Search results for query: *

Hi Jon. I believe you are correct about Dave only selling the boards. At the time of my project, someone happened to be selling (via eBay) a set of boards they had assembled but no longer needed due to a change in plans. I have been happy with these boards and recommend them. If I had not come...

Since my last post, I have trialed various permutations of the first two stages - load lines, operating points, power supply dropping resistor values, bleeder resistor presence/values, and grid resistor presence/values. I learned that I could stagger the operating points of the first two stages...

Thank you John! It was a very positive experience for me as well. I highly recommend @Bananaslug.

This J2 has been sold and is now on its way to a new owner. Enjoy your new J2, @Bananaslug! Thanks for the smooth transaction. And thanks to the forum for hosting my ad post!

Hi John. It is still available. I will send you a message in a few moments.

This looks like a really nice unmolested SCA-35. And factory wired! Seems like a great deal to me. If I didn't already have one, I would probably be trying to convince you to ship it to me over here in TX. :)

I have travelled a little farther down the path since my last post... The load line and operating point in my last two posts reduced headroom in the phase splitter stage. When I trialled it, I saw that there was significant peak distortion at the phase splitter outputs (only on one side of the...

Decided to trial that most recent operating point. I didn’t have 100 kOhm resistors on hand with sufficient power rating, so I used two 47 kOhm in series. Other than that, it is per my prior post. Bleeder resistors removed for this trial. Quick initial observations: Gain is down as anticipated...

I tried some further load line permutations, and I was only able to slightly improve on my prior examples (higher V+ combined with that same moderate reduction in the anode resistor). But I think the results were still essentially as you said - right on the edge of being able to get away with...

The bleeder resistor is the 330 kOhm that connects between the input stage V+ and the EF86 cathode. The EF86 cathode bias is 1.614 Volts on the left channel and very similar on the right (away from computer at the moment). Thank you for your insight. Thinking about that.

Here are some images that will hopefully more clearly illustrate what I was trying to convey earlier regarding the driver boards... This is the Dyna schematic from my previous post, revised to reflect the SDS Labs EF86 board. Same design, just different tubes. This schematic includes further...

Thanks for your help, @Nerdorama! Yes, I am currently seeing asymmetrical clipping. The positive portion of the waveform is getting clipped. I drove it a bit beyond that level and did not see any clipping on the negative portion of the waveform. I have only looked at the clipping at the amp's...

Thank you, @paul_b! That does sound a lot simpler than I anticipated. I’ll probably go ahead and take an initial look soon then, maybe this evening.

For anyone curious about the objective performance with the changes up to this point, here are a few graphs and measurements... This is the frequency response with an 8 Ohm resistive load on the 8 Ohm tap. This is at about 8 Watts, but the results were pretty similar at a few other power...

I believe I have gained some insight into why the amp noise floor increases by ~3 dB in my system. It seems to be the result of noise induced in the audio interconnects... The analog portion of my main system is simple: DAC->Passive Preamp->Amp. Everything but a couple of my amps support both...

Some further information about the driver board: In summary, this amp has a driver board whose design and component values are consistent with the Triode Electronics ST-70 EF86 driver board design (using a board by SDS Labs). More details... The board is an SDS Labs board (name etched in the...

This particular board already uses a reduced value of 220 kOhm for that plate resistor. I had looked at the curves and it seemed like the original values would provide an operating point that was at last decent, so I figured I would start with those and go from there. It also seemed there might...

Update: I noted a few posts ago that I found the noise floor of my ST-70 to be subjectively objectionable while it was operating in open loop with the output stage triode strapped. I have since revisited that configuration to explore that in a little further depth. On the bench, with the...

Hmmm. I wonder how much of the noise and hum I heard in that open loop listening session was contributed by the amp versus other system components and their interconnections. Shortly after I originally got this amp together (in the original UL config), I measured that at about 92 dB (below...

I am indeed using a 5AR4 rectifier. So it sounds like there is no real need or benefit with an additional thermistor in that scenario. I was erring on the side of a little extra caution due to the cap board upgrade and me still being early in the learning curve with vacuum tubes. If it isn't...