What's in a Mars Specialist?

[wsaraceni]

i had one. such a cool little amp. i wish i never sold it. the insides were pretty messy though. i doubt gut shots would help with this one. mine had an octal preamp. but i think it was wired in the circuit exactly like a 12ax7. just different tube pinout. no circuit changes.

[xtian]

I just sold the one I built. You can see my build thread here:

https://tubeamparchive.com/viewtopic.php?t=16996

[Structo]

Weren't they film projector amplifiers?

As in Bell and Howell?

[xtian]

Yup.

[renshen1957]

I have installed VVR to 5E3, AC30 and some other cathode biased amps without negative feedback and it seems that it works best in this kind of amps compared to fixed bias ones. Maybe somebody can help and explain why .

Hi,

You would find the answer to that question over at powerscaling.com as to where to look to incorporate power scaling in amps with fixed bias and nfb loops.

Kevin O'Connor writes on the subject at length in TUT4 and has some additional comments in TUT6 (both theory books, hint two tracking regulators for B+ and a separate bias regulator). TUT5 has a complete schematic and layout for a version of LP Standard amp with a powerscaling board included (for eyelet boards). There's a choice, one can switch between either Fixed or Cathode Bias on the two pairs of power tubes in a nfb loop.

I know the above sounds like a commercial, however I found the books very informative.

Best Regards,

Steve