Yes, no, may be? Who remembers this?

[justin]

Colors Sovietized for effect

 

* this should be in DIY forum

Edited April 3, 2023 by justin

[jose]

I remember reading about the old amps (MIGs) Kevin designed... especially one that was totally overkill but I don't remember their names.

[jose]

@justin bad boy.... I've been looking for the schematic and the sand for an hour 😁

I couldn't find the schematic (KGDT only) but I find it: 

Kevin sayd: 

schematics for mig here.

http://gilmore.chem.northwestern.edu/kgdt1.gif
http://gilmore.chem.northwestern.edu/kgdt2.gif


mig amp can be built balanced or unbalanced, uses grounded
grid 6c33 output tube and solid state current source.
(4 tubes balanced)

mig2 amp can be built balanced or unbalanced uses grounded
grid 6c33 output tube with a 6c33 as the current source.
(8 tubes balanced)

 

 

[grawk]

moved to diy

[justin]

14 minutes ago, jose said:

@justin bad boy.... I've been looking for the schematic and the sand for an hour 😁

I couldn't find the schematic (KGDT only) but I find it: 

Kevin sayd: 

schematics for mig here.

http://gilmore.chem.northwestern.edu/kgdt1.gif
http://gilmore.chem.northwestern.edu/kgdt2.gif


mig amp can be built balanced or unbalanced, uses grounded
grid 6c33 output tube and solid state current source.
(4 tubes balanced)

mig2 amp can be built balanced or unbalanced uses grounded
grid 6c33 output tube with a 6c33 as the current source.
(8 tubes balanced)

 

 

a couple mistakes that I know of in the output stage:

the pot is 100 to 1K

the CCS transistors must be paralleled as 30W from a single TO-220 is a bad idea

Edited April 3, 2023 by justin

[nopants]

I remember looking at this years ago and wanting to build it, then I read some comment about how the 6c33c's have short lifespan?

...am I reading that correctly, 7A filaments?

[spritzer]

Yup, they are very hungry tubes.  Given what these are designed for, tube life should be just fine if not run on the extreme edge. 

[jose]

Kevin gave me a design with 6C33 many years ago (arround 2017). I use it constantly and in fact, it's my favorite amp.

I have changed the preamp tube many times out of curiosity but never the 6C33... and that stuff already accumulates enough hours of use.

 

 

[jose]

Please, could you suggest me a substitute for the 2SJ352?

[justin]

I can send you some

or try this? http://www.exicon.info/PDFs/ecx10p20.pdf

[jose]

Thanks Justin 😊 

[justin]

Here is 1 channel of a blue hawaii running on +/-100v instead of +/-400v,

with a single 6as7 dual triode for balanced output instead of a pair of EL34.

The tube current sources have been increased from 20mA to 75mA, resulting in a grid voltage of about -30 or similar to the original design

Feedback resistors reduced to drop gain from 500-1000x to about 20x

into a high impedance load i tested 1khz/50Vpp out at .008% thd

 

in order to meet "today's standard" of 15W into 50 ohms balanced, I'm estimating 16x 6AS7G tubes per amp?? Sennheisers would work nicely with a baby blue Hawaii but IDK of any protection circuit that could be trusted to run no transformer or capacitor coupling into a dynamic or planar headphone!!

That's why I think this may be a better project for the purpose of phase splitting/inversion, voltage gain, and buffer driver. For example, Kevin's 'tube input unbal/bal' board with the 6922 is basically the first 2 stages of all of the SS/Hybrid e-stat designs at lower voltage but a 6922 itself can't do the job completely if the job is to get to a low distortion 100Vpp balanced output to feed Uber-buffers to get the 15W into 50-ohms

but you could use this baby BH type design, such as this with a single 6AS7 per channel or maybe 2x with the sections paralleled for more power, if wanting to have the ability to drive "Hi-Z" headphones directly with a very very good protection circuit, or maybe more realistically, a large film cap

 

 

 

Edited April 9, 2023 by justin