx is used to provide the high voltage using a 5V4G rectifier and a CLCLC filter with 4.7uF-8H-47uF-8H(Hammond 193D)-47uf. The last capacitor is Clarity TC600, 4 pin Kelvin terminations for decoupling high frequency power supply noise from the signal path. A gorgeous Simpson 600V panel meter is showing the high voltage. The same transformer is used to provide 6.3DC to the 76 filaments, using a DC power supply based on LT1085 regulator. There are 2 Hammond  167Q6 used to provide raw DC supply to the Coleman filament regulators for the 45s. The high voltage comes delayed 25-30 seconds to allow the 45 filament to reach a quasi-steady state and extend their life. The delay timer is based on the 555 IC. The power supply has a 12 pin connector where the umbilical cord is plugged in. The umbilical cord is permanently attached to the main amp case and carries only DC. Here are some pictures of the power supply:

psu-inside

 

The main amplifier case is built out of American cherry solid hardwood stained with light oil urethane, 4 coats. The top plate is gold anodized aluminum made by Front Panel Express. The main amplifier is provided with Neutrik RCAs and Cardas binding posts. A nice Shurite 3V panel meter can be switched to measure each of the 45 filament and allow precise adjustment to 2.5V. There are separate 10 turns 2W pots top panel accessible for this adjustment. The output transformers are James 6115HS. I’ve provided a switch to choose between 5K and 7K load. On the 7K load the sound is more pleasant as the distortions are reduced. Here is the schematics and some pictures:

schematics-45-76-js6115hs

topmain-frontside-bothmain-backback-1fpe-topmain-inside

 

I’ve always measured my amps and in majority of cases the measurements tell the truth about the sound of the device. In this case, as you can see from the distribution of the harmonics, there is a 2nd harmonic dominant SE amp that sound better than it measures. ( as always with early DHTs ).

Input sensitivity:

1 Vrms for 0.25W output, 2.2 Vrms for 1W output,  3 Vrms for 1.75W output max

Frequency response: 20Hz-30kHz @ -1dB

THD  5K load : 1.66% @ 0.5W, 2.5% @ 1W, 3.47% @ 1.5W and 4.9% @ 1.75W

THD  7K load: 1.24% @ 0.5W, 1.77% @ 1W, 2.8% @ 1.5W and 4.08% @ 1.75W

thd-5-and-7k-load-45-amp

fft-1w-7kfft-1w-5kthd-and-harmonics-45-ampfr-at-0-25w

I’ve needed a bit of gain to drive this amp to max power. I found that my 18dB 01A preamp is a great fit. I’ve also tried 26 pre and 10Y pre and they all sound excellent combined with this SE 45.

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7 thoughts on ““Shiny Eyes” SE 45

  1. Nice build Radu, well done!
    I think the driver is suboptimal. The 76 can’t swing linearly enough to drive the 45 and you get fat too much distortion above 1.5W. There are far better drivers, if you chose IHT like C3g, D3a, 6e5P, 6j49p-dr, 6j52p, 6n6p-de and others that will halve distortion.
    Cheers ale

  2. Hi Ale,
    Thank you.
    I’ve tried in the past the 6n6, and the 6j52 and didn’t like the sound…just a matter of personal preference. I’ve used the C3g driving a 300B with very nice sonic results. But you are right, if one wants to drive the 45 to full power with lowering distortions then a more powerful driver is required. However, I like to listen at low levels and I’m more interested in the details of the sound and this setup works for me…
    Cheers,
    Radu

    • Hi Joe,
      Thank you.
      It looks like the 6P5 is similar to 76 and can be used too. The only thing might be different is the distribution of harmonics which may lead to a slightly different sounding. From an engineering point of view it is equivalent.
      Best,
      Radu

  3. Hello Radu,

    The SE 45 amplifier looks great! Thank you for posting such detailed photographs. I see that you are using the Rod Coleman regulators with pre-drilled heat sinks that attach to the top panel with sheet metal screws. Are those pre-drilled heatsinks standard Aavid Thermalloy part numbers?

    Thank you very much.

    Best regards,

    Paul

    • Hi Paul,
      Thank you.
      The heatsinks for Coleman regulators are from heatsinkusa.com. They are 3.5 wide and 3″ tall. I’ve drilled and taped the holes. All 3mm for attaching the Coleman to the heatsink and 4mm for attaching the heatsink to the top plate.
      These heatsinks have a C/W/3″=2.5. The Coleman dissipates on Q4 and Q5 about 6W. That means a 15C temperature raise of the heatsink. So for 30C ambient the heatsink will be at 45C ( maybe slightly higher because the heatsink is in a confined space) which is very good.

      Best regards,
      Radu

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