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OTL Guitar Amplifier

85.45.37.29

Posted on February 19, 2008 at 01:12:20
I have recently built and tested an OTL tube guitar amplifier for my son based on the 1954 Macowsky scheme.
There are several tubes: four 6080 (20W final section), one 6SN7 (phase splitter tube), two 12AT7 (gain stage with feedback) and one 12AX7 (pick-up pre-amplifier).
I have also used two old PC AT power supplies for cathode heating in order to get ultra-low noise (and to save some money).
To me it sounds quite good.
I will be glad to share images, technical information and schematics with all interested people.

Luca Cellai
Rome (ITALY)

 

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Thanks, Luca. Can you post a schematic?, posted on February 19, 2008 at 07:18:19
Lew
Audiophile

Posts: 10911
Location: Bethesda, Maryland
Joined: December 11, 2000
I'm not familiar with a Macowsky OTL.

 

RE: Thanks, Luca. Can you post a schematic?, posted on February 19, 2008 at 07:35:10
Scott Nixon
Manufacturer

Posts: 54
Joined: May 1, 2000
I think he means this one from Audio Magazine


Dickie, D. P., Jr. & Macovski, A. (1954 June). “A Transformerless 25-Watt Amplifier for Conventional Loudspeakers,” Audio, pp. 22-23, 56-58

 

RE (1 of 2): Thanks, Luca. Can you post a schematic?, posted on February 19, 2008 at 08:13:22



Please find attached the main schematic (with three 6080 tubes out of four).

I can also send images and additional documentation to an e-mail address of your choice.



Best Regards

 

RE (2 of 2): Thanks, Luca. Can you post a schematic?, posted on February 19, 2008 at 08:22:02



And this is the input schematic.

 

and here's the schematic of the old amp, posted on February 19, 2008 at 15:11:29
LineArrayNut
Audiophile

Posts: 1953
Location: Tenn.
Joined: December 10, 2002

totem pole stuff
I *like* the loudness button!

 

Lots of capacitor coupling going on there... (nt), posted on February 20, 2008 at 07:17:32
Lew
Audiophile

Posts: 10911
Location: Bethesda, Maryland
Joined: December 11, 2000
nt

 

RE: Lots of capacitor coupling going on there... (nt), posted on February 20, 2008 at 08:02:14



You are right. But I like it anyhow.

It seems that the size of my previous upload images was too large.

I have tried to squeeze the information in a much smaller picture now.

Luca

 

RE: Lots of capacitor coupling going on there... (nt), posted on February 20, 2008 at 08:31:31
Lew
Audiophile

Posts: 10911
Location: Bethesda, Maryland
Joined: December 11, 2000
Thanks, Luca. I have to admit that possibly due to my visual acuity I cannot see the schematic in all its detail, but it looks to have a "totem pole" output, like a Futterman amplifier.

 

RE: Lots of capacitor coupling going on there... (nt), posted on February 21, 2008 at 13:52:36
Coresta


 

Have alook at mines , 2 capacitors only , schemes and pics included at http://retro-forum.com/viewtopic.php?t=13883

cheers !

 

More,More Thanks, posted on February 21, 2008 at 14:34:23
tubevibb


 
what a set of AMPS, some of the best work i have ever seen,GOOD Job
thanks for your Post,

 

Atma-Sphere m-60mkII,well Can you post a schematic?, posted on February 22, 2008 at 14:51:06
tubevibb


 
Is it time the 99,s
well

 

RE: Lots of capacitor coupling going on there... (nt), posted on December 2, 2013 at 19:41:15
Posts: 1
Location: Rochester, NH
Joined: December 2, 2013
Hello
Nice amps. Unable to see schematics. Would please send them to my e-mail.
Henry

 

RE: OTL Guitar Amplifier, posted on January 27, 2014 at 08:56:27
drtechno@rushmore.com
Industry Professional

Posts: 29
Joined: February 25, 2013
I built this amp before. its a neat design using 100% feedback

I used the RCA schematics (3 tubes)

I added a 6 volt winding to an isolation toroid.

other thaughts on this design: I am thinking someday revisiting this and improving on it like adding an output tubes configured as plate load/ccs on the outputs.

 

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