Why 6C45PI?

[adydula]

My b-day is in June and I am going to buy/build a new headamp...I only have 9 of them now!! Mostly DIY and one is a Crack/w speedball.

I am looking for a really great tube amp and the Mainline seems to be one of the better tube amps out there that is reasonably priced. This is one of the things when in retirement and the budget comes to play. There are other "high end" and more costly tube amps out there and most are mega bucks in pricing and with the Mainline you get to build it, etc and if somethings goes south you can repair it....old school, no SMD parts, just good ole wires, sockets, tubes, switches and some wood working as well!! lol.

So one of the questions is why the 6C45PI, this may have been answered or discussed but havent seen it?

Seems like tube rolllers like the ability of rolling tubes etc...me I just want to know that the tubes that come with the kit will work really well in the design as is. I dont relish spending mega-bucks for audio nirvana.....so these tubes hopefully will be just fine for me.

Were other tubes considered in the design of the Mainline?

Thanks
Alex

 

[Paul Birkeland]

So one of the questions is why the 6C45PI, this may have been answered or discussed but havent seen it?

When you look at triode characteristics and consider voltage gain, transconductance (think output current), and internal resistance, often times you can really only optimize one of those characteristics, or potentially push the envelope a little bit on two of them, but not all 3.

The 6C45 is a bit of a special tube, as it has pretty high voltage gain, very high transconductance, and low internal impedance.  The 6C45's limiting factor is that it can't handle high plate voltage.  This allows us to just use one 6C45 per channel (unlike something like the SEX or Crack, which develops voltage gain in the first stage, then uses a second stage with lower impedance/higher current to drive the load). 

Were other tubes considered in the design of the Mainline?

There was the Smack headphone amp before the Mainline that used the 5687.  We found that it did not have sufficient gain under some circumstances, especially as source voltages have dropped over the last decade or so.

A Western Electric 437A will work in place of the 6C45PI, but at quite a cost.

There are some random pentodes that can be triode strapped and reworked into the Mainline schematic, but we'd recommend sticking with the 6C45.

 

[Natural Sound]

Isn't the EC 8020 a close relative as well? That is if you can find a pair.

 

[Paul Birkeland]

Isn't the EC 8020 a close relative as well? That is if you can find a pair.

Yes, they are close relatives.

I guess the TLDR reason for selecting the 6C45PI is that it's a copy of several tubes that sell for $500+ each!