Re: Look at Herbert Keroes original circuits.

Posted by Henry Pasternack on December 4, 2004 at 08:00:59

In Reply to: Look at Herbert Keroes original circuits. posted by grhughes on December 4, 2004 at 07:23:16:

The special output transformers used in the McIntosh amplifiers, aside from being unavailable commercially, impose a daunting requirement on the output voltage available from the driver circuit. These amplifiers aren't generally regarded as the ne plus ultra in subjective performance, so it's unclear what the advantage would be of trying to copy them. Even if you were determined to clone the MC-30, this would be a project well beyond your current skill level.

In my humble opinion, you are coming at this from a backwards, or at least sideways, perspective. This is not the time to be worrying about the types of resistors and capacitors you will use, even before you've got a schematic. What you need to do is complete your top-down requirements analysis.

I believe what you want is a quality implementation of a classic 1950's negative feedback amplifier. I would strongly suggest a variation of the Williamson driver circuit and a single pair of KT88/6550 output tubes with a 450-475V B+ supply giving you 50-60W output power. This type of circuit is time-tested, bullet-proof, and easy to set up. I think one of the Triode Electronics or MagneQuest Dynaco Mk-3 replacement output transformers would be an excellent choice. I would recommend a choke-input power supply with tube rectification and polypropylene filter capacitors. Use decent quality resistors and capacitors and you will get state of the art performance for this type of amplifier.

The main challenges you will face are sourcing the right power supply components to give you your desired voltages, learning how to do a proper physical and wiring layout of the amplifier, tracking down hum and noise in the working prototype, and stabilizing the feedback loop. The latter two challenges may be particularly daunting as they get into the black art of audio design and construction.

I encourage you to undertake this project, but I also think there is a lot to learn. I hope you view it as the starting point, not necessarily the ending point, of what may become a years-long process of experimentation and discovery.

-Henry

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Follow Ups Full Thread

Topic - Starting a DIY project... - 7591 06:40:29 12/4/04 (15)

Consider Plitron / Vanderveen Trannies - Dr Deville 18:20:20 12/4/04 (0)

well - Sector-7G 15:41:25 12/4/04 (2)

Agreed 100% - SomeJoe 19:06:09 12/4/04 (1)

Agreed 100% - Sector-7G 05:15:10 12/5/04 (0)

Why scratch build what you can buy used? - Russ57 09:08:23 12/4/04 (3)

Try rebuilding some used EICO monoblocks - Salectric 14:07:48 12/4/04 (2)

You're certainly welcome. Good luck! (nt) - Salectric 15:48:34 12/4/04 (0)

Re: Try rebuilding some used EICO monoblocks - 7591 15:03:12 12/4/04 (0)

Look at Herbert Keroes original circuits. - grhughes 07:23:16 12/4/04 (3)

Re: Look at Herbert Keroes original circuits. - Henry Pasternack 12/4/0408:00:59 12/4/04 (2)

Re: Look at Herbert Keroes original circuits. - 7591 14:50:25 12/4/04 (1)

Re: Look at Herbert Keroes original circuits. - Henry Pasternack 15:18:38 12/4/04 (0)

forgot to add... - 7591 07:12:49 12/4/04 (2)

One 5AR4 is full wave - Russ57 09:23:51 12/4/04 (0)

Look at the Marantz Model 2 amp - grhughes 07:32:38 12/4/04 (0)

Follow Ups

Re: Look at Herbert Keroes original circuits. - Henry Pasternack 12/4/0408:00:59 12/4/04 (2)

Re: Look at Herbert Keroes original circuits. - 7591 14:50:25 12/4/04 (1)

Re: Look at Herbert Keroes original circuits. - Henry Pasternack 15:18:38 12/4/04 (0)

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