Thanks D. I run the big Heils for tweets crossed at 7khz so I don't really need any more sizzle up there. I run a midrange tractrix horn with the JBL 2441 CD from 500hz to 7khz and the Lambda TD15 from 500hz on down.
I am building three amps at the moment and trying to figure out which one will be the best match for the three drivers. I suppose I will find out after they are all built.
I am building three amps at the moment and trying to figure out which one will be the best match for the three drivers. I suppose I will find out after they are all built.
Seems this project is off to a bumpy start. Out of 4 6C33C tubes received, 1 has a broken glass envelope and the getter is completely gone, one has an almost black getter, and two look OK. I have several more on the way but don't expect them for several weeks.
No standard steel Hammond chassis this time. I'm putting this in a custom homemade chassis with aluminum top plate and oak sides. This is going to be a work of art. And BIG. 4 output tubes per channel will be accomodated. The aluminum top plate should arrive today so I can lay out the components and start drilling holes soon.
No standard steel Hammond chassis this time. I'm putting this in a custom homemade chassis with aluminum top plate and oak sides. This is going to be a work of art. And BIG. 4 output tubes per channel will be accomodated. The aluminum top plate should arrive today so I can lay out the components and start drilling holes soon.
I like the way you breadboard the project, building on an open plywood platform. Easy to make changes and prove a design before committing to a nice chassis with a project that doesn't sound right.
Wish I had learned that years ago, but that's how I do it now.
Stuart
I agree. I like the test setup. Very easy to tweak the amp that way. I need to start doing that.I like the way you breadboard the project, building on an open plywood platform. Easy to make changes and prove a design before committing to a nice chassis with a project that doesn't sound right.
Wish I had learned that years ago, but that's how I do it now.
Stuart
Very interesting amp. Reading all about it now.
Well not to be a downer but I am just about to abandon this OTL as the Glen Orr 6AS7 OTL I just built blows it away.
I have been listening to the Glen Orr amp now for 3 days an it is as close to my rebuilt NYAL OTL3's in sound as any other otl I have built has come to sounding as nice and in some ways better. Great stage, solid bass nice mids. Mellow sound but clean and under control. I am currently using 5 NOS NIB GE 6AS7GA and they do sound better then my NOS NIB GE 6080's but not by much. If you want a nice DIY OTL I suggest you build this amp.
I have been listening to the Glen Orr amp now for 3 days an it is as close to my rebuilt NYAL OTL3's in sound as any other otl I have built has come to sounding as nice and in some ways better. Great stage, solid bass nice mids. Mellow sound but clean and under control. I am currently using 5 NOS NIB GE 6AS7GA and they do sound better then my NOS NIB GE 6080's but not by much. If you want a nice DIY OTL I suggest you build this amp.
Tim Mellows OTL with LESS than 6C33C's!
Hi All,
Recently finished my variant of Tim Mellows OTL. I've used 6C41C's in place of 6C33C's as, for me, around 6W is sufficient and I don't need all the extra heat. (although, this weather?!) The circuit is exactly as Tim did it except that I've used 500mA meters in place of 1A. I run the 6C41C's at 100mA not 200mA and the HT fuses are 500mA too. One thing I did change was the working voltage of C18 in the -430v section as 250v was exceeded. So a 385v rating was used. After a weeks use, the amp. has settled down with bias and balance pot settings remaing stable - and it sounds - GOOD too! I realise that using the 6C41C's compromises the output impedance and damping factor but it still sounds very nice compared to other more conventional amps I have built. My son in law was so impressed that he wants me to build him the original version to (possibly!) replace his 300B amp I built him a few years back! All in all, a very nice sound, thanks to Mr Mellows unusual (and rather novel circuitry - who'd have thought of a dc coupled driver for 6C33C's using an EF86!!) Picture attched.
'Happy Christmas@
David.
Hi All,
Recently finished my variant of Tim Mellows OTL. I've used 6C41C's in place of 6C33C's as, for me, around 6W is sufficient and I don't need all the extra heat. (although, this weather?!) The circuit is exactly as Tim did it except that I've used 500mA meters in place of 1A. I run the 6C41C's at 100mA not 200mA and the HT fuses are 500mA too. One thing I did change was the working voltage of C18 in the -430v section as 250v was exceeded. So a 385v rating was used. After a weeks use, the amp. has settled down with bias and balance pot settings remaing stable - and it sounds - GOOD too! I realise that using the 6C41C's compromises the output impedance and damping factor but it still sounds very nice compared to other more conventional amps I have built. My son in law was so impressed that he wants me to build him the original version to (possibly!) replace his 300B amp I built him a few years back! All in all, a very nice sound, thanks to Mr Mellows unusual (and rather novel circuitry - who'd have thought of a dc coupled driver for 6C33C's using an EF86!!) Picture attched.
'Happy Christmas@
David.
Attachments
Thanks all for your comments - Yes, the box is a Cutlery box - various sizes around at 'boot fairs' etc. One thing I didn't mention in my report is that the box only contains the two transformers for heater supplies (In order to keep the size down - the power for these and the +&- 150v ht's is derived from a 500w isolation transformer (hidden behind a setee!)(extra points for that from wife!) There is a 3 core cable between the two - L,N & E. This probably would't be practical for the higher powered version
As to the DC offset - after a weeks run-in, it seems to settle at around ' +&- 0.005v'! Amazing! This extremely good stability may be in some part due to the lower power 6C41C's - not sure if 6C33C's would be this good (?) My previous OTL using 6C33C's certainly wasn't! Like to know what other builders are getting?
Regards,
David.
As to the DC offset - after a weeks run-in, it seems to settle at around ' +&- 0.005v'! Amazing! This extremely good stability may be in some part due to the lower power 6C41C's - not sure if 6C33C's would be this good (?) My previous OTL using 6C33C's certainly wasn't! Like to know what other builders are getting?
Regards,
David.
When I finished mine and did the testing it was really low, surprising low actually.
It was right around what was reported earlier but in general I was not a fan of the sound overall so she has alreday been dismantled and I am working on this one:
http://www.diyaudio.com/forums/tubes-valves/178353-otl-designed-glen-orr-audioxpress.html
Which I am listening to right now actually as I write this. IMHO a much sweeter sounding amp. I have a regulated PS on the front end. Next for me is the Rozenblit OTL from Audio Reality. I will be starting that today. Hope you enjoy the sound of the amp!
After Bruce's amp there is always The OTL5998L amplifier
Andrew
http://http://users.forthnet.gr/ath/sifakhsg/
Andrew
http://http://users.forthnet.gr/ath/sifakhsg/
As I look at all these different amps it looks to me like there are two and only two output topologies: totem pole and circlotron.
Am I wrong? The gain and driver sections and the way feedback is derived and applied change, but if you strip away the feedback lines and drivers, everything I see is either totem pole or circlotron, drawn differently but identical schematically.