Hey all,
Just wanted to share my experience with building lower power 2 stage SET. I am using 45 as the output valve, swapping with different drivers. If you don't have at least 99dB eff speakers in a medium sized room then 2W isn't going to be enough to play with any authority.
I've tried 417a/5842, 6c45p, and finally the 717a as drivers. Here are my impressions of each:
The 417a can have a very smooth, detailed and extended response, the sound can even tend toward airy and ethereal. The Raytheon 5842 is does not have the last bit of smoothness from what I could tell. Great tube and I would definitely recommend it. I used it as input for a 417a -> 2a3 -> 211/845 SET amp that I sold earlier this year.
6c45p I was disappointed with at first because I left in a lot of FB by not bypassing the cathodes. Once bypassed or switching to battery bias, it does sound nice. Compared to the 417a/5842 though, it is more grainy and does not have as much detail and extended response. This could probably improve if I choke loaded it, so it seems to require more attention to operating point and loading.
Then I tried the 717a pentode, which was my first time trying a pentode as a driver. I was disappointed at first, again because of wrong operating point and setup. At first it sounded very clear but flat and stale. Once I dropped the screen voltage more, mids began sounding very nice. At this point the circuit is almost identical to the Yamamoto 717a -> 45 amp. Then I switched out the auto bias for 3V battery bias (2x 1.5V AA's). Now this smoothed everything and seemed to bring it all together. I really like this amp now, but of course it is its own flavor. It is very detailed and crisp and extracts all the info that it's fed, moreso than the 417a. It doesn't have that ethereal effect that would have you sink into the music, but would be better for you if you enjoy hearing every last bit of detail.
I am thinking to make a bedroom system amp with this circuit, but it's good enough that it could be in a main system too. I am curious what would happen if I try and drive a 300b or 50 with it. The 50 would at least need a grid choke, if not mosfet follower. Some other drivers I need to try with this amp that are just waiting in the shop: c3m and 6c5g
Just wanted to share my experience with building lower power 2 stage SET. I am using 45 as the output valve, swapping with different drivers. If you don't have at least 99dB eff speakers in a medium sized room then 2W isn't going to be enough to play with any authority.
I've tried 417a/5842, 6c45p, and finally the 717a as drivers. Here are my impressions of each:
The 417a can have a very smooth, detailed and extended response, the sound can even tend toward airy and ethereal. The Raytheon 5842 is does not have the last bit of smoothness from what I could tell. Great tube and I would definitely recommend it. I used it as input for a 417a -> 2a3 -> 211/845 SET amp that I sold earlier this year.
6c45p I was disappointed with at first because I left in a lot of FB by not bypassing the cathodes. Once bypassed or switching to battery bias, it does sound nice. Compared to the 417a/5842 though, it is more grainy and does not have as much detail and extended response. This could probably improve if I choke loaded it, so it seems to require more attention to operating point and loading.
Then I tried the 717a pentode, which was my first time trying a pentode as a driver. I was disappointed at first, again because of wrong operating point and setup. At first it sounded very clear but flat and stale. Once I dropped the screen voltage more, mids began sounding very nice. At this point the circuit is almost identical to the Yamamoto 717a -> 45 amp. Then I switched out the auto bias for 3V battery bias (2x 1.5V AA's). Now this smoothed everything and seemed to bring it all together. I really like this amp now, but of course it is its own flavor. It is very detailed and crisp and extracts all the info that it's fed, moreso than the 417a. It doesn't have that ethereal effect that would have you sink into the music, but would be better for you if you enjoy hearing every last bit of detail.
I am thinking to make a bedroom system amp with this circuit, but it's good enough that it could be in a main system too. I am curious what would happen if I try and drive a 300b or 50 with it. The 50 would at least need a grid choke, if not mosfet follower. Some other drivers I need to try with this amp that are just waiting in the shop: c3m and 6c5g
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