845 Amp

[kevinkr]

Originally posted by athos56
Ok then something like this? A diode bridge with the polarity reversed?

I've seen a few with a relay I'll look at them some more

Yup...

[athos56]

Originally posted by kevinkr


Yup...

So then if I used a transformer with a 115v secondary I could get a Amperite 115N02T and put it before the bridge, after a 2 second delay the relay would close and start the B+...

Thanks for all the help!

[kevinkr]

Originally posted by athos56



So then if I used a transformer with a 115v secondary I could get a Amperite 115N02T and put it before the bridge, after a 2 second delay the relay would close and start the B+...

Thanks for all the help!

Better still would be to use a dc relay that operates off of the rectifier - that way if there is a component failure in the bias supply (other than the resistors) you are covered.

[athos56]

To all those who replied! As always I learned a lot. I'll post contruction pictures of what I decide on building (either a se 300b or Kt88 with an akido front end or the simpler of Yves's 845's) when the project gets going.

[jrdmedford]

845 amps are large because the sockets take so much room.
They are not necessarily expensive ; and you can run them at
500V and achieve good results at no more cost than a 300B amp.
The low voltage variants sound very nice... My amp was well received about 4 years ago at some DIY gatherings, I know of at least 5 people who replicated my implementation because it sounded THAT good. Some people even got the amp done under $500 in parts ; but they already had some key parts on hand or made some concessions.

They are quite beautiful too, it's a huge glass tube, and it throws
warm light like a nightlamp. So, there is an aesthetic factor to choosing it over the 300B.

If you're looking at the 1000V+ designs you'll see 10Kohm output
transformers. You can get away with a 6K load very nicely, and
even a 5K load. The door is open for all kinds of great transformers
for 845: Edcor 5K/6K SE, The new Hammond 1628SEA/1629SEA,
the One Electrons, and more. 845's at low voltage also
are wonderful candidates for the Ultrapath topology. You'll
want a driver than can do 160V, which means you can copy a
driver from pretty much any good 300B amp.

-- Jim