Turn RCA RS-177H into EICO HF-81 ?

[getone]

Dear Members.

I have a nice pair of EICO HF-12s and they sound awesome. I guess a HF-12 is kind of half of the EICO HF-81.

I also got an RCA RS-177H iron from a console. I have restored it, but even with the radio/preamp it came with does not sound nice.

Would it be possible to turn the RCA iron into a EICO HF-81 just by adding one more socket (for a 12ax7) and use the existing transformers, B+ section. In other words, just replacing / adding capacitors and resistors?

Thanks!

Schematics:

http://vintagevacuumaudio.com/schematics-manuals/eico/eico-hf-81-owner-manual-schematics.pdf

http://www.audiokarma.org/forums/showthread.php?t=136727 post#9

 

[dcgillespie]

As a basic statement, yes, BUT. Different output transformers have different characteristics, so the NFB circuit would require adjustment requiring a scope and generator to adjust. Also, the NFB is taken from the 16 ohm tap in the Eico circuit, and the only (likely 8 Ohm tap) in the RCA. So adjustments would be required.

Also, the steel chassis of the RCA would require good knowledge of grounding schemes, as revising the build for more gain like the Eico has will make it ripe for hum and ground loop problems.

I'm not sure I understand the extra tube socket statement. If you're looking to build just the power amp section of the Eico, then the RCA chassis already has enough sockets. If you're looking to add the line stage sections of the Eico as well, it would take adding two more sockets. For best results, the project should be built into a new aluminum chassis to greatly reduce the hum problems associated with high gain circuits and steel chassis construction.

Good luck with your (potential) project!

Dave