diytube.com

Anybody knows any simple schematics for 845s? Ones that I see online look real complicated. Thanks!

A start:

http://bonavolta.ch/hobby/en/audio/845.htm

An 845 or 211 amp isn't going to be the typical simple voltage amp / power stage design, like for a 6EM7 or a 2A3 or 300B.

These larger tranmitter triodes need very high (800V to 1200V B+) plate voltage and lots of grid drive (grid bias voltage X 2) for peak to peak audio signal.

In addition to the relatively complex circuitry, the B+ voltages aren't simply "dangerous", they can be outright lethal. A "hit" from kilovolt (or as I call it, a killer-volt) doesn't offer any "second chances".


/ed B in NH

http://www.tubelab.com/845SE.htm

http://www.teresaudio.com/haven/verus/verus.html

http://nekhbet.com/amp/845_amp.gif

http://nekhbet.com/amp/845_as.gif


If you want some big power, but with
a simple drive circuit, look at the 813
tubes. They are easy to drive.

http://homepages.ihug.co.nz/~rwillis/alex/

This is interesting. If you have ever seen those Chinese "Music Angel" SE 845 amps on ebay for about $600, this guy has redesigned the guts of the driver section, and swears that it is "the best secret of hifi market".

http://www.lampizator.eu/AMPLIFIERS/CHI ... 0Kong.html


He is using an srpp and parallelled plate load volt amps to drive the beast.

http://www.lampizator.eu/AMPLIFIERS/CHI ... at_845.jpg


It gets even better... Some other guy, named, DIETMAR, adds his own little tweaks. He removed the srpp entirely, and it looks as though he's got two volt amps and a parallelled cathode follower to drive the 845.

http://www.lampizator.eu/AMPLIFIERS/CHI ... 45_v42.pdf


I wonder if it would be a bright idea to build a new 845 with this drive circuitry (only two 6sn7gts)? I bet DIETMAR's driver would work better with a 211, than an 845.

Two12ax7s as srpps run the 845. It does not get any simpler than that.

http://www.diyparadiso.com/proj/belcanto.htm

Check out this:

6HV5A as the single driver.



However, the schematic is wrong. The 6HV5A is not pentode; It is a triode, and what looks like a screen is the beam plates. It needs to be grounded to be stable - not attached to the anode.

http://www.nj7p.org/Tube4.php?tube=6HV5A


I was thinking of this as the driver for an SE 813...

Here's a schema I just finished up for my 813 project:



Its pretty basic. the 45 is IT loaded into the 813, which I'll run in triode mode. Let me know if you would also like to see the PSU.

SteveH wrote:Let me know if you would also like to see the PSU.

Yes, please. An amp schematic without the psu schematic is like a Harvey Wallbanger without the vodka...

BTW. What interstage transformer are you using?

Here's what I have...I think I will wind up tapping off of the 1 stage cap to use it as a voltage divider, and get my 325vdc that way....Still needs some work.


I've also been tossing around this idea - it could work out well too...



Hope this helps,
Steve

I like the second one. Dropping 900Vdc to 325Vdc is not an option I like to consider.

I am going with a more traditional voltage doubler.

Here is an interesting driver for the 211. An old 27 triode and a D3a wide-band pentode in an srpp config. The voltage on the D3a's anode is higher than it is spec'd for.

I have had personal experience with 2 of the Music Angel 845 Amps.

1st my own - It is now sitting on my shelf with a blown output transformer (shorted primary to secondary) which also took out one of the 845 tubes.

2nd - a local guy who brought his amp to me for repair - it works but has a nasty buzz in one channel, it looks like the 20H Choke in the driver supply has gone short circuit.

That is, out of the 2 amps I've seen both have suffered failures of magnetic components.

As well as that, the rail to the 845 runs at around 900 to 920V. Power supply has series connected 450V rated electrolytics with 330K voltage share resistors. I changed those resistors to far more suitable 100K 5 Watts but even so I don't like to see components like electrolytic caps running at their absolute maximum voltage limits.

Be cautious of the lampizator mods. The schematic he posted did'nt match the 2 amps I've worked on. One of the mods he suggested, deleting the 170V zener to the SRPP front end, would have caused serious problems with these amps. If you don't understand what the mods are doing or if it doesn't seem to match the amp you have then don't do it.

I've bought some superior output trannnies for my amp, but I won't be repairing it, I'll be rebuilding it from scratch with new power supplies and a better driver circuit.

Cheers,
Ian

Gingertube wrote:I have had personal experience with 2 of the Music Angel 845 Amps.

Be cautious of the lampizator mods. The schematic he posted did'nt match the 2 amps I've worked on. One of the mods he suggested, deleting the 170V zener to the SRPP front end, would have caused serious problems with these amps. If you don't understand what the mods are doing or if it doesn't seem to match the amp you have then don't do it.

Cheers,
Ian

The Music Angel factory schematics come from Music Angel, but they sometimes do not match the amps purchased or produced. The lampizator guy points that out.

Music Angel has to be making many variations on the amps.

The 813 Music Angel amp is known to vary from the factory schematic, and its goes through rectifiers the way Tiger Woods goes through women....

Replace the GM-70 with an 845 and your good to go:

http://diyparadise.com/nikcgm70.html

or keep the GM-70 they are far easier to get.