Member
Joined 2009
Paid Member
Well I just wanted you to know we are watching your threads and we won't let you get away with just abandoning them 🙂 🙂
just kidding...
Actually, I thought this was an interesting topology and have been considering something similar myself, so would be very interested to learn what you have to say about it - why it was not the right path ?
just kidding...
Actually, I thought this was an interesting topology and have been considering something similar myself, so would be very interested to learn what you have to say about it - why it was not the right path ?
i am making a 6HF5 push pull amp instead....😉
unlike pp amps, SE is easy to put together but hard to make sound right...
unlike pp amps, SE is easy to put together but hard to make sound right...
I did a similar sort of SE amp with source follower drive, but used a 6JC6A pentode in the front position and a screen-driven 6CD6GA for the output. The transformers were Hammond 125ESE (cheap at the time at ~$35 per, but no big bargain these days). The amp sounded nice for all its rude simplicity.
When I get around to it, I plan to replace the outputs with 6DQ5s (better ranking in the recent Smoking Amp sweep tube run-off), add some partial feedback, and rebias.
My major objection to screen driven sweep tubes in SE duty is the amount of power you need to dump into the filaments versus the amount of output power you can extract. Almost invariably you're blowing more in filament power than you can ever extract from the output. The huge sweep tube cathodes with their high heater power requirement are wasted for SE duty. In push-pull, however, it's a totally different ball game.
When I get around to it, I plan to replace the outputs with 6DQ5s (better ranking in the recent Smoking Amp sweep tube run-off), add some partial feedback, and rebias.
My major objection to screen driven sweep tubes in SE duty is the amount of power you need to dump into the filaments versus the amount of output power you can extract. Almost invariably you're blowing more in filament power than you can ever extract from the output. The huge sweep tube cathodes with their high heater power requirement are wasted for SE duty. In push-pull, however, it's a totally different ball game.
I'm sure most of us reading this aren't too terribly concerned about burning a few extra watts of filament power.😉 And how is a push-pull amp any better, now you have 4 power tubes pulling 2-2.5 amps each?
jeff
Last edited:
Well yeah, but it's still kinda ridiculous to blow 31.5W of filament power for at most 7-8 W/channel output power. The big filament draw also makes choosing power transformers more difficult if you don't want to use a separate transformer for those hungry filaments. I chose a 6L6GC based partial feedback SE output stage for my latest integrated amp based on bang for filament power invested. I was thinking of using a $2 sweep tube, but the filament power draw was too much for my power XFMR.
Those particular considerations didn't stop me from building the amp I described in my previous post, as I used a one-of-a-kind surplus power transformer with plenty of filament capability for that project.
The peak current capability of sweep tubes is a better match for push-pull amps, where that capability can be used effectively. Tubelab's experiments in sweep tube PP amps are a case in point - insane output power can be had, which may then make the investment in filament power more worthwhile.
Those particular considerations didn't stop me from building the amp I described in my previous post, as I used a one-of-a-kind surplus power transformer with plenty of filament capability for that project.
The peak current capability of sweep tubes is a better match for push-pull amps, where that capability can be used effectively. Tubelab's experiments in sweep tube PP amps are a case in point - insane output power can be had, which may then make the investment in filament power more worthwhile.
Last edited:
Can you share the schematic, or, at least the final stage or working point? 125ESE was used in 5k mode? Or 2K5?
Thread was here:
https://www.diyaudio.com/community/threads/6cd6ga-in-enhanced-triode-mode-for-se-amp.75701/
I used 125ESE in 5k setting, with some global feedback.
https://www.diyaudio.com/community/threads/6cd6ga-in-enhanced-triode-mode-for-se-amp.75701/
I used 125ESE in 5k setting, with some global feedback.
There is too much SS IMO. Apart from it, the ouput tube without negative grid bias (it is depicted directly to cathode) and with 500V on its plate, it will be melted in few seconds.
OdB - It's a screen driven design, and needs to have some positive bias at the screen to make it perk up. Did you see the screen driven curves I generated for the 6CD6? No, it did not melt down, it worked in my living room for years. Oh yeah, and I'll put SS in my VT amps whenever and wherever I please...