Greetings!
I recently came into possession of large output transformer with the following data printed on it:
Manufacturer: NWC
Model number: 548C
Cycles: 10 - 200
Watts: 50
Primary: 3600 Ohms CT
Secondary: C, 8 Ohms, 16 Ohms
Date Code?: 5-52
I thought it might be fun to design a sub woofer amplifier or maybe a bass guitar amp around this bad boy.
My parts bins are pretty well stocked with lots goodies: Tubes, transformers, chokes, caps, lots of old stuff like VR Tubes and MV rectifiers.
I’m looking for input from the group to jointly come up with a design that will:
Be all ‘bout dat bass
Not cost me too much
Be totally impractical
I recently came into possession of large output transformer with the following data printed on it:
Manufacturer: NWC
Model number: 548C
Cycles: 10 - 200
Watts: 50
Primary: 3600 Ohms CT
Secondary: C, 8 Ohms, 16 Ohms
Date Code?: 5-52
I thought it might be fun to design a sub woofer amplifier or maybe a bass guitar amp around this bad boy.
My parts bins are pretty well stocked with lots goodies: Tubes, transformers, chokes, caps, lots of old stuff like VR Tubes and MV rectifiers.
I’m looking for input from the group to jointly come up with a design that will:
Be all ‘bout dat bass
Not cost me too much
Be totally impractical
Last edited by a moderator:
If you go bass guitar amp, take this over to the Instruments and Amps "board".
IMO, this is pretty obvious: a sub-woofer amp with PP KT88s operated in a conservative manner and regulated g2 B+. A Mullard style circuit should be OK, given that 10 Hz. low freq. limit. The H/K Cit. 5, with its high gm emphasis, is a superior implementation of Mullard topology. The 12BY7 shown is getting scarce and is (IMO) best saved for already existing units. I've provided a 6922 cascode that substitutes well for the 12BY7.
BTW, it's a good idea to bandwidth limit any setup with a GNFB loop at the I/P to a F3 in the 16 to 18 Hz. range. Filtering infrasonic noise out provides protection against O/P "iron" core saturation.
IMO, this is pretty obvious: a sub-woofer amp with PP KT88s operated in a conservative manner and regulated g2 B+. A Mullard style circuit should be OK, given that 10 Hz. low freq. limit. The H/K Cit. 5, with its high gm emphasis, is a superior implementation of Mullard topology. The 12BY7 shown is getting scarce and is (IMO) best saved for already existing units. I've provided a 6922 cascode that substitutes well for the 12BY7.
BTW, it's a good idea to bandwidth limit any setup with a GNFB loop at the I/P to a F3 in the 16 to 18 Hz. range. Filtering infrasonic noise out provides protection against O/P "iron" core saturation.
Attachments
Eli,
I love the H/K schematic! Thank you for posting it and for your thoughts.
I'm a medium-noob, but I think I could build this one.
This amplifier project was a spur-of-the-moment thought, born when I came in possession of this OP transformer, so I didn't budget anything for it and can't spend too much on it. Fortunately, it looks like I have just about everything I need in my stash.
I found a NOS 12BY7A (happens to be Harman/Kardon branded) and a NOS 6CG7 so I'm good with the front end.
I don't seem to have any 7581 tubes and only one KT88 but I do have a bunch of 807 and several 6BG6G. I believe these are both in the same family. Would I need to change anything on the schematic to use either of these tubes?
As for the regulated G2 B+, I will need some hand-holding on this. We are talking about the 450V connection, right? Could this be done with some OD3 VR tubes (I have a bunch of those, too).
Thanks,
-Joe Y
I love the H/K schematic! Thank you for posting it and for your thoughts.
I'm a medium-noob, but I think I could build this one.
This amplifier project was a spur-of-the-moment thought, born when I came in possession of this OP transformer, so I didn't budget anything for it and can't spend too much on it. Fortunately, it looks like I have just about everything I need in my stash.
I found a NOS 12BY7A (happens to be Harman/Kardon branded) and a NOS 6CG7 so I'm good with the front end.
I don't seem to have any 7581 tubes and only one KT88 but I do have a bunch of 807 and several 6BG6G. I believe these are both in the same family. Would I need to change anything on the schematic to use either of these tubes?
As for the regulated G2 B+, I will need some hand-holding on this. We are talking about the 450V connection, right? Could this be done with some OD3 VR tubes (I have a bunch of those, too).
Thanks,
-Joe Y
The major sticking point is the primary impedance of the O/P "iron". 🙁 6L6 family tubes, including the 6BG6 and 807, usually work into 6.6 Kohms. Sell some 807s to help fund the purchase of a matched pair of "reissue" Gold Lion KT88s. Unfortunately, the weak spot in the lower cost ElectroHarmonix (EH) KT88 is bass extension. Phooey! The "iron" has to mate well with the O/P tube pair. PP KT88s are a reasonably good match for that 1952 manufactured item.
A single gas discharge regulator tube could serve as the voltage reference in a screen grid B+ supply and a 6BG6 could serve as the pass device.
A single gas discharge regulator tube could serve as the voltage reference in a screen grid B+ supply and a 6BG6 could serve as the pass device.
- Status
- Not open for further replies.