still slackin'
Not making much progress lately, too darn busy (or lazy). Haven't been completely idle though, below is a picture of the high voltage power supply breadboard. Damn thing is way heavy. With choke input it puts out 750VDC with about 150mA output. That is all the load I could find to test it. I think when I add the MV rectifiers and up the current it should be around 710-720V at full output. So if I want choke input I need to get going on the A2 problem. I do have three 2uF 2500VDC paper/oils to try in parallel combo at the input to see what voltages I will have available with cap input.
Anybody got any feelings on 6EM7 or 6EW7 as the driver?
Later,
Michael
Not making much progress lately, too darn busy (or lazy). Haven't been completely idle though, below is a picture of the high voltage power supply breadboard. Damn thing is way heavy. With choke input it puts out 750VDC with about 150mA output. That is all the load I could find to test it. I think when I add the MV rectifiers and up the current it should be around 710-720V at full output. So if I want choke input I need to get going on the A2 problem. I do have three 2uF 2500VDC paper/oils to try in parallel combo at the input to see what voltages I will have available with cap input.
Anybody got any feelings on 6EM7 or 6EW7 as the driver?
Later,
Michael
Attachments
off my butt finally
Finally got off my butt for a few minutes and wired up a new driver stage with 6BX7s. First I tried Kevin Carter's direct coupled setup (shown in the schematic link above) linked to my 6SN7 design. In my brief test I couldn't get it to bias properly to get the necessary voltage swing. I did sound good, if distortion was a fair bit higher.
Next I tried it one section/side RC coupled. I could bias for the swing, but it was no improvement over the 12B4 as a driver, A2 wise.
Finally, I tried two tubes with sections paralleled and RC coupled to the 6SN7 stage. Again it sounded good at low levels. I tried quite a few operating points and settled on something like 300V B+, -27V bias, 45mA=Ip. In these preliminary tests it did not seem to offer much improvement in the A2 area. Perhaps a little, but again, these were just some quick measuremets. I fear that if this combo cannot be optimized to perform well in A2, either 1) I am doing something that is systematically wrong or 2) the LL1660/anode drive scheme will not work with any driver tube.
Still thinking about the problem,
Michael
Finally got off my butt for a few minutes and wired up a new driver stage with 6BX7s. First I tried Kevin Carter's direct coupled setup (shown in the schematic link above) linked to my 6SN7 design. In my brief test I couldn't get it to bias properly to get the necessary voltage swing. I did sound good, if distortion was a fair bit higher.
Next I tried it one section/side RC coupled. I could bias for the swing, but it was no improvement over the 12B4 as a driver, A2 wise.
Finally, I tried two tubes with sections paralleled and RC coupled to the 6SN7 stage. Again it sounded good at low levels. I tried quite a few operating points and settled on something like 300V B+, -27V bias, 45mA=Ip. In these preliminary tests it did not seem to offer much improvement in the A2 area. Perhaps a little, but again, these were just some quick measuremets. I fear that if this combo cannot be optimized to perform well in A2, either 1) I am doing something that is systematically wrong or 2) the LL1660/anode drive scheme will not work with any driver tube.
Still thinking about the problem,
Michael
further exploits
Hi all,
Been awhile. I finally worked at optimizing the paralleled plate 6BX7 as a driver. The results look OK on paper in A1, see graph less so in A2. I also implemented my breadboard power supply and I was happy to find hum decreased significantly. After a bit of working at low voltages (745VDC) I inserted a 2uF 2500VDC paper in oil cap in front of the choke to try a little higher B+. That took me up to 980VDC so I biased the 845s at -140 for about 87mA/tube. The results of my distortion analysis are in the graph. Listening tests were quite satisfactory. The increased gain was a good thing with 1V in giving 21V out into 8 Ohms.
The surprise came when I hooked up the 12B4 again to give it a comparison at higher B+.
I was amazed! The amp went from completely OK to a huge Wow. A friend of mine had his first listen a few weeks ago with the 12B4s in and his comment was "Crap, now I've got to sell all my gear and get some of this". Then he was back over a few nights ago with the 6BX7s in and he said the amp sounded different (not a good comment, I think). Anyway, I didn't really think about it until I put the 12B4s back in today. It is noticeable to say the least. Now I have to figure out how to live with the low gain, 1V in gives 11V out and forget A2 maybe.
Still experimenting,
Michael
Hi all,
Been awhile. I finally worked at optimizing the paralleled plate 6BX7 as a driver. The results look OK on paper in A1, see graph less so in A2. I also implemented my breadboard power supply and I was happy to find hum decreased significantly. After a bit of working at low voltages (745VDC) I inserted a 2uF 2500VDC paper in oil cap in front of the choke to try a little higher B+. That took me up to 980VDC so I biased the 845s at -140 for about 87mA/tube. The results of my distortion analysis are in the graph. Listening tests were quite satisfactory. The increased gain was a good thing with 1V in giving 21V out into 8 Ohms.
The surprise came when I hooked up the 12B4 again to give it a comparison at higher B+.
I was amazed! The amp went from completely OK to a huge Wow. A friend of mine had his first listen a few weeks ago with the 12B4s in and his comment was "Crap, now I've got to sell all my gear and get some of this". Then he was back over a few nights ago with the 6BX7s in and he said the amp sounded different (not a good comment, I think). Anyway, I didn't really think about it until I put the 12B4s back in today. It is noticeable to say the least. Now I have to figure out how to live with the low gain, 1V in gives 11V out and forget A2 maybe.
Still experimenting,
Michael
Attachments
Reoptimized driver
Reoptimized the driver circuit a bit today. Had made a few changes for the 6BX7 that I didn't change back before the last 12B4 data. I think I may call it a day with 40W at 0.27% distortion.
Now maybe time to look at getting a chassis or two together.
Michael
Reoptimized the driver circuit a bit today. Had made a few changes for the 6BX7 that I didn't change back before the last 12B4 data. I think I may call it a day with 40W at 0.27% distortion.
Now maybe time to look at getting a chassis or two together.
Michael
Attachments
Michael,
It’s nice to see you making progress. I have always found that 845’s need at least 1KV to really sing. I know you’re skeptical about the 5687, but it will sound much better now with the other changes you have made. The low plate resistance makes it an excellent driver of the 1660.
So let’s get back to the topic of the thread, and start playing around with the 1620. I’m interested in your opinion of the change in plate load on the 845 and how it affects the sound as well as distortion in the output.
Take care, and watch out for that HV!
Chuck
It’s nice to see you making progress. I have always found that 845’s need at least 1KV to really sing. I know you’re skeptical about the 5687, but it will sound much better now with the other changes you have made. The low plate resistance makes it an excellent driver of the 1660.
So let’s get back to the topic of the thread, and start playing around with the 1620. I’m interested in your opinion of the change in plate load on the 845 and how it affects the sound as well as distortion in the output.
Take care, and watch out for that HV!
Chuck
845 load
Hi Chuck,
Still singing along to your 845 amp?
I have gotten awfully lazy of late, but maybe I will get a burst and try the 5687 as the driver.
Re: the plate resistance of said tube, it is still higher than either the 12B4 or the paralleled 6BX7. I would like to give it a chance though, the increased gain would be nice.
Re: 845 plate voltage. I haven't had as much listening time at the HV yet. Earlier experiments with voltages in the high 800s to low 900s seemed to indicate that to my ears the amp sounded better at 700V. Confusing sentence or what? If I could justify the expense and hassle of using the 845s to get 15W I think I might still be in that area. This is not to say it sounds poorly around 1kV, just that I have but a few hours of listening and no other ears have heard it yet.
I did collect data on the distortion profiles with the 6BX7 driver at 11k and 6k plate loads on the 845. If you are interested I can email you the graphs or raw data (eaisier) or I could post them here. Let me know.
Michael
Hi Chuck,
Still singing along to your 845 amp?
I have gotten awfully lazy of late, but maybe I will get a burst and try the 5687 as the driver.
Re: the plate resistance of said tube, it is still higher than either the 12B4 or the paralleled 6BX7. I would like to give it a chance though, the increased gain would be nice.
Re: 845 plate voltage. I haven't had as much listening time at the HV yet. Earlier experiments with voltages in the high 800s to low 900s seemed to indicate that to my ears the amp sounded better at 700V. Confusing sentence or what? If I could justify the expense and hassle of using the 845s to get 15W I think I might still be in that area. This is not to say it sounds poorly around 1kV, just that I have but a few hours of listening and no other ears have heard it yet.
I did collect data on the distortion profiles with the 6BX7 driver at 11k and 6k plate loads on the 845. If you are interested I can email you the graphs or raw data (eaisier) or I could post them here. Let me know.
Michael
a few changes
Made a few more changes today.
The amp is now LL1667->6SN7-RC>EL34 triode connected->LL1660PP->6BX7 choke loaded CF->845->LL1620.
Sounds OK. Does A2 OK. Max output at 1kHz, just for laughs, ~95W at 2.9% distortion. 1W at 0.05%. B+=980V, Vb=-140V, Ip=85mA. The breadboard is a bit messy.
Michael
Made a few more changes today.
The amp is now LL1667->6SN7-RC>EL34 triode connected->LL1660PP->6BX7 choke loaded CF->845->LL1620.
Sounds OK. Does A2 OK. Max output at 1kHz, just for laughs, ~95W at 2.9% distortion. 1W at 0.05%. B+=980V, Vb=-140V, Ip=85mA. The breadboard is a bit messy.
Michael
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