• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Photo Gallery

Sharing a fun power-amp Schematic

Can use
6Dj8 sieris( ECC88,E88CC,CCa,E188CC,E288CC),ECC85 sieris,6BQ7 sieris, 12AX7 sieris( E283cc*, ECC808*```), 12AU7 sieris( ECC40*, E181CC, E80CC``` ), 12AT7 sieris ( E180CC, 6201```)
EL34 sieris( KT77```), KT88 sieris ( 6550```)
tubes.

M400S.jpg
 
211 DHT SE amplifier

This amplifier started out with capacitor coupled design, but ended up with interstage. Basically the 10Y input tube directly coupled to the second 10Y driving an interstage transformer. The output of the interstage drives the 211 in fixed bias. The interstage is hidden under the amp, it was an afterthought.
My GM70 amplifier (picture in previous page used similar circuit but with a pentode strapped triode driving a 6B4G DHT.


I understand. But am curious as to cap coupled or interstage. Am planning an all interstage GM70 with 41PL->300B->GM70 and so yes, I'll also have to build three seperate heaters for each tube. (Coleman)
 
Last edited:
This amplifier started out with capacitor coupled design, but ended up with interstage. Basically the 10Y input tube directly coupled to the second 10Y driving an interstage transformer. The output of the interstage drives the 211 in fixed bias. The interstage is hidden under the amp, it was an afterthought.
My GM70 amplifier (picture in previous page used similar circuit but with a pentode strapped triode driving a 6B4G DHT.
Would you post a schematic?
 
Administrator
Joined 2004
Paid Member
My current amplifiers have been in continuous use since October of 2011 when I completed them. They average about 30hrs a week of use, and are on their second set of tubes. Simple all transformer coupled stage design using a single GM70 and triode connected D3A per channel. The transformer coupled outputs of my line stage float and are direct coupled to the grid and bias networks for the D3As.. Fixed bias is used throughout. No coupling capacitors except in the input of the 26 dht based line stage.

Output power is a little over 20W per channel, and operate full range. The speakers are 100dB+ efficient..

Because of the high voltages involved I have not shared the design. (and won't)

I've sold all of my other amps.. These will suffice and have proven to be extremely reliable in use.
 

Attachments

  • amp-psu.jpg
    amp-psu.jpg
    212 KB · Views: 889
Disabled Account
Joined 2010
My current amplifiers have been in continuous use since October of 2011 when I completed them.

Because of the high voltages involved I have not shared the design. (and won't)

I've sold all of my other amps.. These will suffice and have proven to be extremely reliable in use.
Kevin,

What Op transformer/power Tx did you use?
(Poss PM)?

Regards
M. Gregg
 
Administrator
Joined 2004
Paid Member
All of my power and output transformers were custom built to my specifications. The power transformers for the amps were made to order by Edcor, and the output transformers by Jack Elliano at Electra-Print. The interstages were made by Lundahl.. None were terribly expensive. I use Rod Coleman CCS for heating the GM70s, and LT1084 based pre-regulators to power them. Predictable operating point in the driver stage is provided by a 20mA cascode current source that provides plate voltage to the IT. The plate supply is locally decoupled by large film caps - plate voltage is determined by the transconductance of the driver tube at approximately -2.1V of grid bias. Works quite well, and also obviates the need for a very well filtered plate supply to the driver stage. (Mine still is well filtered)
 
Everyday its OTL

6c33c OTL. 6np2 input and 6np6 drivers. Computer source (mpdpup on ALIX) driving TDA1541A 6np2 buffered DAC. Lightspeed attenuator. Great pairing with OTLs. Blackgates everywhere. :D
 

Attachments

  • tube amp finished - close up tube glow.jpg
    tube amp finished - close up tube glow.jpg
    290.8 KB · Views: 978
  • tube amp finished - top shot.jpg
    tube amp finished - top shot.jpg
    537.7 KB · Views: 877
retro-thermionic: retro-34UL power amp

This amp is my new EL34 the "retro-34UL", Signature EL34 amp. On early listening the amp sounds fast, crisp and SS like. A very natural sounding amp. Valve compliment is NOS Svetlana EL34 and Svetlana 6N1P. Edcor GXSE 6omh ultra-linear OPTs and 10H choke and power tranni are Hammond. Inter-stage caps are Jensen copper, paper and oil with pure silver leads. Biploar caps are used as bypass caps on the EL34s with ceramic sockets for the audio tubes. Rectifier valve is a Golden Dragon 5U4. OPTs are rubber mounted.

Top plate is ABS plastic and base Australian Spotted Gum (oiled). Feet are filled with lead sinkers and rubber glue, silver solder and and silver plated wire used throughout. Topology is Single-end Ultra-linear.
 

Attachments

  • Signature EL34.jpg
    Signature EL34.jpg
    231.9 KB · Views: 1,133