6.66V and 6.65V See a couple of posts up. They're high-ish, but within tolerances.
Then you could add a few zener in series with the 5AR4. 20V @150mA will give 3w as heating, you better locate
the zeners well ventilated or maybe even a heatzink.
Perhaps you need to re-think your expectations of a valve amp imho. Your mains voltage could change by that 2-3% level - certainly the case for many others with valve amps, both now and over the last 7 decades. Perhaps you are being persuaded by audiophoolery comments on the 'optimum' voltage for this or that.
Have you installed any inrush limters in the primary AC? I find that the residual resistance can make the difference in the filament voltages and a proportionate reduction in B+. I don't care as much about the B+ being high a bit, but I like to see the filaments about nominal. Just makes me feel better as running the heaters on the high side, even though in spec, surely must reduce the life of the heater.
Maybe you're right and I'm overthinking it.
I was trying to get them a bit closer together, but I can see that there's not an easy way to do it.
There is an issue of one having slightly higher gain than the other due to the elevated plate voltages on one compared to the other, but that's not an insurmountable problem to overcome.
Right now I've got them both playing music and it sounds pretty good on the speakers. Easy on the ears, too.
User 6L6 suggested to me on page 2 of this thread that I could try a 5R4GYB as it's pretty close to a 5AR4, so I might try that if I can locate one inexpensively.
Otherwise, I might just button them up for now and enjoy the ride.
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The amp includes feedback - that pretty much alleviates any notion of variations in tube gains being a concern - and is why well known and common valve amps of one make (like the Mk3) operate and sound the same, even though all the thousands of valves within that make of amp have individual gain variations (both from manufacture and due to aging) of a level that would imho dominate any gain variation due to B+.
@trobbins, that is a reasonable response, however there are noticeable gain differences at similar levels of feedback between the two.
What I don't want to do is increase the feedback to a point where the amp sounds lifeless. I prefer to use the minimum amount necessary to keep distortion down without killing the boogie factor. I think I have reached a compromise in the feedback level with the two amps, and I'm ok with turning the balance control on the preamp a little to the left, so to speak.
When alternative rectifiers come in the post, I'll be sure to report back. In the meantime...they're burning in nicely, and starting to sound pretty good.
Now that I have a complete set of functional tubes, I am fairly impressed with the sound quality produced by the Psvane output tubes and rectifier.
Defective samples and the hassles created aside, they were certainly dirt cheap compared to say an Electro-Harmonix or a Tung-Sol, and the sound is pretty good!
What I don't want to do is increase the feedback to a point where the amp sounds lifeless. I prefer to use the minimum amount necessary to keep distortion down without killing the boogie factor. I think I have reached a compromise in the feedback level with the two amps, and I'm ok with turning the balance control on the preamp a little to the left, so to speak.
When alternative rectifiers come in the post, I'll be sure to report back. In the meantime...they're burning in nicely, and starting to sound pretty good.
Now that I have a complete set of functional tubes, I am fairly impressed with the sound quality produced by the Psvane output tubes and rectifier.
Defective samples and the hassles created aside, they were certainly dirt cheap compared to say an Electro-Harmonix or a Tung-Sol, and the sound is pretty good!
Feedback is constant and depends principally on the ratio of the feedback resistor network. You are commenting on changes to the forward loop gain, which are effectively suppressed by the feedback action. Any noticeable difference in measured voltage output of two amps is mainly related to feedback resistor network tolerance (which you have made variable and subject to pot rotation), and is compensated by trimming the input volume level of one or other channel. There may then also be differences due to speakers as to what you hear.
Yeah, a good sanity re-check would be to swap amplifier channels (only, leaving everything else exactly the same) to confirm that the imbalance is really in the amplifier. Never hurts to re-check. Personally, I've never been wrong, except for that time I thought I made a mistake. But other folk should re-check themselves.
All good fortune,
Chris
All good fortune,
Chris
If you've experimented with the recommended level of feedback as designed and prefer less, that's fine. If you haven't, I guarantee you that with 20dB of feedback the amp should not sound "lifeless," but should in fact exhibit better frequency response at the extremes of the audible range, and a better sense of control and refinement. But certainly I respect your desire to to tune the amps to your taste.
Update:
Two rectifiers arrived in the mail today. A NOS General Electric 5R4G and a new production Electro Harmonix 5U4GB.
The GE tube didn't bring the joy I wanted - it's output voltage was low and its impedance lowered the voltage quite a lot more than I expected when I increased the bias of the output tubes to near the recommendation in the manual. I couldn't get the output tubes to full bias and at that point the B+ voltage was sagging quite a bit.
In went the new 5U4GB.
Well...that lowered the B+ voltage to pretty much the point where it needed to be to match the other amplifier.
I didn't think it would work, but it appears that the new 5U4GB has a lower impedance and higher a lower voltage drop than the 5R4G. - within 4-6 volts +/-.
So now one amp has the Psvane 5AR4 and the other an EH 5U4G...they sound pretty much identical, which also surprised me a bit.
I am going to button them up now, I think, and run them like that and see how they fare after some hours on them.
Two rectifiers arrived in the mail today. A NOS General Electric 5R4G and a new production Electro Harmonix 5U4GB.
The GE tube didn't bring the joy I wanted - it's output voltage was low and its impedance lowered the voltage quite a lot more than I expected when I increased the bias of the output tubes to near the recommendation in the manual. I couldn't get the output tubes to full bias and at that point the B+ voltage was sagging quite a bit.
In went the new 5U4GB.
Well...that lowered the B+ voltage to pretty much the point where it needed to be to match the other amplifier.
I didn't think it would work, but it appears that the new 5U4GB has a lower impedance and higher a lower voltage drop than the 5R4G. - within 4-6 volts +/-.
So now one amp has the Psvane 5AR4 and the other an EH 5U4G...they sound pretty much identical, which also surprised me a bit.
I am going to button them up now, I think, and run them like that and see how they fare after some hours on them.
Thought I'd circle back to this topic.
After spending a few weeks in the workshop system doing their break-in and fine tuning I brought these modded Mk-IIIs into the main system today.
I am fairly impressed with them. The playback chain is as follows:
Boy, these amplifiers are really quite good! The improvement in low level detail is remarkable. The improvement in overall sound pressure level and dynamic slam is very good indeed. The first album I played, Steely Dan's Gaucho (original Canadian MCA pressing) really brought out the best in the system, and sounds a lot better than I had been accustomed to. Sonically, this album is hard to beat and I am impressed with how it sounds right now.
Next up Dire Straits' 1978 debut played back at 24-96 which sounds better than I've heard it in this system before.
Ditto Brothers In Arms at 16-44.1. (I play files via Volumio on a Raspberry Pi 3 with a HifiBerry Digi+Pro SPDIF card and then through a home-built DAC (PCM1794) with a tubed (12AU7) analog stage.)
Anyway, the end result, I think is a success. I would recommend this as a mod, and with the circuit boards I made it's pretty easy, too.
After spending a few weeks in the workshop system doing their break-in and fine tuning I brought these modded Mk-IIIs into the main system today.
I am fairly impressed with them. The playback chain is as follows:
- Restored Oracle AC Turntable fitted with restored Mission 774 tonearm and a Soundsmith Aida cartridge.
- Hafler IRIS Preamp, using its internal MM phono stage
- The two Dynaco Mk-III amps in question (with bog-standard Psvane KT88 output tubes)
- Martin Logan Aerius speakers in a small-ish room with minimal room treatment
Boy, these amplifiers are really quite good! The improvement in low level detail is remarkable. The improvement in overall sound pressure level and dynamic slam is very good indeed. The first album I played, Steely Dan's Gaucho (original Canadian MCA pressing) really brought out the best in the system, and sounds a lot better than I had been accustomed to. Sonically, this album is hard to beat and I am impressed with how it sounds right now.
Next up Dire Straits' 1978 debut played back at 24-96 which sounds better than I've heard it in this system before.
Ditto Brothers In Arms at 16-44.1. (I play files via Volumio on a Raspberry Pi 3 with a HifiBerry Digi+Pro SPDIF card and then through a home-built DAC (PCM1794) with a tubed (12AU7) analog stage.)
Anyway, the end result, I think is a success. I would recommend this as a mod, and with the circuit boards I made it's pretty easy, too.
