Hashimoto OPT

[Selmerdave]

Those are real numbers from Diligent Discover. It’s all I have. Here’s the Square wave.

That looks remarkably similar to a sine wave though...

 

[TriodeLuvr]

I just think this can't be right, especially if this is an amp with no GNFB. I would expect 4W distortion characteristics to be markedly worse at 30Hz unless the OPTs are massive. Also, have you by chance swapped tubes channel-to-channel to help determine why the two channels are so different?



Jack

 

[TriodeLuvr]

I'm not familiar with that program. Does it use your sound card, or is there other hardware? I've been using ARTA for a number of years. It's not as automated as some apps and doesn't perform swept distortion, but it does seem to be very accurate. I have also built a few accessory items, including an adapter to allow measuring distortion and response directly at the anodes of drivers.

I'm using Sophia Electric 274b, Gold Lion 300b and NOS (1945 era) RCA 6su7gty/VT-231. Do you think this could be the reason for the better than expected results?

No, the typical increase in low frequency distortion seen in single ended amplifiers is primarily a function of the output transformer.

Jack

 

[StepheK]

Tested at 4w.

Oh, now I see what threw me off, you have the resolution scale set differently. On mine I have the top set at 10% and the bottom at 0.1%. when you have it at 100% and 0.01% it makes the line look much flatter. And the R300 has GNFB, with it disabled the distortion is MUCH higher as you suspected.

 

[THD+N]

Ok, i will reset that and retest. I'm not a tube tech, but i can follow directions and not much i can't do. I will switch the tubes around and see what that does also. My Hashimoto's have not shipped yet, so its gonna be a minute for that swap and test. That's gonna be a head scratcher figuring what wire goes where on those OPT's.

It's easier than it looks. We'll get you going.

 

[StepheK]

Ok, i will reset that and retest. I'm not a tube tech, but i can follow directions and not much i can't do. I will switch the tubes around and see what that does also. My Hashimoto's have not shipped yet, so its gonna be a minute for that swap and test. That's gonna be a head scratcher figuring what wire goes where on those OPT's.

I'm actually going to be installing a pair of these on a R300 soon!

 

[THD+N]

Doesn't look too bad, but the distortion curve looks very flat which is unusual. If it is indeed that flat, then that is a good thing.

 

[TriodeLuvr]

And the R300 has GNFB, with it disabled the distortion is MUCH higher as you suspected.

I'm curious whether you measured the feedback (dB) while you were working on your unit.

Switching tubes from left to right made no difference.

So something is significantly different between the two channels, other than the tubes. That shouldn't be the case. Incidentally, those square waves are pretty nasty for 1kHz. Am I seeing correctly that you're measuring at 10V RMS output? If so, that's way too high. Maybe they'll clean at 1V pk-pk.

Jack