Welcome! Need support, you got it. Or share your ideas and experiences.
Return to MagneQuest/Peerless Forum
108.3.211.32
I want to build a tube amp, and one of the options I've zoned in on is Kurt Strain's Cobalt SET 45:
http://www.magnequest.com/diy2.htm
Is the current EXO-45 a drop-in replacement for the cobalt version in the schematic? I don't suppose Magnequest is thinking of building any more cobalt transformers?
The plate choke, EXO-004, is no longer listed in the catalog. What would the equivalent be? BCP-15?
I wonder if Kurt ever made any changes to the circuit in the 14 years since it was published? I have searched and found a few older posts, but nothing recent.
I also wonder what changes might need to be made for this amp to run a 50 output tube, or maybe to run in A2. I think I will need a bit more power for my speakers, which are ~96db 1W/1m.
Thanks!
Follow Ups:
You might also want to check out the Wavelength Audio Bugle 45 SE amp. It has proven to be both popular and durable and it sounds great. See the hotlink below for further info...
Builder of MagneQuest & Peerless transformers since 1989
Yes I've looked at that design many times. I am sticking with the "cobalt" though I need to get a few things clarified. I'm going to upload the circuit after I redo it in Visio and highlight a few things I have questions about.
Does Magnequest offer power transformers and chokes? It would be cool to do the entire amp in MQ iron.
Yes I've looked at that design many times. I am sticking with the "cobalt" though I need to get a few things clarified. I'm going to upload the circuit after I redo it in Visio and highlight a few things I have questions about.
Does Magnequest offer power transformers and chokes? It would be cool to do the entire amp in MQ iron.
http://www.audioasylum.com/forums/magnequest/messages/2919.html
I think these are the only suggested changes I can find so far. I found a reference to the EXO-004 plate choke (60ma, 50H, 317Ohm)
http://www.meter.com/forums/tubediy/messages/22/edit/22785020140508122642.html
It looks like the EXO-003 is a closer match than the BCP-15, though it has lower inductance, higher dc resistance, and I would guess a larger voltage drop. If the only concern is inductance, then why not just go with the Dowdy?
Are there any further updates or changes you would suggest?
On DIYAudio, Audiowize suggested the following change as well:
"The only change I would make is to replace the zener diode and cap in the current source with a 33K resistor in parallel with a 10,000uF/6V cap. Without spending a lot of extra money, a pair of 0D3's in series would give you a regulated voltage supply for your driver, allowing you to control the potential voltage across the MJE-350."
What do you think of those suggestions?
The EXO-004 was the bell ended version of the EXO-003.
The BCP-15 is a very good choice for use with the 45 tube. It is the most frequently chosen plate choke for use with the 45 tube.
The Dowdy is a "super plate choke"... is physically much larger, costs much more and has double plus the inductance.
MSL
Builder of MagneQuest & Peerless transformers since 1989
Is the EXO-004 something you could easily wind? Also - is your shop open to visitors? I work in Kennett Square a few times a week.
It would be cost prohibitive to wind a single pair of EXO-004. Electrically the 004 is equivalent to the EXO-003. The 003 is supplied in steel channel frames with solder lugs. Brass channels may be available as an option.
But again... my recommendation would be to use the BCP-15's with the 45 tube. We can gap it for 40 mils and yield 50 henries. You will get good sub 10 hz performance if you then use a blocking cap of approx 5 mfd.
ahhh... as soon as I get the shop in shape (shelving up and materials organized) I would welcome visitors.
MSL
MSL
Builder of MagneQuest & Peerless transformers since 1989
The Type 50 would require substantially more voltage, including a different driver that could operate at higher voltage, and of course a different filament supply.
However, a 2A3 could operate at the same voltages, running higher plate current (55mA) into a lower impedance transformer (2500-3000 ohms). It would produce about the same power as a Type 50. This is, after all, the reason the 2A3 was developed - to get more power than a Type 45 without raising the power supply voltage. A couple different resistors, and new audio iron, seem to be the only changes needed.
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: