DIY Airbrake...

[lilkeysdad]

Thanks for sending that so quickly!

[kapa21]

It would be great if I could get a copy of the schematic and layout as well, please.
Thanks!
-KP

[dobbhill]

The schematic is on page three of this thread.

https://tubeamparchive.com/viewtopic.ph ... c&start=30

D

[gberglund]

Please send a copy of the layout and schematic to bergl023@umn.edu.
Thanks

[don]

I'd appreciate a copy of the schematic and diagram...requested one before but lost it thanks in advance .....


Disregard please.....just found it in my other hard drive

[Wilco]

Hi,
First post here.
This looks like a great project to make, but I was wondering about impedance matching. I did a search on this forum and some other forums, but found only a few answers, that where completely different from each other as well. So here it goes...
I am considering building this attenuator to use with my '63 Blonde Bassman, which has just one speaker out at 4 Ohms and uses a 4 Ohm cab.
Is the Air Brake safe to use with this amp? I would hate to blow up my nice 4Ohm output tranny of my lovely NOS output tubes.
Any experience with using the Air Brake at 4 Ohms?
Is there a way to alter the Air Brake (different resistor values?) to make it a closer match to a 4Ohm amp, as the Air Brake is supposed to be closest to 8Ohms as it is right now?

Edit:
I started a topic in "Technical Discussion" subforum about this question.

[Noel Grassy]

Read here----https://tubeamparchive.com/viewtopic.php?t=3441

[Wilco]

Thanks.
I did find that thread, but it didn't answer my question. It does clarify the, quite large, changes in impedance that occur when changing the settings on the airbrake. It doesn't solve the question wether it is safe to use it with your amp.
Basically, in that thread it is just one guy telling that he would never do that. Of course, he seems to know what he is talking about (I even checked out his website), but if a guy like Ken Fisher says there will be no problem, I need more than just one guy saying it isn't safe.
KF would have had nothing to gain by selling a "one size fits all" attenuator that will harm your amp. He would have probably made more money selling a different attenuator for every impedance (like all the rest).
Of course, I am not so sure myself that it's safe, otherwise I wouldn't have been asking these questions, but I am looking for arguments and explanation so I can understand why or why not to do it. If there are some of you out there who have used the airbrake with a 4 Ohm amp and cab that could share their personal experiences with it, that would be great too.

[Noel Grassy]

Well put. Do you suppose maybe most output xfmrs are rugged enough to permit the attenuator's use? I've heard Fenders were more forgiving of L mismatches than others. I used an Altair for years[when called for]and it never let anything fry. Slightly more Flinstonian but wire wound R's just the same. Did the pages on Aiken's site touch on this? I'll have to look again. I wonder why some EE types don't horn in & splane it.

[Wilco]

I guess even the EE types are at a loss with this one?

[Doug H]

Read the Tube Amp FAQ at R.G. Keen's GEO site. He explains impedance mismatching- what you can get away with, what you can't, and why.

[Lonely Raven]

I googled it really quickly for those of you that don't know the address of above noted site:

http://www.geofex.com/

[Wilco]

I did know about R.G.'s website from my effects building days, but I didn't know he talked about tube amp stuff to this extent. This is great stuff and answers a lot of my questions.
Nice detail: On the Komet website their version of the Airbrake is described as being built exactly according to KF's design (although it doesn't have a "bedroom" control if I'm not mistaken), but contrary to what KF has always claimed it is NOT suitable for 4 Ohm amps, just 8 and 16. This seems to be what R.G. says as well: a 2:1 amp-cab mismatch is tolerated better than a 1:2 mismatch.
If you check the graph by Randall Aiken in this thread on TGP you can see the mismatch occuring at 4, 8 and 16 Ohms.
http://www.thegearpage.net/board/showth ... +impedance

[mhuss]

I've never had any problems with any amp mismatching impedance by 1:2 or 2:1. Maybe I'm just lucky.

The "overvoltage" reflection on a too high impedance seems more dangerous to the output stage (to me) than does the "overcurrent" reflection on a too low.

--mark

[blinddog]

Considering this thread is still going strong. Has anyone heard any reviews besides the Guitar Player review of the BC Leash?


http://www.badcatamps.com/badcat_pedals.html GP said it was good and it seems pretty heavy duty. Just wondering if anyone had any experience with it.