Hi ISCMMS,
Nice to see this as I've just recently ordered and received a pair of ISO RC-160-15W plate chokes...looks like a good option to try. I could use some help in way of schematic...
I'm an old guy who is trying to catch up from many years (ago) as Sound Practices follower. Maybe you've said enough already...Thank You!
Happy New Year!
Robert
I'm jealous! Nice chokes. Mine are NP Acoustics amorphous ones - very good too. I love plate chokes!
Hi Robert,
They're near enough perfect for this: well built, shielded, been around for decades and -3dB at 25Hz and 40kHz (10k Rp and 5mA Ip).
Schematic, just like everyone else is doing, filament bias (use a coleman reg and a resistor) and pick an operating point that suits and sounds well.
Other than DC coupling, I found some real happiness in using a series CCS in the B supply with plate choke loaded tubes. Decouple with the final filter cap as you would with an LC filter - the cap can be really small and you can define the plate current without using a CCS as plate load.
Feel free to PM if you're stuck for ideas, Happy New Year to you and everyone else as well.
Last edited:
Hi ISCMMS,
When I hear "DC coupling" I immediately think Loftin-White, and I've done some of those.
I think I need to know what your block diagram looks like...how are you using your "preamp"?
Never mind putting a CCS in a B+ supply, we can deal with that later.
Or, fess-up a schemo...
Cheero!
Robert
Hi Robert,
Grid to ground via whatever you like (resistor/choke/transformer secondary), filament return to signal common via resistor which carries also the current of the filament, heat the filament with a coleman reg and load the plate with the inductor. That's it.
At my place, the 01A is the input stage to an amplifier which is driven by a DAC through E55L and 1:1 to an AVC. The 01A is direct coupled to a choke loaded 71A which is again direct coupled to a 2A3/300B. Start up is via a mix of SS and tube rectification, plus a series tube damper in series with the 2A3/300B supply, so that it all comes up (starts) as it should. There are coils in series with the CCS B supplies (fixed voltage across the coil of an electromagnet) which energise contacts which keeps it all safe.
You can do all sorts of things with DC level shifting between stages, and its a trip! (challenge/puzzle), you might like www.labjc.com if you havent already been there.
If you're looking for more, PM will be better, but I dont have much more apart from schems, pics and protos - if you're after an 01A stage.. you have it all here already.
Grid to ground via whatever you like (resistor/choke/transformer secondary), filament return to signal common via resistor which carries also the current of the filament, heat the filament with a coleman reg and load the plate with the inductor. That's it.
At my place, the 01A is the input stage to an amplifier which is driven by a DAC through E55L and 1:1 to an AVC. The 01A is direct coupled to a choke loaded 71A which is again direct coupled to a 2A3/300B. Start up is via a mix of SS and tube rectification, plus a series tube damper in series with the 2A3/300B supply, so that it all comes up (starts) as it should. There are coils in series with the CCS B supplies (fixed voltage across the coil of an electromagnet) which energise contacts which keeps it all safe.
You can do all sorts of things with DC level shifting between stages, and its a trip! (challenge/puzzle), you might like www.labjc.com if you havent already been there.
If you're looking for more, PM will be better, but I dont have much more apart from schems, pics and protos - if you're after an 01A stage.. you have it all here already.
Last edited:
Thanks Andy, I've ordered some from sovtube now...... along with a few other bits from that store.... lets hope they make it here OK.
Hi ISCMMS,
I don't know how to PM you. I thank you for your replies.
I tried to start a Conversation but that didn't work...here's what I said:
I'm not sure how to send you a PM, but will try this...
Thanks for the prompt on labjc...I've been there many times over the years, but never with as significant a context as yours today, went there, and found more direct coupled, and started reading into that. Which leads me to think I missed an earlier direct coupled post. Do you have a copy of that? Could you send it to me?
One of the amplifiers I've built, (a pair of monos), was the Screen Drive amplifier jc presented in SP 14. Those are alive and well and powering a pair of Altec A7s in the Schoolhouse systeme. They are also DC coupled...no caps in the signal path. Hmm... I'm somewhat a victim of Andy Evans' plate choke designs on the 01A Question thread with coupling caps, thinking I have to do it that way...what other way to level adjust? I'm curious.
I'm an ME, not an EE, but I do remember checking plate characteristics in an EE lab course for a 2A3 in 1960 or 61.
One of the curios about the link to jclabs is finding out about his LP recording on No Business Records entitled DUX Orchestra, of which I'm in the process of ordering (since it has two baritone saxaphone players). We shall see what we shall see.
I'm interested in learning more about DC coupling and the challenges of interstage level adjustment.
Any help/direction you might provide would be much appreciated!
Very Best Regards,
Robert
Hi Robert,
I dont know how to PM people either
If you can DIY, then absolute best solution is to put it on the same chassis as the rest of the amplifier and direct couple.
I think at that point it becomes more about what you're trying to do - what is the bias voltage of your output tube, and working back from there, what is the gain of the driver (bias voltage as well). Once you have the fundamentals, you can have fun being mental.
Cheers
I dont know how to PM people either
If you can DIY, then absolute best solution is to put it on the same chassis as the rest of the amplifier and direct couple.
I think at that point it becomes more about what you're trying to do - what is the bias voltage of your output tube, and working back from there, what is the gain of the driver (bias voltage as well). Once you have the fundamentals, you can have fun being mental.
Cheers
