Tag: Gyrator Rev08

VT-25/801a/10Y DHT Preamp with SiC filament bias

For quite some time now I wanted to share one of the variations of the famous VT-25/10Y pre-amplifier. As usual due to work, business travel and family duties, I’ve struggled to find the time to update the blog.

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D3a driver w/ Rev08 board

A friend from Canada ordered a pair of boards and I used the opportunity to test the newly arrived hybrid mu-follower (aka as gyrator) Rev08 PCBs.  He will be using these boards in the 300B design posted here.

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Hybrid Mu-follower (aka Gyrator) Rev08 PCB Update

It’s been far too long since I last posted on this blog. With the limited spare time I’ve got these days, I concentrated in setting up the new workshop and system since we moved back to our place. I’m nearly there, so now it’s time to get back to work

I made some updates to the “gyrator” PCB. I’ll stop referencing it gyrator from now on, since the name is misleading. However, it got popular that way. Nevertheless, it’s a hybrid mu-follower circuit but if only if you take the output from the anode, it behaves like a “gyrator” from a frequency response perspective. If you’re interested in this circuit in more detail, please read the lecture I gave last year at ETF.18. You can download it from here.

Back to the board, here are the few changes made:

  1. Moved the trimpot P1 for easier fixing of the board with the M3 standoffs.
  2. Added a gate stopper resistor (R9) to avoid oscillation at low anode current (<10mA) when using high-gm MOSFETs in the lower position J4. This was evident with devices like BSH111BNK
  3. Added an LED (D4) indicator and a series resistor (R8) at the drain of M3. This enables indication of:
    1. Normal operation subject to  value of R8
    2. Source current into load (e.g. like in A2 operation) subject to value of R8.
    3. Short output to ground. Depending on duration and current limitation of power supply, this may prevent damaging M3 MOSFET. Not guaranteed, but in some scenarios will work.

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